CIRCUIVOU CAN I - World Radio History

SEW PUSH-PULL CIRCUIVOU CAN I

JULY1934

PICTURESby WIRE and WIRETHERE IS a LIMIT LESS

to ALMPLIFICATION

THEM" BALANCE

andCONTROLAMPLIFIERS

Wireless Magazine. July, 1934 I

Get Your CopyEvery Friday!

Every Friday RADIO PICTORIAL revealsin pictures and in words the home life ofpopular broadcasters. Scores of lifelikephotographs of the favourites you listen to,thrilling fiction, clever humour, a corner forthe children, a splendid feature for the wife,etc., etc. RADIO PICTORIAL puts you inintimate touch with the human side of broad-casting and adds greatly to your enjoymentof listening -in. A great twopennyworth!

GET YOUR NEWSAGENT TO DELIVER" RADIO PICTORIAL " EVERY FRIDAY

RAMOPICTORIAL

the Familywill enjoyit too ! !

ON SALE AT ALLBOOKSTALLS andNEWSAGENTS

Editor -in -Chief:BERNARD E. JONES

Technical Editor:.1. H. REYNER

B.F.c. (Hons.), A.M.1.E.E.

Radiovision Editor:H. CORBISHLEY

Wireless MagazineThe Best Shillingsworth in Radio

Vol. XIX : JULY 1934 : No. 114

Editor:D. SISSON RELPH

Research Consultants:

W. JAMES andPERCY W. HARRIS

Assistant Editor:T, F. HENN

Published by EERNARD JONES PUBLICATIONS, LTD., 58/61 Fetter Lane, London, E.C.4. Telephone: Central 4341 (four lines). Telegrams: "Beejapee,Fleet,London." Subscription: Great Britain and abroad, ISs. 6d. a year, post paid (Canada only, 13s. 6d.). Next issue published on Wednesday, July 25.

You All Want to KnowAbout AMPLIFIERS!

yOU will find the July "Wireless Magazine" a soundand useful number, presenting a general survey ofpracticalities and other "-alities" and reaching a

good level of achievement.Perhaps its note is its articles on amplification ; three

thoroughly good sets covering most ordinary requirements ;and an article " 'Balance and Control' at the B.B.C.,"revealing the clever work done behind the scenes bymembers of the B.B.C. staff, this being by Whitaker -Wilson, who explains how microphones for outside broad-casts are arranged, managed, and controlled so that theypick up little else than the sounds suitable for broadcastpurposes.

Now as regards amplification, G. S. Scott explains whythere is a limit to amplification. There are limits, ofcourse, and the author shows that the deciding factor isthe ratio of signal (the sound that is wanted) to noise (soundthat is not wanted), and he explains how noises are intro-duced and their effect on reproduction.

In "A New Push-pull Method," F. E. Cox gives circuitdiagrams illustrating a new system which he claims willgive even better quality than the generally acceptedmethods.

We receive letters from many readers to whom the costof a set, as long as it is at all reasonable, is not theimportant factor. Quality is what they want and for theseparticular readers S. Rutherford Wilkins has designed the"W.M." Radiogram Super, a large set built in two sectionsand employing eight valves, half of them in the super -hetradio unit and half in the power -amplifier unit, includingtwo large P X4 triodes which give an undistorted outputof 5 watts-quite enough for small functions out-of-doorsor for dances in small halls.

For the reader who does consider cost (and mostreaders have to, of course), we give this month the Six -guinea A.C./D.C. Three, designed especially to meet theneeds of thousands of people whose houses have electricmains. The price mentioned includes every componentand a moving -coil loud -speaker, but not the cabinet. Thisthree-valver can be worked off A. C. or D.C. mains withoutalteration and the test report which we publish shows ahighly satisfactory performance.

The All -wave Battery Three is for a different section ofreaders-a growing section keenly interested in short-wave listening. It is a cheap set covering from 20 to 80metres in addition to the normal broadcast wavelengthsand gives its user a lot of pleasure in tracking down theshort-wave stations as well as in providing him with theusual broadcast entertainment.

Alan Hunter shows how the new Droitwich station willaffect listening in this country and exploins how, once itcomes into operation, several of the present regionalstations will become unnecessary ; he has a word to say,too, about the proposed new transmissions in North Wales,Scotland, and Newcastle.

We have many good articles of a general nature, andamong them I will just mention the Lowe and Phillipsarticle, "Sending Pictures by Wire and Wireless." Thisis really a comprehensive survey of the history of picturetelegraphy, a science whereby you have up-to-the-minutenews pictures of an event-which perhaps took placehundreds of miles away-in your newspapers an houror so after it took place. The article is well illustrated,and to prove to you the perfection that has been attainedevery photograph is printed without retouching.

B. E. J.

El

FOR THE CONSTRUCTORTHE W.M." RADIOGRAM SUPER. Designed

by S. Rutherford WilkinsTHE SIX -GUINEA A.C./D.C. THREE. By

the " W.M." Technical Staff . ,

THIRTY-SIX STATIONS IN AN HOUR'S TESTTHE ALL -WAVE BA'rTERY THREE. By the

" W.M." Technical Staff.. ..

TECHNICAL FEATURESA NEW PUSH-PULL METHOD. By F. E.

NEW CONVERTERS FOR SHORT-WAVE I ISTEN-ING. By the " W.M." Technical Staff ..

WHY THERE IS A LIMIT TO AMPLIFICATION.By G. S. Scott ..

OUR TESTS OF NEW SETS. By the " W.M."Set Selection BureauCOLUMBIA SUPER -HET BATTERY GRANDPYE CR/DC CAMBRIDGE SUPER -HET

CONSOLE

El

KEBTEX PROSCENIUM STRAIGHT FOURFERRANTI ARCADIA SUPER -HET RECEIVERPHILCO MODEL 16 TABLE SUPER -HET

503

519524

557

494

510

513

531532

533534535536

ContentsREACTION AND DETECTOR OUTPUT CIRCUITS.

By Percy W. Harris, M.Inst.Rad.E.PRACTICAL POINTS IN AMPLIFIER DESIGN.

By the " W.M." Technical StaffTESTS OF NEW APPARATUSALL THE LATEST IN CAR RADIO. By the

" W.M." Technical Staff.. ..

537

551555

566

GENERAL ARTICLESGUIDE TO THE WORLD'S BROADCASTERS. By

Jay Coote .. 482WORLD'S BROADCAST WAVELENGTHS .. 484IN TUNE WITH THE TRADE. By Fetter

Lane 488RADIO MEDLEY. By BM /PRESS .. 491SENDING PICTURES BY WIRE AND WIRELESS.

By W. T. Lowe and E. Phillips .. 495DROITWICH MEANS NEW REGIONAL PLANS.

By Alan Hunter .. 500HAVE You LOGGED WLW ?.. 515NEW STATIONS FOR OLD ! By W. Oliver .. 516

" BALANCE AND CONTROL" AT THE B.B.C.By Whitaker -Wilson 525

WIRELESS JOBS MADE EASY FOR MR.EVERYMAN. By. R. W. Hallows, M.A. .. 528

THE VATICAN SHORT -WAVER 541NEWS OF THE SHORT WAVES. By

Kenneth Jowers 546PROGRAMME NOTES AND NEWS. By T. F.

HennMAKE AND BREAK IMY IMPRESSIONS OF THE " Two H.F."

PORTABLEON THE CREST OF THE WAVES. By Jay CoateNOTES AND JOTTINGSSHORT WAVES ON THE SEVENTY-SEVEN SUPERCOUPONS : INDEX TO ADVERTISERS

TELEVISION SECTIONTELEVISION COMPONENTS-AND ALL ABOUT

THEM. By H. Corbishley

GRAMOPHONE FEATURESCHOOSING YOUR RECORDS. By Whitaker -

WilsonADDITIONAL RECORDS REVIEWED. By

Chopstick

548554

564570572573576

542

562

563

NEXT MONTH-MAKING AND USING A UNIVERSAL TESTERRegistered a: the General Post Office for transmission b/ Canadian Magazine Post

481

Postage on th,s iSSU.! 3d. (inland and abroad)

O

Wireless Magazine. ,Aily, 1934

Guide to the Worlds BroadcastersSpecially Compiled for "Wireless Magazine by JAY COOTE

Metres: 29.04 RUYSSELEDE (ORK) Kilocycles :Power: 8 kw. (Belgium) 10,330

Distance from London: Approximately 158 miles.Standard Time: Greenwich Mean Time (Belgium adopts SummerTime).

Announcer: Man.Call: "Id Bruxelles, Poste Colonial Belge."Times of Transmission: B.S.T. 1945, news in French; 2000-2100,concerts; 2100-2115, news in Flemish.

Transmits programmes for Belgian Congo and frequently relaysBrussels (INR).

Closes down with the usual goodnight greetings and the BelgianNational Anthem.

(Revised)Metres: 31.28Power : 20 kw. SYDNEY (VK2ME) Kilocycles:

9,590(New South Wales)

Distance from London: Approximately 10,550 miles.Standard Time: British Summer Time plus 9 hours.Announcer: Man.Opening Signal: Song of the Kookaburra bird (laughing jackass)on sound film.Call: "This is VK2ME, the Australian National Empire short-wavestation broadcasting on 9,590 kilocycles, 31.28 metres."Times of Transmission: B.S.T. 0700-0900, 1100-1500, 1530-1830(Sundays only).Closes down with call, followed by Kookaburra song and God Save theKing.Occasionally tests are tried out on 7 metres (42,860 kilocycles).

(Revised)Metres: 328.6Power : 60 kw. RADIO TOULOUSE Kilocycles:

913(France)

Distance from London: Approximately 560 miles.Standard Time: Greenwich Mean Time (France adopts BritishSummer Time).Announcer: Man.Opening and Closing Signal: March : La Toulousaine.Call: " Allo ! Allo ! Ici Radio Toulouse, Emissions de la Radio-phonie du Midi !" Between items : "Ici Radio Toulouse."Interval Signal: Gong (about fifty beats per minute).Main Daily Transmissions: B.S.T. 0800, gramophone records;1230, news; sacred service (Sundays), then continuous broadcastsuntil 1430; 1815, orchestra, records, or sound films; 1930, news,songs, relays from local catis.The station closes down usually at 0030 with the usual Frenchgoodnight greetings.

Metres: 483.9Power : 20 kw. CAIRO

(Egypt)Kilocycles:

620

Distance from London: Approximately 2,100 miles.Standard Time: Eastern European (British Summer Time plus1 hour).Announcer: Man.Call: "Cairo calling." In French: "Id Poste de Radiodiffusion duCaire" (phon. : "Care.")Times of Transmission: B.S.T. 1100-1330 and from 1700-2230.Concerts consist mainly of Oriental compositions, but gramophonerecords of Western music are also broadcast.News and announcements are given out in Arabic, English, andFrench; where special entertainments are transmitted for othernationalities, also in Italian and Greek.Relay (under construction) : Alexandria (Ras -el -Tin), 267.4 metres(1,122 kilocycles), 5 kilowatts.

Metres : 30.43Power : 20 kw.

(Revised)

MADRID (EAQ) Kir;ciges(Spain)

Distance from London: Approximately 802 miles.Standard Time: Greenwich Mean Time (British Summer Time less1 hour).Call: "Aqui Madrid Radiodifusion Ibero-Americana."Announcer: Man.

Languages: Spanish, French, and English.Times of Transmission: B.S.T. 2330-0130 daily; also 1900-2100(Saturdays).Transmits programmes for European listeners and occasionallyrelays Madrid (EAJ7).News bulletins are sometimes given in the English language.Closes down with goodnight greetings in Spanish, French, andEnglish, followed by Spanish Republican National Anthem, Himnode Riego.

Metres: 41.84 GRANADA (YN3RD) Kilocycles:Power: 0.2 kw. 7,170(Nicaragua)

Distance from London: Approximately 4,350 miles.

Standard Time: British Summer Time less 7 hours.

Announcer: Man.

Languages: Spanish and English.

Interval Signal: Bugle call.

Call (in English) : "This is the amateur radio station, YN3RD,Granada, Nicaragua."

Times of Transmission: B.S.T. 2000-2100 daily.

Metres : 476.9Power : 20 kw. LISBON

(Portugal)

Kilocycles :629

Distance from London: Approximately 975 miles.Standard Time: Greenwich Mean Time (Portugal adopts SummerTime).

Announcer: Man.Call: "Estacao Nacional Radio Lisboa."Times of Transmission: B.S.T. 2145-0030.For the present the programme schedule is an experimental one, butthe broadcasts include news bulletins, studio concerts, gramophonerecords, talks, and dance music by English bands.The station closes down with goodnight greetings in several languages,followed by the Portuguese National Anthem, A Portuguese.

(Revised)Metres: 522.6Power: 100 kw. STUTTGART

(Miffilacker)cycles:

(Germany) 524Distance from London: Approximately 454 miles.Standard Time: Central European (coincides with British SummerTime).Announcer: Man.Language: German only.Call: " Achtung ! Hier Reichssender Stuttgart."Interval Signal: Three notes (C, D, G) repeated.Main Daily Transmissions: B.S.T. 0545, choral concert, weatherforecast, physical exercises, news bulletin; 0615, relay of concertfrom liner at Hamburg (Sundays), then continuous broadcast until2000, news, main evening programme, relay of opera, play, or con-cert, talks; 2220, news and time signal; 2300, late musical transmis-sion from studio and almost nightly a relay from Frankfurt -am -Mainor Munich from midnight to 0100.Closes down with the playing of Horst Wessel marching song, orDeutschland Ueber A lles.

482

Wireless Magazine. Jut)y, 1934

VALVE SUPERHETBATTERY RADIO

THAT IS EQUIVALENT TO A NINEMains -set performance without a mains electricity supply

This set must be heard to be believed. For no battery set has been producedbefore that is in any measure equal to it. In accuracy of reproduction it isequivalent to an expensive mains set. There is a technical reason for theastonishing performance of this Battery Set. Although it is actually a five -valve radio, one valve, which is of a special type, does the work of three, andtwo others each act as two ! This represents the highest achievement to datein battery radio. Not only is the tone of this new Columbia Model superiorto that of any other battery set, but its selectivity and range are phenomenal.Every station is kept distinct. If you have no electricity supply, or live in adistrict where good results cannot be got from a mains set, this is undoubtedlythe instrument to buy-for it gives you the quality of reception that has hithertoonly been possible from " mains " -radio.

Col"MAGIC NOTES"

TRADE MARK

The new COLUMBIA SUPERHETBATTERY GRAND, Model No. 1006Hear this new Model to -day. The more you knowof it, the more positive you will be that this is theinstrument you have been waiting for-the instru-ment you want ! Hear it at any Columbia dealer's

to-day-or write straight-away for this descriptiveleaflet, "Hearing is Be-lieving." The Couponbelow, posted in an un-sealed envelope with a Id.stamp will ensure that it

OR BY HIRE PURCHASE is sent.

NS

COUPON. Please send me particulars of the new ColumbiaSuperhet Battery Grand Model No. too6, without obligation.To the Columbia Graphophone Co. Ltd.,

98-508 Clerkenwell Road, London, B.C./

Name

Address

(Prices do not apply in I.F.S.) W.M.1.7.34

Better service results from mentioning " Wireless Magazine " when writing to advertisers

483

Wireless Magazine. July, 1934

0,

RIPSamnziniC 1111

,

BRPtagcn45ir MELICfE8Isles are indicated in bold type

Note : Names in brackets are those of stations relayed

Wave-length Name of Station Dial

Readings Country Wave-length Name of Station Dial

Readings Country

13.92 W8XK, Saxonburg (KDKA) United States 31.41 Jeloy LCL .. .. .. Norway13.97 Daventry GSH _ .. .. _- Great Britain 31.48 Schenectady W2XAF (WGY) --United States14.49 Buenos Aires LSY .. .. Argentine 31.545 Daventry (Empire) GSB .. Great Britain14.58 Bandoeng PMB .. .. .. Java 31.55 Melbourne VK3ME .. .. Victoria15.5 Bandoeng PMA .. .. .. Java 31.55 Caracas YV3BC .. .. Venezuela15.92 Bandoeng PLE .. Java 31.58 Rio de Janeiro PSA .. .. Brazil16.36 Lawrenceville (N.J.) WLA . : United States 31.71 New Brunswick WKJ .. .. United States16.38 Rugby GAS .. .. .. Great Britain 31.9 Bandoeng PLV _ .. .. i Java16.5 Drummondville (CFAS) . Canada 32.71 Lawrenceville WNA .. United States16.56 Bandoeng PMC .. .. .. Java 32.79 Maracay YVQ .. .. .. Venezuela16.56 Buenos Aires LSY3 .. .. Argentine 32.88 Szekesfehervar HAT4 .. .. - Hungary16.8116.85

Bandoeng PLF .. .. ..Kootwijk PCV .. .. ..

JavaHolland

33.26- 33.59

Rugby GCS ..Rocky Point (N.J.) WEC ..UnitedGreat Britain

States-I16.86 Daventry Empire GSG Great Britain 34.68 London VE9BY. _ .. Canada16.878 Boundbrook W3XAL (WJZ).. United States 36.65 Rio de Janeiro PSK (PRA3) Brazil16.88 Eindhoven PHI Holland 37.04 Quito HCJB .. .. .. Ecuador16.89 Konigswusterhausen DJE : : Germany 37.33 Rabat (CNR) .. .. .. Morocco17.05 Transatlantic liners

(WGY)37.41 Suva VPD .. .. .. Fiji Isles

19.56 Schenectady W2XAD. United States 38.07 Tokio JIAA .. .. .. Japan19.61 La Paz CP4 .. .. .. Bolivia 38.47 Radio Nations HBP .. .. Switzerland19.63 New York W2XE (WABC) .. United States 38.65 Kootwijk PDM .. .. .. Holland19.67 Coytesville N.J. WIXAL (WEEI) United States 39.34 Tashkent RIM .. . .. U.S.S.R.19.67 Tashkent (Rim) .. .. .. _ U.S.S.R. 39.76 Moscow RKI .. .. .. U.S.S.R.19.68 Radio Colonial FYA .. _ France 39.82 Riobamba PRADO .. .. Ecuador19.72 Saxonburg W8X.K. (KDKA) .. United States 39.89 Moscow RKI .. ... .. U.S.S.R.19.737 Zeesen DJB .. .. .. Germany 40.3 Radio Nations HBQ .. .. Switzerland19.815 Daventry (Empire) GSF .. Great Britain 40.5 Bogota HJ3ABB .. .. Colombia19.84 Rome (Vatican) HVJ .. .. Italy 40.54 Rocky Point WEN .. .. U.S.A.19.88 Moscow (RKI) .. .. .. __ U.S.S.R. 41.1 Amateur band .. .. .. -20.27 Rocky Point WQV .. .. - United States 41.55 Bogota HKE _ .... Colombia20.31 Rocky Point N.Y. (WEB) .. United States 41.6 Las Palmas EA8AB .. .. Canary Isles20.97 Amateur band .. .. .. - 41.67 Singapore VSIAB .. .. Sts. Settl'mts.21.43 Cairo SUV .. .. Egypt 41.84 Grenada YN6RD .. .. Nicaragua21.53 Rocky Point WIK .... United States 41.9 Manizales HJ4ABB .. .. Colombia21.58 Rocky Point WQP .. ..

_United States 43 Madrid EA4AQ .. .. Spain

21.605 Rocky Point WQT _ .. United States 43.86 Budapest HAT 2 .. .. Hungary21.83 Drummondville CJA8 .. - Canada 44.61 Rocky Point WQO .. .. United States22.26 Rocky Point WAJ .. .. United States 44.96 Maracay YVQ _ _ .. Venezuela22.48 Santa Rita YVQ .. .. Venezuela 45 Constantine FM8KR .. .. - Tunis22.68 Liners .. .. . - 45.02 Guayaquil HC2RL .. .. - Ecuador22.684 Zeesen (DHB) .. . ..

CNR - Germany 45.38 Moscow RW72 .. .. .. U.S.S.R.23.39 Radio Maroc (Rabat) .. Morocco 46.53 Barranquilla (HJIABB) .. Colombia24.41 Rugby GBU .. .. .. Great Gritain 46.69 Boundbrook W3XL (WJZ) .. United States24.9 Kootwijk PDV .. .. .. Holland . 46.7 Boston WIXAL .. United States25 Moscow RNE .. - _ U.S.S.R. 47 Cali HJSABB .. .. Colombia25.25 Radio Colonial, Paris (FYA) _ _

France 47.5 S. Domingo HIZ .. Dominican R25.25 Saxonburg (Pa.) W8XK (KDKA) United States 47.8 Domingo HIAA .. ..

1 Dominican R.25.28 Daventry (Empire) GSE .. Great Britain 48.75 Winnipeg CJRO .. ..

ICanada

25.34 Wayne W2XE (WABC) --- United States 48.78 Caracas YV3BCI Venezuela

25.425.45

. ..Rome 2R0 ..Boston WIXAL .(WEEI)

_ ItalyUnited States

48.8348.86

Saxonburg (Pa.) W8XK (KDKA)Moscow (RKK) .. ..

United StatesU.S.S.R.

_I25.51 Zeesen DID .. .. .. Germany 49 Johannesburg ZTJ .. .. I South Africa25.532 Daventry (Empire) GSD ..__ Great Britain 49.02 Wayne W2XE (WABC) .. I United States25.58 Winnipeg (CJRX) .. Canada 49.08 Caracas YVIBC .. .. Venezuela25.63 Radio Coloniale FYA ..

---France 49.1 Halifax VE9HX (CHNS) .. Canada

26.8327.65

Funchal CT3AQ ..Nauen DFL .. .. ..

MadeiraGermany___49.18{ ..Boundbrook W3XAL (WIZ)Chicago W9XF (WENR) ..

--United_ StatesUnited States

__27.86 Rugby GBP .. .. .. Great Britain 49.22 Bowmanville VE9GW (CRCT) Canada27.88 Marapicu PSG . _ .. Brazil 49.26 St. John VE9BJ (CFBL) N. Brunswick28.28 Rocky Point (N.J.) WEA .. United States 49.3 La Paz CP5 .. .. .. Bolivia28.5 Sydney VLK .. .. .. N.S. Wales 49.34 Chicago W9XAA (WCFL) .. United States28.98 Buenos Aires LSX .. Brazil 49.39 Maracaibo V5BMO .. .. Venezuela29.03 Bermuda ZFD _ ... .. West Indies 49.4 Vienna OER2 .. .. .. Austria29.01 Ruysselede (ORK) .. .. Belgium 49.43 Vancouver VE9CS (CKFC) .. Brit. Columbia29.16 ..Zeesen (DIQ) . .. .. Germany 49.47 Nairobi VQ7LO Kenya Colony29.35 Marapicu PSI -I _ .. ..Brazil 49.5 Philadelphia W4X.AU.(VVCAth United States29.59 Leopoldville OPM .. .. Belgian Congo 49.5 Cincinnati WIXAL (WLW) .. United States29.64 Marapicu PSI .. .. ..Brazil 49.586 Daventry (Empire) GSA .. Great Britain29.84 Abu Zabel, Cairo SUV.. .. Egypt 49.6 _ .Bogota HJ3ABI..

.

Colombia30 Radio Excelsior LR5 .. .. Argentine 49.67 Boston WIXAL (WEED) .. United States30.1 Rome IRS .. .. ..Italy 49.83 Zeesen DJC .. .. .. Germany30.4 Lawrenceville WON .. .. United States 49.9 Singapore ZHI .. .. ..F.M. States30.4 Tokio JIAA .. .. .. Japan 49.92 Havana COC .. Cuba30.43 Madrid EAQ .. .. , .

__Spain 49.96 Drummondville VE9DN

30.77 Lawrenceville WOF .. United States (CFCF) .. .. .. Canada30.9 Rugby GCA .. .. .. _ Great Britain 49.97 Caracas YV2BC .. .. Venezuela31.08 Nauen DGU _ .. .. I

Germany 50 8 Barcelona EA3AB .. .. Spain31.23 Mexico City XETE .. .. I_ Mexico '

{ Moscow RNE .. .. U.S.S.R.31.25 Lisbon CTIAA .. .. .. -I Portugal 50.26 Rome (Vatican) HVJ .. ..

____ Italy31.26 Radio Nations HBL Switzerland 50.42 Domingo HIX .. .. .. Dominican R.31.28 Philadelphia W3XAU.(VVCAI.I) United States 50.6 Medellin HJ4ABE _ ..31.28 Sydney VK2ME .. .. - N.S. Wales 56.9 KOnigswusterhat a -al (DTG) .. Germany31.297 Daventry (Empire) GSC .. Great Britain 57.03 Rocky Point WQN .. .. United States31.35 Millis W1XAZ (WBZ) .. United States 58.03 Bandoeng PMY .. .. Java31.38 Zeesen DJA Germany 58.31 Prague .. .. .. .. I Czechoslovakia

(Continued on page 486'

484

Wireless Magazine. Juty, /9341

KEBTEX PROSCENIUM FOUR

KEBTEXPROSCENIUM FOUR

as reviewed on page 534 of this issue

Gives beautitul reproduction from any Mains,A.C. or D.C., anywhere. Illuminated StationNames include American as well as 55 otherson medium and long waves.

SPECIAL OFFERPurely as an introduction we will allow10% discount for cash with order from the

fixed price.

23/-wmDISCOU NT ,E11-11-0

SENT CARRIAGE PAID ON RECEIPT OFf10-8-0 BY THE MAKERS

KEBTEX CO., BIGGLESWADE, BEDSMAKERS OF THE SPECIAL

CABINET for TWO H.F. PORTABLE/IN Post Free 32/6

TRIBUTE AGAINto the safety of Eries

Aifor the "Wireless Magazine"

Radiogram Super"The Specification is Erie quality-Erie Safety

31 ERIE RESISTORSAND THE NEW INCOMPARABLE

ERIE VARIABLE RESISTANCE

II

Erie Resistors are specified because of theirexclusive Stability, their life -time's noiselessaccuracy. And for a radiogram especially, theperfect, smooth and silent efficiency of the ErieVariable Resistance is an important specification.Have you seen this new Erie triumph ?

Eries are economical

PER WATT INALL VALUES

Hand -tested, colourcoded and labelledERIE VARIABLE

Ask definitely for Eries. Also unite for Colour Code Chart. RESISTANCE 3/6

THE RADIO RESISTOR CO., LTD.I GOLDEN SQUARE, PICCADILLY CIRCUS, LONDON, W.I.

DIRECT RECORDING SYSTEMRecording machine with electrical drive,of solid construction, as illustrated, £45.Special Recording amplifier, 6 watts speechoutput, of straight line characteristic, £36.Write for full details of these, and alsoMicrophones, etc.Also available special black type recordingrecord supplied with one cutting needlesuitable for playing two sides, togetherwith two playing -back needles, price 2/6each.

PARTR I DGE& MEE, LTD.74 New Oxford Street,

LONDON, W. C.1.Museum 5070.

"Parmeko" Works,Aylestone Park,

LEICESTER,Aylestone 487.

Better service results from mentioning " Wireless Magazine " when writing to advertisers

485

Wireless Magazine. July 1934

WORLD'S BROADCAST WAVELENGTHS CongueerWave-length Name of Stations Dial

Readings Country Wave-length Name of Station Dial

Readings Country

60.3 Rugby GBC .. .. Great Britain 321.9 Brussels (2) _ .. _ Belgium62.5

..Long Island (N.J.) W2X .. United States 322.2 Algiers .. .. .. .. North Africa

65.93 Rocky Point WAD - .. United States 325.4 Brno .. .. Czechoslovakia68.18 Moscow (RFCK) .. - 328.6 Radio Toulouse .. .. .. 1-I France69.44 Rugby GDB .. Great Britain 331.9 Hamburg .., - - Germany70.2

..Khabarovsk RV15 .. .. U.S.S.R. c Limoges PTT .. .. .. France

73 Quito (HCJB) .. .. Ecuador335 2

' 1 Helsinki .. .. .. _ _ Finland76 Maracay (YV11AM) Venezuela 338.6 Graz .. .. .. _ Austria80 Lisbon CTICT .. .. .. Portugal 342.1 London Regional .. .. Great Britain84.5 Berlin D4AGE .. . . Germany 345.6 Poznan .. _ .. .. Poland84.67

..Mozambique CR7AA .. East Africa 349.2 Strasbourg .. .. _ France

85.9 Boston WIXAL .. .. United States 350 Bergen .. .. .. Norwayf Plymouth .. . Britain 352.9 Valencia .. .... .. Spain

203'5 1 Bournemouth .. .. ..__Great

Great Britain 356.7 Berlin .. .. - .. Germany204.2 Pecs .. .. Hungary 360.6 Moscow (4) .. .. .. USSR206

.. ..Fecamp .. .. .. .. France 36.2A Radio LL Paris - - France

208.6 Miskolcz .. .. .. .. Hungary 364.5 Bucharest .. .. .. Roumania209.5 Beziers .. .. .. .. France 368.6 Milan . .. .._

'RegionalItaly

209.9 Newcastle .. .. Great Britain iii Scottish .. .. Great Britain211.3214

..Tampore .. .. ..Sofia .. .. .. ..

FinlandBulgaria

"'"''3778

Salonika .. _ _Lvov .. , -- Greece

Poland215 Radio Lyon ...France Barcelona (EAJ l) .. .. Spain216.8

.. ..Warsaw No. 2 .. .. .. Poland 382.2 Leipzig .. _ _ Germany

218.2 Basle, Berne .. .. .. Switzerland 386.6 Toulouse PTT .. - France219.6221.1

Cracow .... .. ..Turin (2) .. .. ..

_ PolandItaly

286.9391.1

Frederikstadd .. .. ..Midland Regional - ..

-

_NorwayGreat Britain

222 Dublin .. .. Irish F. State 395.8 Katowice .. .. .. Poland.. ..Bordeaux S.O. .. .. France 400.5 Marseilles PTT .. .. .. France

222.6 f Konigsberg .. .. .. Germany4°5 1Xleville - Germany

Milan Vigentino (2) .. Italy *4 .. .. . Spain224

..Montpellier .. .. .. France 410.4 Tallinn .. .. .. __ Estonia

224.1 Lodz .. .. .. .. Poland Dorpat .. .. .. .. _ EstoniaHanover _ . , _ Germany 414.4 Madrid (Espana) .. _ SpainBremen .. _ .. .. Germany 415.5 Kiev .. .. .. .. __ U.S.S.R.

225.6 Flensburg{ Germany 420.8 Rome .. .. ItalyStettin .. : : .. Germany 426.1 Stockholm .. .. .. SwedenMagdeburg _ .. .. Germany 431.7 Paris PTT .. France

227.6 Magyarovar (2) .. .. .. Hungary 435 Belgrade _ Yugoslavia230.2 Danzig .. .. .. . . Germany 443.1 Sottens .. .. .. .. Switzerland

Linz .. .. .. Austria 449.1 North Regional .. .. Great Britain231.8 Salzburg.. Austria 455.9 Langenberg .. .. .. Germany{....

Klagenfurt ,.. .. ..-

Austria 463 Lyons PTT .. .. .. _ France

233.5DombirnAberdeen .. .. .. ___ Austria

Great Britain470.2476.9 {

Prague (1) .. ..Trondheim .. .. ..

__ CzechoslovakiaNorway

234.3 Dresden .. .. _ .. Germany Lisbon .. _ .. .. Portugal235.1 Stavanger .. .. .. Norway 483.9 Brussels (1) .. - _ Belgium236.8 Nurnberg .. .. .. Germany 483.9 Cairo .. .. _ .. _ Egypt

-238 5 I' 1

San Sebastian .. ..Rome (3) .. .. ..

SpainItaly

491.8499.2 {

FlorenceSundsvall .. __ Italy

Sweden240.2 Juan-les-Pins France Rabat .. .. .. Morocco241.9

.. .. ..Cork .. .. .. .. Irish F. State 506.8 Vienna .. .. .. Austria

243.7245.5247.3

Gleiwitz .. .. .. ..Trieste .. .. .. ..Lille PTT .. .. ..

GermanyItalyFrance

514.3514.6522.9

Agen .. .. .. ..Riga .. _ .. ..Milhlacker .. ..

FranceLatviaGermany

249.2 Prague Strasnice (2) Czechoslovakia 531 Athlone .. .. .. .. Irish F. State.. ..Frankfurt -am -Main .. ..

_Germany 539.6 Beromunster _ .. Switzerland

251 .{TrierFreiburg-im-Breisgau .. ..

GermanyGermany

549.5559.7 {

Budapest .. .Wilno .. .. .. ..

__ HungaryPoland

Cassel Germany Bolzano .. _ Italy

253.2255.1257.1

. .. .. ..Kaiserlautem .. ..Kharkov (2) .. ..Copenhagen .. .. ..Monte Ceneri .. _ ..

__ _ _

L_

GermanyU.S.S.R.DenmarkSwitzerland

569.3 1

578

Viipuri .. .. .. ..Ljubljana .. .. ..Innsbruck .. .. ..Hamar - _ .. ..

____

FinlandYugoslaviaAustriaNorway

259.1261.1 {263.2265.3267.4

Morayska-Ostrava .. ..London NationalWest NationalTurin (1) .. _ _Horby .. .. .. ..Belfast

_ - CzechoslovakiaGreat BritainGreat BritainItalySwedenN. Ireland

696726.2748 J.

I.775.2824

Oulu .. .. .. ..Ostersund .. .Moscow .. .. Geneva .. .. .. ..Boden .. .. .. ..Smolensk .. .. ..

___-_FinlandSwedenU.S.S.R.SwitzerlandSwedenU S S R.

267.4269.5269.6271.7

.. .. .. ..Nyiregyhaza .. ..Kosice .. .. .. ..Radio Vitus (Paris) .. ..Naples

__HungaryCzechoslovakiaFranceItaly

833.4845

1,1071,132

Budapest (2) .. .. ..Vadso . .. .. _Moscow (RCZ) .. .. ..Madona .. .. .. ..

___- HungaryNorwayU.S.S.R.Latvia

273.6276.2

.

. .. .. ..Madrid EAJ7 _ .. ..Falun .. .. ..

__SpainSweden

1,1811,209.6

Oslo .. .. .. ..Scheveningen -Haven .. ..

__ NorwayHolland

277.2 Zagreb .. .. .. .. Yugoslavia 1,239 Leningrad278 Bordeaux PTT .. .. .. France 1,250 Vienna (Exp.) .. .. .. Austria280.9283.3

Tiraspol .. .. _ ..Bari .. .. _ ..

U.S.S.R.Italy

1,2611,293

Kalundborg .. .. ..Kharkov .. .. .. ..

__ DenmarkU.S.S.R.

285.7288.6 1

Scottish National - ..Leningrad (2) .. .. ..Rennes PTT .. .. ..

(treat BritainU.S.S.R.France

1,3041,3121,339

Luxembourg .. _ _Ankara .. .. _Warsaw .. .. .. ..

- LuxembourgTurkeyPoland

2912913293.5296.2298.8301.5

Heilsberg .. - ..Parede .. .. .. ..Barcelona (EAJ15) .. ..North National .. ..Bratislava .. - ..Hilversum .. ..

___ GermanyPortugalSpainGreat BritainCzechoslovakiaHolland

1,3891,3951,4421,4421,5001,570.7

Motala .. .. .. ..Eiffel Tower .. .. ..Minsk .. .. .. ..Reykjavik .. .. .

Daventry National .. ..Deutschlandsender .. ..

___._-__ Sweden

FranceU.S.S.R.IcelandGreat BritainGermany

c Genoa Italy 1,621 Istanbul .. .. .. .. Turkey..,

304.' 1..

.. - ..Cracow Poland 1,648 Radio Paris _ .. _ France307.1

.. .. .. ..West Regional Great Britain 1,724 Moscow No. 1 .. .. USSR

312 Grenoble PTT .. .. France 1,807.2 Lahti .. .. _ .. Finland312.8 Poste Parisien, Paris .. .. j France

1 875f Kootwijk .. .. .. Holland

315.8318.8

Breslau .. ..Goteborg

_l GermanySweden

' 11,935

Brasov .. .. .. ..Kaunas .. .. ..

RoumaniaLithuania

486

11!

0-10,000 ohms.0-60 00001,200,0000-3 megohms.

40I Complete in case

, _ with pair of leadsand interchange-able crocodile

clips and testing prods.DEFERRED 7'ER37S IF DESIRED.

YNE


EASN'TOIA/ININ CASHAND OTHER

WIN

El A WEEKFOR A YEAR10/- a Week for a Year

£10 CASHor one of 25 other Prizes.

1111V011TRADE MARK

TEN TESTING INSTRUMENTS IN ONE

If you had a rich uncle, and he died, and(good old chap) left you a windfall, thatwould be fine. But as things are, hereis an equally opportune and much surerway of winning some welcome extracash. By simply being a radio man-interested in radio-you can win £1 aweek for a year, 10s. a week for a year,£10 cash or one of twenty-five otheruseful prizes, easily and very enjoyably.

Just as long as you are normally interested in radio andradio results, there is a prize awaiting you in a novelcompetition that anyone can enter and win without costor difficulty, without technicalities or cleverness.

Ask your nearest radio dealer for full particulars andFree Entry Forms for the AvoMinor competition-andwin an easy prize. Ask to -day l All radio shops haveEntry Forms.

But, if you have any difficulty, write for them direct.

THE AUTOMATIC COIL WINDER & ELECTRICAL EQUIPMENT CO., no.

WINDER HOUSE, DOUGLAS STREET, LONDON, S.W.1. Phone: Vic 3404-7.

""Fimmosio""'"A.C./D.C.

"w--=aSECEIVERSequipped with a Westinghouse Metal

Rectifier are more simple, reliable and

safe.

There can be no high anode to cathode

voltages, and . . . the metal rectifier

lasts for ever.

If you built the "Universal Merrymaker"

you can make it into an even more reliable

receiver by convertaingdc

mleteetal

instruc-rectifi-

cation. Blueprints n

tions are available, price 6d. post free.

METAL RECTIFIERSThe Westinghouse

Brake & Saxby Signal Co., Ltd.

82 York Road, King's Cross, London, N.!

HERE ARE THESPECIFIED

v11111iEA 1161

Regd. Trade Mark COMPONENTS

RADIO -GRAM SUPERI set of G.N.4. Coils ... 40s. Od.2 H.F.S. Chokes ... (each) 4s. 6d.I - intermediate type OTI 7s. 6d.I - intermediate type OT2 7s. 6d.

. . . and HERE IS THEUNIVERSAL' COIL

Tunes 180-550 & 850-1950 metresSpecially designed to coverthe Lucerne Plan. One Type PRICEof Coil suitable for H.F. PERAerial and Band Pass Tuning COIL

COUPON To MESSRS. WRIGHT & WEAIRE, LTD.,740 High Road, Tottenham, London, N.I7.

Please send me a copy of your booklet No. M.12, together withdetails of your Universal Coils and .. L.P." (Lucerne Plan) Circuits,particulars of your Class " B " Components (andCircuits) and alsoH.T. Power Packs with circuits.NAME

ADDRESS

W.M. 7/34

fa) 5205

487


TradeFETTER LANE'S Review of the Latest Catalogues

SEND TO US FOR THESECATALOGUES!

Here we review the newest bookletsand folders issued by eight manufac-turers. If you want copies of any or allof them, just cut out this coupon andsent it to us. We will see that you getall the literature you desire.

Just indicate the numbers (seen atthe end of each paragraph) of the cata-logues you want below :-

My name and address is :-

Send this coupon in an unsealed en-velope, bearing id. stamp, to "CatalogueService," WIRELESS MAGAZINE, 58-61 Fetter Lane, E.C.4. Valid till July 31.

CABINETS AT HUGEDISCOUNTS

T MET Mr. Salaman, of Caning -1 ton's, in Fetter Lane last week.He pressed into my hand a copy ofCarrington's cabinet catalogue andsaid that they were offering many ofthe 1933-4 models at huge discounts-40 per cent. is the figure, I believe.

There is no need for me to tellyou about the fine workmanship,design, and finish of Cameo " boxes."Believe me, there are some real bar-gains going, and I advise you to bequick and get the best of them.There are not many of thesecabinets available and they areselling like hot cakes!

You can get a Camco cabinet cata-logue with all the reductions markedthrough this free service. 396

SILENT HIGH TENSIONQILENT high-tension supply isL., essential for efficient short-wavereception and here we have it.

Milnes claim that their system isthe most efficient, convenient, andeconomical. To prove that the unitwill work your set well, you canarrange for a dealer to demonstrateit on your set.

A booklet, giving details of how thesystem works, what it is, and thecost, can be obtained free throughthis service.

You can read in this booklet what

some of the users of Milnes' unitsthink of them. 397

SMITH ACCUMULATORSACATALOGUE of S. Smith

and Sons, Ltd., the well-knownaccumulator people, has just arrived.

Details of accumulators suitablefor all radio requirements are to befound in this useful catalogue.

Names of commercial receivers arearranged in alphabetical order, withthe corresponding suitable types ofSmiths' accumulators given, so thatyou can tell at a glance whichaccumulator is required when areplacement is necessary. 398

SAVAGE SOUND SYSTEMr -r HIS Savage catalogue contains

I information about amplifyingequipment for almost every use.Secretaries of social clubs will do wellto consult this catalogue if they areconsidering the purchase of amplify-ing apparatus.

There are several types of com-plete units, which contain the ampli-fier, turntable, and pick-up in astrong wooden cabinet.

Also included are details of ampli-fier chassis, microphones, and loud-speakers of the exponential -horn,permanent -magnet, and baffle type.

399A NEW SERVICE

ALEAFLET describing a newservice for valve replacement is

something new.The V.B. Guarantee Corporation

undertake, for an agreed sum, toreplace any valve which for anyreason goes wrong in the registeredcustomer's receiver. This is thebrief outline of one of many schemesavailable.

You should send for this leaflet;it is one way of solving valvereplacement troubles. 400

NEW B.T.H. PICK-UPANEW needle -armature pick-up

has been produced by EdisonSwan Electric Co., Ltd.

488

The output is ample for all normalamplifying equipment and requiresno special high -gain preliminaryamplifier.

The pick-up and arm are sodesigned that record wear is reducedto a minimum. The head of thepick-up swivels upwards to facilitateneedle changing and volume controlis supplied with the pick-up.

It should be noted that the pick-upcan be operated at full output with-out unpleasant resonance on anyparticular frequency.

I am sure every reader will beinterested in this new pick-up.Details, of course, are free.

401

SHORT-WAVE FANS-NOTE!r -r HE bother about short-wave units

is that they seldom can be usedon batteries and A.C. mains at will.That trouble is finished. Unit Radiohas sent along a copy of a bookletdescribing a converter that can beused on either batteries, A.C. orD.C. mains. Further, it can beused as either a detector unit orsuper -het converter.

This is a real opportunity tobecome a short-wave fan. I willhave a catalogue sent along if youfill in the coupon. 402

EVER -READY BATTERIESHAVE you ever had the annoy-

ing experience of the batteriesof your portable set running downat the moment you are enjoying animpromptu dance in the country ?Take a tip from me and alwaysexamine the wet and dry batteriesbefore you take the portable out intothe country.

The new Ever Ready cataloguegives details of batteries that willfit most portable receivers, whetherhome -built or commercial.

Also included are the standardbatteries for the " home " receiver.

Send for this catalogue; you willfind it useful for reference. " A birdin the hand is worth . . ." You knowthe old saying. 403

CONSISTENCY

Corn and Condensers-what a curious combination! Yet, justas corn is a living symbol that nature never fails man-so theT.M.C. HYDRA mark on a condenser is a warrant of consistent,good performance. This unfailing consistency is only possiblebecause T.M.C. HYDRA condensers are made from the finestraw materials, with up-to-date plant under the strictest scien-tific control, to tolerance figures of the narrowest margin.

Take advantage of these new standards in condenser production.Equip your set with T.M.C. HYDRA condensers-it will bebetter for your set and better for your pocket. They are made inall standard capacities.

Write to the Distributors ifyou have any difficulty in obtain-ing supplies.

T. M . EBRITISH MADE

HYDRACONDENSERS

Price List from Distributors:

T.M.C.-HARWELL (SALES) LTDThe Sessions House, Clerkenwell Green, London, E.C.I

Telephone : Clerkenwell 6905

Made by TELEPHONE MANUFACTURING Co,ltd.


ALIZ///.7

HE NEVERGOES OUTNOW WE'VECHANGED TO

SMITH'SACCUMULATORS

To attain that purity oftone and absolute freedomfrom distortion whichconstitute perfect radioit is essential to use anaccumulator of the veryhighest grade.Supplied by a firm, inter-nationally famed for thequality of its products, aSmith Accumulator willhelp you to achieve thisideal.

cob

S. SMITH & SONS(MOTOR ACCESSORIES) LTD.CRICKLEWOOD - LONDON - N.W.2

Advertisers like to know you " saw it in the Wireless Magazine ' "

489


FLUID -LIGHT

TUNING"HIS MASTER'S VOICE"

to get finest results from extreme selectivity

All Electric SuperhetPORTABLE FLUID=LIGHT SIX

This new "His Master's Voice." Mains Portable with automatic volumecontrol and fluid -light tuning, works off the mains electricity supply andneeds neither aerial nor earth. It is the answer to all who have waited fortrue to life "mains reception " in a portable set. Its selectivity is so acutethat it is fitted with fluid -light tuning-the sensational new device thatensures accurate tuning always. In this model, two illuminated arrowsgradually approach each other until they show the exact point of perfectreception. So that by sight alone, unassisted by ear, yoti can tell when thisset is tuned to concert pitch.

MODEL. 463. Mains Portable, with self-contained earth and aerial (six valves includingrectifier). Fluid -light tuning incorporated in wavelength scale. Automatic volume control.For A.G. only.

MODEL 442

15 ONSor by hirepurchase

111

All Electric SuperhetFLUID:LIGHT FIVEA new five -valve superhet table model with automatic volume control

and fluid -light tuning. It is a delight to look at, a joy to hear, and a

pleasure to handle. Its range is extraordinary and every station is

kept distinct. The fluid -light tuning device in this model is a thin

column of light which rises and falls in a slender central window,indicating the exact spot at which perfect tuning is reached. Only

by means of this fluid -light can the extreme selectivity of this set be

fully appreciated.MODEL 442. Superhet Table Model (five valves including rectifier). Fluid -lighttuning in central window. Automatic volume control. For A.C. only.

MASTER'S VOICE"Write to -day for special illustrated leaflets.

THE GRAMOPHONE COMPANY, LTD., 108c CLERKENWELL ROAD, LONDON, E.C.1. (Prices do not apply in 1.F.S.)

Mention of the " Wireless Magazine " will ensure prompt attention

490

RadioMedley

A Radio Fan's Causerie

Conducted by BM/PRESS

The Position of theConstructor

NOBODY can deny thatthere has been a fallingoff in constructional

interest during the past year-and many and interesting are theexplanations going the rounds ofthe component manufacturers.

The chief factor, of course,has been the price reductionsmade by producers of completereceivers; many a man who wasonly a luke-warm constructorand who built his own sets in thepast because it was cheaper todo that than to buy one, now

uys his new receiver ready made.

Real ConstructorsBut people who only built sets

because of their comparative lowcost were never home construc-tors in the real sense of the term.Your real constructor had, andstill has, a greater interest in thehobby than the very material oneof saving a few shillings.

I know that some of the keen-est constructor readers of " Wire-less Magazine " are wealthyenough to buy themselves severalsets if they felt that way inclined;indeed, there are some whoactually buy complete receiversfrom set manufacturers and then compare them care-fully with their own home -constructed efforts! That isenthusiasm, isn't it ?

Another cause of hesitation on the part of construc-tors, as I have pointed out on several occasions in thesenotes, is the high cost of components in comparisonwith the cost of complete sets. That is a trouble thatwill be remedied by the manufacturers in the near

Wireless Magazine. Jul.); 1934

Chandler photoGETTING READY FOR AN S 0 S ?

Two yachting enthusiasts rigging up an aerial ontheir craft. Although far from the madding crowdthey will not be cut off from the world entirely!

ments from

H.M.V. photoTWO " STARS "!

Yvonne Prin temps, the star of " Con-versation Piece," about to play, overone of her own records from theshow on an instrument that is a" star " among radio gramophones

future, I feel sure. But I thinka gesture from the valve makersis long overdue.

What Will Olympia Reveal ?Last year's components at

Olympia were conspicuous bytheir absence; they were there,of course, but you had to lookfor them-they certainly werenot displayed in such a way thatthe visitor simply could not helpnoticing them.

I hope that the Radio Com-ponent Manufacturers' Federa-tion will take steps to see that itsmembers remedy this defectwhen this year's show opens onThursday, August 16 (by theway, it remains open untilSaturday, August 25).

From what I hear, there will 'be some interesting develop -

several quarters; and when it comes tocomponents we badly need them. If you take a lookround you will find that there have been no radicalalterations or improvements in component design forquite a long time. Radio is not so far advanced yetthat development can have come to a standstill, pro-vided our designers really get their coats off and comedown to brass tacks.

491

"Wireless Magazine. July 1934

H.M.V. photoBRITAIN'S TRAVELLING RADIO SHOWROOM

Visitors learning all about the latest radio sets and radio gramophones in the train that istouring the whole county-the most ambitious propaganda effort ever made by a radio

manufacturer. Full details for visiting the train are on page $72

At present everybody is caught in a vicious circle.The manufacturer complains that the constructor is notbuying enough and rather tends to let things slidebecause he does not receive much encouragement fromhis prospective customers. And then the constructorlooks round and sees that, apart from one or two valves,there is nothing much new in radio on which it isworth his while to spend time and money.

I put the question of money a long way secondbecause I am convinced that the constructor will spendmoney when he is offered something worth buying.

A Great Autumn Revival ?From all of the foregoing you will see that I am one

of those who firmly believe that construction has notcome to an end-and that it will not come to an end.Like everything else, I think it isinevitable that interest in con-struction among the " border-line " cases will come and go incycles (no pun intended!)

We have seen rapid develop-ments dining the past ten years;I think we shall see still greaterdevelopments during the nextten years. And, not to go toofar ahead, I think we shall seeseveral developments thisautumn that will pull radio outof the rut into which it has fallenas far as the constructor is con-cerned. The future very largelylies in the hands of the com-ponent manufacturers-and, ofcourse, the " Wireless Maga-zine " Technical Staff is dili-gently engaged in the search forworth while developments.

As you know from experience,it has never been their policy to" stunt " in any way. Only newideas of real outstanding value findtheir way into the pages of" Wireless Magazine."

Inefficient Loud -speakersLOUD -SPEAKER manufac-

turers, please do not startthrowing bricks at me when youread that heading!

I know all the improvementsthat have been made and howvastly superior is the loud -speakerof 1934 to that of, say, 1930. Butwhen is somebody going to intro-duce an entirely new loud -speakerprinciple that will give us a muchgreat conversion factor ?

Speaking (or, rather, writing)without the book, I believe that theefficiency of even the best loud-speaker is only about 5 per cent.What would happen to radio setsif we had a loud -speaker of 50 percent. conversion efficiency ? (WhenI use the term conversion I mean,

of course, the conversion of electricity into sound).With a reproducer of this type we should probably

be able to drive the reproducer direct from the detectorstage, and then where would all our quality enthusiastsbe ? There would be practically no low -frequencyarrangements for them to wrangle over!

Some time radio will resolve itself, I suppose, into acombination tuner/detector/loud-speaker no larger thanan orange. But I hope that I do not live to see thatday; half of the fascination of radio is in the size of theapparatus, I think. Which is one reason why construc-tors as a whole have never taken much interest inmidget sets.

How much more impressive it is to have a set witheleven valves and about 5 ft. long-which is the size ofan amateur's super -het that I was able to see recently.

I at once felt that I must knockmyself up at least a twelve-valver, 6ft. long !

Marconiphone photoGRANNY LISTENS -IN

The older generation still gets a thrill out of themarvels of radio; and it is a great boon to thosegetting on in years to have the world's best enter-

tainers brought right into their homes

492

That Television CommitteeWITHIN a few months it is

likely that we shall knowwhere we stand with regard totelevision broadcasts. The wholeposition is chaotic at the moment.Some people want the 30 -linetransmissions retained indefin-itely; others say that televisionwill never get anywhere until weget the real high -definition stuff;and others are arguing as towhether the latest form of enter-tainment should be controlled bythe B.B.C. or by some newcorporation or company.

Well, the P.M.G.'s television

committee has a nice little problem to solve-and it willprobably take them some time to come to a conclusion.Whatever their decision, it is certain that it will notplease everybody, but some definite policy will be betterthan no policy at all.

It is no secret that Mr. Noel Ashbridge, the B.B.C.'schief engineer, is in favour of high -definition televisionon short waves (which means of the order of 7 metres),but there are the claims of those with 30 -line apparatusto be considered.

Whatever happens, as far as I can gather, we shallnever have the same position that we had when broad-casting began-that of one corporation holding asufficient number of key patents to control the wholetrade. There is nothing new about the cathode-raytube, and if high -definition television does come soonmany manufacturers should be in a position to producethe necessary gear.

If we come to 7 -metre stuff, it seems as if the greatestproblems will be in the actual radio end of the reception


Marconi photoNEW FOUR-ENGINED IMPERIAL AIRWAYS LINER

A new four-engined Irrperial Airways lin.r the " Scylla," built by Short's and radio -equipped by Marconi's. This photograph was taken by the hangars at Croydon Airport

PREPARING FOR BIG RADIO DEVELOPMENTSAt least one manufacturer is convinced that radio is going to boom again soon. Cossor's,Who already have extensive works at Highbury, are building a new factory to accommodate

over 1,000 workers, It will be ready in the Autumn

493

Cossor photo

Marconi photoTRANSMITTER -RECEIVER

The transmitter covers the waveband of500 to 1,000 metres, and the receiver isthe well-known "screen -grid, detector,

pentode" arrangement

and not in the pure television partof the business.

By the way, isn't it a pity thatthe Committee's deliberations willbe held in private ? I think that thepublic ought to have had theopportunity to know what evidencethe Committee takes so that it canform its own opinion of the justi-fication for the final decisions.

Car RadioALTHOUGH I am still not able

to make up my mind as towhether I want a car radio set ornot I am glad to see that oneBritish manufacturer has got downto a mass -production job. If radioon the road is to grow it is as wellthat British manufacturers shouldget what business is going insteadof letting it go to their Americanrivals.

At a luncheon I attended recently,to introduce a new car radio outfit,several people got up and pointedout the difficulty of getting suchsets installed and suggested the needfor a series of properly organisedservice stations. I think that weshall see definite moves in thatdirection shortly.

(London, W.C.2, BM/PRESS).


A New Push-pull Method/T is accepted as commonplace

fact that of all methods of coup-ling two valves together for low -

frequency amplification, resistance -capacity provides the best quality.This is because it gives even ampli-fication over a large range of frequen-cies, and can be designed to dealfaithfully with transients (quickchanges of low -frequency signals).

The logical conclusion in designis that in some way the advantages ofresistance -capacity coupling shouldbe combined with push-pull to

RESISTANCE -CAPACITY PUSH-PULLFig. 1.-A circuit for resistance -capacity push-pull with anindirectly -heated driver valve for two directly -heated triodes

avoid amplitude distortion due tocurvature of valve characteristics.

Until now this has been accom-plished by using not less than fourvalves : two as output valves-letus call them v, and v2-working theloud -speaker, and two, v3 and v4, todrive the output valves.

To obtain push-pull workingfrom the two output valves v1 and v2it is necessary to apply to the gridof v2 an input voltage which is 180degrees out of phase with corres-ponding voltage at the grid of v1.

Old MethodUntil now, using resistance -

coupling, this is done by letting v3feed v1, and at the same time v3 givesv4's grid a small fraction of itsoutput. Then v4 feeds the outputvalve v2.

In this process the necessaryphase reversal is obtained.

The writer has found (see Prov.Patent No. 9625/34) that by usingone indirectly -heated valve as driverthis valve can supply signals to twooutput valves and provide phasereversal as well. The output valves

By F. E. Cox, B.Sc.

need not be indirectly -heated.The principle involved is that

the A.C. output at the anode of avalve is 180 degrees out of phasewith the A.C. voltage output at thecathode of the same valve, supposingthat both an anode load resistanceis being used together with a cathodeload resistance.

It may be recalled that it is quiteeasy to dispense with all forms of

anode -lead loadHT+ and put it instead

in the cathodecircuit, using anysuitable couplingdevice between itand the nextvalve. Such isknown as acathode - couplingcircuit.

All the writerproposes to do isto divide the out-put of the drivervalve betweenanode and cath-ode. For this

purpose, as shown in Fig. 1,an anode resistance of, say, 10,000ohms is put between the anodeand high-tension positive; also a10,000 -ohm resistance is put betweencathode and high-tension negative.

A condenser and grid -leak couplingconveys a signal from the anode topower valve v1, and a similarcoupling takes a signal from thecathode to powervalve v2.

The loud-speaker may havean output trans-former incor-porated. In thiscase its primarywill connect withterminals x and Yon the centre -tapped low-fre-qu e n c y chokeused as outputload to the twopush-pull powervalves. Alterna-tively, this outputchoke may bereplaced by a

494

centre -tapped output transformeror even by two output resistancesif a sufficiently high anode voltagecan be given, in which case theloud -speaker will be connectedacross from plate to plate withoutusing the usual stopping condenser.

It will be noticed that the drivervalve up to now is acting as a grid -leak detector, but it may equallywell be an amplifying valve followinga diode detector or Westector orgramophone pick-up. The suggestedcircuit with full decoupling is Fig. 2.

Balanced InputsTo obtain the best results it wilt

be necessary to balance the inputsto v1 and v2. The writer suggeststhat the grid resistances R1 and Rabe variable. Set both at maximumand, having pulled out v2, take itsgrid lead to v, instead.

Now although v1 will give goodworking of the loud -speaker withoutv2, yet when v1 receives inputs fromboth grid -leak resistances signalsdie away, having cancelled out.Vary R1 to find if possible a moremarked minimum signal and, if not,restore R, to maximum and varyR2. With the best 'setting found,v2 is inserted in its valve holder,but R2 is returned to the grid of v2.

If the two power valves do notrequire a large input the circuit ofFig. 1 suffices, but where very largepower valves are required, thenNT, and v2 must serve as intermediatelow -frequency valves, passing onsignals by resistance -capacity to thetwo chosen power valves.

d

e f

Va

I -1T+

HT -

UNUSUAL METHOD OF PUSH-PULLFig. 2.-In this circuit the input to the two output valves can beindividually controlled. Separate automatic bias allows the

careful matching of each output valve

Wireless Magazine. July 1934d

Many of the topical pictures seenin the newspapers are sent to theprinters by wire, and frequentlyby wireless, from places often1,000 or more miles away. Inthis interesting article the methodsby which pictures are transmittedand received are explained byW. T. LO WE and E. PHILLIPS.So that readers can appreciatethe high quality of the trans-mitted pictures, every illustrationin this article is reproducedwithout any retouching and exact-

ly as received from abroad

Sending Picturesby Wire and

WirelessTHE idea of telegraphing pic-

tures and fascimile is not anew one by any means.Indeed, F. C. Bakewell, an

Englishman, invented such a systemas far back as 1850!

Shellac -ink (which, as you know,is a non-conductor of electricity)constituted the pri-mary factor fortransmission. Withthis, the writing ordrawing to be tele-graphed was in-scribed on a metalcylinder. A finemetal pointermoved over the sur-face of the cylinder,tracing a spiralfrom one end to theother. Naturally, asthe pointer passedover the shellac -ink, current ceasedto flow.

At the receiving

end a cylinder, similar to that in thetransmitter, rotated at the samespeed. The current decomposed achemical with which a piece of whitepaper had been impregnated. Thispaper was mounted on the cylinder.Current passing through a metalpointer caused a brown stain to

PICTURE -TELEGRAPH ROOM AT THE G.P.O.This is where pictures are sent and received at the General Post Office, London.From left to right are the power board, telephone board, sending machine, control

panel and receiving machine

495

Keystone photoOne of the authors of this article, E.Phillips, with a Siemens Karolus-

Telefunken picture transmitter

appear. The picture, or writing,came out in white on a brown back-ground. For various reasons, thissystem met with no success.

In 1862 the Abbe Caselli inventedan apparatus on similar lines. Thiswas actually in use for some years onthe Paris -Amiens wire. It trans-mitted diagrams and drawings.

Black and White DesignsAnd then in 1878, d'Arlincourt, of

France, introduced a picture tele-graph which reproduced designs inblack and white. The British PostOffice experimented with this instru-ment at the Central Telegraph Office.

The picture, which measured 12 in.by 2 in., took seven minutes totransmit. This wasn't quick enoughfor St. Martin's -le -Grand, and thesystem was turned down. They

gave the system alonger trial inFrance, but even-tually scrapped it.

Most of thetrouble was due todifficulties ofsynchronisation.This is as essentialin picture tele-graphy as in tele-vision. In the for-mer case, variationin speed producesresults which arenot rectangular.They becomerhomboidal.

The solution

Post Office photo

Wireless Magazine. Juty, 1934

TELEGRAPHED FROM MUNICHLittle detail has been lost in this telegraphed picture of theinterior of St. Stephen's Church, Vienna. The picture was

telegraphed from Munich to London

was not discovered until 1919. Sincethen the tuning -fork has been usedto obtain this precision in syn-chronism. So sure is the tuning -forkcontrol that it is now used in allsystems of picture telegraphy.

This branch of the science oftelegraphy did not make much head-way, however, until the year 1873.The period coincided with the dis-covery of the light-sensitive pro-perties of selenium.

Use of SeleniumAn Englishman, Mr. Thorne -

Baker, and a German, ProfessorKorn, both used selenium for trans-lating the light and shade of a pic-ture into electric current. The lattersystem was so successful that theGerman police actually made use ofit on more than one occasion. Notonly that, but our own Daily Mirrormade a scoop by experimenting withit, and acquiring the British patentrights.

Owing to the slow response ofselenium to variations of light, thesystem did not attain any great use.Also, it must be remembered thatthe lines used for transmission werenot technically so good as they aretoday.

The discovery cf the thermionicvalve, the photo -electric cell, and

improvement inphotographic ma-terials providedsolutions to most ofthe problems. Pic-ture telegraphy be-came a definitepossibility, and in1926 three systemswere introduced ascommercial proposi-tions-the Siemens-Karolus Telefunkenin Germany; the Be-lin in France; andthe Bell in America.

Except for rapidtransmission ofnewspaper photo-graphs, the com-paratively small dis-tances between citiesand towns in theBritish Isles did notoffer much induce-ment for its use.From this countryto the Continent,and between citiesin the U.S.A., how-ever, the interveningdistance made it

possible to open up working agree-ments.

Consequently, in 1930, Londoninaugurated its first public picturetelegraph service with Berlin. At thepresent day the service is available tothe following Continental cities:Frankfort -am -Main, Berlin, Copen-hagen, Munich, Vienna, Stockholm,

Rome, Oslo, Amsterdam, Paris,Lyons, Marseilles, Nice, Bordeaux,and Strasbourg. London also acts asan intermediate station between theseplaces and America.

Although their functions are close-ly allied, the difference in size be-tween a televisor, whatever theparticular system, and a commercialpicture -telegraph installation isenormous.

Three Rooms of Gear !The plant for running the Sie-

mens-Karolus apparatus, which is inoperation at the Central TelegraphOffice, occupies three rooms. Oneroom contains the operating instru-ments; another is devoted entirely tobanks of secondary cells, and a thirdis used for developing and printing.

Transmitter and receiver are sepa-rate. Both are contained in metalcases measuring about 3 ft. square.

A motor for driving the mechan-ism is enclosed and on top a smallermetal case holds the actual sendingand receiving gear. Amplifiers andother necessary details adorn a con-trol panel, and the operator keeps intouch with the station to which he isworking by means of a telephoneconnected to this panel.

Transmission GearComponents consisting of a photo-

electric cell, a spot -light lamp, atooth -edged disc, Kerr cell, etc., areemployed for transmission.

The matter to be telegraphed isclipped on to a metal cylinder. This

Daily Mirror photoSPEEDING UP NEWS PICTURES

This photograph of the Irish mailboat "Duke of Lancaster" being inspected by diversand salvage men in Heysham Harbour was telegraphed to London by the Siemens process..

Picture telegraphy is a great help in speeding up news pictures

496

REMARKABLE PICTURE FROM COPENHAGENHere is a remarkable example of the detail that can bemaintained in telegraphed pictures. As you can see, little

detail has been lost

N.P I T t..- It 11,.. it JUL_LL:s:,,,LS k 1 1 E 1 11. P

0611171.4jrailj, ;411188111SAP TOW 3.

Ill k W A

7

E ), ig...--

'0

' 4oLbar6

f/f$/lle.nsaiSa

.

ll'i'INAA'T A

# 3

- .'Hamburg

, '9 Cottiel

V3.4./e-----IP 1

4°..-, ; ' 1 PCLAXI,

85 14 i

Al'

'0111,'

ug't'...""*SP,,.... '0 slog,. .1.4,PW4 '..

08E057

$ '

L

........,A SZE3110-',,P,

re 7,A .. 5...8. 0 V A X 1 W -

, :,,,,:,.,k , '-5n1rat, ,... S t it

.

461/8.1 SET

ofann, ..s., p4t..,

--_.?saiin V Z agrS

lb JUZ0SLAV'S

la 11

7

$ P A 16 Privs*

I t E EPAWEAS Nal§ AOHL T"

°SSA

SENDING MAPS BY WIREThis line drawing showing communication between Londonand the Continent was sent by a system of facsimile telegraphy

497


ANOTHER PORTRAIT SENT BY TELEGRAPHThis picture was telegraphed from Copenhagen to Londonon August 2, 1930. Like all the illustrations in this article,.

this picture has not been retouched

TELEGRAPHED DRAWING FROM BERLINMeasuring 315 square centimetres, this drawing was sentfrom Berlin to London. The cost for this drawing was f3 5s. 7i d.

Wireless Magazine. Jilt)! 1934

CONGRATULATED ON WINNING A TOURIST TROPHY RACEStanley Woods, the well-known racing motor -cyclist, being congratulated on winning aT.T. race in the Isle of Man. This picture was telegraphed to the "Daily Mirror" in

London. The &tail is especially good.

revolves continuously in front of thephoto -electric cell. The spot -lightlamp directs a beam of light upon thesurface of the picture, and the tooth -edged disc rotates in the path of thislight.

Form of a RingIn the Siemens-Karolus picture

telegraph the photo -electric cell ismade in the form of a ring. Thelight passes through the central holeto the picture.

So that the light shall be focusedon the picture, a lens is mountedjust behind thecell, the wholesystem beingmounted on ascrew. This isturned by gearingwith the drivingmotor.

The cell isplaced close to thecylinder on whichthe picture is clip-ped. If the light -tight case could beremoved youwould see thecylinder revolvingand the photo-electric cell andlens graduallymoving up anddown. Point bypoint the pictureis being scannedby a spiral of light,top to bottom.

If a telephone be placed in circuit,we should hear a burbling note,similar to that heard in televisionvision broadcasts.

Preparatory to reception, a film isclipped on to a cylinder in the darkroom. This is then enclosed in thelight -tight case, which has a shutter.When the case is placed in thereceiver, the shutter opens.

Focused on the film through thelens, light from the spot -lamp passesthrough an optical system of nicolprisms and Kerr cell, and the varia-tion in light value, due to incoming

Daily Mirror photosADMIRAL BYRD IN ARCTIC KIT

This photograph of Admiral Byrd inArctic kit was telegraphed from New

York to London by cable

HIGH -DEFINITION PHOTOThe definition of this picture, tele-graphed by cable from New York to

London, is really quite satisfactory

498

currents passing through the Kerrcell, affect the photographic filmpoint by point according to lightand shade in the picture beingtransmitted.

The film is then taken into a dark-room, developed, fixed, washed anddried; about thirty minutes being

Daily Mirror photoVIA ATLANTIC CABLE

This fire -rescue picture was telegraphedvia Atlantic cable by the Bart -lane system

to the" Daily Mirror"

required to turn out the finishedprint.

Incidentally, the light spot at bothends traverses a surface of about 7 in.by about 10 in., or 18 by 25 centi-metres-the size of the cylinders inuse. The area of the whole surface isapproximately 450 square centi-

metres. The spot-light travels at therate of four linesto each millimetreof depth. Thisapproximates 100lines to the inchand therefore 720lines from top tobottom completethe picture.

Each spot oflight is contiguouswith the preced-ing one, so thatthe finished pic-ture shows no signof roughness.

The total dis-tance travelledfrom top to bot-tom by the spotof light is 661 ft.and takes 121minutes for a full-size picture.

The Post Office, however, has aminimum charge for an area of 96square centimetres; but between thetwo extremes, any area can betelegraphed at appropriate charges.

The apparatus used in France isthat invented by M. Edouard Belin.This employs the photo -electric cellfor transmission, but for receptionuses an oscillograph. This is a smallmirror vibrating between the polesof an electro-magnet.

French MethodsA rectangular beam of light is

directed on to the mirror and thencereflected on to a triangular opening.A lens is placed behind which con-centrates the beam into focus on thereceiving cylinder.

The light may shine either on thebroad base or at the apex of thetriangle. The amount of light pass-ing through the lens thus varies.Movement of the mirror is affectedby the currents from the sendingapparatus, and the picture is built upby means of the consequent vibra-tions.

This system scans at the rate of5-1 lines per millimetre, approxi-mately 130 lines to the inch.

On the Marconi -Wright picturetelegraph installation it is possible tosimultaneously transmit two mes-sages or pictures. The system differsconsiderably from any other. Mes-sages occupying a space of 10 in. by4 in. have been received in the fasttime of four and a half minutes.


FROM THE MIDLANDS TO LONDONA photograph of the Princess Royal in the hunting field telegraphed by the Siemens

system from the Midlands to London

In the interests of speed-alwaysthe first consideration in telegraphy-a useful feature is that it, is notnecessary to stop the apparatus everytime another picture is placed in thetransmitter, or taken from thereceiver. The instrument runs con-tinuously. Time taken in repeatedsynchronising and restarting istherefore obviated.

The Bart -Lane system, whichworks over the Atlantic cables, givespictures with a heavy grain, but showa good range of tones.

Three pictures typical of theBart -Lane system are reproduced-

TELEGRAPHED PICTURE OF A RAILWAY SMASHA picture of a railway smash at Wardleworth, near Rochdale, which was telegraphedto the " Daily Mirror" in London. The caption is transmitted with the picture

499

without retouching-on the oppositepage. There is no difficulty inidentifying the subjects although thegrain is definitely coarse.

Pictures are also flashed across theAtlantic by wireless. Imperial andInternational Communications, Ltd.,has coined the word " Photograms "and the system is known as theWireless Photogram Service. Inci-dentally, this company publishes anillustrated brochure which presentsinformation of the service in aninteresting and picturesque manner.

At least a week is saved by thussending pictures and facsimile acrossthe Pond.

Use in RussiaIn Russia, wireless is extensively

used for the same purpose. Muchnewspaper work is conveyed by thismethod-sheets of printed matterbeing dealt with in extenso.

Although Knudsen obtained onlycrude results, it will perhaps benews to the majority of readers thatthe transmission of pictures by wire-less was first attempted in 1908.

And we daresay our enthusiasticfriends will be delighted to knowthat, with a simple form of apparatusinvented by Mr. Thorne -Baker, it ispossible to pick up broadcast pic-tures with a two -valve receiver!

There seems to be room here foryet another feature of fireside enter-tainment. Many readers will, nodoubt, still remember the attemptsof the B.B.C. to broadcast picturesby means of the Fultograph someyears ago.

Wireless Magazine. thity 1934

Very soon we shall be hearing the lastsignals from Daventry National. Hereyou see the first control panel used in

the transmitting hall at Daventry

DROITWICH may have calledyou by the time these wordsare printed. We are as near

as that, I mean, to a complete changein the B.B.C.'s system of broad-casting.

For many years we have beenapproaching the completion of whateveryone knows as the RegionalScheme. Twin centres of broad-casting, giving to listeners usingrelatively simple sets a choice of atleast two programmes, one nationaland the other of local or at least ofregional interest and origin.

Five of these centres went into themaking of that broad plan. Brook -mans Park for London and thesouth-east of England; Daventry forBirmingham and the Midlands;Moorside Edge for Manchester andthe vast industrial north; Westerglenfor Glasgow, Edinburgh, and theLowlands of Scotland; and, lastly,Watchet for the West Country andSouth Wales.

Indeed, a brave scheme of broad-casting, conceived at a time when

stations were relatively few in num-ber and most certainly low in power.The scheme aimed at providing atruly homogeneous service of pro-grammes if not to every nook andcranny of the country, at least toevery area of dense population.

Progress in broadcasting all overthe world, and particularly in Europe,

Broadcasting Union made it clear toall that watertight national schemesof broadcasting must needs fit inwith international obligations.

Foreigners looked with criticaleyes on this Regional Scheme of ours.Why, they asked, do you need somany wavelengths for your nationalprogramme when you have inDaventry a station fully able to servethe whole of the country ?

It was a question the B.B.C. couldnot with real justice brush aside.

In this country, too, listeners beganto realise that, although there mightbe five centres of twin radiation, oneprogramme from each was the com-mon National-a programme alreadyavailable to them from Daventry.

Droitwich MeansNew Regional Plans

says ALAN HUNTER

did not stand still while this RegionalScheme crystallised. Stations sprangup, powers increased, and demandson the ether became ever moreonerous.

Conference after conference underthe auspices of the International

That the B.B.C., in pursuing itsidealistic Regional Scheme, was guiltyof an indefensible wastage of wave-lengths became palpably obvious.From that moment the RegionalScheme as originally conceived wasdoomed-the more especially as the

NEW STUDIOS FOR WESTERN LISTENERS"The B.B.C. is well developed with up-to-date studios," says Alan Hunter. This is one

of the palatial new studios recently built at Cardiff

500

" nooks -and -crannies " listeners ofthese islands were growing restlessfor want of reliable programmesdenied them under the five -centresystem of transmission.

At this point it is only fair to saythat when the Regional Scheme wasconceived no one had any idea howbroadcasting would develop-cer-tainly no one imagined there wouldbe such a colossal increase in thepower of transmission.

When Daventry was brought intoservice with its 35 kilowatts it washailed as a veritable giant amongbroadcasters, which, of course, itwas in comparison with prevailinglow -powered transmitters in thiscountry and in Europe generally.

Any idea of expecting the PostOffice to grant permission for a

power of over 100 kilowatts wouldhave been absurd. The B.B.C. hadfight enough to get as much as35 kilowatts.

Yet it was possible, even in thosedays, to say that while Daventrywould give a very good signal withinsay, 150 miles of its site, it wouldfade out appreciably at the farpoints, such as Devon, Cornwall,and Northern Scotland and Wales.

Unfortunately, the twin centres ofradiation that followed the erectionof Daventry did nothingto help these out-of-the-way listeners. In fact,amazing though it mayseem in retrospect, eachof the " little Nationals"at Brookmans Park,Moorside Edge, andWatchet did little morethan duplicate theDaventry Nationalprogramme, withoutappreciably extendingthe reliable range of theNational programme.

That is to say, listen-ers who could obtainfade -free reception oflittle Nationals at nightcould in any case getDaventry quite well,whereas those who wereon the fringe of theDaventry service areawere still quite hope-lessly outside the ser-vice areas of the littleNationals.

Droitwich, with its150 kilowatts, will pro-vide an average of twoand a half times the

strength of signalof Daventry. Itseffect will bemostly felt in theoutlying districts-beyond thepresent reliablerange of Daven-try, that is.

In this way,then, we can hailin Droitwich thefirst real nation-wide servicestation. Every-one, no matterwhich nook orcranny of thecountry he maydwell in, shouldbe able to rely onDroitwich for hisNational pro-gramme. That isa real advancefrom the B.B.C.'sservice point ofview.

If the little Nationals were tendingto be redundant with Daventry, theymost certainly are redundant withDroitwich. Without any qualm, theB.B.C. intends to shut down theNationals at Brookmans Park, Moor -side Edge, and Watchet.

[Wireless Magazine. Juty, 1934

DIESEL I \GI \L.s Al LAITHWAITEThere alit two of these huge DI2sel eng nes at Slaithwaite-one for driving each ransmitter. Both engines will be usedfor driving an improved Regional transmitter under the new

plan

Few will mourn their passing. Onmediocre medium wavelengths theyhave not been the success anticipated-at least, not outside a very shortradius from the station site.

For example, living about forty-five miles from Brookmans Park, I

have never been able toget London National atnight without severe dis-tortion and fading. Sinceit has been synchronisedwith West National re-ception has been a farceexcept in the early after-noon.

AT THE FOOT OF THE HUGE DROITWICH MASTSWorkmen putting the finishing touches to the two 700 -ft. steel masts atDroitwich. The new Droitwich aerial will be slung between the twomasts and the new Midland Regional aerial will be slung from the top

of one mast to a point near ground level

501

Thousands of listen-ers must be similarly

placed in relation to theother little Nationalsand, like me, they havefor years gone over to" woomphy " Daventryfor the National pro-gramme.

Such listeners willbenefit enormouslyfrom the coming ofDroitwich. Quality oftransmission will un-doubtedly be very muchbetter than from Daven-try, a station whichwe ought not to forgetwas in the nature of anexperimental plant, any-way.

By the closing down


of the three little Nationals at Brook -mans Park, Moorside Edge, andWatchet two wavelengths will bereleased-not three, because as alreadystated, London and West Nationalsare sharing a common wavelength.

Three transmitting plants are alsoreleased. Not to be scrapped, of

course, for the B.B.C. is using theopening of Droitwich to slide gradu-ally from twin -station broadcastingto its new and saner system of one -point regional transmission.

London National as a station willbe moved to Droitwich, where it willbecome, with new power plant, thenew Midland Regional transmitter.

West and North Nationals, withan entirely new plant like them, willbe shared out among the projectedNorth -Ireland Regional, North-eastern Regional and North -ScottishRegional.

North -Ireland Regional will prob-ably take over the present Belfastwavelength, while Midland Regionalwill be accounted for by somechange over of its present wavelengthwith another. The two releasedwavelengths of North and WestNationals will help when North-eastern and North -Scottish stationscome on the air.

At the moment it is impossible tosay how one present group of

wavelengths will be rearranged.Considerable alteration is certain.The Midland Regional, for example,with its higher power and closerproximity to Birmingham, will haveto manage with a shorter wavelengththan now.

Incidentally,while listeners arewaiting for thechangeover fromthe present twin -station system tothe one -point sys-tem the B.B.C.will utilise itsreleased wave-lengths forAberdeen andNewcastle.Whether this isfor fear of foreign-ers " jumping ourclaims " is notofficially stated-but I have my ownopinion.

At each of theRegional stations,all of which I

have had the pleasure of examiningas they were opened, there are threegiant Diesel engines, two in use andone in reserve. When the sites aredenuded of their little Nationals allthese engines will remain in order toboost up the power of the Regionalsto a power of 70 kilowatts. TheB.B.C. has no intention, you see, ofallowing foreigners to shout usdown.

Some scrapping of plant is inevit-able, naturally. The transmitters atDaventry giving us the MidlandRegional and the Daventry Nationalprogrammes will both go. They haveserved their turn more than well.

As a site, then, Daventry will beleft free for the Empire stations. Forthe present it is intended to keep upthe 500 -ft. Daventry masts, whichwill serve to support short-waveaerials to radiate to various Empirezones. Meanwhile, 350 -ft. masts aretaking the place of the original 80 -ft.masts with which the Empire servicewas started.

So that, even when Daventry is nolonger a part of the home broadcast-ing scheme, it will go on being oneof the most important links in B.B.C.activities.

For reasons best known to them-selves, the B.B.C. engineers con-sider the synchronising of Londonand West Nationals a success. Thiscan be the only reason for their ideaof erecting a relay transmitter toserve neglected South Wales, to besynchronised with West Regional.But that is looking ahead, rather.

Droitwich will have other import-ant effects. For instance, when it

provides the south coast with areally good National programme, thelow -power transmitters at Bourne-mouth and Plymouth will not berestricted to relaying the Nationalprogramme. They will be able totake a pick of the Regional pro-grammes, and thus give their locallisteners an alternative.

Claims of the extreme west and ofthe Duchy of Cornwall cannot

be indefinitely ignored. It is likelythat, to placate these listeners, whoundoubtedly have a real grievance,the B.B.C. will move the presentlow -power Plymouth plant to apoint outside the city and increaseits power.

Another idea, which is not morethan a remote possibility, is to erecta low -power relay right in the Duchyand synchronise it with Plymouth orWest Regional.

So much, then, for impendingstation changes-all following thesuccessful operation of the newDroitwich National. I have told youenough to prove that the oldRegional Scheme is dead and a newscheme is coming.

I ought to have mentioned, per-haps, that Scotland will retain itslittle National, as the B.B.C.. engin-eers are not confident that Droitwichwill be able to supply a really goodsignal over the border.

As for feeding all these new radia-tion points, the B.B.C. system

is remarkably well developed withup-to-date studios. Very littleadditional accommodation is con -

t e m plat ed.

TRANSMITTING HALL AT WEST REGIONALOn the left you see the National transmitter and on the right the Regional gear.Very soon the National gear will be dismantled and erected in one of the new

projected Regional areas

502

Bangor will be theonly importantaddition, to serveWales and WestCountry.

North-easternRegional will befed from the new-ly enlarged New-castle studios andwill be able todraw upon thepalatial Man-chester and Leedsstudios; the Westwill have itsstudios at Cardiff,Swansea, andBristol; Scotlandwill be well pro-vided by Edin-burgh, Glasgow,and Aberdeen.


Here we give full construc-tional details of an ambitioussuper -het radio gramophone.It has been designed by

S. Rutherford Wilkins and isdescribed by the "WirelessMagazine" Technical StaffThe set is arranged with a

push-pull output stage givingabout 5 -watts undistortedspeech output. One -knob

tuning and delayed self-adjusting volume control aretwo outstanding features of

the design.

The"W.M."

RADIOGRAM

SUPERALTHOUGH this set is not everybody's meat-

its size and cost preclude that possibility-yetevery constructor will learn something from

reading the description of it. It represents the last wordin circuit arrangement and in construction-everyworth -while trick of modern technique has been usedin its production, and in its class it will be extremelyhard to beat.

Many Months of WorkA receiver of this kind cannot be knocked up in a

few days; it takes a week or two to get the best outof a simple three-valver, and when it comes to anambitious multi -valve super -het like this " W.M."Radiogram Super, then the designer has to get down tomany weeks of hard work before everything is workingsmoothly with really tip-top results.

In its final form the set approachesas near the ideal super -het as it ispossible to get with present-daymethods. There is, of course,tremendous power-both in the wayof range and actual output-and itgoes without saying that the selec-tivity is of a very high order.

As a radio set the " W.M." Radio-gram Super is something to take noteof; and on the gramophone side itsarrangement is equally impressive.

Let us look into this he-man's setstage by stage and see how and why

certain things have been done. But before we do thatlet us just say that the set is arranged to operate from A.C.mains; and care should be taken to order the mains trans-former for the correct voltage and frequency of supply.

Nine Valves Pulling their WeightIt will be seen from the photographs that there are

nine valves in the set altogether, but not all of theseare used at once. For radio reception seven valves areused in addition to the mains rectifier; and for gramo-phone -record reproduction four valves are used inaddition to the mains rectifier.

The seven -valve radio part of the outfit comprisesa six -stage super -het with One intermediate -frequencystage (working at 126 kilocycles, as is usual with all" Wireless Magazine " designs). There are only sixactual amplifying stages because the last two valves

503

Wireless Magazine, July, 1934

CONTROL LAYOUT ON THE RADIO UNITThe four control knobs on the radio unit are, from left to right, the wave -change switch,

the main tuner above the noise suppressor control, and the radio volume control

SIMPLE AND EFFICIENT LAYOUTAs you can see from this back view of the radio unit, the condensers, coils, and two ofthe valves are screened to ensure complete stability. On the back of the chassis are the

aerial and earth sockets

are arranged in a push-pullcombination and count there-fore only as one stage.

For gramophone work the firstfour valves are switched com-pletely out of circuit, but anadditional low -frequency ampli-fier to allow of good tone com-pensation is automaticallyswitched in; thus there are fourvalves comprising three actualamplifying stages.

As the power stage remainsunaltered the output n mainsthe same whether the gear isused for radio or gramophonework; in each case there isbetween 4 and 5 watts un-distorted speech output. This,

I/ 0005

05

50

of course, is enough to drive severalloud -speakers, and anybody buildingthe set up will have ample powerto wire a number of reproducers upin various parts of the house.

The set would be ideal for a clubhouse and is also suitable for use inquite large sizes of halls where theaudience may be as many as 300 or400 people.

Looking into the radio side first,we find that the six stages arearranged in the following sequence:

Very Latest Valves(1) Preliminary high -frequency

stage, making use of one bf thelatest high -frequency pentodes. Thisvalve gives really good high -frequency amplification and, ofcourse, obviates any possibility ofsecond -channel interference. It isrecognised that the preliminaryhigh -frequency stage is desirable,and even essential, for the bestresults in the present congestedstate of the ether.

(2) The second valve is a com-bined detector -oscillator, and here apentagrid is employed-the bestvalve that has yet been producedfor this dual function. That, ofcourse, is because it is really twovalves in one (by the way, a pentagridis the same thing as a heptode).

Intermediate -frequency Stage(3) Then we come to the single

intermediate -frequency stage, whichis another high -frequency pentodegiving a high degree of amplifica-tion. This valve amplifies at afrequency of 126 kilocycles and needstwo intermediate -frequency trans-formers; these, however, are fixed -tuned and do not need any adjust-ment at all by the operator.

10,000

0.1

03,000(5000

20,000- - 15,000

Tm 1F13.

4MFD.

.000o

MO

30,000

00,000

C12:_0

5M, lift.

AMA30,000

CIRCUIT OF THE " W.M." RADIOGRAM SUPERAs you can see from this circuit, four valves are used in the radio unit, and in the amplifierthere are two stages of low frequency amplification besides the push-pull output. Only oneof the low frequency amplifiers is used when the set is on radio, both ore brought in use for

gramophone reproduction

504

(4) The second detector is anothercombination valve, a double -diode -triode. One diode rectifies in theusual way; the second diode is usedfor getting self-adjusting volumecontrol; and the triode amplifiesthe rectified signals before passingthem on to the next stage.

(5) The fifth valve is an inter-mediate low -frequency amplifier,not often found in present-day setsbut needed here because a large gridvoltage is needed to load up thetwo push-pull power valves.

Push-pull Output(6) The sixth stage is the push-

pull output arrangement. For thesake of quality-tone compensationwould be needed if pentodes wereemployed-triodes are used in thisstage. Each gives an undistortedoutput of the order of 2.5 watts, sothat the set will give all that anyordinary user can possibly requireof it.

That is all very well, you will say,but how many controls do all thosevalves entail ? That is a point thathas been carefully watched, with theresult that there are only fourcontrols on the front of the set. Butbefore we go into their functionsthere are the tuning arrangementsto be considered.

Eight Tuned CircuitsIn all there are four variable -

tuned circuits and four fixed -tunedcircuits, making a total of eight:this number means that the selec-tivity is all that can be desired andthat stations working on adjacentwavelengths under the Lucerne Plan,except when the set is used within afew miles of a broadcasting station,can be separated without difficulty.


ANOTHER BACK VIEW OF THE RADIO UNITThis photograph emphasises the simplicity of the radio unit. The set has been designedso that the beginner with little experience at set construction will find building a really

easy fob. The metal chas_is can be obtained ready drilled

HOW THE AMPLIFIER SECTION IS ARRANGEDThe amplifier unit contains the whole of the low frequency portion of the set, togetherwith the mains -rectification and smoothing circuits. The plugs and sockets are for

the mains input and a spare one for use if required

000The aerial circuit is of the single

type, but there is a band-passcoupling between the first high -frequency pentode and the pentagriddetector -oscillator. There are anumber of advantages of having theband-pass circuit in this positioninstead of in the aerial circuit, notthe least being that the ganging isconsiderably simplified. The fourthtuned circuit is the oscillator coil.

NW-4-

It will be noted that the coilsused in the " W.M." Radiogram- BrIFD BrIFD

ma8,0

Super are of the air -core type andare not iron -core models. In a super -het with a number of tuned circuitssufficient selectivity can be obtainedwithout the use of iron -core coils;which is why few manufacturers have

505

250


Quarter -scale Wiring Plans-- 4- 4" .1. 4.

no ty. .

\-. urLAVEPRISITI

mai,

0_75) )

'-------7

00 °O 0

©

© 8_

g4

©

t

I

t1[1( --..____--

CIPRP

lit ' --------,

III//

_...--__ 4,

, ,/

....1.

'A'1"a

li.

1::/-CII

0

0 0° 00

,:,

. .. 0 .

k1

, rip

II.1,

..

0

METAL OIAS613 IfiLia'ReVE.L. 0 °

QUARTER -SCALE WIRING PLAN OF THE RADIO UNITFull-size blueprints of the radio unit, shown above, and the amplifier section, shown onthe next page, can be obtained for half price-that is 9d., post paid-if the coupon to befound on the last page is used before July 31. Your application' be addressed tothe "Wireless Magazine" Blueprint Department, 58-61 Fetter Lane, London, E.C.4

yet worried about developing iron -core models forsuper -het work. In practice very little would be gainedby the substitution of iron cores for air cores, and thereis no doubt that the ganging would be mop difficultthan it is.

All four circuits are tuned by a single four -gangcondenser. Ganging is not as difficult in practice as itis with some sets using fewer valves. It will be seenfrom the circuit diagram that the aerial coil is pro-vided with an aperiodic winding so that the aerialload remains substantially constant. Because the aerial

506

load has been removed from theband-pass circuit this part is easierto keep in gang. And the oscillatorcoil, which is of a new type, alsoremains in step throughout the waveranges covered by the set without alot of fiddling.

Double -diode TriodeThe chief interest in the set centres

in the double -diode triode. The

THE SET IN ITS CABINETThe radio unit fits snugly into the top halfof the cabinet while the amplifier is fixedvertically behind the loud -speaker at the

bottom

self-adjusting volume control isdelayed so that full amplification isobtained on weak signals. This" delay " simply means that thefirst high -frequency and inter-mediate -frequency valves are notbiased until signals reach a certainlevel; when they do reach that level,the self-adjusting volume controlcomes into action.

Full A.V.C.The self-adjusting control voltage

(or A.V.C., if you prefer to call itthat) is fed back to both the pre-liminary high -frequency stage andalso to the intermediate -frequencystage so that full control is obtained.In practice it will be found thatfading of signals is reduced to such

an extent that to all intents and purposes it is non-existent for the majority of stations that you are likelyto want to pick up.

Unavoidable FadingOf course, with bad fading on distant low -power

stations there will be a variation in strength, but that isunavoidable with any system of this kind.

The decoupling incorporated in the set is extensive-as it needs to be when there are so many valves that arelikely to go " up the loop " unless adequate precautions

are taken. It will be noted that the grid circuits of thepush-pull valves are decoupled to obviate low -frequencyoscillation in the output stage.

High tension is obtained by means of a valve rectifierconnected to the mains transformer; this is of the full -wave type, and a double smoothing circuit is employed.With seven valves it is necessary to take what mayseem to be elaborate precautions to keep down themains hum; but the hum has been kept down to limitsthat will satisfy the most fastidious, and we do notanticipate any criticisms on this score.

Advantages of Large Electrolytic CondensersMost of the large -capacity condensers used in the set

are of the electrolytic type to save both space andmoney. Electrolytics are much smallerthan paper types for a correspondingcapacity, and they are also muchcheaper.

So much for the radio end of thegear; now let us consider the giamo-phone arrangements for a moment. Ashas already been pointed out, the firstfour valves are automatically switchedout of circuit when the gramo-radioswitch is put over for electrical repro-duction of records.

Full Tone CompensationMore than this, however, an extra

low -frequency valve is brought intouse. This is employed so that full tonecompensation can be obtained withoutaffecting the total amount of amplifica-tion available. Tone control resolvesitself into cutting down the strength ofthe frequencies above a certain level,and if the volume is not to suffer it isobviously necessary to provide amplifi-cation to make up for this cut-off,

THE FINISHED OUTFITYou can see very clearly how the set andamplifier chassis are arranged by this photo-graph and that at the top of the previous page

Camills, BY

I 'Wireless Magazine. Juty, 1934

which may be at either end of the frequency scale.The tone -compensating arrangement used is a

resistance and condenser in the anode circuit of thisextra valve; the tone being controlled as the user desiresby altering the value of the resistance, which is madevariable for this purpose. Once the tone has beenadjusted to suit individual tastes, it will not be necessaryto change it, so this resistance has been mounted onthe back of the chassis, out of the way.

Controls for Radio and GramophoneSeparate radio and gramophone volume controls are

provided, the former on the front of the set and thelatter on the motor -board under the lid of the radio -gramophone cabinet. Whilst mentioning that, let us

METAL CliA3515 1.'&5'DLEI

5 o

MAIMS THATIVOAPIEK

ETEIT .B.Bj

e 0

QUARTER -SCALE WIRING PLAN OF THE AMPLIFIER SECTIONIn conjunction with the above wiring plan and that on the previous page, you shouldfind no difficulty in building up the " W.M." Radiogram Super. Of course, you willfind a full-size blueprint of immense value; they can be used as templates and

every wire is numbered in the best order of assembly

507


PLAN OF THE AMPLIFIER UNDERSIDEThere are very few components mounted on the underside ofthe amplifier section and the wiring, as you can see, is quite

straightforward

point out that the model used for housing ouroriginal set is provided with compartments at eachside for storing a selection of discs.

For the sake of convenience we have used a motor -board that is obtained from the makers completewith turntable, pick-up and volume control, allmounted together as a single unit on a stout metalplate. This can be fitted into the top of the radio -gramophone cabinet without difficulty and the useris spared the trouble of drilling holes for fitting upthe various components.

How the Controls are ArrangedThe controls on the front of the set are four in

number and are arranged in the following way, aswill be clear from the photographs.

On the left is the wave -change switch. The setcovers the usual medium and long wavebands, that is,from 200 to about 550 metres, and from about 800to 2,000 metres.

In the centre at the top is the knob of the four -gang condenser; below this is a noise control. Thisdelays the rectifying action of the signal diode on the

weak mush signals. On the right is the radio volumecontrol.

Besides these controls there are, as alreadymentioned, the gramophone volume control on themotor -board and the tone control on the amplifierchassis. The radio gramophone switch is alsomounted on the motor -board.

Using an On -off SwitchIt will be noted that we have said nothing about

an on -off switch. Actually we have not incorporatedone anywhere in the original design. As the currenttaken by the whole outfit is comparatively heavy, it

TOP OF THE AMPLIFI I \I INothing difficult about this! The two smoothing chokes are atthe top, the electrolytic condensers in the centre, and the push-

pull and mains transformers at the bottom

AN OUTFIT FOR THE CONNOISSEUR !Builders of the " W.M." Radiogram Super will have a super set of which they will have

every right to be proud :

508

FRONT VILA' OF THE AMPLIFIERThe control on the right is the tone compen-sator and the valve -holder socket is for insert-ing the plug which carries high- and low-

tension current to the radio unit

is safer to switch the set on and offat the mains socket. For thisreason we advise the use of a wallsocket that is combined with aswitch and fuses. A suitable unitis made by M.K. Electric, Ltd.,and Varley's also make a similarfitting but with a power switch.

When it comes to constructionthe first point to note is that the setis built up in two sections; the firstcontains the first four valves and is

TOP OF THE RADIO UNITUsed in conjunction with the wiring plan on page 506, constructorswill be able to see exactly how the wiring is carried out on this

side of the radio unit

purely a radio combination. The second part of theset contains the low -frequency stages (including thetone -compensating valve) and all the mains -rectifyinggear.

Both parts are built up on stout metal chassis andlook very professional in appearance, although theyare quite accessible and easy to assemble and wire.

In these pages we reproduce at quarter scale thelayout and wiring guides for both parts of the set;as usual, a full-size blueprint is available at half price,that is, 9d., post paid, for those who desire one. Itshould be noted that this price includes both parts ofthe set; they are not supplied separately. Applicationsfor these half-price blueprints must be accompanied bythe coupon to be found on the last page of the issue andmust reach us not later than July 31; the address is


UNDERSIDE PLAN OF THE RADIO UNITHow the few components on the underside of the radio unit arearranged can be seen from this plan view. All the fixed resis-

tances are supported by the wiring

" Wireless Magazine " Blueprint Dept., 58/61 FetterLane, London, E.C.4. Remember to ask for blueprintNo. WM366 when ordering.

Two points should be noted about the blueprints,and the quarter -scale reproductions that appear in thesepages. All the connecting wires are numbered in thebest and most convenient order of assembly, and theholes in the chassis for leading wires through from thetop to the bottom are marked with small letters so thatthere shall be no confusion as to which is which.

If the constructor intends to drill his own chassis(they can be obtained already drilled with holes forfixing screws and connecting leads for a few shillings)the full-size blueprint should be used as a templatefor marking out the positions of all the holes to be drilled.

Continued on page 571

COMPONENTS NEEDED FOR THE " W.M. " RADIOGRAM SUPERCHASSIS s. d. 1 -British Radiogram 4 -pin £ s. d. RESISTANCE, VARIABLE £ s. d.

1-Peto-Scott aluminium 16 in. by adaptor ... 2 0 1 -Claude Lyons 6,000 -ohm (or12 in. by 3 in. ... ... 7 6 1-Bulgin single -pole change -over Ferranti) 5 6

CHOKES, HIGH -FREQUENCY toggle, type S81T ... ... 1 6 SUNDRIES2-Wearite, type HFS (or Goltone)

COILS9 0 4-Bulgin knobs, types K14 (3),

K12 ... 1 712-Bulgin flush -mounting mains

plugs and sockets, type P20 ._ 4 01 -Set Wearite, type GN4 0 0... ..: ...

Round tinned copper wire No. 20 Round tinned copper wire, No. 20CONDENSERS, FIXED

5 -British Radiophone, type tubu- gauge, for connecting, say ... 9Oiled sleeving, say ... ... ... 1 0

gauge, for connecting, say ... 9Oiled sleeving, say ... ... 1 3

lar, values :.00005-, .0001- (2),.0003-, .0005-microfarad (or

4 yds. thin flex, say ... ... 41-Clix terminal strip, marked :

3 yds. thin flex, say 3TRANSFORMERS, LOW -FREQUENCY

T.M.C. Hydra, Telsen)... 2 6 Al, A2, E ... ... 7 1 -Ferranti, type AF5c 1 14 01-T.M.C. Hydra, type tubular,value .05-microfarad 1 0

...TRANSFORMERS, INTERMEDIATE -

1 -Ferranti, type OPM6c ... 1 6 6TRANSFORMER, MAINS

10-T.M.C. Hydra, type 25, values: FREQUENCY 1 -Sound Sales, type 25M... ... 2 2 6.1- (6), 1- (2), 2-, 4-microfarad(Dubilier, T.C.C.)

.

1 62-Wearite, types OT1, OT2 ... 15 0

AMPLIFIER UNIT ACCESSORIES1-T.M.C. Hydra, type 40, block CHASSIS CABINET

comprising .1- (3), 1-microfarad 1-Peto-Scott aluminium, 16 in. by 1-Peto-Scott, type Adaptagram(1) .. 5 0 11 in. by 3 in. ... ... 7 0 de Luxe _ 6 10 0

'PICK-UPCONDENSERS, VARIABLE CHOKES, LOW -FREQUENCY GRAMOPHONE MoTOli.AND1 -Polar four -gang .0005 -micro - 2-Parmeko 15 -henry 120 -milli- 1 -Garrard, type 202A with volume

farad, type Star Minor, complete ampere, type D15/120 ... 3 10 0 control ._ ... 4 6 9with semi -circular slow-motiondrive 1

HOLDERS, VALVE6-Clix, type chassis -mounting,

four -pin (2), seven -pin (4) ...RESISTANCES, FIXED19 -Erie, values: 250- (2), 300-, 1,000-,

5,000-, 10,000-, 15,000-, 20,000-(3), 25,000-, 30,000 -ohm (2),V,- (3), %-, 1-, 2-megohm (or

Telsen) _ ...

13

5

19

9

4

0

CONDENSERS, FIXED4-T.M.C. Hydra, type 25, values :

.25-, .5-, 2-microfarad (2) ... 9 91-Dubilier, type BE328, value :

.02-microfarad centre -tapped 2 62 -Ferranti, electrolytic type 92,

value : 50-microfarad ... 7 05-Dubilier, electrolytic type 500 -

volt working, values : 4- (2),8-microfarad (3) 6

HOLDERS, FUSE1-Bulgin twin, type F14, complete

with 1 -ampere fuses ... ... 2 3LOUD -SPEAKER

1 -Magnavox permanent -magnet,type 252 ... 3 3 0

VALVES2 -Mazda AC/VP1 (pre -high -fre-

quency and intermediate -frequencyamplifiers) 0

1 -Ferranti VHT4 *Meted or-oscd-RESISTANCES, VARIABLE HOLDERS, VALVE lator) . . 1 0 0

1 -Claude Lyons 1,000 -ohm, type 6-Clix, type chassis -mounting 1 -Marconi MHD4 (second detector) 15 6Ml 5 6 four -pin (3), five -pin (3) 4 3 1 -Marconi MH4 (tone - corrector

1 -Claude Lyons 1/2-megohni, type RESISTANCES, FIXED valve) _ ... 13 6MHIA6 6 12 -Erie, values : 100- (2), 800- I -Marconi (low frequency

SUNDRIES1 -British Radiogram 1% in. metal

(2), 750- (2), 25,000-, 50,000- (2),100,000-, 150,000 -ohm, 1/4 -meg-

amplifier) .........13 62 -Marconi PX4 (output valves) ... 1 13 0

mounting bracket ... 4.} ohm (or B.A.T., Telsen) ... 13 1 -Ferranti R4 (rectifier) ... 15 6The prices mentioned are those for the parts used in the original set; the prices of alternatives as indicated in the brackets may be either higher or lower

509


An enthusiastic amateur, W. E. Everard, uses a MurphyA8 super -het receiver with a R.I. Antinodal short-waveconverter. He has picked up hundreds of stations from

all parts of the world

NOW that world-wide short-wave stations are radiatingprogrammes that can be

picked up on the simplest apparatus,the more important set manufac-turers have been quick to realise theimportance of short-wave listening.

In the early days we used to pickup America on headphones, butbackground noises and fad-ing made the transmissionvalueless from the enter-tainment point of view.

Not Luck !In these days of high -

power short-wave stationseveryone with a wirelessset of any kind should takesteps to make sure thatlong-distance programmesare receivable.

No longer is it a matterof luck whether you pick upany stations at all, for somuch data has been col-lated from all parts of theworld that we all shouldknow what stations can beheard and when.

Short-wave fans will bear

New Convertersfor Short-wave

ListeningBy the " W.M." Technical Staff

witness to the factthat with a moder-ately good short-wave set an averageof twenty to thirtystations can be reliedupon to give pro-grammes of reason-able entertainmentvalue to while awayan evening's listen-ing.

If any furtherproof is required,just consider for amoment the positionregarding the various

stations in many big countries thathave been erected for the sole pur-pose of providing programmes forColonial listeners.

There are four examples thatinstantly spring to mind. Our ownEmpire stations which, in addition tobeing picked up in the Empire, areheard by foreigners all over the world.

UNIVERSAL MAINS SHORT-WAVE CONVERTERThis short-wave converter, made by Universal High VoltageRadio Co.. incorporates its own power pack and can be used

on both A.C. and D.C. mains

510

FYA, Radio Colonial in Paris, isanother example of the efficiency ofthe short waves, for this station main-tains a regular schedule with differentFrench colonies, including Indo-China.

Stations Worth HearingAnd so we go on-Pittsburgh,

Schenectady, Zeesen, Nairobi; theseare but names to the ordinarylistener, but to the owner of a short-wave converter or adaptor thesenames mean programmes of realentertainment value.

Unfortunately owners ofwhich only cover broadcast wave-lengths have, until just recently, beenin a difficult position, for suitableadaptors were few and far between.

Efficient Super -het ConverterOne of the first set makers to come

to the rescue of such listeners wasKolster-Brandes, who made specialprovision on most of their receivers

for the use of a short-waveconverter. They went stillfurther and designed aspecial all -wave super -hetfor new listeners.

After improving theoriginal K.B. converter outof all recognition, it is,as may be well imagined,one of the best of its kind. .

This converter is de-signed for use with Kolster-Brandes receivers, but itcan be used with anycommercial or home -builtreceiver-with one or morehigh -frequency stages-andwill turn it into a powerfulshort-wave super -het.

It consists of one of thelatest high -frequency pen-todes used as a combined


oscillator-detector,with internal dual -range coils for all wavelengthsbetween 15 and 80 metres.

As these wavebands cover all ofthe more important stations, such asBoundbrook, Pittsburgh, Sydney,Cape Town, Buenos Aires, and Riode Janeiro, one can fairly claim to bein touch with the whole world.

In order to obviate the necessityof mains pack duplication, the unit isprovided with a plug, which is con -

SHORT -WAVE ADAPTORThis neat -looking short-wave adaptor, made byJ.J. Eastick & Sons, incorporates a dual -range coil

of special design

nected to the family set to obtain thelittle current required.

The total cost of the unit is only10s., and this figure represents

the total expenditure of convertingyour set into a short-wave super -het.Remember that the conversion onlytakes a matter of seconds.

Universal ConverterWhen the family receiver is oper-

ated from D.C. mains a little diffi-culty may be experienced in obtaininga suitable converter or adaptor. Ihave used for some time a uniqueunit that embodies its ownpower pack and, at the sametime, is suitable for either A.C.or D.C. mains, without anyalteration.

This converter, marketed bythe Universal High VoltageRadio Co., is a two -stage affairusing a high -frequency stage infront of a combined first detec-tor and oscillator. This extravalve increases the range verygreatly and makes quite surethat a lengthy aerial will notcause blind spots.

As the mains equipment isself-contained, there is no needto worry about tapping thebroadcast set. All that one hasto do is to link the converter tothe broadcast set by means of

a single wire and the jobis done.

With this unit all wave-lengths between 12.5 and180 are covered, so that itis doubly universal. Thereare two receiving valves anda mains rectifier in thisunit, which costs only£6 6s.

Such a unit can be madeup by the home construc-

tor using Ostar-Ganz valves and,as you can see bythe circuit Fig. 1,reproduced in thesepages, constructionwill not be a difficult job.

Where a more simple typeof broadcast set is in use,such as one without a high -frequency stage, a modifiedcircuit must be used. This iscalled an adaptor and mustnot be confused with theconverter we have just men-tioned, which can only beused with sets having one ormore high -fre-quency stages.

An adaptor is a unitwhich consists of a tuningcircuit for the short wavesonly and is plugged intothe detector valve holder ofthe ordinary set. Thisadaptor then takes the placeof the detector stage as faras the tuning circuit is con-cerned; the low -frequencystages are used in the nor-mal way.

Although the adaptor isnot so good as the con-verter, it is simple to

WELL -SCREENED DESIGNThis short-wave converter is made by Kolster-Brandes for use with their own sets, but it can be

used with most commercial sets

511

INTERESTING SHORT-WAVE CONVERTERThis Unit short-wave converter is interesting inthat it can be used on A.C. and D.C. mains or with

batteries as the user desires

operate, cheap to build or buy and,in a beginner's hands, is likely tobring in more stations.

Suitable AdaptorsOne of the best known adaptors is

that made by J. J. Eastick & Sonsand called the Eelex Duplex modeland costing 12s. 6d.

It is suitable for either battery ormains -operated receivers; an internal

IDAPTOR BY PETO-SCOTTAn efficient adaptor for short-wave working is thatmade by Peto-Scott and selling for 45s. It operates

from batteries and A.C. mains

switch changes over from onesource of supply to the other.

The special coil providedcovers all wavelengths between16 and 30 metres and 28 to60 metres. When it is used witha receiver having one or morelow -frequency stages it is acomparatively easy matter totune a large number of Americanstations as well as some fromAustralia and Asia.

A new firm with the rightidea about short-wave receptionis Unit Radio, who have designeda very interesting unit. It canbe used with batteries, A.C. orD.C. mains and as either aconverter or an adaptor.

This unit, although only cost-.


ing £1 17s. 6d., covers all wavebandsbetween 15 and 100 metres and issupplied with two plug-in coils.

It is simple to operate, there beingonly one main tuning control and anunimportant reaction condenser.

Peto-Scott have long been asso-ciated with short-wave gear, so thattheir latest adaptor must not be for-gotten. This consists of a highly

Fig. 2.-This is a circuit for a simplebattery -operated short-wave adaptor

Fig. 3.-A circuit for a unit for converting adomestic set into a short-wave super -het

efficient tuning coil covering thewavelengths of all the worth -whileshort-wave stations without switch-ing. The unit is suitable for batteryor A.C.-mains working withoutalteration, and it can be used withalmost any standard broadcastreceiver.

Simple OperationThis Peto-Scott adaptor is, with-

out question, a simple unit to oper-ate and, at the price of £2 5s., it is areal short-wave investment.

A circuit of a simple plug-inadaptor for the home constructor isshown in Fig. 2. It consists of atuning coil, a .00015-microfaradtuning condenser, a .00025 -micro -farad reaction condenser, the usualvalve holder, high -frequency choke,and grid -leak condenser circuit.

In Fig. 3 we have shown the cir-cuit of a simple battery -operatedshort-wave super -het converter, witha screen -grid valve used as a com-bined detector -oscillator. The values

of all the components are given in thecircuit diagram and, therefore, youwill be able to build it up at homewith little difficulty.

There are two low-tension con-nections, but no high-tension nega-tive connection. In practice the twofilament leads are taken either to the2 -volt accumulator of the set or thelow-tension terminals on the setitself, in which case there is, ofcourse, no need for a high-tensionnegative lead.

On the other hand, if for somereason or other you use a separateaccumulator, then the two negativeterminals of the accumulators mustbe joined together.

A Magnum unit manufactured byBurne-Jones & Co., Ltd., appears-from our initial tests-to be morethan usually simple to operate.

This unit is suitable for almostany kind of British or Americanmains -operated or battery -driven set,which makes use of one or morehigh -frequency stages. It is theusual type of combined oscillator -detector and is connected betweenthe receiving set and the aerial sothat all of the valves in the receivingset are used. This is a great advan-tage over the picture type of unitwhich only uses the low -frequencyamplifying valve.

With the unit are supplied twoshort-wave coils covering all wave-lengths between 18 and 40 metresand 38 and 80 metres. The price isonly £2 5s. As it requires a specialvalve and in some cases entirelyseparate high and low tension, thenecessary batteries can also besupplied on request.

With these additional componentsthe cost rises to £3 3s.

Simplicity of operation is of greatimportance with short-wave listen-

ing. The Magnum unit has onlythree controls; a master tuner, com-bined reaction and volume controland an on -off switch. Two aerialand two earth terminals are providedso that the external aerial and earthcan be connected directly to theunit; connections from the unitare linked to the aerial and earthterminals on the receiver.

No difficulty will be experiencedin tuning -in such stations asW2XAD, Pittsburg, as well as otherwell-known short-wave stations pro-vided care is taken in operating.

Standard ComponentsAdaptors and converters of the

varying types mentioned in thisarticle can all be constructed by theamateur; in the majority of casesthe components are standard types.The coils, for example, can bepurchased from any of the manu-facturers specialising in short-wavecomponents or, on the other hand,Kenneth Jowers, in his short-wavenotes on page 547, gives details formaking a short-wave coil at home.

Making H.F. ChokesHigh -frequency chokes can be

purchased for a few shillings. Ifyou are of a constructional turn ofmind this is one of the componentsthat really can be made and is wellworth the making.

Any chemist will supply a glasstest-tube of i-in. diameter and about4 in. long. This tube, completewith cork, only costs about 2d.Wind on the tube about 100 turnsof 30 -gauge double -silk -covered wirefasten the ends by means of someChatterton's Compound and fix thewhole to the baseboard by screwingdown the cork. This makes anefficient short-wave choke:

TiCONSTRUCTOR -BUILT UNIVERSAL MAINS CONVERTER

Fig. 1.-This circuit for an A.C./D.C. converter uses Ostar-Cans high -voltage valves anddoes not rely for its power on the domestic set. Constructors should find no difficulty in

building up an adaptor to this design

512

OW much does a set amplify?It is rather difficult to say,because of the different

transformations of energy betweenthe ether and the final air wave fromthe loud -speaker. Overall specifica-tion of amplification also becomesimpossible because of the interposi-tion of detection, and we may havetwo such stages (as in a super -heter-odyne) giving frequency conversionswhich completely upset simpleequations such as x times y equals z.

The intermediate -frequency stagesof a multi -valve super -heterodynemay have a voltage amplification ofthe order of 10,000; amplifiers ofspecial characteristics and of gainsof a million times (in voltage) andmore are in use for various purposes.

W hy There isa Limit to

AmplificalionBy G. S. SCOTT

But for our present purpose thequotation of actual limiting figuresis of little concern.

The main point is that there aredefinite limits of amplification-wecannot go on indefinitely.

Inherent InstabilityThese limits, or rather the factors

governing them, have, however,varied in the history of amplifierdevelopment. The very first seriouslimit encountered was that of theinherent instability of a number ofstages, especially in the bad olddays before we knew all the trickswe do now.

Instability is, . of course, anotherword for oscillation, but is appliedparticularly to uncontrollable andundesirable oscillation.

Even in the very earliest days-when we used to pile up low -frequencyamplification-it was not very diffi-cult to run into audible " hooting."Later, when high -frequency ampli-fication with three -electrode valves

Wireless Magazine. Ju.b; /934

became fail ly general, Ugh -ft equencyinstability became the bane.

Super -heterodyne methods, neu-trodyning, the screen -grid valve,and general screening within the set,all represent successive steps in thestruggle to combat it. Neutrodyningin broadcast receivers is now effec-tively dead, but the others men-tioned still play their parts in thebuilding up of high -frequency am-plification without instability.

Incidentally it is interesting torecall that this was practically thesole genesis of the super-hetrodynesystem. The development of thescreen -grid valve eclipsed it for afew years, and its revival in recentyears has been dictated as much asanything by the ease with which itgives us band-pass characteristics-more, indeed, for this reason thanfor needs of stability. At the sametime, the division of total gain intodifferent frequencies is inherently agood thing.

Problems of instability are now

513

Cro shy photoJoseph Chambers, engineer of theAmerican Crosley stations, handling oneof the huge 100,000 -watt water-cooledvalves at WLW, the new 500 -kilowatttransmitter whkh has just been put into

regular service

pretty well solved, but we still havean outstanding problem which im-poses a very definite limit on theamount of amplification that we canuse. This is noise !

Signal to Noise RatioIt is being increasingly recognised

that the final factor governing recep-tion in all cases, broadcast or com-mercial, is the ratio of signal to noise.If, for any reason, this ratio is bad,then our efforts at amplification areuseless, for amplifying is of littlevalue if it brings up noise and leavesthe signal unintelligible.

While uncontrolled oscillation wasa real difficulty, it was almostinvariably the case that instabilitytook charge first and noise as suchwas not so serious. Now it is !

Noise ExplainedThe term " noise " is, of course,

a very wide one. A.C. hum mightreasonably be regarded as comingwithin the description. Interferencefrom atmospherics and from man-made static definitely comes withinthe general description of noise,especially so far as concerns a goodsignal-to-noise ratio, which deter-mines whether our signal is intellig-ible as communication or enjoyableas a programme.


HUGE SHORT-WAVE RECEIVERA new Marconi receiver which operatesby the diversity method of reception toprevent fading. A huge amount of ampli-fication is used, twenty-nine valves in all

being utilised

Apart from this incoming noise,however, there is still a serioussource of noise which can best bedescribed as self -generated in the set.In the first place set -noise can begenerated by a number of means.Loose contacts of any sort are awell-known source of aggravatingnoise. Defective high-tension bat-teries can give a good approximationto the same thing.

Sources of NoiseSo can badly fitting valves, and

badly soldered joints can producequite a fair imitation of any type ofannoying noise that can be imagined.Internal defects in valves, also, arenot unknown, and a noisy high -frequency valve can produce effec-tive modulation of the carrier whichcomes through the detector andlow -frequency stages as an audiblenoise.

Different valves of the same typecan, and do, behave very differentlyas noise -producing agencies whenused as oscillators in a super -het.Incidentally, however, the increaseof noise in a super -het when theoscillator is introduced must notnecessarily be blamed on that valve.The introduction of the oscillatorgives an enormous increase of

sensitivity to the detector and thismay bring up noise from an earlierhigh -frequency circuit which thedesensitised detector (in the absenceof heterodyne) failed to reveal.This is quite apart from differencesin sheer noise -production as betweenone valve and another of the sametype.

All these internal sources can,however, be regarded as artificialin that they are all capable of beingcorrected by methods within theknowledge and skill of man.

There still remain, however, twofurther sources of noise which mustmeantime be regarded as funda-mental and natural because they arecaused by electrons, and by thefact that we cannot get away fromelectrons.

These are, respectively : (a) spon-taneous noise in the electrical con-ductors (particularly of the inputcircuit) attributable to what isgenerally described as thermal agita-tion; and (b) " Schrot effect " or" shot " effect generated in the valvedue to the fact that the filament -to -anode path is not completely con-tinuous, but is made up of a numberof electrons.

Both effects are, indeed, differentaspects of the fact that our essentialelectrical agenciesare those minuteparticles known aselectrons.

For many yearsthe view has beenheld that the knownfacts of electricalconduction, as inmetals, could beregarded as due toa large number offree electrons mop -ing about the mole-cular interspaces.Thus we picture itthat every where inthe conductors thereis a " gas " offree electrons whichare in frequent col-lision with themolecules of themetal.

If we consider asmall length of con-ductor where thisis happening, thereare, on the average,as many electronsmoving in any onedirection as in anyother, and the net

514

effect is zero. This, however, isonly on the average.

If we consider a sufficiently smallinstant of time there may well be anexcess movement at that instant inone direction, giving us a smallvoltage generated in that section.Naturally any such effect is extremelyminute, but if it exists in the inputcircuit of a high -gain amplifier it isin the very place to make its presencefelt.

Proved by ExperimentThat the effect becomes real in

these conditions has now beenproved beyond doubt. Recentexperiments have shown that thenoise generated in this way varies,for example, with temperature, inexactly the manner that purelytheoretical considerations suggestthat it should do.

The noise is mainly dependenton the resistance of the inputcircuit, increasing with the resistance.It is always in the form of a scratchyhissing noise, but the general levelof pitch varies with the frequencyof the circuit.

The seriousness of the noise alsovaries with the width of frequenciespassed by the amplifier. Forexample, it is often possible to use a

PLENTY OF AMPLIFICATION HERE !Two Marconiphone engineers are seen busy at work on oneof the amplifiers used at the World Economic Conference

held in London last year

narrow -band amplifier with highamplification for key -speed morse,while the noise becomes excessiveif the same amount of amplificationis used over a wide band for goodcommercial telephony quality, letalone high -quality broadcast recep-tion.

Amplifier ProblemsThe very wide band of frequencies

necessary in television is alreadycausing the amplifier problem tobecome a serious one, for example,in the circuits between the photocell and the modulator, while thephotocell and its associated circuitis also an unhappy type of inputcircuit so far as concerns noiseproduction.

The second electron effect, des-cribed before as " Schrot effect " isdue to the fact that the currentpassing from filament to anode of avalve is a stream of individualelectrons. The passage and arrivalof each electron thus causes adisturbance among the electronsalready on the anode, and conse-quently produce shock -excitation inthe anode circuit.

There is thus a separate effect dueto the arrival of these individualelectrons which is different from,and additional to, any effect due tothermal agitation. The effect issomewhat similar to that of rainfalling on a roof. Even our traditional" sheets of rain " consist of individualdrops, at least the writer hasmercifully been spared a literal" solid " mass of water.

A Serious ProblemExperiment has shown that the

effect is least when the valve isworking in its rated conditions.

Either or both of these electroneffects may exist, and it is difficultto say which is the more important.Opinion is, indeed, still somewhatdivided as to their relative import-ance. Neither is of absolutely newdiscovery, but the progress anddevelopment of high -gain amplifiershave brought them into prominence.

In commercial receivers, such asthose used for transatlantic reception,the problem of noise is definitelyone of the utmost seriousness. Evenin broadcast receivers the problemis sufficient to cause makers con-siderable worry and to set a limitto the design of the most sensitivereceivers.

That is why the makers even ofthe most sensitive sets usually


HIGH -GAIN MARCONI RECEIVERThis huge Marconi short-wave receiver uses two stages of high frequency amplification,first detector, first oscillator, three stages of first I.F. amplification, second detector andsecond oscillator, followed by three more I.F. stages, third detector and low frequency

amplifiers. Some set for short-wave fans !

recommend something in the wayof even a small outdoor aerial orany other method which gets thestrongest input signal and thereforethe best ratio of signal to noisethroughout the set.

It is very doubtful if the problemis capable of a complete solution,but several methods of attack appearto be worth considering-for ex-ample, the relative amounts ofamplification at high -frequency, in-termediate -frequency and low -fre-quency, the type of detection,

upper -frequency cut-off character-istics, etc.

Theoretical considerations suggestthat the " Schrot effect " can beminimised by attention to valvedesign, for example the constructionof screen -grid valves giving greatermutual conductance at lower valuesof anode current.

In any case, the problem is nowengaging the attention of boththeoretical and practical men. Andit is not the first problem that radiohas set us to :Ave.

Ha),e. You Logged WLW ?AMERICA has joined in the

great race for high -powertransmitters. As you may

have heard, the Federal Board,which controls the American broad-casting stations, has given per-mission for WLW, a 500 -kilowattstation at Cincinnati, Ohio, ownedby the Crosley Radio Corporation,to work on a wavelength of 428metres during regular Americanbroadcasting hours.

Many readers have reported strongreception of this new Americangiant during its tests. WLW'spresent schedule is from 6.30 a.m.right through the day until 1.30 a.m.the following morning. This isAmerican time, of course!

The Crosley Corporation hasalways been one of the pioneers ofhigh -power stations in the States.Their new station aims at havinga vast service area with a possiblereception area of about 5,000 miles.This means, of course, that the wholeof the British Isles is included in thepossible reception area.

515

WLW's aerial is of the newvertical type, the aerial itself beingin the form of a huge steel mast.WLW's mast is 831 ft. high andweighs 136 tons. The system is thesame as that used at the Hilversumtransmitter, which was describedin these pages last month.

Providing Reliable ReceptionPowel Crosley, jun., president and

founder of Crosley Radio Corpora-tion, believes that listeners in anypart of the world and in a goodlocation should be able to pick upsignals from this new Cincinnatigiant, providing they have a fairlyup-to-date set.

The Crosley president also believesthat the only way to provide reliablereception, free from static inter-ference, is by means of really high -power signals.

Jot down the wavelength andtimes of WLW's transmissions inyour notebook. You stand a reallygood chance of hearing Americaclearly on the medium waves !


Marconi photoAIRCRAFT INSTALLATION -1920

An operator on a Handley -Page machine using one of the earlier'plane transmitters. The aerial of the 'plane is seen partially

wound up in the bottom right-hand corner

THE design of broadcast re-ceivers is constantly changingfor the better. Each year

sees a steady progress towardshigher efficiency, more compactassembly, neater appearance andeasier control.

As with receivers, so it is withtransmitters. The same steady im-provement is evident in the designof equipment at important trans-mitting stations carrying on land,sea, and air services.

Just as the home -built crystal setof 1924 looks like a museum curiositybeside the super -het of 1934, someof the early transmitters seem almostincredibly quaint, untidy contrap-tions in comparison with theirup-to-date counterparts !

The outcome of the past fourteenyears' progress in the design ofbroadcasting transmitters, for in-stance, is exemplified in the modern60 -kilowatt installation at Athlone,illustrated in these pages.

By way of contrast, compare thisgleaming giant of efficiency with the

Marconi photo

New StationsW. OLIVER Reviews the

obsolete 2MT, the pioneer broadcasting station at theMarconi Works near Chelmsford. "Two Emma Toc "used to send out speech and music (of sorts !) as farback as 1919, and, as you can see from the photograph,the announcer used to read news items into a handmicrophone in immediate proximity to the actualtransmitting plant.

In other branches of radio communication, almostequally great strides have been made. Aerodromestations are a case in point, and of these the installationat Croydon Airport may be cited as a typical example.

Contrast the primitive and untidy -looking gear inthe photograph of the transmitter at the old aerodrome(at Waddon) with the fine installation which supersededit when the new airport was opened in 1928.

Four Transmitters at Croydon AirportThe present station is situated at some little distance

from the actual airport to avoid interference withdirection -finding reception there. The transmittersare remote -controlled by landline from the CroydonControl Tower.

There are four independent 3 -kilowatt units whichcan maintain communication in telephony and tele-graphy, on different wavelengths, with other aerodromesand air liners in flight. As the photograph shows,these sets are typically modern in their straightforwardsimplicity of layout and design.

The sending and receiving sets installed in the bigair liners, which enable the operators on board to keep

1902 MARCONI SHIP INSTALLATIONThis photograph of the radio equipment on the s.s. "Minneapolis" was taken in thevery early days -1902. This was one of the first spark outfits to be installed on a ship.

The lead to the ship's aerial is in the top centre of the photograph

516

for OldProgress of Transmitter Design

in constant touch with aerodrome stations whilethe machines are in flight, have also been improvedto a remarkable extent during the past fourteenyears or so.

The operator in our photograph is using a wirelesstelephone set installed on a Handley -Page air linerflying on the London -Paris route in 1920: Comparethis with the fine example of modern design providedby the transmitter and receiver installed in the Atlantatype of air liner used on the Indian and Africanroutes of Imperial Airways.

Radio Gear on a Modern Air LinerThe transmitting and receiving equipment shown

in the Atlanta photograph works with telephony andtelegraphy and covers the short wavelengths of from40 to 80 metres as well as the 500 to 1,000 -metre band.The top section of the set is the transmitter, the middlesection the receiver, and the smaller section at the

bottom is a special Marconi "hom-ing " device. This ingenious adjunctis a valuable aid to navigation.

Not only on land and in the air,but on the sea, also, great progresshas been made in the design ofwireless installations. The quaint -looking spark transmitters, withtheir big induction coils and spark -gaps, shown in the photo of theequipment of the liner Minneapolisis typical of a ship station more thanthirty years ago. The date on thecalendar hanging on the wall behindthe apparatus shows that the photo-graph was taken in 1902 !

Thirty years on-and we come tothe highly efficient and luxuriouslyconvenient installation carried bythe C.P.R. liner, Empress of Britain.The equipment shown in the photo-graph is of the long -wave telegraph


Marconi photos

(Above) The latest type of aircrafttransmitter as used by ImperialAirways on their Indian and Africanservices. (Left) An example ofup-to-date design in broadcasttransmitters is shown by thisphotograph of the Marconi trans-mitter at the Athlone high -power

station in Ireland

CI 0

SUPER RADIO GEAR OF THE PRESENT DAHere is a corner of the radio room on board the C.P.R. liner, "Empress of Britain."On the left is the long -wave telegraphy transmitter, and on the right is the latest

Marconi direction -finder, a fine aid to navigation

517


Marconi photo

apparatus. A 2 -kilowatt transmitteris on the left ; beside it, at thetop right, is an emergency trans-mitter.

In front of the operator is thereceiving equipment covering theenormous waverange of from 15 to20,000 metres. Beside the type-writer, within easy reach of theoperator's right hand, is a specialtype of telegraphic sending -key usedfor tapping out morse messages.

The neat -looking instrument witha sloping panel, on the right of thepicture, is one of the latest Marconidirection -finders which is an invalu-able aid to navigation.

(Right) This is the main transmittingroom for Croydon Airport. It is situated atMitcham Common and operated by re-mote control from Croydon, three miles

away

A lot has been .aid of theadvantages of the direction -finder.With it a ship can obtain bearingsfrom several shore stations, and byplotting these bearings on the ship'schart, find out its exact position.On the North Atlantic, particularly,where there is always a great deal offog, these direction -finders are anessential part of a ship's navigatingequipment.

Although some of these up-to-datetransmitters look as if they hadalmost attained perfection, in thirtyyears time, no doubt, they will seemas primitive and old-fashioned as thespark set of 1902 seems to us to -day !

(Left) Compare this installation used atWaddon aerodrome before 1928 with thepresent up-to-date installation shown in

the lower photograph

Marconi photoReading the news in 1919 ! W. Ditcham at the microphone of "Two Emma roc," the experimental broadcasting station at the

Marconi Works at Writtle, near Chelmsford. Seasoned listeners will well remember the thrill of logging 2MT !

518

Designed

by the"W.M.Technical

Staff

11

The Six-guinea

A.C./D.C. ThreeHere we present details of a reliable all -mainsthree-valver that can be operated from both A.C.and D.C. supplies without alteration. The priceof £6 6s. includes every component used in the set

with the exception of the table cabinet

THIS set will come as a blessing in disguise tomany thousands of listeners who desire mainssets but cannot afford the cost of ten or twelve

guineas for the small commercial models. We had inmind when we designed this six -guinea outfit the vastnumber of people with very moderate means who havemoved out to the borders of the countryside into newlybuilt houses and who are probably tasting the advantagesof electric light for the first time. These people usuallyhave not a lot of money to spend on radio.

A.C. and D.C. Mains Without AlterationTo these, and to anyone else who requires a reliable

mains three-valver that will work on either A.C. or D.C.mains without alteration, we draw attention to this I w.m.,, design.It is up to date inevery way and willgive satisfactory re-ception of home anda large number offoreign stations.

The price of sixguineas given in theset's title includesevery part necessaryto build the set-components, valves,loud -speaker, and soon, in fact everythingexcept the cabinet.


You wilt agree with us that this six -guinea set is a neat -lookingjob. And it works well, too

Let us get right down to business and see what ourSix -guinea A.C./D.C. Three is, and what it will do.In the first place, you will notice from the photographsthat the set has four valves. Of these, three are receivingvalves, the fourth being a rectifier, the only job of whichis to rectify A.C. to D.C. when the set is used onalternating -current mains.

Simple Straightforward CircuitAt first the circuit may seem rather unusual, but if you

look closely you will see that it is not merely straight-forward but highly simplified. First, A.C. 'D.C. valveshave been used with their filaments connected in seriesand heated directly from the mains.

There is, of course, a dropping resistance in circuitto ensure that the correct filament voltage is appliedThe use of these A.C./D.C. valves does away with thenecessity of using a mains transformer and so helpsto keep the price of the set to within low limits.

Unusual but Efficient IdeasAnother feature of the set is that block condensers

have been used in place of separate ones, both in thedecoupling and in the high-tension smoothing circuits.In the latter instance we have used a dry electrolyticcondenser consisting of two 8-microfarad capacities in

the same case, one

*sown

0002

00051.

;

5000smo

FWDEmn

0005

NOTHING COMPLICATED ABOUT THE CIRCUIT!As you can see, the circuit of the Six -guinea A.C./D.C. Three is very simple.valve combination is a high frequency pentode, detector, and pentode. A

rectifier comes into use when the set is worked on A.C. mains

,n0.55

Thevalve

519

of which acts as areservoir con-denser and theother as a smooth-ing condenser.

Another im-portant feature,which also helpsin the prcductionof a cheap set, isthat we have uti-lised the fieldwinding of anenergised moving -coil loud -speaker


These two photographs are a good guide to the arrangement on the top ofthe metallised wood chassis. In the lower photograph the valves, readingfrom left to right, are the detector, output pentode, high -frequency pentode

and the valve rectifier

for a smoothing choke.This does away witha separate choke. Inthis way the currenttaken by the valvesserves to energise theloud -speaker.

Let us look into thecircuit and see whathas been done. Youwill see that a three -valve arrangement hasbeen used consisting ofa high -frequency pen-tode, a triode detector,and a pentode for theoutput stage.

A differential con-denser is connected inseries with the aerialand the aerial tuningcoil, and this acts as ahigh -frequency volume

Four dials and a wave -change switch form the controls on the front.The two tuning condensers are on top and underneath, from left to right,are the aerial -series condenser, wave -change switch, and reaction control

520

control and a selectivity control. It is the usualpractice to use an ordinary condenser in thisposition, but with a differential condenser thecapacitative load across the aerial coil remainsconstant at any setting of the condenser. This isuseful because it means that the setting of theaerial condenser is not altered as the capacity ofthe aerial -input condenser is altered.

Unscreened Dual -range CoilsTwo small dual -range coils are used, both

unscreened, with the waveband switching broughtout to a switch on the front of the panel. Byfitting one of the coils on the top of the metallisedwood chassis and the other underneath, adequatestability is obtained.

Tuned -grid coupling is used between the high -frequency pentode and the detector, separatecondensers being providing for both the aerialand grid tuning circuits.

The grid leak and condenser follow normalpractice, and need no comment. It will benoted, though, that provision has been madefor a pick-up between the grid of the detectorvalve and the cathode circuit.

It is perhaps as well to remind readers thatwhen a pick-up is used it is preferable to use onewith a built-in volume control or some form ofexternal volume control will have to be adopted.

Arrangement of the DetectorThe detector valve is transformer -coupled to

the output pentode. It will be noticed that wehave not included a high -frequency choke in theanode circuit of the detector. We found duringour initial tests that the choking effect of theprimary of the low -frequency transformer pro-vided enough feedback for reaction purposes.A .0003-microfarad by-pass condenser is used toprevent unwanted high -frequency currents fromgetting through to the low -frequency stage.

The detector anode resistance has a value of5,000 ohms, and with aby-pass condenser of.1-microfarad is suffi-cient decoupling to pre-vent instability.

A very unusualfeature of this set isthat no by-pass con-densers have been con-nected across the bias-sing resistances of thehigh- and low -frequencypentodes. Theoretic-ally this is not goodpractice, but we foundthat by careful designof the rest of the cir-cuit, the omission ofthese two condensersdid not cause instability.Again, another pointthat helped to keep theprice of the set low!

As far as the outputpentode circuit is con-

CHASSIS1-Peto-Scott 12 in. by 9 in. by

21 in., with Metaplex top ... 2 3

CHOKE, HIGH -FREQUENCY1-Wearite screened, type HFPJ

(or Bulgin)COILS

2-Kinva, type PDRCONDENSERS, FIXED :

4-Lissen mica type, values :.0001-,.0002-, .0003-, .01-microfarad(or Telsen, T.C.C.)

1-T.M.C. Hydra block of .1- (3)and 1-microfarad, type B1004

1-Ferranti twin 8-microfarad elec-trolytic, type CE100

CONDENSERS, VARIABLE2-Polar .0005-microfarad, type

Compax (or Lissen, Telsen)1-Graham - Farish .0005 - micro -

farad, differential type 2 01-Graham - Farish .0005 - micro -

farad, reaction type (or Telsen,Lissen)

2 0

5 6

2 6

5 0

7 9

5 0

2 0

The prices mentioned are those for the part

cerned, the arrangement follows standard practice;a .01-microfarad condenser connected across theloud -speaker terminals prevents undue accentua-tion of the high notes.

If you look at the filament circuit of the detectorvalve you will see that one side is connected tohigh-tension negative. This is important, andis done to prevent hum occurring, owing to thehigh -voltage filaments of the valves used.

And now for a most important danger sign.You will see that a .1-microfarad fixed condenseris included between the earth terminal and thehigh-tension negative circuit in the set. This is toprevent any short-circuit occurring when the setis used on D.C. mains having the positive mainearthed.

Earth Lead to the Earth TerminalOn no account must an earth lead be joined to any

part of the set except to the earth terminal on theback of the wooden chassis. Don't forgetthis important point!

No fuse is provided in the set, but we havespecified a wall plug in which a fuse is incor-porated. These are not expensive, and shouldbe used, for if a short-circuit did occur no damagewould be done to the set.

So much for the technical features of the set.Let us turn our attention to more practicalconsiderations.

In the first place we must point out that theneatness and compactness of the set is due to theuse of chassis construction. The set has been builtup on a wooden chassis with the top sidemetallised-it is easier to drill than metal, andthe finished appearance of the set is just as good.

How the Components Are ArrangedMounted on the top of the chassis are the four

valves, the aerial tuning coil, the mains droppingresistance, the high -frequency choke, and one ofthe fixed condensers. The two main tuningcondensers are mounted on brackets also fixedto the top.

The remainder of the parts are all mounted on


Used in conjunction with the half -scale wiring plots on the nest page,these two plan views will be found most helpful to constructors. As

you can plainly see, the construction could not be simpler

LIST OF PARTS NEEDED FOR THE SIX -GUINEA A.C./D.C. THREE£ s. d. SWITCHES s. d.

1-Bulgin, type SSOT (or ClaudeHOLDERS, VALVE

3-Clix five -pin, type chassis -mounting (or Wearite, W.B.)... 2 3

1-Lissen, type LN739 1 3

RESISTANCES, FIXED5-Siemens, type SS I/2 watt,

values : 350- (2), 5,000-,100,000 -ohm, 2-megohm (orB.A.T., Erie) ...

1-Bulgin series filament, type

SUNDRIES5-British Radiogram 1% -in. metal

mounting brackets ...Aluminium strip, 7 in. by 1 in., say1 ft. shielded sleeving, say... ...Round -tinned copper wire No. 20

gauge for connecting, say ...Oiled sleeving, say ...Plywood 2 in. by 2 in., for mounting

screen -grid valve holder, say ...1-Ferranti 5 -ampere fuse plug ...

used in the original set; the priceshigher or lower

s. d.

2 11

4 0

1 82 0

2

6

9

1

2 0

1-Bulgin, three-point shorting,type Junior ...

TERMINALS, ETC.4-Belling-Lee, type R, marked :

A, E, Pick-up (2) .

1 3

1 0

1 0

TRANSFORMER, LOW -FREQUENCY1-British Radiogram (or Telsen,

Varley) ... 4 6

ACCESSORIESCABINET

1-Peto-Scott, type No. 141017LOUD -SPEAKER

1-Peto-Scott, type DC2500VALVES

1-Tungsram HP21181-Tungsram R20181-Tungsram PP20181-Tungsram V2018

of alternatives as indicated in the brackets may

12 6

... 15 0

14101710

be either

6

06

521

Hal

f -sc

ale

Layo

ut a

nd W

iring

Pla

n -

2"2"

-14.

&-

2

ik4

criE

cKvi

dYtig

j

DE

T. 0

TO

AU

XIL

IAR

YG

RID

46"

fi

I00

05

TO

AN

OD

E

TO

AU

XIL

IAR

Y G

RID

TO

L.5

.F

IELD 0

0 0 0

RE

CT

.

BLU

EP

RIN

T ti

eV

/ M36

4

37M

ET

ALL

I5E

D T

OP

WO

OD

01A

5515

inn

12''X

9'N

23/

4 D

EE

P

Thi

s ne

at -

lock

ing

cabi

net i

s su

pplie

dco

mpl

ete

with

an

ener

gise

d m

ovin

g -c

oil

loud

-sp

eake

r fo

r th

e m

odes

t sum

of

27s.

6d.

the

unde

rsid

e.A

gla

nce

at th

eph

otog

raph

s w

ill s

how

that

ther

e is

noth

ing

com

plic

ated

abou

tth

eco

nstr

uctio

n of

the

unde

rsid

e.T

here

are

, how

ever

, tw

o po

ints

that

mus

t be

men

tione

d. T

he f

irst

is th

at th

e bl

ock

cond

ense

r an

d th

efi

xed

resi

stan

ces

are

not f

itted

with

term

inal

s, a

nd th

eref

ore

they

hav

eto

be

sold

ered

. The

sec

ond

is th

atth

e ot

her

tuni

ng c

oil i

s fi

xed

to th

esi

de o

f th

e ch

assi

s un

dern

eath

.

Sim

ple

to B

uild

A g

lanc

e at

the

half

-sc

ale

blue

-pr

int a

nd w

irin

g pl

an r

epro

duce

din

thes

e pa

ges

shou

ld c

lear

up

any

doub

ts a

bout

this

par

ticul

ar p

oint

of th

e co

nstr

uctio

n. W

e w

ant t

om

ake

it qu

ite c

lear

that

ther

e is

noth

ing

diff

icul

t abo

ut th

e bu

ildin

gof

this

set

.A

ll th

e es

sent

ial d

etai

lsar

e in

clud

ed in

thes

e pa

ges.

How

ever

, man

y co

nstr

ucto

rs m

aypr

efer

to w

ork

from

one

of

our

full-

size

blu

epri

nts.

Cop

ies

of a

full-

size

blu

epri

nt o

f th

e Si

x -g

uine

aA

.C./D

.C. T

hree

can

be

had

for

half

pric

e, th

at is

6d.

, pos

t pai

d, if

the

coup

on o

n th

e la

st p

age

isus

ed b

e-fo

re J

uly

31. T

he a

ddre

ss to

whi

ch

58

Cr

0:7

P.U

.M

AN

S

O O O

000

5LA

ST

WIR

E N

° 65

MA

INS

ON

-O

FF

SW

ITC

H,

1 0 50

WA

V E

CN

AN

GE

SW

ITC

H

8-t8

MFD

.

Oh

51N

}

FP

FP

1!13

M.P

.

I "

I°n

os

--L

t4'

HO

W T

O O

BT

AIN

A F

UL

L-S

IZE

BL

UE

PRIN

T F

OR

HA

LF-

PRIC

EIf

des

ired

, a f

ull-

size

blu

epri

nt c

an b

e ob

tain

ed f

or h

alf

pric

e, th

at is

6d.

, pos

t pai

d, if

the c

oupo

n to

be

foun

d on

the

last

pag

e of

this

issu

e is

use

d be

fore

Jul

y 31

.A

ddre

ss y

our

appl

icat

ion

to th

e "

Wir

eles

s M

agaz

ine"

Blu

epri

ntD

epar

tmen

t, 58

-61

Fette

r L

ane,

Lon

don,

E.C

.4, a

nd a

sk f

or N

o. W

M36

4.T

here

is n

o ne

ed to

rem

ind

read

ers

that

our

full-

size

blu

epri

nts

show

the

posi

tion

of e

very

wir

e, n

umbe

red

in th

e be

st o

rder

of

asse

mbl

y.T

hey

can,

of

cour

se,

be u

sed

by c

onst

ruct

ors

as te

mpl

ates

the

appl

icat

ion

shou

ld b

e se

nt is

fam

iliar

by

now

, but

her

e it

is in

case

it h

as s

lippe

d yo

ur m

emor

y:"

Wir

eles

sM

agaz

ine

"B

luep

rint

Dep

t., 5

8/61

Fet

ter

Lan

e, L

ondo

n,E

.C.4

.A

sk f

or N

o. W

.M.3

64.

The

fir

st th

ing

to d

o af

ter

the

set h

as b

een

built

and

the

valv

esin

sert

ed in

thei

r co

rrec

t hol

ders

-th

e po

sitio

n of

the

valv

es is

giv

enon

the

blue

prin

t and

in a

cap

tion

to o

ne o

f th

e ph

otog

raph

s-is

toge

t fam

iliar

with

the

cont

rol l

ayou

t.

Lay

out o

f th

e C

ontr

ols

At t

he to

p on

the

left

is th

e ae

rial

tuni

ng c

onde

nser

, and

on

the

righ

t,al

so f

itted

abo

ve th

e ch

assi

s, is

the

othe

r tu

ning

con

dens

er.

In th

ece

ntre

und

erne

ath

isth

e w

ave

-ch

ange

sw

itch,

whi

ch is

pul

led

out

for

med

ium

-w

ave

rece

ptio

n, a

nd to

itsri

ght

isth

e re

actio

n co

ntro

l.T

he o

ther

con

trol

, on

the

left

, is

the

aeri

al -

inpu

t con

dens

er w

hich

is, i

npr

actic

e, th

e se

t's v

olum

e co

ntro

l.C

ontin

ued

on th

e la

st p

age

ofth

is is

sue

As

you

can

see,

ther

e is

ple

nty

of r

oom

for

the

set b

elow

the

loud

-sp

eake

r.T

he te

rmin

als

on th

e ba

ck o

f th

e se

tch

assi

s ar

e fo

r pi

ck-u

p, a

eria

l and

ear

th

LWireless Magazine. July, 1934

The Six -guinea A.C.,D.C. Three is very easy tobuild-you need no experience. The test reportgives a good idea of the results that can be obtained

by the average person

TAKING into considerationthe cheapness of this set,I did not expect very great

things from it. I was agreeablysurprised at the results obtainedduring my short test at Upminster,Essex, the other night; thirty-sixprogrammes at good loud -speakerstrength, during an hour between9 and 10 o'clock in the evening, isno mean feat.

Hum -free BackgroundQuality was quite good, especially

considering the small loud -speakerused. Tone was crisp and particu-larly well balanced.

On D.C. mains the backgroundwas absolutely hum -free, and amplevolume was obtained on nearly allthe stations listed to fill a large living -room. On A.C. mains the volumeoutput, if anything, was slightlygreater than on D.C., but there wasa slight hum background.

Adequate SmoothingThis hum gave me the impression

that it was not due to any 50 -cycleA.C. ripple, which appeared to beadequately smoothed out, but wasvery probably due to some extraneousnoise getting in via the filaments,which are heated directly from themains supply.

When first switching on the set,tuning appeared to be quite flat, as

Thirty-six Stationsin an Hour's Test

The Six -guinea A.C./D.C. Three Proves its Worth !

was to be expected whenthere were only two tuningcircuits before the detector.By careful use of the inputvolume control, however,combined with the judi-cious application of reac-tion, a marked improve-ment in selectivity wasnoted, and I was able to getScottish Regional at loud-speaker strength clear ofLondon Regional.

This I considered ex-cellent for a simple set ofthis description. When Iobtained Copenhagen withonly a slight background ofthe London National, how-ever, my opinion went up

still further. Medium -wave tuningrange is another excellent feature ofthis little set. Fecamp at 206 metrescame in at 5 degrees on the right-hand dial, and Budapest was ob-tained just above 90 degrees. Ishould say that the medium -wavetuning range extends from 200 metresto well over 600 metres.

On long waves the sensitivity

seemed well up to standard, all theusual transmissions coming throughat full loud -speaker strength. Selec-tivity was also quite good, as aftersome juggling I was able to listento a programme from Konigs-wusterhausen without any notice-able interference from either DaventryNational or Radio Paris.

Good Daylight RangeDaylight range was quite good, for

in a half an hour before breakfastone morning I was able to listen toprogrammes from the medium -waveHilversum, together with Radio Parisand Luxembourg on the long waves.

Entirely apart from the abovequalities, however, the major pointthat should induce you to build thisexcellent little set is its price.

I understand that it only costsabout £6 6s., which is, as far as Ican see, far lower than that whichyou would have to pay for any three -valve all -mains set on the market.This is an achievement on whichthe " Wireless Magazine " TechnicalStaff is to be heartily congratulated.A really good set ! S. T. B.

STATIONS LOGGEDA.C./ D.C.

Right-handCondenser

LONG WAVES DialStation Reading

ON THE SIX -GUINEATHREE

Right-handCondenser

DialStation Reading

Huizen 80 Rome ... 50Radio Paris 74 Munich ... . 48Konigswusterhausen 69 Midland Regional... ... 46Daventry National 63 Leipzig ... ... 44Eiffel Tower 55 Lvov ... 42Luxembourg 48 Scottish Regional ... ... 40Kalundborg ... 46 Strasbourg... ... 37Oslo ... ... 35 London Regional ... ... 35

MEDIUM WAVESBudapest ... 88Beromunster ... 78

West Regional ...Hilversum...North National ...

30... 28... 26

Athlone ... ... 70 Scottish National ... ... 25

Vienna ... ... 66 Bordeaux ... 24

Florence ... ... 64 London National ... 20

Brussels No. I 62 Copenhagen ... 16

Prague ... ... 59 Lille ... 13

Lyons 58 Gleiwitz ... ...North Regional ... 55 Nurnberg ... ... 101

Paris PTT ... 52 Fecamp ... 5

524

BALANCING programmes atBroadcasting House is dividedinto two sections-music

under Stanton Jefferies, drama andvariety under Paul Askew.

" Balancing a programme," Stan-ton Jefferies says, " is placingmembers of a musical ensemble insuch relative positions to the micro-phone as will ensure the ensemblebeing heard perfectly in the musicalsense by the listener.

" In other words, the idea is tore -present the music to the listeneras nearly to the original presenta-tion as broadcasting conditionspermit."

In order to make his methods plainto you I asked him to draw diagramsfor each of the various combinations


The man who controls and ()dances all serious -music broadcasts, Stanton Jefferies

"Balance and Control"at the B.B.C.

How the microphones in the broadcasting studio and concert hallare arranged and controlled to pick up programmes suitable forbroadcast reception is revealed in this interesting article by

WHITAKER-WILSON

in common use. He sketched themroughly, and they have been repro-duced in these pages.

It is very obvious to me that thefirst essential for anyone aspiringto balance a programme is musician-ship. I go so far as to say that if Dr.Boult is conducting a Beethoven

symphony, and Stanton Jefferies isbalancing, Jefferies must have studiedthe score just as much as Boult.

If the balancer has not done so,he is quite likely to let the conductordown.

It is for the conductor to presenthis programme and for the balancer

Loudest effect in hell

Limit of loud effectin broadcasting

51

la

Limit of soft effectin broadcasting

Softest effect in hall

Fig. 1.-The wide lines show the variation in volume produced by an orchestra in Queen'sHall. The narrow lines show how this volume variation has to be controlled for broad-

cast purposes. There is a lot of work attached to this side of broadcasting

525

to re -present it to the listener.Failure on the part of one is asserious as on that of the other.

Fig. 1 shows the main aim in pro-gramme control. The wide curvesrepresent the line of sound as heardin Queen's Hall, the narrow curvesshow what the listener hears afterthe sound has been balanced forbroadcasting.

At first sight it might appear asthough the whole subject was capableof a very simple solution-merely acase of keeping within limits. Nevertoo loud, never too soft. Unfortu-nately, it is not quite so simple.

ost of you have heard Ravel'sBolero. If you haven't, it is

easily described. A tune repeats.It has sections to it, but the main ideais the repeated tune-each time withan added instrument or two.Gradually it increases in volume fromthe softest possible to the loudestpossible.

Mr. Jefferies pointed out to methat this is " the very devil " tocontrol. Supposing he made theinitial mistake of setting the strengthtoo heavy at the start-unless hemodified the graduated effect byturning it down (as soon as hehad realised his mistake) the workwould go on increasing everymoment and end up by blastingheavily

I have mentioned this because Iwant to show how necessarymusicianship is. Without actuallyquoting any specified musical workas an example, I will try to give youan idea of how the control is effected.The increase of volume-the decrease


Paul Askew, who was music director of the B.B.C. at Aberdeen, is in charge of the balanceand control of such items as plays, dance music, light comedy, talks, and sound television

broadcasts. He is seen here at a music control panel at Broadcasting House

of it, for that matter-goes onthroughout an orchestral work, justas the composer has directed.

Those increases and decreases arebrought into effect at the con-

ductor's instigation. Fortunately,however, they begin and endlogically; they are musical sentences.This is where the balancer has tobe a musician. He has his scorebefore him. He sees, for example,an outburst of trumpets and trom-bones-probably drums as well.

He has been at rehearsal and heknows just what is likely to happen.If he lets it happen (without actionof any kind on his part) the resultwill be chaos from your loud-speaker. Instead, he watches for aconvenient chord in the music andacts so quickly that the brass andpercussion instruments are given nochance to " blast."

He has thus controlled the volumeat the beginning of a new phrase insuch a way that you, who may befollowing with a score, have notdetected where he did it withoutdestroying the light and shade ofthe music. Balancing is a tricky job !

If you want a good example of theactual effect of control, listen for theoutburst of applause after a workhas finished in Queen's Hall. Youmay hear the diminution of volumeas the volume con-trol is turneddown. The con-troller is beatenthere because hedoes not knowwhat reception awork is going toreceive in terms ofhand -clapping.

Also, he is notso particular. Itdoes not matter ifhe does show hishand, whereasduring a sym-phony it wouldmatter very much.

So much forcontrol, except to add that this stageis not final. After a programme hasbeen balanced it goes from Queen'sHall to Broadcasting House, wherethe quality is again checked up beforebeing sent on to the transmittersat Brookman's Park.

ViolasB

1st. Violins Conductor

Jc

2nd Violins

Line of Plolforni}

Fig. 2. --ShowingSir Henry WoOd.

A

1st Violins

Fig. 2 shows at a glance thedifference between Dr. Boult'smethod and Sir Henry Wood's ofarranging the orchestra on a concertplatform. Dr. Boult divides hisviolins; Sir Henry keeps his together.The microphones have to be adjustedaccordingly.

These microphones are so placedthat it is possible to bring into

prominence any part of the orchestraor, conversely, to fade it down.

In Fig. 3 you see the methodemployed for a choral work atQueen's Hall. Note the micro-phones placed on the top balconiesin order to take the sound from thechorus. Also, incidentally, from theorgan if used. If the chorus issinging as an accompaniment to asoloist, and seems too loud, thebalcony microphones can be fadeddown and the soloist's microphonebrought up. A perfect balance forbroadcasting will then be produced.

I have often felt in Queen's Hall

Microphoneson top balcony

Orchestra

Soloists Conductor Soloists

height of baloony Va waydown hall

and Violins

Below conductor

Fig. 3.-Showing how the microphones are arranged atQueen's Hall for a symphony concert in which a chorus is

taking part with the orchestra

that the orchestra has sounded alittle heavy for a singer at a WagnerPromenade Concert. It is naturalbecause Wagner scores heavily. Yet,when I have heard the same workand singer by wireless the balancehas been perfect. Balance and control!

Line of Platform-"

Violas

(77eiW;;\51r Menry WoodConductor

d.U

Cellos

the positions of the microphones for a symphony concert at Queen's Hall (1) under Dr. Boult and (2) underA is the main " mike " used for orchestral purposes and B and C for soloists playing or singing with the orchestra.

Note that A is to the left when the violinists sit together

526

Wireless Magazine. July 1934Fig. 4 shows the method used at

Covent Garden Opera House. Itwill be seen that two microphonesare suspended near the top of theproscenium arch, one on each side.In addition to these, a " wanderingmike " is sometimes used for theValkyries in Die Walkure, and in otherinstances where special effects arewanted. A microphone is placedcentral, well down stage in thevicinity of the prompt box, and twomore appear on the rail of theorchestra.

By judicious balance and controlany part of the production, whethersoloists, chorus, or orchestra, can bebrought up into prominence orfaded down as required.

These are the more elaborate sec-tions of the work. Mr. Jefferies hasalso under his control the lessermusical combinations. String quar-tets, for example, need carefulbalancing.

Here it is not a case of suiting themicrophone to the players, but of theplayers to the microphone. Theywill not form a perfect squarebecause the 'cello is moved furtheraway from the microphone than theviola. The same thing appliesto a singer with a piano. The micro-phone is placed in position and theperformers arranged accordingly.

Enough has been said to showhow musical the controller has

to be. It is not a case of an engineerwho is musical. It must always bea musician who has some technicalknowledge. Stanton Jefferies, ofcourse, is a first-rate musician. Youremember him as conductor of theWireless Orchestrain the very earlydays of radio.

Drama andvariety come underPaul Askew. Theactual placing ofactors before amicrophone in abroadcast play isgenerally a matterfor the producerwho works in con-junction with Mr.Askew or one of hisassistants, of whichthere are four. Allare experts at theirwork. Sometimesthe microphone ison a stand. Thenthe actor seems tospeak into it.

N

STAGE

Recently, however, different typesof microphones have been suspendedabove the actors' heads, when theyspeak under it. This techniqueallows freedom of action.

Although I prefer personally totalk to a mike I can see, when theplay demands a large cast the othermethod is more convenient.

It must be realised that themultiple -studio method is usedbecause back-ground effectsmay have to beused while theactor is speaking.In order that bothactor and effectscan be dealt withseparately, he andthey must not bein the same studio.

Mr. Askew hasunder his care thebalance and con-trol of all plays,the Children'sHour, talks, de-bates, dance bands-all light comedyof the Frederica type, and the soundpart of television transmissions.Also all variety, whether studio orin St. George's Hall.

It is now well known that stagetechnique is used by Mr. Askew atSt. George's. An elaborate diagramshowing how Paul Askew is able tobalance a show in that hall is shownin Fig. 5. The original was drawnby him actually in the control boxon the side of the stage.

Paul Askew is a musician-aviolinist-and an old member of the

Producer

eio,yN

is 5tanci by

cr. s,N. Micro -'b

-\ Phone

___3. 4{1-

psis

./-"Artists

./ Microphone

Control box; /Standby

1 2 3 4 1,3 6 7 8(

° 0 ° O.P.

mixer

st

Chairman

1-

0

3 OrchestralMicrophone

( Microphone -5 ont:

7;7

ProxenhunQ rch

Footlights

Scottish Orchestra, and for someyears he was musical director at theAberdeen Station of the B.B.C.

If you will study Fig. 5 you will seeexactly how his panel operates

in the control box. It shows howthe microphones are used at oneof the Old-time Music -hall shows,where they have a chairman and dothings in the old-fashioned style.

(-0Proscenium

CV:Ft

Box

Orchestra

ConductorU 0orchestra ,ails

Fig. 4.-The five microphones used at Covent Garden OperaHouse are arranged as shown in this diagram

Two tables are provided forthe use of the chairman and hiscompany.

From the diagram it will be seenthat there are eight faders on themixing panel. The first of thesecontrols the volume from the micro-phone placed for the artists. No. 5,incidentally, is a stand-by in case ofa breakdown.

The second microphone is placedover the chairman and the third isthe orchestral microphone. No. 2will also take part of the orchestra.

The fourth takesthe applause of theaudience.

During a re-hearsal Mr. Askewfaded down Nos.2 and 3 and gaveme the effect of theorchestra in thegallery of thetheatre by bringingup the fourthmicrophone.

The mixer takesthe sum -total ofall the units andconnects the resultwith BroadcastingHouse, from whichthe transmission isfinally sent out tothe transmitterstaking the show.

I.

/

/

/

Fig. 5.-Elaborate arrangements are made in the position and control of themicrophones at St. George's Hall for variety broadcasts. This plan was specially

drawn by Paul Askew, who is in charge of the arrangements there

527


Wireless JobsMade Easy

DO you know that very use-ful tool known as the ex-panding bit which is illus-

trated in Fig. 1 ?It fits any standard brace and its

purpose is to allow clean-cut holesof large diameter to be made in wood.

corMr. Everyman

8y R w He ow.

Other Jobs for the Bit

If your set is a bit " boomy "about the bass owing to cabinetresonance, you can often improvematters a whole lot by making a

number of large

USEFUL TOOL FOR THE CONSTRUCTORFig. 1. The expanding bit is among the most useful of tools

for the home constructor

If you look at the drawing you willsee at once how it works. Thecentre is fixed, but the cutter runs ina slot.

It can be moved in either direc-tion by loosening the screw and thenfirmly fixed by tightening it. Theexpanding bit can thus be set tomake a hole of any size within itscapacity.

The most useful size for wirelesswork is that with a range of dia-meters from fin. to 3 in. If youthink for a moment, you willrealise how handy it is.

You're making a set, for instance,which incorporates chassis -mount-ing valve holders. You could makethe necessary holes in the base witha fretsaw or with another neat littlegadget that I shall describe in amoment. But with either tool thejob is a long and rather fiddling oneand you can do it in the proverbialtwo ticks with the expanding bit.There are dozens of other little jobswhere this bit will be found handy.

round holes in theback of the cabinet(and perhaps in thesides as well) withthe expanding bit.

If you want tomount a milliam-meter on your panelas a visual tuningmeter for your super -

het, the job is a simpleone with the expanding bit.

Why not make a standfor your spare valves ? Fig.2 shows how it is doneand I can assure you that itis a great safeguard againstcasualties. Instead of astand, I actually use a specialvalve shelf fitted into acupboard in which I keepspare parts. Either thestand or the shelf are equallyuseful. They keep yourvalves safe and you cantake out instantly any onethat you want.

Valve caps vary a gooddeal in size. The best

M . A .

Saws Made at Home

The little home-made saw seen inFig. 3 is one of the most time -and -trouble -saving gadgets you ever . . .

no, I won't inflict that one on you.The only ingredients required

are the haft of an old pocket knifeand a good quality hacksaw bladesuch as the Eclipse -Flex made byNeill's of Sheffield. It must be agood blade and it must be of the kindthat will stand an occasional bit ofbending; otherwise it will " come topieces in you hand," like the chinathat the charwoman washes up !

The first thing to do is to dis-

HANDY STAND FOR SPARE VALVESFig. 2. This simple rack for keeping spare valveswill be found useful. It will lessen the risk of

"casualties" among spares !

all-round diameter for the holes isjust under 11 in. For some of thefat seven -pin valves, the holes haveto be made a little bigger.

All you need to make the stand issome r plywood, the bit, screwsand common sense. It's quiteeasy !

528

member the old knife by punchingout the rivets that hold it together.There are generally three of these.With a small file remove their headson one "side ; then drive them outwith a fine punch.

What ? You haven't a fine punch ?Very well, then, use a nail.


You must now soften one end ofthe hacksaw blade, the softenedportion being just about the samelength as the knife haft. To do this,bring it to red heat with the help ofa burner of the gas cooker and thenallow it to cool slowly.

Mind that you heat up only thispart of the blade.

Shaping the Blade

When it is cool, lay the blade on aflat piece of wood and put one halfof your knife haft upon it. Insert adrill of suitable size into one of theholes that formerly housed a rivetand drill through the blade. Removethe drill and fix both haft and bladetemporarily to the piece of woodbeneath by means of an escutcheonpin. You will now have no diffi-culty in drilling the remaining twoholes in exactly the right places,using the haft as a template.

Pull out your escutcheon pin andthen rivet the two halves of theknife haft to the saw blade. Ishowed you last month how to doriveting and you will find that smallescutcheon pins are just what youwant to make the rivets.

The next process is to point offthe blade as shown in Fig. 3. Thepart protruding beyond the haftshould not be more than about 4 in.long. Grind it to a point with agrindstone or better still an emerywheel.

What the Saw can Do

You now have a saw, the finepoint of awhich will go into quitesmall holes and which is capable ofcutting anything from brass toebonite, from wood to mild steel.

A SAW YOU CAN MAKE AT HOMEFig. 3. This little saw, made out of a haft of an old pocket knife and a hacksaw

blade, is worth its weight in gold !

It is the very thing for making largeholes of any shape in metal chassis,ebonite or wooden panels.

If you are making either circularholes or the special shaped onesrequired for condenser escutcheonsand the like, mark them out in pencil,then drill a number of I- or fin.holes inside the pencilled lines andcut away the webs between themwith the little saw. A rasp andafter that an old file of D -sectionwill enable you to finish up the worknicely. Besides jobs of this kind,the little saw will tackle almost anylight work in the way of cutting outor cutting off.

Remember when you are using it,that you must go carefully since theblade is unsupported.Don't therefore tackle workin the proverbial bull -at -a-gate manner. Use it gentlyand this little saw will serveyou well. When a new bladeis required, it doesn't takelong to make and fit it.

Eliminating Knobs

Though I don't believein unduly cutting down thenumber of controls in thereceiving set, there are someknobs that can often beeliminatedwithout makingany difference to the set'sperformance or impairingfine tuning.

Many sets have no lessthan three switches, each

00

with a knob of its own. These are(1) the on -off switch, (2) thewave -change switch and (3) theradiogram switch. In many casesit is quite easy to make one knobwork the whole lot.

Solving the Problem

Here's the way in which I dealtrecently with this problem in con-nection with a particular set ofganged coils. The coils have arotary wave -change switch, arrangedto take you over from the long wavesto the medium and vice -versa butnothing else.

For each complete revolution ofthe knob there are four positions

et, MEDIUM

/1111111.11.1111,:_f--_:'_1111111111111.11111.111---

5.3.

0MORE WORK FOR THE WAVE -CHANGE SWAT(: !

Fig. 4.-This is the first stage in one -knob switch-ing. The on -off switch is fitted on the end of the

wave -change spindle of the coils

4.1O i0C, ICA

-v

PKK-UP

6RiDcorm.,

*-11

/TemLW(

GBIZ

GBI

ONE -KNOB SWITCHING IN A SIMPLE CIRCUITFig. 5.-A simple three -valve circuit in which all switching is done by the knob of thewave -change switch. SI, Si is the ganged wave -change switch and S2 and S3 the radio-

gram and on -off switches respectively

HT+

529

The first click means that you areon the medium waves, the secondthat you are on the long. Thenclick No. 3 brings in medium wavesagain and click No. 4 the long oncemore.

I didn't see the use of having twomedium -wave and two long -wavepositions for a full rotation. BeforeI had finished with it, the switchwas so arranged that it would rotatein one direction only. Starting fromthe off position the next switchedon the set and brought in themedium waves, then came longwaves and lastly, the gramophonepick-up. A stop pin prevented theswitch from being rotated clockwise

I Wireless Magazine. July, 1934

beyond the gramophone position.Fig. 4 shows how the first stage

of the work was carried out by fittingan on -off switch actuated by theknob working the wave -changearrangement.

A three-point switch of the Bulgintoggle type with split dolly wasmounted below the baseboard insuch a position that a small brasscam attached to the rear end of thespindle of the wave -change switchmeshed with the cleft in the dolly.

is applied in a simple three -valvecircuit, consisting of a variable -muhigh -frequency stage, detector andan output valve. s1, s1 is theganged wave -change switch, s2 theradiogram switch, and s the on -offswitch.

It will be seen that the filamentswitch, when in the "off " positiondisconnects the grid battery of thevariable -mu valve. This is neces-sary, for otherwise current wouldalways be flowing from the battery

through the volume -control

ON -OFF AND RADIOGRAM SWITCHINGFig. 6.-A step forward in one -knob switching.The radiogram switch can be mounted on a bracketand worked from the cam fitted on the wave -change

spindle. An effective idea

Possibly you don't know that youcan obtain almost all varieties ofthese toggle switches with the splitdolly illustrated in Fig. 4. You canand they are most useful.

Look at the drawing and you willsee what happens when the knob isrotated. Remember that you arelooking at the rear end of the coilassembly, which means that whenthe knob is turned clockwise, thecam appears to travel counter-clockwise.

In the position shown in thedrawing, the set is " off ". Thefirst click makes the cam move thedolly over and switch on the set,besides bringing in the medium -wave range of the coils. At thenext click the set is still switched onand the long -wave range comes intoaction. At the third click, the setis still on so far as this switch isconcerned : another switch actuatedby a separate cam is used for radio-gram switching.

The knob cannot travel anyfarther because the cam comes upagainst the stop. In Fig. 5 is seenthe way in which one -knob switching

potentiometer.The radiogram switch is

worth attention. It is ofthe double -pole double -throw type and, like thefilament switch, is of thetoggle pattern with splitdolly. In the radio positionall valves are brought intooperation and the grid ofthe detector v2 is takenstraight through to the gridcondenser and grid leak.

When the switch isturned over to the pick-upposition, the filament circuitof v1 is broken. The valvebeing thus cut out, thepossibility of radio break-through from a powerfullocal station is eliminated-and both high- and low-

tension current are saved. Notethat in the pick-up position s,breaks the positive filament ofv1; the chassis and its associatedcomponents thus remain earthed.

At the same time, the grid of v2is connected to one of the pick-upterminals, the other being per-

manently connected to the negativepole of a small grid -bias battery.

Though a simple battery circuit isshown in Fig. 5, the one -knobswitching arrangement is applicableto circuits of all kinds, mains aswell as battery.

The double -pole change -overradiogram switch, again of the toggletype, with split dolly, may bemounted in the rear of the on -offswitch and operated by a second camattached to the spindle of the wave -change switch. Or, if there is notroom to place the radiogram switchas suggested, it may be mounted ona bracket attached to the baseboardor chassis as shown in Fig. 6.

A comparison of Figs. 4 and 6makes the working of the one -knobswitching arrangement quite clear.In Fig. 4 the wave -change switch isactually in one of its two long -wavepositions, but as the cam has movedthe dolly of the toggle switch s3 tothe " off " position, the whole setis out of action.

An Idea Worth Trying

The first quarter -turn clockwiseswitches on and brings in themedium -wave windings of thetuning coils. A further quarter -turn keeps all valves " on " andchanges over to long waves. Thenext quarter -turn actually brings usto the second medium -wave positionof the wave -change switch, but thetuning coils and the filament (orheater) of v, go out of action asthe cam has now turned over thedolly of s2.

But what about those cams ?Well, they are made byColvern for operating anon -off switch in theirG -type coils.

If, though, you preferto make your own, youwill not find it difficultto file them up from piecesof Fin. thick brassmeasuring fin. by in.

Fig. 7 shows the threestages of the work. Firstof all the cam is roughlyshaped with the hacksawor with a coarse file.Next it is shaped up androunded off by finefiling. Lastly the holefor the spindle is drilledand a set -screw or grub -screw is fitted to fix itto the spindle.

4 -- 3/4'4 5/8

,ilii1111111111111111111i

C

-B

1111111

Illnlll

MAKING THE CAM AT HOMEFig. 7.-Here are the three stages for making the camat home. Incidentally, it can be obtained ready

made from Colvern, Ltd., of Romford

530

OUR TESTS OF NEW SETS

Our Tests ofNew SetsBy the " W.M." Set

Selection Bureau

ACHAIN is as strong as its weakest link! Thetruth of that old saying nobody will dispute,and how readily it can be applied to radio.

The rapid reduction in the price of modern receivershas meant a very big increase in sales. This reductionis all very well in a way, providing that the standardof sets is kept up to the original high level. Justrecently we have been subjecting commercial receiversto far more stringent tests necessitating the sets beingsent by train to our country laboratories, some fortymiles away from town.

While the majority of commercial receivers performvery creditably before transport, there is a differentstory to tell when they are tested a second time. Noneof the receivers are actually damaged in transit, but theshaking up they get does bring to life any weak points.We were surprised to find a very big percentage ofreceivers are faulty after this comparatively short trainjourney.

A fter collating our records we were able to divide!X these faults into two distinct classes-one whereit was obviously due to the low price, and the otherwhere the fault was outside the control of the manu-facturer. The first includes faulty connections, badworkmanship so that the components become loose,and, finally, but to a lesser - degree,faulty components.

The weak link-outside the con-trol of the manufacturer-is faultyvalves. The percentage of receiversthat fail through a faulty valve, orvalves, is exceptionally high. Insome instances the receivers fail tofunction from the very beginning,while others " give up the ghost "after two or three days' working.

In spite of specially hooked fila-ments and anchored electrodes, westill get battery valves, such asdouble -diode -triodes, with the fila-ments touching the grid, while thenumber of output valves that go softis also very high.

There is much to be said for theAmerican type of multi -valve re-ceiver using nine valves. As eachvalve is much less efficient than itsEnglish equivalent, the percentageof breakdowns is very small. We


Kolster-Brandes photo

On Whit Sunday congregations of 220 churches in the Ripondiocese listened to their Bishop's broadcast sermon from RiponCathedral. Sets were lent by Kolster Brandes, Ltd., to the poorerparishes, and here is the Vicar of Hunslet installing a K. B. 666 in

the pulpit of his church

must say that in all the American receivers we havetried this year, the faults located have not been worthmentioning.

You must not think from this that we are in favourof boosting American -built receivers-far from it-but

in view of the ever -decreasing prices

FREE ADVICETO PROSPECTIVE

SET BUYERSTo make the most of this free advice

service, we ask you to answer thefollowing questions :-

(1) The maximum price you wish topay, and whether you are prepared toexceed this if there is no suitable set atyour desired price.

(2) The locality in which the set willbe installed.

(3) The stations required, that is,locals only or a selection of foreigners.

(4) Whether you want an entirelyself-contained set or one with externalaerial and earth.

(5) Whether battery or mains driven.If the latter, whether A.C. or D.C.

A stamped -addressed envelope forour reply is your only expense. Addressyour inquiry to Set Selection Bureau,"Wireless Magazine," 58-61 FetterLane, E. C.4. Tell your friends about thisuseful service, exclusive to "W.M."

531

of British sets, we do not feel thatthe same amount of care is taken inthat final test, which is so importantand upon which so much depends.

We feel sure that the time willcome when the efficiency of

each component is decreased, theoverall efficiency of the receiverbeing kept up by the simple methodof increasing the number of stages,as is done in America.

There are distinct signs that nextseason the popular sets will be threeand four -valve super-hets, withamazingly complicated multi -electrode valves-combined detector -pentodes, seven- and eight -electrodefrequency changers.

This, combined with the gentlemanner in which railway portershandle radio sets, is not likely toimprove reliability.

Wireless Magazine. July, .I934

" The cabinet is of medium -tone walnut, wellfinished and very compact. The tuning controls

are as simple as it is possible to make them"

FEW new receivers have beenintroduced by Columbia duringthe last twelve months, so we

were very glad to hear of the newbattery super -het.

This receiver is the culminationof many months' research, and wemust say that it is undoubtedly oneof the most efficient battery -operatedsuper-hets we have ever tried,

BRIEF SPECIFICATIONMAKERS: Columbia Graphophone Co., Ltd.MODEL: 1006.PRICE: L15 I 5s.VALVE COMBINATION: High -frequency stage

(Marconi 523), combined oscillator -detector(Marconi 523), single intermediate -frequencystage (Marconi V524), double -diode -triodesecond detector (Marconi HD2 I ), quiescentpush-pull output (Marconi QP2 I ).

POWER SUPPLY: Internal combined high-ten-sion and grid -bias battery, with wet low-tension accumulator.

TYPE: Self-contained battery -operated super -hetreceiver, table model.

REMARKS: A highly recommended battery set.

irrespective of the number of valvesemployed.

Although it uses only five valves,these really do the work of eight ornine, for there is the three -in -onedouble -diode -triode and the QP21,which is two pentodes in one bulb,both of which pull their weight tothe highest degree. Consequently,as might be imagined, the results areexceptionally good.

The cabinet is of medium -tonewalnut, well finished and very

compact. The tuning controls are assimple as it is possible to make them.There are two main knobs, butconcentric with them are twoswitches, both with a decisive action.


Columbia Super -hetBattery Grand

The outer right-handknob is the master tuner,which drives a tuning drumwith a scale calibrated withstation names and wave-lengths. This dial, ofcourse, is illuminated whenthe set is on. The left-hand knob is a mastervolume control, operatingon both radio and gramo-phone.

On the centre of this knobis the four -position switch,controlling the long andmedium waves, gramo-phone pick-up, and, at thesame time, switching the

set on and off.The remaining switch is rarely

used as it is the local -distanceswitch. It is only brought into circuitwhen one is close to the local stationor wishes to cut down the volumefrom a powerful transmitter.

A 120 -volt high-tension battery isfitted internally, and the averageanode current when the set is nottuned to a station is 12 milliamperes,this rising to 14 milliamperes withnormal volume. The maximumspeech output is a little over 1,250milliwatts, which is ample for theaverage house, and is the maximumone can obtain from dry batteries if

" Only uses fire valves ; these really do the workof eight or nine, for there is a three -in -one double -

diode triode and the QP21"

532

running costs are to be considered.A glance at the circuit immediately

shows up a whole host of novel ideas.The aerial is coupled to the grid ofan S23 high -frequency amplifierthrough an aerial coupling trans-former, one-half of the secondaryof which acts as a second -channelwhistle suppressor. This method ofsuppression automatically cuts outsecond -channel interference withoutaffecting the volume of the stationsthat are tuned in.

Thegrids of the high -frequency

and intermediate -frequency am-plifiers are controlled-giving delayedautomatic volume control-by nega-tive bias supplied by one diode of thedouble -diode -triode second detector.

An entirely new Marconi valve,type HD21, is used as the seconddetector, and this feeds directlyinto two push-pull pentodes-bothin one bulb-which give really goodquality.

The loud -speaker is of the per-manent -magnet low -resistance type,complete with matching transformer.

The receiver was tested thirtymiles north of London, and afterwe had connected up the batteryand accumulator and switched on,we noticed that the local stations, aswell as Radio Paris, could be tuned

in on the loud -speaker inbroad daylight, without anyaerial or earth.

This was a good start,and gave us some idea ofwhat we might expect inthe way of sensitivity. Butthe point which instantlystruck us was the quality.It was really equal to thebulk of mains driven setsthat we have tested.We connected up an externalaerial-ours was 80 ft. longand were rewarded withcolossal volume from' thelocal station, which evenwith the local -distanceswitch in circuit was tooloud for a small room.

With this receiver select-ivity need never be consid-ered, as all of the stationsaccording to the LucernePlan can be separated.


Pye CR/DC CambridgeSuper -het ConsoleWE very strongly admire the

policy of the Pye people inproducing receivers of the

highest quality rather than com-promising between quality and price.Their latest Cambridge rangeincludes, without question, some ofthe finest receivers that have everbeen produced in this country.

The cabinet work alone is sufficientto sell the receiver, while thetechnical reader will go into rhap-sodies over the highly efficient circuitand layout used. An original notehas been struck in the design of thecabinet. It is constructed ofgrained walnut and is the onlycabinet we have seen of this design.

All of the controls are groupedtogether underneath the lid, so thatonce the receiver has been tuned -inthe lid can be shut down, making a

" The technical reader will go into rhapsodies over the highlyefficient circuit and layout used. . . . A local -distance switch is

fitted on the back of the chassis"

self-contained unit and more a pieceof furniture than a radio receiver.

On the left-hand side of the cabinetis the on -off switch and is entirelyseparate from the wave -change andgramophone switch in the centre ofthe cabinet under the lid. On theleft-hand side of this switch is thetone control, on the right-hand sidethe master tuner, and at the bottomthe volume control.

All these controls are clearlymarked so that there will be nodifficulty in obtaining satisfactoryresults from the very beginning. Aningenious visual tuner, or " tuningcompass," as Pye call it, is visiblethrough an opening in the moulded

escutcheon plate beneaththe tuning dial.

When the set isswitched on, but nottuned to any particularstation, the tuning metreneedle will remain overto the left-hand side.When the set is tuned into a station the pointerwill move over to theright in the direction ofthe arrow. The receiveris correctly tuned whenthe needle is deflected asfar as it will go to theright-hand side.

A local -distanceswitch is fitted at theback of the receiver im-mediately above the aerial terminal.The tuning dial is brilliantly lit

by means of a15 -watt minia-ture bulb, andas the dial isboldly cali-brated withstation names,as well as inwavelengths, itis quite a simplematter to deter-mine to whichstation the re-ceiver is tuned.

The manualvolume controloperates on bothradio and gram-ophone andshould be used

in addition to the automatic volumecontrol, which prevents fading with-out any external adjustments beingmade. Provision has been madefor an external loud -speaker, andthe two sockets for this are at theback of the chassis.

A noise suppressor is providedwhich reduces electrical interferenceand the general background noise.

The output stage consists of twoD.C. pentodes, giving a veryhigh output. As may be expected,the quality is superb, and the loud-speaker handles the huge outputfrom these two pentodes without theslightest trace of dither or distortion.

With a gramophone pick-up

533


" An original note has been struck in the design ofthe cabinet. It is constructed of grained walnutand is the only cabinet we have seen of this design"

plugged into the two sockets providedat the back of the chassis the outputis sufficient for quite a large hall.As a rough estimate we would saythat the volume is sufficient fordancing by forty or fifty couples.

The first point noticed duringour test was the exceptional smooth-ness of all the controls, the entireabsence of background noise, ormains hum of any kind, and theunusual sensitivity.

BRIEF SPECIFICATIONMAKERS: Pye Radio, Ltd.MODEL: CR/DC.PRICE: 121, or 123 2s. with stand.VALVE COMBINATION: High -frequency stage

(Mazda DC2/SG/VM), first detector (MazdaDC2/5G), oscillator (Mazda DC3/HL), singleintermediate -frequency stage (MazdaDC2/SG/VM), double -diode -triode second de-tector (Mazda DC2/HL/DD) and two pentodesin push-pull (Mazda DC2/Pens).

POWER SUPPLY: D.C. mains only.TYPE: A highly sensitive D.C. super -het with

push-pull output.REMARKS: A receiver for the connoisseur.

On an aerial 80 ft. long the selec-tivity was of the order or 8 to 9 kilo-cycles on medium waves, and a littlebetter than 10 kilocycles on the longwaves.

During our tests we were able toreceive the sixty-eight stations

marked on the tuning scale and anadditional twenty which were notidentified, making a total of eighty-eight stations.

Selectivity, sensitivity, quality, andappearance are all of a very highstandard, and the receiver at twentyguineas is exceptionally cheap.

Wireless Magazine. Juty 1934

" The cabinet is obviously the product of an artist.It is of dark grained walnut, with a high degree of

polish"

WE were glad to have theopportunity of testing theproduct of the Kebtex Com-

pany, who are comparative new-comers to radio.

This firm is concentrating on onefine receiver that is suitable for eitherA.C. or D.C. mains at will. Wesoon discovered how they arrivedat the name of Proscenium for theloud -speaker fret takes the form of atheatre stage and is very realistic asit is slightly recessed, giving theimpression of depth.

BRIEF SPECIFICATIONMAKERS: Kebtex Radio.MODEL: Proscenium Four.PRICE: Ell 1 1 s.

VALVE COMBINATION: Screen -grid high -frequency stage (Tungsram SE2018 ), triodedetector (Tungsram R2018), multi -grid outputvalve (Tungsram PP2018), and half -wave valverectifier (Tungsram PV4018).

POWER SUPPLY: A.C. or D.C. mains of anyvoltage between 110 and 260 volts, any fre-quency A.C.

TYPE: Table receiver for A.C. or D.C. mains.REMARKS: A really fine straight set.

The cabinet is obviously the pro-duct of an artist. It is in darkgrained walnut with a high degree ofpolish which we were surprised tofind is permanent. We understandthat the cabinets are actually cellu-losed which accounts for this polish.

Although the receiver is entirelyself-contained, it is far from beingbulky. The overall height is 191 in.with a width of 141 in. and a depthof 9n in. The controls are quiteconventional. In the centre is themain tuner, while beneath it,from left to right, are the


Kebtex ProsceniumStraight Four

reaction condenser, volumecontrol, which varies thegain in the high -frequencystage, and on the extremeright a combined wave -change and gramophoneswitch.

The on -off switch isentirely separate and isfitted to the left-hand sideof the cabinet. A tonecontrol enabling one tovary the pitch to suitindividual taste is fitted onthe right-hand side of thecabinet.

This is the first receiverwe have evertested that has the

tuning dial calibrated withcertain American stationsas well as with the normalmedium- and long -waveEuropeans. In view ofthis we were inclined tothink that the manufac-turers were taking ratheran optimistic view of thecapabilities of the receiver,but after we had made onlya few tests we were obligedto change our opinion.

The circuit uses threereceiving valves and a rec-tifier, which comes into useon A.C. mains only. Thefirst valve is a variable -muscreen -grid high -frequencyamplifier which is coupledto a steep -slope triodedetector. Transformercoupling is employed be-tween this valve and themulti -grid output valvewhich gives a large output of2.5 watts.

On test the receiver more thanjustified the claims of the manufac-turers. The tuning dial is of uniquedesign, and it is so accuratelycalibrated that it is a simple matterto identify the numerous foreignstations received.

On an aerial having a total lengthof 80 ft., and without an earthconnection-this as specified by themanufacturers-we were able toobtain 12- to 14 -kilocycle selectivity.

If a short indoor aerial has to beused, we suggest 8 to 10 ft. of wire

round the picture rail. With thisan average of twenty stations can he

"The circuit uses three receiving valves and arectifier. . . . A metal chassis is used and all the

smaller components are fitted beneath"

over

Quch little things as careful match-ing between output valves and

the loud -speaker and by using atransformer of massive dimensionshave produced quality of a high level.This, in conjunction with a tonecontrol, really does make the receiveran outstanding one.

A metal chassis is used and all ofthe smaller components are fittedbeneath this so that the chassisappearance is very clean and busi-nesslike.

534

heard on the loud -speaker, speakingwell for the efficiency of the high -frequency stage. After dark nodifficulty is experienced in loggingsixty European stations.

Those readers who listen to lowwavelength relay stations or Fecampneed have no fear about the set nottuning down to 200 metres, forFecamp comes in with about eightdegrees to spare. One evening dur-ing a late test we were able to pickup no less than seven Americanmedium -wave transmitters, includ-ing W1OD, Miami Beach, WCAUKDK" and WT1C.

OUR TES TS OF NEW SE TS

Ferranti ArcadiaSuper -het ReceiverWE spent a good half-hour

amusing ourselves with theamazing tuning dial on the

Ferranti set before we evenattempted to test it. This newFerranti product is, without ques-tion, a most interesting receiver,which, although costing but fifteenguineas, embodies all the finer pointsthat one only thinks of finding in areally expensive set.

Every knob seems to move anindicator on the tuning dial. Thewave -change switch, for example,moves a little pointer which tellsone to which waveband the receiveris tuned. The left-hand knob indi-cates another pointer showing theposition of the volume control.

The centre knob actuates a longupright knife-edge which travelsacross a silver scale calibrated inblack with station names. Correcttuning is indicated by means of avisual tuning device.

One might well expect that withall those little refinements the

controls would be complicated, buthere again there are only threeknobs, all of which are simple andflexible in operation. There is, ofcourse, a tone control, but this doesnot often have to be adjusted.

The cabinet is an entirely new

departure. It is of theupright type in three tonesof walnut inlaid with maple,which, combined with achromium plated escut-cheon, looks very effective.

The circuit is a veryspecial one evolved byFerranti to suit Ferrantivalves. The first valve isa combined oscillator -detec-tor (VHT4 heptode).Without this valve fullautomatic volume controlwould not have been pos-sible. It is followed by asingle intermediate - fre-quency stage using a vari-able -mu high -frequencypentode. This is in turncoupled to a double -diode -triodesecond detector.

Contrary to usual practice theoutput valve is a power triode givingexcellent quality and an output of2.5 watts.

An energised loud -speaker isused with a built-in switch soenabling an external loud -speaker tobe used on its own.

The receiver is supplied ready for220 to 230 volts A.C. mains, but itcan be adjusted for any voltagebetween 200 and 250, 40 to 100cycles.

" The circuit is a very special one evolved by Fer-ranti to suit Ferranti valves. . . An energised

loud -speaker is used with a built-in switch

On the left-hand side atthe back of the chassis aretwo terminals for the gramo-phone pick-up leads.Through the hole in thechassis, immediately abovethe top terminal, comes awire which must be discon-nected before the pick-upis used.

For our first test we usedthe mains aerial and withthis we were able to logquite an appreciable numberof the stations calibrated onthe tuning dial. The onlypoint against the mains aerialwas that our noisy supplycaused the background noiseto be rather objectionable.

With a short externalaerial of about 30 ft., and agood earth connection wewere immediately impressedwith the absence of back -

535


" Every knob seems to move an indicator on thetuning dial . . . only three knobs, all of which are

simple and flexible in operation"

ground noise and mains hum. Whenthe receiver was not actually tunedto a station it was almost impossibleto detect that it was working. Theonly indication was the illuminateddial.

The minimum wavelength on themedium band is approximately

198 metres. Fecamp could be tunedin on its wavelength of 206 metres agood loud -speaker strength at anytime of the day or evening. At theother end of the scale Budapest wasreceivable during the late afternoon.

BRIEF SPECIFICATIONMAKERS: Ferranti, Ltd.MODEL: Arcadia Consolette.PRICE: LI5 15s.VALVE COMBINATION: Combined oscillator

and first detector (Ferranti Heptode VHT4),single intermediate -frequency amplifier (Fer-ranti high -frequency pentode VPT4), double -diode -triode second detector (Ferranti H4D),super -power triode output (Ferranti LP4), andfull -wave valve rectifier (Ferranti R4).

POWER SUPPLY: A.C. mains, 200 to 250 volts.40 to 100 cycles.

TYPE: An unusually handsome super -het receiver.REMARKS: Outstanding value for money set in

every way.

All the intermediate stations with9 -kilocycles or more separation couldbe heard without interference andwithout having to increase thevolume control to anywhere near themaximum point.

As one would expect with aFerranti receiver, the quality is of avery high order, even when the out-put is increased to the maximum of2.5 watts.

Wireless Magazine. July, 1934 1

" Owing to the extraordinary compactness-there is notan inch wasted anywhere-the receiver is no larger than

many English four -valve sets"

WE must hand the cake tothe Philco people when itcomes to designing multi -

valve receivers. Our tests showwithout any doubt whatsoever, thatsome of their seemingly extravagantclaims for the model 16 receiver are,after all, a trifle conservative. Theaverage reader cannot possiblyrealise the results that can beobtained with an eleven -valve set ofthis kind.

With only single -dial con-trol, five waveband switchingwith five separately calibratedand separately illuminatedtuning scales covering allwavebands between 13 and556 metres, one can, in fact,hear the whole world.

When we were told thatthe Philco model 16 was

ready for test we imaginedthat as it had eleven valves itwould be a colossal receiverand would require a bench allto itself, To our surprise,owing to the extraordinarycompactness-there is not aninch wasted anywhere-thereceiver is no larger thanmany English four -valve sets.

Owing to the elaboratescreening nothing can beheard whatsoever without anaerial or earth, although with9 in. of wire Europe can betoured with ease. Through-out our tests we used a 30 -ft.aerial, at a distance of 40miles from London.


Philco Model 16Table Super -het

The receiver is cali-brated in frequencieswhich will please thosewho are accustomedto thinking in kilo-cycles rather than inmetres, but for theuninitiated a conver-sion table is supplied.We can confidently saythat at any singleminute of the twenty-four hours a largenumber of stations canalways be heard.

The short wave-bands are sheer joy.The bottom band

tunes between 13 metres or 23 mego-cycles, and 27.3 metres or 11 mego-cycles. On this band we were ableto hear all the more importantAmerican commercial broadcaststations, well over one hundred20 -metre amateur stations and wholehosts of ships and other stations of asimilar kind.

During one evening we heard noless than 110 20 -metre amateurstations in a little over one hour and,

" Owing to its elaborate screening, nothing can be heardwithout an aerial or earth. The circuit . . . is absolutely

full of brand-new ideas"

536

in addition to these, we heardbetween seven and eight Americanbroadcasters, Atlantic liners, etc.

Such stations as K4SA in PortoRico, W8XK in Pittsburgh, and

other long distance stations came inat amazing volume.. Even on thelowest possible wavelength of 13metres the receiver was perfectlystable and quite as easy to handle asa medium -wave broadcast set.

BRIEF SPECIFICATIONMAKERS: Philco Radio and Television Corpora-

tion of Gt. Britain, Ltd.MODEL: 16.PRICE: £36 5s.VALVE COMBINATION: Oscillator (Philco 76),

first detector (Philco 77), two intermediate -frequency stages (Philco 78), diode seconddetector (Philco 37), first low -frequencyamplifier (Philco 77), driver stage (Philco 42),class -A output (two Philco 42's). Q.A.V.C.control valve (Philco 78), and full -wave recti-fier (Philco 80).

POWER SUPPLY: A.C. mains, 200 to 250 volts,40 to 100 cycles.

TYPE: An eleven -valve all -wave super -het.REMARKS: Truly a set to pick up the whole

world!

A two -speed tuning control isprovided, which enables one to tunein short-wave stations by merely a

little knob twiddling. The secondtuning band is between 25 metres(12 megocycles) and 51,7 metres(5.8 megocycles), and betweenthese wavelengths one can hearnumberless short-wave stationsat good strength. For example,VK2ME of Sydney was heardfor a whole hour at 11 o'clockon a Sunday morning, Between50 and 200 metres, which iscovered in two steps, there werefar too many stations for us toenumerate.

Little trawlers on the NorthCoast of Scotland or the

Irish Sea were coming in atfull loud -speaker strength. Onthe medium waves the resultswere equally as good, everydegree on the dial bringing in aprogramme at full loud -speakerstrength.

It is the first receiver that wehave actually tried where wecan be assured that the non-technical listener will be ableto receive shortwave stationswithout previous experience.

Principles of Set Design-No. 6

-Wireless Magazine. Jut)y, 19341

Reaction andDetectorOutput

CircuitsBy Percy W. Harris,

M.Inst.Rad.E.

SO far we have considered theprinciples of set design up tothe point where signals are fed

into the detector valve. We nowcome to some very important con-siderations which merit our closestattention, for unless they are properlyunderstood the whole functioningof the receiver may be upset.

Simple Tuned CircuitConsider Fig. 1, in which I have

drawn a simple tuned circuit con-nected to the conventional grid -leakand condenser detector. We haveseen from previous articles that gridcurrent plays an important part inthe rectification, and the net resultis that in the output circuit we have

Fig. 1.-A simple tuned circuit connectedto the detector by the conventional leaky -

grid method

Fig. 2.-Similar to Fig. 1, with the anodecurrent flowing through the primary of a

low frequency transformer

A member of the"W.M." Tech-nical Staff busyat work in theFetter Lane labor-atories at London

a combination of high -frequency andlow -frequency currents. What dowe want to do with them ?

The beginner sometimes forgetsthat a low -frequency valve differsfrom a high -frequency valve only incertain relatively minor points, thelow -frequency valve being moresuited for its particular purpose.Both valves, however, will magnifysignals at almost any frequency, andthis is the reason why it is sodangerous to allow high -frequencycurrents to get into the low -frequency part of the circuit. Onthe other hand, the high -frequencycomponent in the output side of thedetector is of great value to us whenwe want to obtain reaction.

In Fig. 1 I have joined in the platecircuit nothing but a high-tensionbattery, so that we have changes ofcurrent only, there being no resist-ance or impedance of any high valuein this circuit across which a prac-ticable voltage can be set up.

If now we want to use transformercoupling (the various low -frequencycouplings will be dealt with in aseparate article) we connect it asFig. 2. Here again I have simplifiedmatters as much as possible, showinga separate battery for the detectorvalve. When a common battery isused for several valves the arrange -

537

ment will be slightly different, butwe are not at the moment dealingwith any other than the detectoroutput itself.

Only One PathIn Fig. 2 the changes of current

flow through the primary of thetransformer and set up voltagesacross the secondary s. Actuallymatters are not quite so simple asthis, but at the moment this explana-tion will serve.

The point I want to make is thatas the diagram is drawn both high -and low -frequency currents haveonly one path-through the trans-former and the battery-and if thetransformer is a good modern oneits primary inductance will be suchas to make it impossible for thehigh -frequency current to take aninductive. path.

Experiment You Can TryIt has got to get back somehow,

and therefore it will choose the self -capacity of the windings (which maybe considerable) and will thus getback to filament that way.

If you have the odd apparatus,try fixing up a detector and one low -frequency stage in this way, usinga transformer of good quality butone which does not include a fixed


WHERE ALL THE DESIGNS ARE WORKED OUTHere is a corner of the Fetter Lane laboratories of " Wireless Magazine," showing a

member of the Technical Staff busy engaged testing a " W.M." design

condenser inside the casing. Listento the strength of signals, and thenshunt across the transformer acapacity of, say, .0002 microfaradand notice how signals go up owingto the fact that the efficiency of thedetector is greatly improved by pro-viding a proper path for the high -frequency current,

Not a Good MethodIt may be, however, that the set

will be unstable because the high -frequency currents are still passingthrough the common high-tensionbattery, and the mere shunting ofthe transformer primary by a con-denser is not, by any means, acomplete method of keeping thehigh -frequency currents where wewant to keep them.

Let us take our design a stagefurther and in Fig. 3 see what canbe done with a simple reactiondetector circuit followed by atransformer -coupled valve. Thereis considerably more complicationnow, but each part has a specialpurpose. We have, for example,connected to the plate circuit of thevalve a variable condenser c3 joinedround to the reaction coil coupledto the tuning coil L1.

Very High InductanceEqually at the point where the

condenser is joined to the platecircuit we have one terminal of aradio -frequency choke HFC, whichis made to have a very high induc-tance sufficient to offer a high

impedance to any radio -frequencycurrent within the wavelength rangeswe desire to receive with this set.

Although this inductance is highit will not afford any appreciablebarrier to the flow of low -frequencyor rectified currents which we desireto pass on. Thus these go throughthe primary of the transformer T,and out through a resistance (aboutwhich we shall speak later) to high-tension positive.

Theoretically, at least, we seemto have got rid of the radio -frequencycurrent through the path c3-1.,, back

Fig. 4a.-An ordinary reaction circuitwith a fixed condenser between the anodeand filament and a variable condenser to

control reaction

Fig. 4b.-Another form of reaction usinga differential reaction condenser. This

scheme has several advantages

538

to filament, passing on only theaudio- or low -frequency currentswe want. If, however, things wereas simple as this the lot of the setdesigner would be a much easier one!

There are several possible sourcesof trouble here. The first concernsthe condenser c, which, beingvariable, may have a very low value(insufficient for good detection) atthe point of minimum reaction whichwe require. If this figure is actuallyreduced to zero then we no longerhave any condenser to by-pass theradio -frequency currents, and if weincrease the capacity up to a pointwhere it is doing its job satisfactorilywe may get too much reaction.

Simple Reaction MethodsThere are two ways of overcoming

this difficulty, shown in Fig. 4a and4b respectively. In Fig. 4a wehave a small condenser joinedpermanently between the plate of thevalve and the negative low-tension,while the condenser c3 remains asbefore, variable, and thus, evenwhen the reaction is set at zero,there is still an adequate by-passfor the high -frequency currents inthe fixed condenser.

In Fig. 4b we have what is knownas a differential -reaction condenser,conventionally drawn as shown, andin which we consider the uppercurved line as the moving plates.When the moving plates are com-pletely enmeshed with the plates onthe right, then we have the fullreaction effect, and the capacitycan be arranged to be fully sufficientfor our maximum.

Differential ReactionOn the other hand, when we move

the moving plates over to left untilthey are fully enmeshed with theother set, then the radio -frequencycurrents have one path only-straight to the filament.

At intermediate positions thecapacity is shared between thereaction condenser and the straightcondenser, and the total capacityat any position of the moving platesis such that the capacity throughthe reaction coil to filament, plus thatdirect to the filament, is always thesame.

The differential reaction schemehas several advantages. First of all,the total capacity shunted across thedetector is always kept constant;secondly, this capacity, which is alsoacross the primary of the transformer;does not vary, and this may be very

important if we are designing a setfor the best possible audio -frequencyoutput ; thirdly, we have less diffi-culty in designing a suitable reactioncoil.

There are numerous variations ofthe reaction circuit, and a wholearticle could easily be given to thesubject, but as space does not permitthis I will refer to only one variationof the scheme, namely, that givenin Fig. 5. It differs from the schemepreviously shown, because the pathof the radio -frequency currents fromthe detector plate instead of goingthrough the condenser and thenthrough the reaction coil, is throughthe reaction coil first and thenthrough the condenser.

Hand -capacity EffectsAt first glance a beginner may

think this change an unimportantone. In practical design the changeis by no means slight. In all setdesigns it is customary to arrangethe moving plates of the variablecondenser as near as possible toearth potential so as to reduce hand -capacity effect.

In the scheme shown in Fig. 3 or4, both fixed and moving plates areat a radio -frequency potential aboveearth, and therefore there may be,if we are not careful, slight hand -capacity effects.

Satisfactory ReactionNormally, in a well -designed set

hand -capacity effect will not benoticed, but in short-wave receiversthey may become very important.The advantage of the scheme shownin Fig. 5 is that the moving platesof the reaction condenser are directlyat earth potential, andtherefore the handlingof this condenser isless liable to producehand -capacity effects.

Against this mustbe set the fact that thewindings are com-pletely separate, andthis may complicateswitching schemes. Itis no longer possible,too, to adopt the simpledifferential -react ionscheme shown in Fig.4b, and we must usea condenser c4 to affordthe necessary by-passfor radio -frequencycurrents when the con-denser c, is set at aminimum or at a very


low value. It is possible to designa differential reaction scheme toavoid this trouble, but we will notgo into this here.

The next series of problems con-cerns the radio -frequency choke.It is comparatively easy to wind aninductance high enough to act as aneffective choke for currents in themedium waveband, and if slot -honeycomb, or other forms oflow -capacity winding are used, thedistributed capacity can be kept quitesmall and a good -choke made.

It must beremembered,however, thatevery winding hassome capacity-it is impossibleto design a purelynon -capacitywinding-andwhen we haveraised the induc-tance sufficientlyhigh to give a proper choking effecton the long waveband the straycapacity together with the induc-tance will form a tuned circuit, thefrequency of which may fall some-where in one of the wavebands wewish to receive.

Poorly designed radio -frequencychokes are often found to have anatural frequency right in the middleof the long waveband, and in Fig. 6I have shown just why this can beso pernicious.

Once more I have explained thematter very simply so that theprinciples may be understood clearly.Here we have in the plate circuit aradio -frequency choke with its dis-

lin itxt ifli 44' 44 A41104'

1614 itit 44'

it 140 iff4 aI

WHERE BIG AND SMALL CONDENSERS ARE TESTED THOROUGHLYThousands of electrical tests are made daily in the works of the Dubiliercondenser people. Here is a scene in the factory with the main

switchboard on the left

539

tributed capacity dotted, the primaryof the transformer and the high-tension battery, with a dotted con-denser across the primary of thetransformer and the battery torepresent the distributed capacityhere.

Now this radio -frequency chokeand its distributed capacity will forma tuned circuit, the natural frequencyof which may fall somewhere withinone of the wavebands we wish toreceive. If then the tuned circuit

Fig. 3.-A simple circuit, with a leaky -grid detector and reactioncoupled by a low frequency transformer to a low frequency

amplifier using a triode output valve

1,1-c, is tuned to the same frequencyas that of the circuit formed by thechoke and its capacity, resonance willoccur.

Self -oscillation

In this case there will be no needof any reaction circuit to bring aboutoscillation, for the inter -electrodecapacity of the valve itself will bequite sufficient to couple these twocircuits together, even if there is nostray coupling between the chokeitself and the coil which oftenhappens.

In such circumstances the symp-toms are generally as follows. Firstof all we tune our set in the ordinary

way and adjust thereaction to be suitablefor the signal werequire. As we tuneup the scale therebyincreasing the capacityc, and reducing thefrequency, we increaseour reaction a littlemore-quite a normalproceeding as every-one who handles a setknows.

Then, as we go stillfurther and approachthis point of resonance,of which I havespoken, we find thatinstead of increasingthe reaction settingwe have to decreaseit to prevent self-


oscillation, and we rapidly approacha point where we have reducedour reaction condenser to itsminimum setting and still theset is not stable. In fact, it mayoscillate violently whenever thecondenser is anywhere near thesetting of resonance between thetwo circuits.

If you carefully examine thecircuit shown in Fig. 6, you will seethat the condenser connected directly

NEW MARCONI MIDGETSMarconi-Osram have produced a newrange of midget valves with a filamentcurrent of only .1 ampere at 1 volt. Theirsize can be gauged from this photographof a midget and a standard type detector

between the plate of the valve andthe filament is virtually in parallelwith the stray capacity of the radio -frequency choke-a point which isoften overlooked by set designers.For this reason a radio -frequencychoke which may be perfectly satis-factory in a non -reaction circuitmay upset the whole design if usedin a reaction circuit.

Preferable SchemeFurthermore, if we use the circuit

shown in Fig. 4a, the total shuntingcapacity, being variable, may intro-duce a further complication, for thepoint at which the set may beunstable can easily vary with differentsettings of the reaction condenseras well as with the tuning. For thisreason the scheme shown in Fig. 4bis often preferable.

A well -designed radio -frequencychoke will have its point of resonancewith its self -capacity outside of thewavebands on which we wish toreceive. It does not follow that aset will not work if we omit a radio -frequency choke. What we want todo is to provide an alternative andmuch easier path for the radio -frequency currents than they will

have by going through the low -frequency portions of the circuit.

It is possible to use a resistancein place of a choke for the purposeof offering the necessary high im-pedance. A resit tance, of course,will have no resonance problems,but on the other hand if it is highenough to do what we want it maycut down our voltage wastefully.

Speaking of alternative paths, oneeasier than the other, if you referback to Fig. 3 you will see that afterthe low -frequency currents haveleft the transformer they have twopaths, one through the resistanceR2, the high-tension battery and thusback to filament; and the otherthrough the condenser c4 direct tothe filament.

If we connected the transformerstraight to the high-tension batterywithout this resistance there wouldbe only one path back to filament forthe low -frequency current, that isthrough the high-tension battery.

A good high-tension battery infirst-class condition will have acomparatively low resistance, but itwill still be an appreciable one,and these currents flowing throughsuch a resistance are bound to setup voltages across it. Furthermore,as this battery is common to all ofthe valves, it follows that any voltagesset up across this resistance of thebattery must automatically be handedto any other valves connected to thesame battery, thus giving a couplingeffect and a frequent source ofhowling and instability.

By inserting a resistance R2

Fig. 5.-A form of reaction control inwhich the radio frequency current flowsfirst through the coil and hen through the

reaction condenser

Fig. 6.-The condenser connected betwefnthe plateof the detector and the filamentis virtually in parallel with the straycapacity of the high frequency choke

540

(theoretically a choke will also servethe same purpose, except that wecannot design a practical one verywell without heavy expense) andproviding a condenser c4, there aretwo alternative paths. If c4 is of2-microfarads or more capacity itwill offer a very low impedance tothese audio -frequency currents,whereas the resistance of the orderof 20,000 to 50,000 ohms will offera difficult path, so the low -frequencycurrents go through c4 back to thefilament, only a negligible proportionof them going through the battery.This is called de -coupling, and isessential in a well -designed set.

About FeedbackToo many beginners in set design

think a set is stable if it actuallydoes not howl. Now howling orself -oscillation represents a degreeof feedback sufficient to makenormal reception impossible, but itshould be remembered that a certainamount of feedback, sufficient tospoil quality, can occur without theuser of the set realising the effectis there at all.

The modern transformer is sowell designed that if properly usedin a correctly de -coupled circuit thequality can be of the highest order,but unfortunately in comparativelyfew sets (owing to the expense andtrouble probably) is there sufficientde -coupling to . enable the low -frequency portions of the set to workas the designer originally intendedthey should.

Resistance -capacity CouplingIt is also assumed quite wrongly

in most cases that if resistance -capacity coupled amplification isused good quality is assured, pro-vided, naturally, that adequate decoupling is included.

Again, in super-hets, which havetheir own special problems andcannot be dealt with to a large extentin this series of articles, we are facedwith the second -detector problem,different from that of the ordinarystraight set in that the high -frequencyside of the detector (more accuratelycalled intermediate -frequency side)is so low in frequency in some casesas almost to come near the upperlimit of the audio frequency and,therefore, offer difficulties in thedesign of the radio -frequency choke.

Next month we will consider thevarious forms of low -frequencycoupling and how to use them so asto get the best quality.


(1) This delightful viewis taken from the roof ofthe Vatican station. Inthe background is thefamous dome of St.

Peter's, Rome

(2) This shows thepicture telegraph re-ceiving apparatus at theVatican broadcastingstation. It was pre-sented to the Pope byits French inventor, M.

Belin

(3) One of the Vaticanengineers at the controlpanel of the transmitterchecking the quality ofthe outgoing pro-

grammes

TheValican

SkortwaverHJV, the Vatican station, works onwavelengths of 19.8 and 50.26 metres.The station, built in the heart of theVatican, is intended to keep Catholicsthroughout the world in touch with Rome

(5) This is the central switchboardat HJV, where all the connec-tions between the micro-phones in the VaticanPalace, St. Peter's, etc.,can be switched to thetransmitter. (6) PereGianfrancesci, thefamous scientist, isresponsible for thetechnicalities of allVatican broadcasting.(7) The mast of theVatican station is justinside the great wall

(4) This is the chiefengineer of the Pope'sbroadcasting station

at the Vatican

541


OMETelevision Components

and All About ThemBy H. CORBISHLEY

AT the present time prac-tically all television re-ceivers are home assembled,

and this means, of course, that acertain number of componentsmust he purchased which are

32 -gauge aluminium, and near theperiphery are punched a series ofholes in spiral formation, the sizeof the holes being .02 in. square.A plain disc will answer quite well,but it is usual to provide it with

The simplest receiver of all-the disc; note the use of the beehive -typelamp, a single viewing lens and spo::ed disc

beyond the ability of the amateurto construct. How many are theparts that are purchased will dependupon the inclination and thefacilities of the experimenter, soit will be helpful to consider theparts in detail. For conveniencewe can divide the receivers that aremost generally used into four types-the disc, the mirror screw, themirror -drum, and the cathode-ray,in order of simplicity and cost.

The Scanning Disc

The disc receiver consists ofthree essential parts-disc, motor,and neon lamp, a refinement beingadded in the way of a lens formagnifying the image. The discconsists of a circular piece of

eight spokes. There are tworeasons for this, one being that aspoked disc is somewhat lighterand will require less power todrive, and the other that the eight

spokes when viewed by the lightof a lamp operated from 50 -cycleA.C. supply provide a stroboscopiceffect and appear to be stationarywhen revolving at the correct speedof 750 revolutions per minute.This gives us a frictionless speedindicator of great value.

Scanning discs can be, and oftenare, amateur made, but the workentailed necessitates great accuracyif a successful disc is to be producedThis will be appreciated if it isremembered that when the disc isrevolving the holes must passacross the field of vision on exactlyadjacent lines and be exactly spacedangularly, otherwise the picturewill be marred by black or whitelines and have a stepped appearance.

Motors

The disc, as stated before, mustbe driven at a speed of exactly 750revolutions per minute, so thisentails the use of an electric motor.Practically any small motor will dofor this purpose, though it is advis-able to use one of a power whichwill just be capable of the correctspeed. A motor of too high a

A small television motor fitted with synchronising gear. On the rightare two resistances, one variable and the other semi -variable for

speed control

542


power will be difficult to maintainat the correct speed which is soessential to successful reception.Motors which are available com-mercially and have been designedfor the purpose will run very con-sistently at about the correct speed;also they are fitted with speciallylong spindles for a purpose whichwill he noted later.

A photograph of a mirror screw; thisis for ninety line transmissions and

horizontal scanning

As the load on the motor ispractically constant the type alwaysused is series wound, which isanother factor in ensuring steadyspeed. Small toy motors can beused, but as a rule these have asmall number of armature sectionsand do not run steadily. It is

"TELEVISION"will keep you acquainted with

all the latest developments

MONTHLY - 1/ -

important that the motor shouldbe able to run for considerableperiods without getting more than.appreciably warm, and, needless tosay, there should be no sparkingat the brushes, as otherwise a greatdeal of interference will be causedwhich will have its effect upon thepicture received.

Finally, of the essential com-ponents of the disc machine wehave the neon lamp which providesthe light from which the pictureis produced. For this class ofreceiver there are two types ofneon lamp ordinarily used-thebeehive and the flat plate. Theformer is an ordinary commercialarticle which has happened to lend- itself to television purposes,

and the latter is a speciallydesigned type for this class ofreceiver.

A neon lamp requires a mini-mum voltage of about 185before it will strike or lightup, and for its successful usein a television viewer a cur-rent of from 20 to 25 milli-amperes must be availableaccording to the type. Aparticular feature of the neonlamp so far as television is con-cerned is that the light pro-duced is exactly in accordancewith the current that is passingthrough it, and also its actionis practically instantaneous. Itwill be understood, therefore,that in the neon lamp wehave a device which will pro-duce a value of light corres-ponding exactly with the inputenergy. This energy is sup-plied from the wireless set,the lamp taking the place ofthe loud -speaker.

These remarks applyeither type of neon lamp, theonly difference being in theelectrode structure. In thebeehive lamp there is a spiralof wire of beehive shape, henceits name. Better and moreeven illumination, however,is obtained by the use of aflat plate in place of the spiral.When the beehive type is usedit is usual to mask a portionof the bulb leaving a smallwindow which is then coveredwith oiled paper in order tosecure an even field of light;with the flat -plate lamp thisis not necessary and so greaterlight efficiency is secured. Arecent development of theflat plate neon lamp is afine wire grid in place ofthe plate, and behind this thereis another plate which forms theother electrode and also acts as areflector, partially reflecting thelight through the wire grid.

to

It was mentioned earlier that itis usual to employ a lens in con-junction with the disc machine.The simplest type of lens is adouble convex about four inchesin diameter, but better resultsare obtained by using two lenses,one four inches in diameter andthe other about two inches. Sucha combination will reduce distortion.

"TELEVISION ff

The journal for the experimenter

MONTHLY - 1/ -

Another refinement is a smallneon lamp of the indicator typewhich is supplied from current fromthe mains and is used to providelight for viewing the spokes ofthe disc and producing the strobo-scopic effect. This is arranged sothat it can be switched on and offat will.

It is not usual to fit synchronisinggear to the simple disc machine, forthe speed can be controlled fairlywell either electrically, by means ofa resistance, or mechanically with africtional device of a simplecharacter.

However, provision is madeon the motor for the fitting ofthis auxiliary piece of apparatus ifdesired, this being the purpose of

MIRROR PLATES

This diagram shows how the plates of themirror screw are assembled on the central boss

through which the spindle passes

the extension of the motor spindleremarked upon earlier.

In order of simplicity the' nexttype of scanner is the mirror screw,and with the exception of the actual

543

Wireless Magazine. ality, 1934

screw the units used for thismachine are the same as those usedfor the disc. A neon lamp of theplate type must, however, beemployed as a line of light is re-quired and this is obtained bymasking the lamp and leaving anarrow slit.

The mirror screw consists of anassembly of flat metal platesapproximately three and a halfinches long, three-quarters of an

A stroboscopic device is alsoprovided with the mirror screw,and in this case it takes the form ofeight webs on the boss, the edgesof which are painted white. Speedcontrol is rather more difficultwith the screw than the disc, forthe weight/diameter ratio is muchless and so there is not the sameflywheel effect.

Synchronising gear can, how-ever, be added quite simply.

A lens is not

This is the Baird mirror -drum receiver. The grid cell will beseen at the bottom and a little to the left of the wheel. At the

front are the reflecting mirror and lens

inch wide, and about a sixteenththick. One edge of each plate issilvered, and the whole series ofplates are arranged in spiral forma-tion, their number correspondingto the number of scanning linesit is wished to produce.

The mirror plates are mountedon a central boss through which aspindle passes, and it is customaryto drive the whole assembly which,of course, is run horizontally, bymeans of a rubber belt from themotor. The use of a rubber belthas two advantages, it allows of astep-up drive so that the motorcan be run at a higher and moreeconomical speed, and it also actsas a mechanical filter and preventsany irregularities of the motor beingtransmitted to the screw.

required withmirror screwapparatus, buta plane mirroris used to re-flect the lightemerging fromthe slit in themask over thelamp on to thescrew uponwhich theimage appears.

So far wehave only con-sidered appar-atus withwhich theimage isviewed sub-jectively andin which thelight is modu-lated direct.The mirrordrum receiver,however,throws theimage on to ascreen, and theusual type

employs a constant light source,and this light is modulated on itsway to the screen; there is, how-ever, apparatus of this type inwhich a special neon lamp, calledthe crater point, is used.

The mirror drum consists of awheel, usually made of aluminium,upon which are mounted thirtysmall plane mirrors each one beingset at a small angle with the axisof the wheel and with each precedingmirror, so that a spot of light whenreflected from the mirrors as thewheel is revolving travels up thescreen in a series of lines, thirtylines of traverse being producedat each revolution of the wheel.As there is what may be termed alarge optical leverage with thistype of scanner, it will be appre-

ciated that the mirrors must beset very accurately on the wheeland the construction must be suchthat variations of temperature willnot affect the positions of themirrors.

Some mirror drums are providedwith means of adjusting the mirrors,but the Baird Co. employ a wheelwith accurately machined mirrorbeds, and the mirrors once set inposition are a fixture. Variousmeans are employed for adjustingmirrors which are not fixed perma-nently, some sort of screw adjust-ment or ball-and-socket mountingbeing the usual methods. What-ever means are provided for adjust-ment, this is a rather tedious task,though it is usually within theability of the average amateur.

Mechanical Filters

The best mirror drums areprovided with a mechanical filterwhich compensates to some extentfor any uneven torque of the motor.The actual drum is mounted sothat it can turn either one way orthe other, within limits, upon acentral boss. This boss is securedfirmly to the motor shaft, and thereis a spring link between the bossand the drum so that a small amountof spring -controlled movement cantake place between the two.

It was remarked earlier that aconstant source of light was usuallyemployed in conjunction with themirror drum. This is obtainedfrom an ordinary incandescent lampof the bunched filament type, thecandle -power being approximately

Television is developingrapidly every day. Read

"TELEVISION ff

for the latest news

200. Modulation of this light isobtained by passing it first througha prism of Iceland spar, thenbetween a number of small metalplates arranged something like acondenser and immersed in nitro -benzine, and finally through anotherIceland spar prism. A varyingpotential is applied to the metalplates, and the light which passesis in accordance with this potential,so that the arrangement acts as aninstantaneous light shutter which

544


has no moving parts. A cell of thisdescription is known as a Kerr cellor grid cell. As a rule about eightplates are used, and the surfaces ofthese between which the light passesare approximately an eighth of aninch square. It is most important thatthe nitro -benzine used in the Kerrcell should be pure and free frommoisture, so in order to preventthe absorption of moisture fromthe air the Baird Co. seal thewhole assembly in a glass bulb.

Mirror -drum Light Sources

There are two special types oflamp which can be used withmirror -drum apparatus in place ofthe ordinary projection lamp, andthe use of either of these eliminatesthe necessity for using a Kerr celllight valve, as they both can bemodulated directly in the same way

ing sound on film, but it lendsitself excellently for televisionreception with mirror -drum appar-atus. A photograph is shown ofthis also. The cathode is the centralelectrode, and is contained withinan inner glass tube. The outerenvelope contains a mixture of

voltage obtained from a smallspark coil.

Smaller Screens

The use of either of these typesof lamps simplifies the construc-tion of mirror -drum apparatus con-siderably, but there is one dis-

A RECEIVER FOR MIRROR -DRUM RECEPTION

Full Details in the Julyissue of "TELEVISION "

neon and mercury vapour, and thenormal operating colour of thelight is bluish -white which fills thewhole of the inner tube. Whenused for television purposes it isusual to mask the envelope, leavingonly a small aperture at the endthrough which the light can pass.

P.M.G'S. TELEVISION COMMITTEEThe first meeting of the committee set up by the Postmaster General to advise on the conditionsunder which a public service of television should be provided. From left to right the membersare : Sir John Cadman, The Rt. Hon. Lord Selsdon (chairman), F. W. Phillips, J. Varley Roberts(secretary), 0. F. Brown, Vice -Admiral Sir Charles Carpendale, Noel Ash bridge and Col. A. S.

Angwin

as the ordinary neon. One is, infact, a neon lamp of special con-struction-the crater-point-towhich reference has been madeearlier. This, as will be seen fromthe photograph and drawing, con-sists of two electrodes separatedby an insulator within a glassenvelope. In the outer electrode,which is the anode, there is a smallaperture, and the discharge is con-centrated here. The discharge,therefore, is of small area and veryintense.

The Mercury -vapour Lamp

The mercury -vapour tube hasbeen primarily designed for record -

Both the crater -point and themercury -vapour tubes are con-nected directly or coupled to theoutput valve of the amplifier.

One disadvantage of the mercury -

advantage in their use in that thevalue of the light obtainable is notso great as can be obtained by theuse of a projection lamp and Kerrcell combination, and this meansthat the screen on which the imageis projected must be smaller orsome amount of brilliance

sacrificed.The lenses used with

mirror drum apparatusare of the simplesttype. When a pro-jection lamp is usedthere is a short focuscondensing lens of thepiano -convex typewhich is used to con-centrate the light uponthe elements of theKerr cell and thenbetween the reflectingmirror and the mirrordrum there is a doubleconvex lens of longfocus for the purposeof concentrating thespreading beam oflight on to the mirrorsof the drum, fromwhich it is reflected

to the screen where it forms aspot.

It will be clear from the fore-going that all the components usedin mechanical television receiving

Articles in the July issue of " TELEVISION " include"An Experimental Light Chopper""Reception with a Stationary Mirror Drum"" Making a Valve Voltmeter ""Facts and Figures of Public Opinion"

" TELEVISION - - Monthly 1/ -

vapour tube is that it requires ahigh initial voltage to enable it tostrike, though this can be producedquite simply in a variety of ways as,for instance, by a condenser dis-charge or a momentary high

gear are of quite a simple natureif the special ones such as the lampsjust described be excluded, andthe assembly of them is wellwithin the ability of the averageamateur constructor.

545


News of the dart WaivesDURING the past month or so

I have been able to persuadea fair number of ordinary

listeners-all absolute disbelieversin my short-wave claims-to buildup simple sets and to see if there isany thrill in short-wave listening.

In the early days of radio-aboutthe year 1922, say-before there weresuch things as tuning dials calibratedin wavelengths, super high -powerstations and foreign -programmeguides, hearing good foreign pro-grammes was a matter of luck.

Fun Out of RadioAll who remember those days

will surely agree with me that therewas much more fun to be obtainedout of the radio set than can behad today, in spite of all the super-hets with multi -electrode' valvesand all the other paraphernalia ofmodern sets.

I well remember using a three -valve super -regenerative set with apair of headphones and raking inall the European stations there wereon the air. There was great excite-ment when Nottingham and someof the other relay stations were tunedin, of course accompanied by theusual super -regenerative whistle.

Short-wave UncertaintyThe position on the short waves

to -day is somewhat similar to thoseearly days. It is not possible to sitdown and tune in a certain station100 times out of 100, although thereare always a number of interestingstations on the air.

It is the uncertainty of the shortwaves that makes them so fascinating.Signal strength, fading, or back-ground noises cannot be taken as aguide as to whether any station heardis a local or not. Very often thelocal station is a weak signal, whileanother station that comes in likethe local is some far-off little trans-mitter at the other side of theworld.

From the very beginning do notimagine that the short-wave set isgoing to take the place of the broadcastset. Nothing is farther from the truth.On the other hand, I listen tostations below 50 metres far more

than I do to the ordinary B.B.C.stations.

On the short -waver, except thatI know just what stations are on theair, I have no idea what stations Ishall hear. The station I want maybe unobtainable through bad con-ditions or morse interference, while

By Kenneth Jowers

stations considered miles out ofrange oblige with fine entertainingprogrammes.

Let me tell you some of the itemsheard during the last month, andthen, after weighing up the cost of asimple set, I think you will agreethat there is a thrill waiting on theshort waves.

You remember the French flyers,Rossi and Codos, who were goingto fly non-stop to San Franciscolast month ? I came home from theoffice on the Monday evening, wentinto the radio den and tuned to the19 -metre band just to see what wasdoing.

W2XAD of Schenectady, on19.56 metres, at 1950 playing acinema -organ record was the firstsignal logged. A record, by the way,is played at this time every eveningso that long -.distance listeners canadjust their receivers. Two degreeshigher up the tuning scale wasW8XK on 19.72 metres broadcastinga musical programme. There weretwo stations on this band.

As W2XAD was the stronger ofthe two I hung on to hear the openingannouncements at 2000. Mypatience was well rewarded, for themicrophone was taken over to theFloyd Bennett flying field for a relayof the speeches made by the Frenchflyers.

I was able to hear all about theflight-straight from the horse'smouth! Rossi spoke in English,while Codos had an Americaninterpreter. This programme wenton for twenty minutes or so, and,believe me, it was worth hearing.

On going back to W8XK I hearda programme of organ music coming

546

from New York. It can be said thatwe hear quite enough organ musicfrom the B.B.C., but, say what youwill, the American style is so differentthat it makes a welcome change.

Searching for EntertainmentA great deal, of course, depends

on knowing where to look for yourentertainment. It is a waste of timesearching over the short wavebandswhen all but 20 per cent. of them maybe quite useless at the time you arelistening. Do not get despondentabout this, for it does not mean thatyou will not hear a signal; even thebiggest ham-handed Henry cannotfail to tune in some stations, nomatter how badly he tunes his set.

2"DIA.

}TURNS18 5W6.

FORMER

TO

GRID COND. EARTH REACTION GONG

HOME-MADE SHORT-WAVE COILSHere are the dimerisions for making thegrid and reaction coils described in this

article

To get the utmost out of a short -waver with the minimum of troublestudy world times. Remember thatthe time of the east coast of Americais five hours behind us, so it will notbe any good trying for Americanstations much before 1500 or after0600 or 0700.

On the other hand, Australian timeis 10 hours fast, so the morninghours will be better when lookingin that direction.

Put these notes in your diary forimmediate use; they will help a lot.

Using a simple three -valve setthere is not much to be heardduring the morning except theEmpire stations and the 19 -metreVatican station at 1000. At 1500W3XAL Boundbrook, New Jersey,on 16.87 metres is a certain bagthree times out of four. Round

3 TURNS8 swe.

TO PLATE

about 1600 W8XK comes in atfair strength, reaching a peak at2000 - the wavelength is 19.72metres.

Times to ListenBetween 1600 and 2000 reception

will be confined to the stationsmentioned, and the Europeans suchas Berlin, Kootwijk, the Empiresfrom Daventry-which can be veryuseful if you have missed the newsfrom the local station-Paris,Moscow on 45.38 and 50 metres,and an odd South American or two,Buenos Aires and Rio in particular.

At a few minutes to 2000 don'tforget W2XAD, for signal strengthfrom this station is colossal. After2100 to 2200 forget the 19 -metreband and concentrate on 25 metres,and a little later 31 metres. After2330 the 50 -metre band will offermost entertainment, usually fromAmerica and Canada.

Tuning -in AmateursThese times all apply to the broad-

cast stations and not to amateurs,who come in at quite differentperiods. During the summer thebest amateur channel is, withoutquestion, 20 metres. This is wellworth watching between 2000 and0100. Between 0100 and 0300try the 40 -metre channels, and afterthis go up to the 80 -metre band.As this band is good until 0700 forthe West Coast Americans, trygetting up early in the morning; it'snot bad after you have done it onceor twice.

You can get a lot of fun listeningto the English amateurs on a Sundaymorning. The 80- and -160 -metre channels arethe most favoured, andremember, the time ofday doesn't matter much,although things arequieter when the B.B.C.stations are on the air.

. .I am not going to say

much about tuning theshort -waver; it will takefar too long, but if any-one is in trouble justdrop me a line about it.

The selectivity on thegrid -tuning condenser isbound to be good, butthe aerial tuner can beflattened out by connec-ting the aerial to thegrid of the first valve.This will not affect the

Wireless Magazine. Jut); 1934

set to any extent, but it will maketuning easier for the beginner.

The dials must never slip or thepanel allowed to move, otherwisethe calibrations will change andstations will be difficult to tune in.Hand capacity is almost a thing ofthe past, but in case of accidentsmake sure that themoving plates of thetuning condenser goto the " earthy" endof the tuning coil.Similarly with thereaction condenser,see that this has oneside going to earthand not to the anodeof the detector valve.

If the coils are ofthe same make, thetuning dials willprobably be in step. If they arenot, it is an easy matter to takehalf a turn or so off one of them todo the trick.

The receiver should always beon the verge of oscillation whensearching for stations, the finaltuning adjustments being made later.Invariably the tuning condenserwill require readjustment after thereaction condenser has been alteredand vice versa.

Don't have too high a voltage onthe anode of the detector valve, itwill not give a big increase in volume,and the valve is almost bound tobe noisy or microphonic. I alwaysuse a variable resistance to controlthis voltage: it is such a great help.

When on wavelengths below20 metres it is a good idea to usecoils without any former. As you

AN AMERICAN AMATEUR STATION YOU CAN HEAR WELLShort-wave fans in this country regularly tune in to broadcasts by theAmerican amateur station W8CPC, of Buffalo, N.Y., on the 20 -metre band

547

REAGTIOM

.00025

MD COILMT-

CIRCUIT FOR A SIMPLE BATTERY TWO-VALVERWith this simple battery -operated short-wave two-valver youcan taste all the pleasures of short-wave listening. The valvesequence is a detector transformer coupled to a triode output

will only want two to three turns atthe most, the coils will keep rigidwithout any help if you use 14S.W.G. copper wire. This will makea big difference to the signal strengthon these very short waves.

. . .Do me a favour! Make yourself

0

a two -valve short -waver. The com-ponents can be bought from thelocal man or Stratton's, of Birming-ham, or, alternatively, you can makesome of them at home.

The tuning condenser is a .00025-microfarad, and will cover a widewaveband without making tuningdifficult.

Winding the CoilWind the coil on a piece of 4 in.

by 2 in. ebonite or paxolin former.Put on four turns of 18 -gauge wireand space each turn from its neigh-bour by twice the diameter of thewire. Leave long leads, and the gridcoil is finished. For reaction, windon three turns of the same wire andin the same direction.

The drawing will show you howeasily the job is done. The circuit

reproduced on this pageis the simplest form ofbattery - operated two-valver for use on theshort waves. The valueof every component isgiven, so there shouldbe no difficulties.

The short-wave coilcan be wound to coverany waveband under 150metres. And further,the waveband coveragecan be adjusted to suityour own tuning con-densers. It is a greatadvantage to be able totune -in the requiredwaveband towards theend of the tuning conden-ser. These coils will workefficiently in a short-waveadaptor or converter.


Mantovani with his Tipica Orchestra

TIME is in the news again.You remember what I saidabout the stupidity of the

B.B.C.'s attempt to foist the twenty-four hour clock upon listeners?The last time I visited BroadcastingHouse I passed the entrance toQueen's Hall, which is just oppositeB.H., and I noticed that the "Prom."announcements on the hoardingsoutside stated that they would begin

Reginald Foort is now broadcastingfrom the Regal Cinema at Wimbledon

at 2000. I laughed heartily andpassed on.

Inside I told an official exactlywhat I thought of their time, andasked if they intended to stop it.The reply was that the B.B.C.would return to the use of sane time,but when was not yet decided.In any case, twenty-four hour timewould last the summer out. Anotherexperiment fails 1

As I revealed last month, Reginald

hectic time. Mr. Foort was recentlyin Rome, where he opened the firstcinema organ to be installed inthat city. He left immediately afterthe ceremony by 'plane for Hilver-sum where he had an engagementto play the organ in the broadcastingstudios.

The machine in which he wastravelling got up to 10,000 ft.when one of the engines failed. The'plane eventually got back to Romewhere Mr. Foort chartered anotherand set off again for Hilversum,which he reached just half an hourbefore his broadcast.

NOTE5

oft EWSBy T. F. HENN

Foort has returned to broadcasting.I have just received the news thatthe organ at the Regal Cinema atWimbledon is the second largestcinema organ in Europe. I believethat the Trocadero Cinema at theElephant and Castle, London, stillholds the record.

The Wimbledon organ was builtby a North of England firm whohave been building church organsfor nearly a century. Reggie Foortdesigned the instrument, and it wasbuilt under his supervision.

These cinema organists have a

A famous soprano, Eva Turner has made awelcome appearance in June programmes

548

Soon after he got down to workat Hilversum, the transmitter wasstruck by lightning, and there wasno more Dutch broadcasting thatnight. All that excitement for atwo -minute broadcast !

It was unfortunate that we didnot have the pleasure of hearingGreta Keller with Ross and Sargent,the American duettists, during theEntertainment Hour in June. Thereasons for their non-appearancewere outside the scope of theartists and the B.B.C., and the

Diana du Cane made her first broadcastin the "Songs of the Shows"

arrangements had to be cancelled.It is, anyway, good news that

another tentative date, again in theEntertainment Hour, has been fixedfor a broadcast. So unless anythingunforeseen happens we shall hearthese famous variety artists in theNational programme on July 4.

Excerpts from the ParliamentaryPageant will be relayed to listenerson July 2. The pageant will be aspectacular affair depicting cere-monial parliamentary events throughthe past centuries. The final scene,which will be broadcast, will depictthe modern period.

Full details are not available atthe time of going to press,but some of the items wewill hear sound most at-tractive. Callenders bandplaying Eric Coates'Knightsbridge will accom-pany the Procession of thePeople of Today, thenLeslie Bridgewater and theorchestra will play Mar-quardt's Regal Episode dur-ing the assembly of thepeers and peeresses, andfinally there will be a per-formance of a new poemby Rudyard Kipling, NonNobis Domine, set to musicby Roger Quilter, and sungby the Royal Choral Society.

The relay will take placein the National programme after thesecond news bulletin.

. .I was glancing through some

Saturday -night programmes f o rJuly when I came across what isundoubtedly, to my mind any-way, the ideal type of Saturday

Yvette Darnac, the French singer, isa favourite broadcaster


night entertainment.I have translated the

times into English andhere is the programme.At 6.50 the Band of theIrish Guards start theentertainment, at 7.45Christopher Stonegives a recital for halfan hour of gramophonerecords, then followsforty-five minutes ofJack Hylton before thenews. After the newswe have an hour of theTheatre Orchestra andHenry Hall's GuestProgramme.

I do give the B.B.C. some creditfor this selection; I hardly thinkthey will better Saturday -night enter-tainment of this sort.

By the way, Sunday, July 8, willsee an outstanding relay fromHolland. During the evening pro-gramme we shall have the pleasure

One of the oldest of broadcast singersJohn Thorne, the famous baritone

549

Our old friend Norman Longwith Joe Batten getting a laughout of his new tongue -twistersong, "I've brought you somenarcissus, Cis." (Left) Jenny,Howard, the famous comedienneand her companion, Percy King,

were heard last month

of hearing Beethoven'sFifth Symphony played bythe famous ConcertgebouwOrchestra of Amsterdam.The concert will be relayedin the National programme.

I have spent many apleasant Sunday afternoon listeningto this orchestra broadcasting fromone of the Dutch stations. Acousticsare especially good. Make a note ofthis; the concerts usually start at2.10 p.m.

. .Max Kester, who recently joined

the light entertainment staff of theB.B.C., is producing a broadcastentertainment on July 7. It is calledSketch Book, and will consist of fiveor six short sketches ranging from athriller to a comedy. Incidentalmusic will be played on two pianos,but Max Kester makes it plain thatno jazz items will be included in themusical programme.

Max Kester has written one of thesketches, called The Interview. Theplot concerns a film star who hashad her jewels stolen by a crookposing as a newspaper man.

Max Kester has done practicallyeverything since he left school. Hehas worked on a farm, been on anewspaper, been a music teacher,and has worked a linotype machinein a newspaper office.

Wireless Magazine. July; 1934

A newcomer to broadcast dancemusic, Lou Preager who broad-casts from Romano's Restaurant

He is not new to broad-casting by any means. Hewas on the staff of theLeeds station in the earlydays and has two hundredsketches, mostly for broad-casting in the Children'sHour. programmes, to hiscredit.

In 1928, he became managerof a gramophone shop in Doncasterwith the idea of gaining a commer-cial insight into the gramophonerecord business.

He succeeded in this aim andjoined the staff of H.M.V., wherehe was in the recording department,specialising in comedy and burlesquerecords, until he rejoined the staffof the B.B.C. a couple of monthsago.

At the moment, members of theB.B.C. Symphony Orchestra areaway abroad, at the seaside and inthe country enjoying a well-earnedrest after their busy time last season.They are due back at BroadcastingHouse about the middle of July andwill immediately start rehearsals forthe eight -week Promenade season,which opens at Queen's Hall onAugust 11, at eight in the evening.

Anew photograph of the famous artist, Eve Becke, whois frequently heard on the air

At the time of writing, Sir HenryWood, in conjunction with the musicdepartment of the B.B.C., is arrang-ing the programmes for the forty-nine concerts. A part of everyconcert will be broadcast either inthe National or Regional pro-grammes.

This will be the fortieth season ofpromenade concerts, all of which,with very few exceptions, have beenconducted by Sir Henry Wood.

Whilst at the B.B.C. recently Imade inquiries about the vaudevilleand variety shows that are to begiven again at Radiolympia thisAugust.

Except for the fact that the theatrein Olympia will hold 3,000 people,instead of 2,000 as last year, a veryhush-hush attitude is being main-tained over the programmes that willentertain visitors. I do know, how-

ever, that they will beproduced by John Wattand arranged by EricMaschwitz. The onlyinformation I could getabout the shows themselvesis that they will be" gigantic." A visit toRadiolympia should be wellworth while this year!

Tessa Dean has been heard in manyvaudeville and music -hall shows

With a good dance band, Billy Merrin broadcasts from Midland Regional every Saturday afternoon. It is about time he took aregular late evening turn in National programmes

550

[Wireless Magazine. July 1934

AST month, you will remem-ber we delved into thesubject of suitable public-

address gear for the amateur andgave much practical information onthe choice of suitable amplifiers andequipment.

For those who wish to build uptheir own amplifiers, we are taking amore technical line on amplifierdesign this month by giving usefulinformation on typical amplifierswith numerous circuits for all typesand to operate from both mains andbatteries.

Let us consider the battery -operated amplifier as being the

Practical Points inAmp#er Design

By the "W.M." Technical Staff

easiest and cheapest. We want to make the most of ourhigh-tension current, so that the obvious solution isclass -B amplification.

Valves such as the Cossor 240B with 150 volts high-tension will give an output of a little over 2 watts,providing it is driven by a small pentode valve. Fig. 1shows a typical class -B circuit of this kind.

Most Economical Battery AmplifierThe microphone or pick-up input is connected to the

grid of a triode amplifier, which is in turn resistance -capacity coupled to a small pentode valve acting as adriver to the 240B. Such an amplifier will consume acurrent of a little under 25 milliamperes and is the me steconomical thatcan be devised.

The only alter-native arrange-ment is the use oftwo pentodes ofthe Mazda Pen220A eh- ss, as inFig 2, w hi.th willgive 2,200 milli -watts with ananode current ofat least 35 milli-amperes.

This arrange-ment has the add-ed advantage thatthere is only onelow -frequencystage, so it issimple to con -

Schoolboy wireless enthusiasts inspectingthe gear at the Croydon Airpo, t transmit-

ting station at Mitcham, Surrey

struct and less expensive than theclass -B method. Here again thepick-up or microphone is connectedto the grid of a triode amplifier whichis transformer coupled by means of ahigh -ratio transformer to two Pen

220A valves in a push-pull arrangement.

Excellent Quality, but One SnagSuch an arrangement will give excellent quality, but

has one snag. It is necessary to use loud -speakers withspecial input transformers-this means twin loud-speaker leads.

The same amplifier, arranged as in Fig. 3, with twopentodes in parallel will give a little under 2,000milliwatts, but with a choke -filter output circuit only asingle loud -speaker lead is required. We always advisea choke -filter output circuit for this reason.

The quality from the amplifier should tend to be on thehigh side. This is really necessary for immediately the

amplifier is usedin a hall with a

20,000 75,00o 10,000

2MFDil amrD

01 HL

0-JINPUT

Ina

oos

01 25,000

2MD

2000

9 I

\3)

Elm005

11

\I.005

OHTt150-170 V.

IT -

L

OLT+TYPICAL CLASS -B AMPLIFIER

Fig. I.-A class -B battery amplifier with a triode resistance -capacity coupled to a smallpentode which drives the class- B output

551

number of peoplethe pitch willdrop to normallevel.

If the quality ispreviouslyadjusted with anempty hall, thereproduction willbe very boomywhen the hall isfilled. This pointmust be borne inmind.

However, it isadvisable to fix atone controleither betweenthe anode and


50001165°3° mil

PEI.

--- --PEI.

IMFD.

ANOTHER BATTERY -OPERATED AMPLIFIERFig. 3.-This circuit is similar to Fig. 2, except that the two pentodes are arranged

in parallel instead of push-pull

earth of the output valve or across the loud-speakers. The latter arrangement has oneadvantage. If you have loud -speakers in differenthalls, the pitch of each loud -speaker can beadjusted to suit the acoustic properties of eachhall. Fig. 4 shows a typical circuit for such a tonecorrector. It consists of a .01-microfarad conden-ser, two variable resistances and a small choke.

Amplifiers for D.C. MainsAmplifiers for use on D.C. mains are a little

more flexible and there is more scope for origin-ality in design. The most suitable amplifier is atwo-valver with pentode output, as shown inFig. 5. With the valve filaments in series with themains and automatic grid bias incorporated, it isentirely independent of battery supply and givesan undistorted output of a little over 3 watts.

Here again we have a triode amplifier trans-former coupled to a pentode valve connected tothe loud -speaker by means of a choke -filter outputcircuit. The output could be increased by modify-ing it to use two driver low -frequency stages fortwo pentodes in parallel.

10,000

.5-1 20,000

2ms-0,4'

02t1FD.

D.C.PEN

Imn

00 .01

IWO

ti

.01

Timv. TMFD.

0L.50

500011

OFfr+ In this case, instead of using a150V. low -frequency transformer, the low -

frequency stages are resistance -capacitycoupled. This does not give the samestage gain as the transformer, but thequality and stability are considerablybetter.

This type of amplifier, illustrated inFig. 6, is the most useful that we can

25,000 advise for D.C. mains. It is inexpen-sive, gives quite a reasonably largeoutput, and is simple to construct.

-01 Offr- Where very large volume is requiredthe D.C. amplifier described in theJune issue of " Wireless Magazine "should be constructed, which has four

OLT+ pentodes in parallel. The minimumoutput from this is 10 watts and isenough for all practical purposes.

You will notice that with all these

-.N25,000

OHT+

L

OLT-

-OLT+

BATTERY AMPLIFI ZR WITH PUSH-PULL PENTODESFig. 2.-A simple battery -operated amplifier with a triode transformer

coupled to two pentodes arranged in push-pull

01

D.C.20050

500

SIMPLE AMPLIFIER FOR USE ON D.C. MAINSFig. F.-A two -valve a uplifter for D.C. mains working, giving an undistortedoutput of 3 watts. The valve sequence is °detector followed ty a pentode output

552

amplifiers we have embodied tone control.This is essential as it enables the pitch ofthe loud -speaker to be varied according tothe type of hall and the number of peoplein it.

Universal Mains AmplifiersThe introduction of the new Mullard

universal valves makes the universalamplifier an accomplished fact. In Fig. 7we have shown two low -frequency stages,followed by two pentodes in parallel, whichwill give well over 5 watts, but the mainattraction is that the amplifier can beplugged into either A.C. or D.C. at Will-a very useful amplifier for the radio dealer.

Variations can be made by using thehigh -voltage type of valve or the 16 -volt.25 -ampere D.C. valves, such as theCossor or Marconi-Osram types.

With A.C. mains available we really candesign the highest -quality amplifiers. A

simple two-valver, using a triodeamplifier, transformer coupled to avalve of the PX4 type is shown inFig. 8. This arrangement is verycompact, inexpensive, and will givean output of over 2 watts. It isshown complete with fader, auto-matic volume control, and tonecontrol.

Interesting A.C. AmplifierAn interesting circuit we have

developed is shown in Fig. 9. Itconsists of a screen -grid amplifier ofthe variable -mu type, resistance -capacity coupled to two PP5/400's inparallel. This ingenious circuitmakes use of the variable -mu charac-teristics of the screen -grid valve forcontrolling the stage gain and actu-ally is one of the few circuits wherethe volume can be controlled logarith-mically.

With a gramophone pick-upgiving an output of 1.5 volts thestage gain is sufficient fully to loadthe PP5/400 valves to give an undis-torted output of 10 watts. Fig. 10shows an amplifier that we havefound to give exceptional qualitywith ample output. It is a two -stageresistance -capacity arrangement feed-ing a triode valve of the Cossor 660Ttype, which gives well over 11 wattsat 500 volts.

The same circuit can be adapted totake the Mazda ES75 output valve, which gives anundistorted output of 17.5 watts. The only disadvantage

of using theES75 is that it

.25 h. requires ananode voltage of1,000. Of course

10,000 the original20,000 circuit using the

Cossor 660Tcan be modifiedto use two ofthese valves in


30012

0 KT+

0L.S.

0

Ot Conne' ToL.S.Terminals

TONE -CORRECTOR CIRCUITFig. 4.-A simple tone -corrector arrange-ment for fitting across a loud -speaker

.25Mn

25,0oo 15,00omFD. 2 mrD.

50,000

mrD

1000

(Di M.O.

2MFD

30,00001

51.111

-114MFD.

I00,000

0 t1T-

THREE-STAGE D.C. AMPLIFIERFig. 6.-Good quality is assured by using a D.C. amplifier of this type. Here the com-bination is two low frequency stages and two pentodes in parallel, resistance -capacity

coupled throughout

TWO-VALVFig. 8.-A simple

transformer c

. c jowl-T

OEM 4MF0. 8

_ L _

25011

L5.0

MFD

E AMPLIFIER FOR A.C. MAINSform of A.C. amplifier with a triodeoupled to a power triode output

HT+ parallel which would givean output of 20 wattswith only 500 volts andan anode consumption250 milliamperes. Thisarrangement is greatlyfavoured in talkieequipment.

These amplifiers willbe more satisfactory ifthey are constructedupon a metal chassis ormetallised-wood chassis,so that the negative con-nections can be takendirectly to the chassis.This form of construc-

tion simplifies the wiring, reduces the number ofconnections, and makes the whole job look veryworkmanlike.

Of course, there are snags to the idea-there alwaysare. Take particular care to see that all of the connec-tions that go through the chassis are insulated by meansof ebonite bushes or two thicknesses of good -qualitysleeving.

Wisdom of the Choke -filter OutputWhen dealing with voltages over 200 or 300 it is

surprising how easy it is for arcing to take place betweenthe positive high tension and a negative chassis, causing3o M. a breakdown.

In almost every circuit we haveshown a choke -filter output and youwill see the wisdom of this idea whenyou come to wire up the loud-speakers.

Even if the idea of public-addresswork does not appeal to you, someof the amplifiers mentioned can beused after the radio set to giveadditional volume or better quality.

01

MAIMS

000

5 -WATT AMPLIFIER FOR UNIVERSAL USEFig. 7.-An undistorted output of over 5 watts is given by this arrangement of two low -frequency stages feeding into two pentodes In parallel. The circuit is for universal

A.C./D.C. valves

553

In most cases, if the output fromthe detector valve is taken directly tothe input of the amplifier, cutting outthe low -frequency side of thereceiver, results will be greatlyimproved.


Wireless Magazine, ,hity, 1934

Make and Break!" ISTEN," nudged one of the H.T. leads. " I'm

-I'm going to " . . . he swelled into openand glorious revolt . . . " Yes, I am-I'm

going to come unstuck and stop functioning. Whyshould I be a mere slave to some snob of a knob -twister ? I'm all for the liberty of the individual.Freedom is the birthright . . . "

" You've been reading Rousseau," interposed theHigh Tension complacently. " Did the same myselfwhen I was young. You'll grow out of it. All theseyoung fellows think they're the only ones who . . . "His gurglings became indistinct.

The H.T. lead shivered irritably." Well, I hope you all realise that I mean what I say.

The whole set goes phut without me, and I'm stopping.See ? "

His neighbour temporarily free-whilst a famoussoprano drew breath-said shortly: " Don't be liverish;you can't leave us to do everything." He bent to histask again.

0

.25o r. 10

1MFD.500

75,000

ITt500 V.

YHT-

INGENIOUS CIRCUIT FOR AN A.C. AMPLIFIERFig. 9.-This circuit consists of a variable -mu screen -grid amplifier resist-ance -capacity coupled to two large triodes in parallel. The output given

exceeds 10 watts

LARGE AMPLIFIER FOR USE ON A.C. MAINSFig. 10.-An output of 10 watts is obtained with two resistance -capacitycoupled stages feeding a triode of the Cossor 660T type. This circuit can be

adapted to give larger outputs

554

The Grid Bias lead, who had had a better educationthan the rest, insisted gently:-

" But, old chap, you can't do that. It wouldn't beplaying the game. I mean to say . . . "

Unfortunately no one heard him. His delivery wasrather weak, and he was beginning to feel the strain.Socialism was all very well in its way, but it mustn't beallowed to interfere with the welfare of the circuit.

The H.F. valve winked knowingly. " I've heard allthis before-but he never does anything."

" Don't know so much," mused the L.F. valve. " Ifeel something isn't pulling its weight." He glimmereduneasily.

The detector valve giggled." I'm feeling so silly," she oscillated. " Ooh-ooh-

don't touch me. I'm ticklish."The first valve strained fiercely." Something's up," he muttered. " Thought the

detector would be the first to give. She's always been abit weak. Where's everybody-I can't see any more . . . "

" That," said the H.T. lead a trifle defi-antly, " is that. At last I'm free from theshackles. No more blind obedience, and nomore eternal continuity."

He sizzled uncertainly." But where do I get out ? I can't see with-

out the valves, and everything's gone dead."He thrust gropingly towards the Terminal." Say, I'm sorry-please . . . "The contact revived him.Hth ! you fellows, I'm on again."The dead current leapt to life and galvanised

the circuits-the soprano's voice rang outclear and true.

" Henry, dear, what happens when the setstops suddenly like that and then goes onagain ? "

" Oh, it's nothing to do with the set, mydear; just a temporary fault at the transmittingend."

Which is, of course, one explanation.S. J. H.

PRACTICAL POINTS IN AMPLIFIER DESIGNContinued from page 553

The only trouble likely to be encounteredis low -frequency instability, which is com-monly known as motor -boating. This can beovercome by increasing the values of thedecoupling resistance in the detector stage orin extreme cases by double decoupling.

Room Strength with 12 WattsWhen an amplifier of 10 or 12 watts output

is used, do not get the idea that the volumecannot be turned to reasonable room strength.A good high -resistance potentiometer will cutdown the output from the largest set. It ismainly for quality that we suggest that you usea large amplifier after the radio set.


,BESTS OF NEW

PPARATUOsram Double -diode Triode :: B.T.H. Senior Pick-up :: Mains Power Trickle Charger :: Ferranti

Screen -grid Valve :: Gard Lightning Arrester :: Bulgin Tone Control

OSRAM DOUBLE -DIODETRIODE

APPARATUS: Double -diode triode.MAKERS: General Electric Co., Ltd.PRICE: 9s.

THE new Osram HD21 is a 2 -voltvalve comprising a triode and

double -diode assembly in one bulb.In order to obtain the maximumefficiency a separate filament systemis used for the triode and diodeportions, the valve being arrangedsomewhat similar to a class -B assem-bly. This particular construction alsoenables the two diodes to be ade-quately shielded from the triodes-apoint of some importance.

The valve has a variety of applica-tions. It may be used as a straight-forward detector -amplifier using oneor both diodes for rectifying and thetriode for subsequent amplification.The efficiency of this arrangement isequivalent to that of theordinary grid -detector, butthe usual bugbear of over-loading is largely avoided.

The valve may be usedto provide combinedrectification and automaticvolume control. In thiscase it is desirable to usethe diode in a special way.One diode is nearer to thepositive end of the filamentthan the other and there-fore commences to conductslightly earlier. This diodeis used for the signalrectification, while theother diode is employedfor A.V.C., thus obtaininga slight delay.

The HD21 is mountedin the customary five -pinholder, but the grid of thetriode is brought out at

A 2-voldiode trreleas

Os

the top. Instead of thefamiliar screw terminal ametal cap is provided overwhich a clip is located similarto standard American prac-tice. The valves can besupplied either clear ormetallised.

The triode portion is rated The new B.T.H. Senior needle -armature pick-upto have an amplification gives exceptional results for a pick-up of its typefactor of 27 and an impedanceof 18,000 ohms, corresponding to aslope of 1.5 milliamperes pervolt.

We found on test that the valvewas up to its rating and that it canbe used with very satisfactory results.

B.T.H. SENIOR PICK-UPAPPARATUS: 13.T.H. Senior needle -armature pick-up.MAKERS: Edison Swan Electric Co., Ltd.PRICE: E2.

t double -lode justed byram

IN view of the extremelylow output voltages

usually associated wit hneedle -armature pick-upswe read the makers' claimsto a big advance in sensi-tivity with more thanusual interest. An ex-amination of the pick-upalso proved interesting.

This showed that whilstthe needle is free at theinput end, it is held bynon-magnetic material atthe far end in such amanner that it is still inthe magnetic field andboth ends are free.

Exceptionally pleasantresults were obtained fromlistening to a variety ofrecords with this pick-up,and although there wassome little accentuation of

555

the upper register, this was notdispleasing. Measurements of thevolts output over a wide range offrequencies showed that the makers'claims were substantially correct.

A voltage output table at fourdifferent frequencies when usingdifferent needles is reproduced onthe manufacturer's instruction sheet.

The volume control is smooth andthe general finish of the pick-up andtone -arm, which is of oxydisedmetal, is pleasing. In general, wefeel that this component marks adistinct advance in needle -armaturepick-ups.

MAINS POWER TRICKLECHARGER

APPARATUS: Trickle -charger kit.MAKERS: Mains Power Radio, Ltd.PRICE: .5 -ampere type LI 2s. 6d.; I -ampere type,

£1 6s.

THE assembly of the componentsof this trickle charger is ex-

tremely simple and can be accom-plished in less than an hour with theaid of two tools only-a screwdriverand a pair of pliers. No soldering isnecessary.

There are only five componentsand the designers have providedagainst danger of shock. The kittested was for use on 200-250 volts,with a charging rate of .5 -ampere,

WirelessMagazine. July 1934

This trickle charger is supplied by Mains PowerRadio as a kit of parts. It is easily assembled

but we are informed thatalternative kits are avail-able for use with 100-120 -volt mains and thateither type is suitablefor charging at 1 -ampere.The requirements shouldbe made clear whenordering.

Metal rectification isemployed, and a ballastresistor in the positiveoutput lead ens u r escurrent regulation andalso places a limit onthe current should thebattery be wrongly con-nected. A fuse of aneasily replacable type isincorporated, so makingthe kit practically fool-proof.

After assembly, weused the kit on 240 -voltmains and measurements showedthat a voltage of 2.8 at .5 -amperewas being supplied, an adequatefigure for battery charging at home.

. . .FERRANTI SCREEN -GRID

VALVEAFPARATUS: Variable -mu screen -grid valve.MAKERS: Ferranti, Ltd.F RICE: l5s. 6d.

THEVS2 valve is a short -basescreen -grid valve used by Fer-

ranti in their own sets. It is more orless normal in construction, exceptthat the anode is oval in shapeinstead of consisting of a flat plate,as is more usually the case.

It is finished with the standardfour -pin cap, having the anodebrought out to the top terminal, butinstead of a screw terminal a push -onfitting is employed, similar toAmerican practice. Copper metallis-ing is used.

The valve appears to have beendesigned to give a rapid control witheconomy of current. At zero volts on

Economy of high-tension current is afeature of the newFerranti VS2 screen -

grid valve

the grid the anode currentwas only some 1.25 milli-amperes. The amplificationfactor was 500 and theinternal impedance 500,000ohms.

This corresponds to aslope of 1, which is a littlelower than usual, but is,presumably, deliberate inorder to allow reduced high-tension consumption to beobtained.

At 4.5 volts negative biasthe slope was reduced to .07

milliamperes per volt, adecrease of nearly 20 to1 in the sensitivity.

The valve will befound useful where rapidcut-off is required,coupled with economy ofhigh-tension current.

GARD LIGHTNINGARRESTER

APPARATUS: Gard automatic light-ning arrester.

MAKERS: Graham Farish, Ltd.PRICE: 2s.

ANEW Gard auto-matic lightning

arrester has been pro-duced and replaces theearlier model. We find,on examination, that it isintended for connectionto the aerial -earth systemout of doors and thatadequate protectionagainst weather con-

ditions to maintain its efficiencyis provided.

An erinoid tubeinto the ends ofwhich two threadedbrass rods arescrewed provides apassage to earth forany heavy discharge,the inner ends of therods being justseparated from eachother by an insulatedwasher to providethe necessary gap.

The tube is en-cased in a double -metal outer coveringthat can be reliedupon t o provideprotection f r omdamp. The arrestercan be easily fittedto an existing aerialin a few minutes.

No ill-effects onreception are likely

556

This Gard lightning arrester willgive adequate protection during

thunderstorms

A useful "luxury" componentis the Bulgin de -luxe tone control

to be experienced when usingthis gadget, as steps have beentaken to ensure that any capacity isnegligible, while it should respondreadily to any lightning discharge,since we found that the gap brokedown at just over 2,000 volts A.C.It forms an inexpensive insuranceagainst damage to a set duringthunderstorms.

BULGIN TONE CONTROLAPPARATUS: Dual tone control.MAKERS: A. F. Bulgin & Co., Ltd.PRICE: 7s. 6d.

WITH the object of obtainingtonal balance to suit every ear,

A. F. Bulgin & Co., are now market-ing a de -luxe Controlatone. It isintended to be connected across theoutput load on a receiver or, in caseswhere more than one low -frequencystage is employed, across the load ofthe penultimate valve.

Designed for panel -mounting, theunit, which consists of a small con-denser, an air -cored choke and avariable resistance, is enclosed in acylindrical bakelite case finished inmottled green and measuring 11 in.in diameter by 21 in. in length,exclusive of terminals.

Two terminals are fixed at the endand side respectively. A smallindicator dial-marked Deep,Normaland High-- is included for fixingbehind the knob on the front of thepanel.

On test in a receiver, we found theeffect on the reproduction of speechand music to be most marked.

With the unit set at" Normal," no alter-ation in the tone orvolume was noticed,but on turning toeither the " Deep "or High " settings,the results wereapparent.

After listening toan orchestral piecewith the unit set togive a good bassresponse, it wasfound a greatadvantage to be ableto turn to the" High " setting for

speech, which hadthe effect of re-moving all " boomi.ness " with littlereduction of signs.strength.

A good and usefulcomponent!


The AllPaneDesigned by the

" Wireless Magazine"Technical Staff

In these pages the " Wireless Magazine " Technical Staff describes the construction of a battery -operated three-valver using efficient screened coils covering the short wavebands of from 12 to 84 metresin addition to the normal broadcast wavelengths. Interest in short-wave listening is growing, andwith this set the battery user will have a reliable receiver covering all wavelengths between 12 and

2,000 metres. The set is cheap to build and gives especially good results

NOW that the short-wave That the short waves are of pro -stations are comparatively gramme value and that they arereliable and it is possible to extremely popular has been proved

obtain good entertaining programmes many times over, but in these daysfrom all over the world, a receiver when cost is of primary importancethat will tune down below 100 metres few home constructors can spare theis a great advantage. money to build a separate short-wave

set, or even a simple short-waveShort-wave Advantages converter.

The original thrill obtained when Last year in Amateur Wireless wastuning -in far away medium -wave described a four -valve all -wavestations is partially gone, for receiver using special coils, withmost efficient three- or four -valve internal switching, so that short-,sets of modern design will tune in medium- and long - wave station3some forty to eightystations withoutdifficulty.

A short-wave orall -wave :et will helpto regain some of thethrill of the earlydays when, duringthe early afternoon,the whole family canlisten to programmesfrom America, SouthAfrica, and evenAustralia. Whennormal broadcaststations are nottransmitting anyprogrammes thatsuit you, it is veryuseful to be able togo down to below100 metres and takeyour pick there.

could be tuned -in at will. Theamazing success of the receiverembodying these coils Made it quiteobvious that all -wave receivers arevery popular amongst home con-structors.

Improved CoilsThese coils have been improved

and modified out of all recognitionand are supplied completely screened,so they can be included in highlyefficient receivers, using valves withhigh amplification factors

Realising that a

a

1000

Vz00005

6000

00 OCO

610- GB+

moo

01

..1MFD.

LS+

L 5-

11T+

HT-

LT -

4 -.LT+

CIRCUIT OF THE ALL -WAVE BATTERY THREEThe circuit is quite simple, yet has features that ensure satisfactory results.A high frequency pentode is used in the high frequency stage followed by a

triode detector transformer coupled to the output pentode

557

four -valve all -waveset was no longernecessary in view ofthe improved com-ponents, we decidedto try a three-valverwhich would be assimple to operate on15 metres as it is on1,500 metres. Thiswould enable thefamily man to tune -in American andother long-distancestations with almostthe same degree ofreliability, as hewould some of themore -distant Euro-pean stations.

With this end inview, the All -wave

Wireless Magazine. Ju ty 1934

LOW -FREQUENCY SIDEThis close-up photograph shows thelow -frequency side of the set. It will benoticed that the fixed resistances are

suspended in the wiring

Battery Three was evolved. This is areceiver using two multi -electrodevalves so that the performance ismore like that of a four- or five-valverthan that of a simple three-valver.

Selectivity and SensitivityThere is no doubt that screened

pentodes used in conjunction withhighly efficient tuning coils accountfor the exceptional selectivity andthe sensitivity of this simple receiver.

We have always been of the opinionthat in the hands of the home con-structor a simple set will give moresatisfactory and consistent results,for it is only the ardent experimenterwho can satisfactorily operate areceiver that is a mass of controlknobs.

Coupling the AerialIn this all -wave three we have the

aerial coupled to the special all -wavecoil through a .0003-microfarad pre-set condenser or directly to the,coil. On the medium waves theselectivity is adequate when theaerial is taken directly to the coil(omitting the condenser), but on theshort waves, when the aerial is oftenon the long side causing dampingand lack of oscillation, the aerial -series condenser more than justifiesits inclusion.

The aerial coil is tuned by meansof a .0005-microfarad condenser,which ensures a wide wavebandrange and, as it is controlled by an

exceptionally smooth slow-motion dial, no difficulty isexperienced in logging theshort-wave stations.

One of the new Cossorscreened pentodes is usedin the high -frequency stageand this valve does givevery high stage gain-andeven below 20 metresamplifies the incoming sig-nal many times. No onecan really appreciate thevalue of an efficient high -frequency stage on the

short waves until they have actuallytried tuning in weak stations with ascreen -grid set after they have beenused to a straight two- or three-valver. Not only is the volumegreater, but the receiver is moresteady in every way.

In the anode circuit of the high -frequency pentode is an all -wavechoke which tunes between 12 and2,000 metres, but as some readersmay feel inclined to put in any oldchoke they may have beside them, toprevent trouble, we have included asecond choke in series with it, which

is suitable for all wave-lengths between 12 and200 metres. The idea ofthis extra choke is thatshould the reader use anordinary broadcast choke,the use of the additionalspecial short-wave chokewill ensure the receiveroperating satisfactorily onthe short waves.

TWO HIGH -FREQUENCY CHOKESTo make certain that the results are satisfactoryover all wavebands, two high -frequency chokes

ha, e been inclu led in the design

Primary WindingA tuned -grid circuit

couples the high -frequencyand detector valves, but theoutput from the high -frequency valve is not feddirectly to the grid coil. Inboth the aerial and gridcoils the input is fed into aprimary winding, and aseach wave -range on thecoil has its own primary theefficiency is kept at anextremely high level.

BACK VIEW OF THE ALL -WAVE BATTERY THREEHere is the set, complete with valves and coil covers, ready for fitting into the cabinet.The valves from left to right are the detector, output pentode, and high -frequency

pentode. The high frequency and detector valves are of the metallised type

558

L

Many may wonder at the unusualvalues of the grid condenser and gridleak in the detector stage. Afterexhaustive tests we found that a.00005 -microfarad grid condenser wassuperior to the conventional .0001-microfarad or .0002-microfarad onwavelengths below 150 metres andas it did not affect the results on themedium or long wavebands it wasobviously the best value to use.

Grid -leak ValueSimilarly with the grid leak.

Although the 2-megohm leak origin-ally used was satisfactory, by increas-ing it to 5 megohms the reaction wasConsiderably smoother.

Reaction is by the conventionalReinartz method, but notice that themoving plates of the reaction con-denser are connected to earth, sopreventing any possible trace ofhand -capacity.

High Primary InductanceA 1 : 3 low -frequency transformer

with a high primary inductancecouples the detector valve to thepentode valve.

Very special care was taken inchoosing this low -frequency trans-former, for this component can affectboth the reaction and quality. The.25 megohm resistance across thesecondary helps to attenuate the topnotes and in conjunction with the.01-microfarad condenser across theloud -speaker acts as a tone corrector.

The 100,000 -ohm resistance in


AN EFFICIENT DESIGN FOR ALL BATTERY USERSThe three separate windings on the all -wave coil can be seen in the centre. At the top isthe long -wave winding, in the centre the medium waves, and the short-wave windings

are at the bottom

series with the control grid of thepentode prevents any unwantedhigh -frequency currents reaching theloud -speaker and so causing feed-back. The use of adequate decoup-ling and plenty of by-pass condensersaccounts for the exceptional stabilityof this receiver, even down to theminimum wavelengths to which thecoils will tune.

So much for the theoretical circuit.Full constructional details are

given in these pages, as well asnumerous illustrations showing thelayout of the various components.We would, however, remind ourreaders that a full-size blueprint,

PLAN VIEW OF THE ALL -WAVE THREEUsed in conjunction with the half -scale wiring plan on page 560, readers should haveno difficulty in making a good constructional effort. There are no snags and the set

should be built up quite easily in an evening

559

showing every wire numbered andwith the exact positions of the com-ponents, is available.

If you use the coupon on the lastpage of this issue by July 31, theblueprint can be obtained for 6d.post paid, instead of 1s. Addressyour application to the " WirelessMagazine " Blueprint Department,58-61 Fetter Lane, London, E.C.4,and ask for W.M.365.

Constructional HintsNow a few hints on the construc-.

tion. The metal panel and the metal-lised baseboard are held together bymeans of wood screws along the baseand not by panel brackets. As thereceiver is almost bound to be fittedin a wooden cabinet, our opinion isthat brackets are redundant. Bothof the tuning condensers are fitteddirectly to the metal panel, but toprevent noisy contacts the movingplates are earthed separately.

On the extreme left of the panel isthe aerial pre-set condenser. Takespecial care to isolate this fromthe metal panel by means of theebonite bushes supplied, otherwisethere will be a dead short and youwill not hear any signals.

Preventing NoiseOn the right of the panel is the

reaction condenser (.0005 -micro -farad), and although the movingplates of this are connected to earth,instead of relying on the automaticcontacts between the spindle and thepanel we have separately earthed themoving plates to prevent a noisybackground.

The on -off switch is fitted to a

1 -Wireless Magazine. July 1934

Half -scale Layout and Wiring PlanCHECKED BY

A full-size blueprint can be obtained forhalf price, that is 6d., post paid, if thecoupon to he found on the last page isused before July 31. Ask for No. 365 andaddress your application to the "WirelessMagazine" Blueprint Department, 58-61

Fetter Lane, London, E.C.A.

LS- Lb+

af 4331:

BLUEPRINT N2WM 365

METAL PANELle X 7

WOOD BASEBOARD12"x £3"

560

right-angle metal bracket, one halfof which is screwed to the baseboardand the other half held firmly upagainst the metal panel by means of alocknut on the on -off switch.

An important control on the panelis the wave -change switch, which hasfour positions : S, for wavelengthsbetween 12 and 34 metres; S2 for27 to 84 metres; and the usualmedium and long waves.

Self-cleaning ContactsFor readers living in a relay -station

area or who wish to tune in Fecamp,we took special precautions to ensurethat the minimum medium -wavewavelength was under 200 metres.

Switching on a four -range coilmight cause trouble if it were poorlydesigned, but in a Lissen coil thecontacts are such that the make -and -break action also cleans the contactpoints, thus ensuring clean connec-tions at all times.

Mounting the CoilsBoth of the tuning coils are

mounted off the metallised baseboardby means of a block of three-plywood. The idea of this is not toisolate the coils from the baseboard,but to raise the knob on the panel sothat the edge of the indicating platedoes not foul the table on to whichthe receiver is placed,

Between the two coils is a connect -


*.

No, N N *N4, f

N N

LAY01. T OF THE CONTROLSThe two main tuning dials are in the centre of the panel: the aerial -tuning condenseris on the left and the grid -tuning on the right. From left to right the controls at thebottom are the aerial -series condenser, wave -change switch, on -off switch and reaction

control

ing bush and a 1 -in. square holeshould be cut in the plywood stripto allow the bush to rotate withoutfouling.

The first valve is a Cossor high -frequency pentode, type 210SPT,which is fitted with a standard seven -pin bases The second valve betweenthe grid -tuning condenser and thecoil nearest the panel is the detector,a metallised 210Det. The final valveis a 220HPT pentode which gives ahigh output with very moderatehigh-tension current.

COMPONENTS NEEDED FORBASEBOARD £ s. Gi.

1-Peto-Scott Metaplex 12 in. by8 in. ... 1 6

CHOKES, HIGH -FREQUENCY1-Eddystone, type 505... ... 4 61-Eddystone, type 948... ... 2 91-Wearite screened, type HF?

(or Bulgin, Goltone) ... 3 6COILS

2-Lissen all -wave screened, type5386 ... 1 14 6

CONDENSERS, FIXED3-T.C.C., type 34, values :

.00005- (2), .01-microfarad(or Dubilier, Telsen) ... 5 6

3-T.C.C., type 50, values :.1-, 1-microfarad (2) (orDubilier, T.M.C. Hydra) ... 6 10

CONDENSERS, VARIABLE2-J.B. .0005-microfarad, type

Popular Log ... ... 15 01-Polar .0005-microfarad, type

Compax (or Lissen, GrahamFarish) . 2 6

1-Polar .0003-microfarad, typeCompax (or Lissen, GrahamFarish) 2 6

HOLDERS, VALVE2-Benjamin live -pin (or W.B.,

Telsen) 1 81-Benjamin seven -pin (or W.B.,

Telsen) ... 2 0PANEL

1-Peto-Scott aluminium 12 in.by 7 M. ... 3 6

PLUGS, TERMINALS, "ETC.5-Belling Lee wander plugs,

marked: HT+ 1, HT+ 2,HT-, GB-, GB+ (or Clix,

2-Belling Lee wander plugs,- marked : LT+, LT- (or

Clix, Eelex)

1 0

4

THE ALL -WAVE BATTERY THREEs. el.

6-Belling Lee terminals, type M,marked : Aerial 1, Aerial 2,Earth, LS-, LS+ (or Clix,

RESISTANCES, FIXED6-B.A.T., values : 1,000-, 2,500-,

6,000-, 100,000 -ohm, 250,000-,5-megohm (or Erie, Lissen)...

SUNDRIES2-Ebonite strips 3 in. by 1% in.,

say1 -1 -in. metal mounting bracket,

1 10

5 3

6

23 -ply wood 71/4 in. by 3 in., say 2Round tinned copper wire No. 20

gauge, for connecting, say ... 6Oiled sleeving, say ... 94 yd. thin flex, say ... 4

SWITCH1-Bulgin rotary on -off, type S91 1 9

TRANSFORMER, LOW -FREQUENCY1-Slektun ratio 1 : 3, type

unshro uded (or Lissen, Telsen) 5 6

ACCESSORIESBATTERIES

1-Ever Ready 120 -volt high-tension, type Winner ... 11 0

1-Ever Ready 9 -volt grid -bias,type Winner ... 1 0

1-Smith's 2 -volt accumulator,type 2RGN7 ... 10 6

CABINET1-Peto-Scott, type EN3 ... 15 0

LOUD -SPEAKER1-Blue Spot Star, cabinet model 4 18 6

VALVES1-Cossor 210SPT (met.) 15 61-Cossor 210Det. (met.) ... 7 01-Cossor 220HPT 16 6

The prices mentioned are those for the parts use.1 in the original set; the prices of alternativesas indicated in the brackets may Gs either higher or loner.

561

A double -capacity high-tensionbattery of 120 volts is ample to ensuregood quality and sensitivity. Thereare three high-tension tappingsH.T. negative; H.T. ± 1, pluggedinto the 60- or 70 -volt tapping; andH.T. + 2, plugged into the 120- or150 -volt tapping (if you have abattery with a high voltage). G.B.-1should be plugged into approxi-mately 6 volts when using the Cossor220HPT pentode.

Getting Correct VoltagesThe high tension to the detector

valve is brought down to the correctvalue by means of the fixed resis-tances in the anode circuit of this.valve The same remarks apply to theauxiliary grid of the pentode.

In order to make quite sure thatthe voltage applied to its grid islower than that applied to the anodea resistance of 2,500 ohms must beconnected in series with the auxiliarygrid of the pentode.

Operation is simplicity itself. Onmedium and long waves the aerialpre-set condenser should be adjustedto give the required degree of selec-tivity. Volume is adjusted by thereaction condenser and if the tuningcondensers are kept more or less instep stations will be received at everytwo or three degrees around the dial.

Tuning for Short -waversOn the short wavelengths-that is,,

with the switch turned to either S, orS2-great care must be taken inmanipulating the tuning dials.

The pre-set condenser in serieswith the aerial should be adjusted so


Wireless Magazine. Jut); 1934

H.M.V. photoA. Groom -Johnson, creator of " Soft Lights and SweetMusic," with his vocalist, Elizabeth Welch, admiringthe new H.M.V. Super -het Four -forty. One of their

records is reviewed by Chopstick this month

QUITE the star production of themonth is Richard Strauss's tonepoem, Don Quixote, recorded by theBerlin State Opera Orchestra, with

the composer conducting and with GeorgKniestadt, solo violinist; Kari Reitz, viola;and Enrico Mainardi, 'cello. This is onDecca Polydor records LY6087-6091,costing 3s. 6d. each.

It is a lovely work, exquisitely rendered.This is, of course, for the connoisseur andsomething to add proudly to a collection ofonly the best orchestral records.

A nice group of Parlophones. First, a 12 -in. pianorecord, with Rachmaninoff's Prelude in G Minor, nextin popularity to the hackneyed C sharp minor, and anarrangement by Liszt of a waltzfrom Gounod's Faust. Both areplayed by Eileen Joyce, whoseplaying has won my admiration(E11252, 4s.).

Next (R1832, 2s. 6d.), twosketches written by Geof-

frey Clayton, an old personalfriend, of whom I have lost sightfor some years now. One iscalled a Record Broadcast andthe other The Super -het. I thinkboth will appeal to you. Excel-lent satire.

Lighter still, two piano selec-tions played really remarkablyby Patricia Rossborough. DidYou Ever See a Dream Walking ?When You Were the Girl on theScooter, and other ditties appearon this disc. A clever piece ofplaying (Parlophone R1749,2s. 6d.).

If you want another Tauber

Parlophone photoossborough, the famous syncopated

ho you often hear over the air, hasorded a medley for Parlophone

Patricia Rpianist, w

rec

562

record with orchestra, I sincerely recommendThe Night and one called Ideale. Both are sungin German. The first is by Rubinstein and thesecond by Tosti. Tauber at his best!

M.V. C2668, 4s., is quite a pleasantaffair, especially to Irishmen. It is

called Danny Malone-Medley. He, of course,is the " meddler," and such popularities as theKerry Dance, Off to Philadelphia, and MyAuld Irish Mother fill two sides of an enter-taining disc. He sings sympathetically, with anice Irish inflection, in tune, and with gooddiction. What more ?

Changing the thought entirely, I recom-mend H.M.V. C2662, on which Browning

(Cikoosib

Your LoadsNew Record Releases Critically Reviewed

By WHITAKER-WILSON

Mummery sings On With the Motley and Your TinyHand is Frozen, one from Pagliacci, the other from LaBoheme. A nice voice, not too " tenory," yet with amusical quality. Very expressive rendering of both arias.

H.M.V. C2664 is a record byMiliza Korjus. One side isProch's Variations and the otherStrauss's Voices of Spring.Accompanying her is the BerlinState Opera Orchestra, so thereis not much the matter with it.A fine rhythm characterises theentire rendering. Korjus is finein the Strauss.

Going a little higher in thematter of price-and certainlyno lower in that of quality-youshould aspire to H.M.V. DB2131,6s., where Tito Schipa, tenor,sings Plaisir d' Amour and 0 delMio Amato Ben. I am greatlyimpressed with both sides.

The B.B.C. Symphony Or-chestra plays Beethoven's Corio-lanus overture, under Dr. Boult,on H.M.V. DB2101. If you haveheard it broadcast by the samemeans, you may be glad to havethis. It is a faithful representa-

tion in permanent form of what I, personally, haveheard them do many times on the air and in Queen'sHall. A very good record.

H.M.V. DB4412 attracts me considerably. MariaIvogiin, whom I have not heard before to my knowledge,sings two arias in German with the Berlin Orchestraaccompanying her. A lovely voice and the music byJohann Strauss. Do ask to hear this. I think you willlove it. I do !

I am quite interested in a record called Let's go toGermany. It is a practical travel talk in German, withan introduction in English by Hermann Winter. Veryvaluable if you are going to Germany. An excellentlesson in pronunciation.

Acouple of Deccas of interest. (F3961, ls. 6d.), is aGrenadier Guards record

-Drink to Me Only and a SavoyHunting Medley; F3982 isTommy Handley doing thatentertaining Silly Girl and CoomPretty One, which I think LeslieSarony wrote. It is excellent.

Columbia (DX580, 4s.) andthe B.B.C. Wireless MilitaryBand between them make anexcellent job of the Oberon over-ture of Weber, arranged by DanGodfrey. It comes out amaz-ingly well. This is one of thebest military bands in England.

Some other Columbia recordsof an attractive nature are TheBlue Danube waltz (DB1375,2s. 6d.), played by the OrchestreRaymonde; Harold Williamssings Farming and other songsfrom the fair on DB1376; and


H.M.V. PhotosYou have all heard the story ofDanny Malone's rise to star rankby his H.M.V. recordings. He hasmade a medley which is reviewedhere. (Left) The famous Italiantenor, Tito Schipa, has just madeanother red label disc for H.M.V.

Albert Sandler playing For Loveof You on DB1378.

Norman Long-well up toscratch-in Marrers and theimmortal I've Brought You SomeNarcissus, Cis, too should beheard.

Additional Records ReviewedBy CHOPSTICK

LIGHT SELECTION*Wonder Bar-Film Songs

Selection, The Bohemians, 4s.,COL DX583.

This record will help to conjureup memories of that famousmusical show, Wonder Bar, whichhas now been adapted for thefilms. The show is full of delight-ful tunes and the Bohemians knowhow to get the best from them.Do you need reminding of the bighits? Here are some; " Eliza-beth," " Goin' to Heaven on aMule," " Don't Say Goodnight,"" Why Do I Dream ThoseDreams " and, of course " WonderBar." A good twelve-incher this!

LIGHT SONGS*Carlyle Cousins Medley,

Carlyle Cousins, is. 6d.DECCA F3978

A fine medley of syncopatedchoruses by that famous broad-casting trio, which brought thehouse down at Radiolympia lastyear. They are accompaniedhere by Quaglino's Quartet. Thisis syncopated singing at its bestand will appeal to everyone.Some of the best numbers in themedley are : " California HereWe Come," " I'll See you in theMorning," " Sentimental Gentle-man from Georgia," " I Can'tGive You Anything But Love,"

CC

and, of course, that number thatis invariably included in everymedley, " Dinah."

(a) I've Found a New Baby,(I) Put On Your Old GreyBonnet, The Mills Brothers,as. 6d. BRUNS 1761

Marvellous fellows these MillsBrothers ! I hope you listened totheir " human orchestral " broad-casts. This disc gives you theMills Brothers at their usual highstandard. That is the onlycomment necessary !Soft Lights and Sweet Music,"Elizabeth Welch, 25. 6d.

H.M.V. B8172This is parts three and four in

the series H.M.V. are issuing ofAusten Groom -Johnson's broad-cast series " Soft Lights andSweet Music." Real soothingmusic admittedly, but perhaps onthe too -dreamy side. Here arethe contents ; "Getting Sentiment-al Over You," " Japanese Sand-man," "Goodnight, Sweetheart,""Lazy Day," and "Sweet Sue."

DANCE MUSIC*(a) Because It's Love (f.), (b)

Little Dutch Mill (f.), B.B.C.Dance Orchestra, 25. 6d.

COL CB751A really outstanding B.B.0

dance band disc. In (b) they

have really excelled themselves.I believe that the tune itself isthe best we have had this year.The B.B.C. people have com-bined a real delicate orchestrationwith a splendid piano solo byBert Read and vocal by Les Allento make their greatest recordingsuccess yet.

*(a) Goodnight, Lovely LittleLady, (f.), (b) Lonely Feet,(f.), Jack Jackson and hisOrchestra, as. 6d.

H.M.V. B6489I look forward every month to

these H.M.V.-Jackson recordings,There are always fine tunefulnumbers, well recorded and idealfor dancing. (a), from thefilm, Three Sisters, is good, butthe record is worth half-a-crownfor (b), from the film, We'reNot Dressing. This has the bestvocal trio I have come acrossrecently.

(a) Indiana (f.), (b) 01' ManRiver, (f.), Casa Loma Orches-tra, as. 6d. BRUNS 1755

(a) is typical Casa Loma. Thehigh spot is some fine solo workby the clarinet, tenor saxophoneand trumpet players. You shouldhear this-an example of how toget the most out of dance rhythm.(b) is a super hotted up con-coction of " 01' Man River "-from the Show Boat. Here, Isuppose, we come up against thequestion of whether tunes likethis should be adapted for jazz.My verdict is this : (b) is a

triumph of arrangement and ajolly good entertainment.

*(a) Love's Serenade (slow f.),

Mills Blue Rhythm Band,(b) It Should Be You (f.),

Henry Allen, Jnr., and HisOrchestra, as. 6d.

H.M.V. B6487Love serenading to me sounds

more like a funeral march with astrong rhythmic accompanimentin which the piano plays a veryimportant part. (b) is nothingmore or less than a series of hotinstrumental solos with a fineswinging rhythm. Allen, withhis trumpet, is the star performer.He does blow !

(a) Repeal the Blues (f.), (b) EasyCome, Easy Go, (f.), JohnnyGreen and His Orchestra,20. 6d. BRUNS 1757

Following the batch of Columbiarecordings of piano solos by JohnW. Green, Brunswick gives us adisc of two popular hits played byGreen's own American band. Itis a splendid disc admittedly,but the real bright spot of bothsides is a fine vocal by a " realcute " lady. Gee, she can croon !

(a) True (f.), Swaller Tail Coat,(quickstep), Roy Fox andHis Band, is. 6d.

DECCA F3987This is Roy Fox at his best.

(a) is one of his quiet tunefulnumbers and (b)-not noisy-ajolly hot quickstep with brilliantteam playing by the band.

563

Wireless Magazine. Jul, 1934

My Impressions th"Two H.F." Portable

Last month we published full constructional details of the "TwoH.F." Portable-a self-contained set having two variable -mu high -frequency stages, detector and a twin -pentode output stage. This sethas aroused much attention among readers, and here we presentan independent test report which, besides giving many useful operatinghints, will give you an idea of the outstanding quality and sensitivitygiven by this set. May we remind readers that a full-size blueprint

of the "Two H.F." Portable can be obtained for Is., post paid.

WHEN I was given theTwo H.F." Portable totest I was told that it was

the outcome of many weeks experi-mental work. My reply to this isthat the time has certainly not beenwasted, for it is an excel-lent set. I was privilegedto have it only for oneevening, but that wasquite long.enough to proveits worth.

The first point that struckme was the strength andquality obtained from thelocal station. The outputresembled that of the aver-age mains set and thequality on the little built-inmoving -coil loud -speakerwas excellent-a pleasantsurprise if you are usedto the average " portablequality."

This output was notconfined to the local. Mostof the principal Continental

stations were brought in at" uncomfortable " room strength,many without the use of reaction.

As in all portables, the directionalproperties of the frame were verynoticeable, but as the cabinet is

CHASSIS -BUILT FOR EFFICIENCYThe set is built up on a metal chassis to ensure stability as wellas to give a neat appearance. As you can see, the layout is

particularly clean

564

provided with a small turntablethis feature caused very little trouble,and often enabled me to bring apoor station up to full loud -speakerstrength.

It was also useful from the pointof view of selectivity, as unwantedtransmissions could generally be

ATTRACTIVE EXTERNALAPPEARANCE

The four controls are grouped closetogether on the front of the neat oakcabinet. The set is self-contained with a

moving -coil loud -speaker

eliminated from the programme towhich we were listening by rotatingthe set.

Good SelectivityApart from the directional proper-

ties of the frame, however, thetuning of the set seems quite selec-tive. This is not surprising con-sidering there are three tuningcircuits.

The sensitivity is of a high orderand can be varied considerably by

means of the screen voltageapplied to the high -fre-quency pentode.

Generally speaking, it isbest to work with about 60to 70 volts on the screen,although to obtain themaximum sensitivity it ispossible to put this up tothe full 120 volts withoutintroducing serious instab-ility.

In the latter case, how-ever, the current taken bythe high -frequency valves ishigh and would result inthe high-tension batteryhaving a short life.

The single -knob tuningcontrol is of great advant-age when searching for

stations, although adjustment ofthe frame -aerial trimmer is usuallynecessary to bring the signals up tofull strength. On the set I handled,the trimmer capacity had to begradually increased with increasingwavelength.

The other three controls are thevariable -mu volume control, reactioncontrol, and the wave -change switch.The latter has a positive snapaction and is remarkably free fromnoise.

Forty-five CertaintiesDuring an hour and a half in the

evening I was able to identifyforty-five stations, thirty-four ofwhich were on the medium wave-band. I listened to Hamburg quiteclear of the London Regional andStrasbourg with only a faint back-ground. Frankfurt was also wellreceived clear of London National,

SIMPLICITY THE KEYNOTEThis back view of the portable showsvery clearly the neat arrangement of theset chassis and batteries in the cabinet


STATIONS HEARD ON THE "TWO H.F." PORTABLEMEDIUM WAVES

StationDial

Reading StationDial

ReadingFdcamp 9 Munich ... ... 59Gleiwitz 16 Rome ... 63Lille 17 Paris ... 664Frankfurt 19 North Regional ... 71

Morayska-Ostrava 204 Prague ... 73London National 214- Brussels ... 75Mad rid ... . 23 Vienna ... 90Scottish National 284 Miihlacker 914Heilsberg .. 294 Athlone ... 924Breslau ... .. 314 Beromunster 95West Regional 334 Budapest ... 98Poste Parisien 35 LONG WAVESBrno ... 37 Croydon ... 12

Hamburg 384 Moscow ... 15

Radio Toulouse 39 Kalundborg 36London Regional 414 Luxembourg 39Strasbourg . 44 Unidentified 43Berlin Funkstunde . 48 Motala 46Scottish Regional 504 Eiffel Tower ... 51

Leipzig .. 53 Daventry National ... 55Toulouse ... ... 54 KOnigswusterhausen 59Midland Regional 55 Radio Paris 674Marseilles 574 Huizen . 85

a remarkable feat of selectivity fora portable set.

I was surprised to receive theMadrid station on 274 metres, asthis has only a power of 2 kilowattsand is a poor station in my part ofthe world. Such stations as Bero-munster, Vienna, Rome, Poste Paris-ien and Fecamp, etc., providedexcellent programmes and wereobtained at full loud -speaker strengthwithout the use of reaction.

On the long waves all the usualprogrammes were obtained with theexception of Oslo, which, for someunaccountable reason, I could notfind anywhere-of course, it maynot have been transmitting,

Just before breakfast on thefollowing morning I switched theset on again to see what the daylightrange was like, and succeeded in

getting eight programmes.The whole of the tests were carried

out in or near Leigh -on -Sea, Essex.During one afternoon the set under-went critical examination at my localtennis club. As you can see by thephotograph reproduced in thesepages, some of the players forsooktennis for a while to listen to theradio.

Frame -aerial TipJust one point. During daylight,

when distant foreigners are wanted,do not forget to take advantage of thedirectional properties of the frameaerial. It will make all the differencebetween good and indifferent results.

I have no hesitation in recom-mending you to build the portable-I shall certainly do so myself whenI have a little time to spare. S. 0.M.

LIST OF PARTS NEEDED FOR THE "TWO H.F." PORTABLECHASSIS £ s. d. PLUGS, TERMINALS, ETC. £ s. d. Ebonite rod, % in. diam., 4% in. £ s. d.

1-Peto Scott aluminium, 12 in. by6% in. by 3 in., complete withscreens .. 8

6-Belling-Lee wander plugs,marked : H.T.+1, H.T.± 2,H.T.-, G.B.-1, G.B.-2,

long, say1-Bulgin knob, type K14Aluminium bracket for mounting

3

CHOKE, HIGH -FREQUENCY G.B.+ (or Clix, Eelex)... 1 0 trimming condenser, say ... 31-Varley screened, type 13P26 (or

Bulgin, Telsen)COILS

2-Belling-Lee spade terminals,marked; L.T.+, L.T.- (or ClixEelex) 4

SWITCHES3-Bulgin on -off toggle, type S80B,

with 6 in. length of 5(32 in. rod2-Telsen matched screened, type 6-Belling-Lee sockets and plugs, and K14 knob ... 5 9}

0 type 1077, marked : red (3), TRANSFORMER, LOW -FREQUENCYCONDENSERS, FIXED black (3) (or Clix, Eelex) 2 6 1-Wearite, type PPA ... 13 6

7-T.M.C. Hydra, type tubular,values:.0003-, .001-, .005-, .05- RESISTANCES, FIXED ACCESSORIES,0002-,

microfarad (3) (or Erie)1-T.M.C. Hydra 1-microfarad,

5 3 5-Claude Lyons, values: 30,000.-100,000-(2), 250,000 -ohm, 2

BATTERIES1-Ever Ready 120 -volt high-

type 25 (or Dubilier, T.C.C.) ...CONDENSERS, VARIABLE

2 3 megohm (or Erie, Siemen-Schukert) 4 4

tension, type Portable 18 ...1-Ever Ready 9 -volt grid -bias,

15 0

1-British Radiophone .0005-microf arad three -gang, type 604,with slow motion drive type 803 1

1-Lissen .0005-microfarad, type6 6

RESISTANCE, VARIABLE1-British Radiophone 50,000 -ohm,

with 3 -point switch, type 481 6 0

type Winner ...1-C.A.V. 2 -volt accumulator,

type 2VN11/1 ...CABINET

1 0

14 0

LN5103 (or Telsen, GrahamFarish) 2 6

SUNDRIES2 ft. screened sleeving, say 6

1-Kebtex, type BWDLOUD -SPEAKER

1 12 6

1-Polar .0001-microfarad, type Round tinned copper wire, No. 20 1-Rola permanent -magnet, typeCompax (or Lissen) ... 2 6 gauge, say ... 6 FR5PM70 1 9 6

HOLDERS, VALVE Oiled sleeving, say ... 9 VALVES1-Clix four -pin, type chassis 5 yd. thin flex, say 5 2-Marconi VP21 (or Osram) 1 11 0

mounting 8 14 yd. Litz wire, 27/42, say ... 3 9 1-Cossor 210 Det (or Mullard3-Clix, seven -pin, type chassis 2 oz. D.S.C. wire, No. 28, say ... 1 0 7 0

mounting 3 0 1-J.B. gang coupler, type 2003 ... 9 - 1-Marconi IP21 (or Osram) ... 1 2 6

The prices mentioned are those for the parts used in the original set; the prices of alternatives as indicated in the brackets may be either higher or lower

565


All the Latest

in Car RadioReviewed by the

"WM:" Technical Staff

1,000,000 sets aEASILY DETACHABLE FOR REPAIRS year.

The Motorola set chassis is so arranged that in the event of a breakdown The favour -it can easily be removed from its metal container and repaired able Americanor replaced without ony trouble

DURING the past year or sowe have tried to form someideas on what would be the

ultimate end of car radio. Wouldit become universal and even fittedby car manufacturers, or would itdie the slow death of so many newideas ? So far we have failed tofind any definite facts upon whichto base a conclusion.

Coming into FavourThe radio exhibition last year saw

the first serious attempt by setmanufacturers to popularise thecar radio type of receiver.

What has been the result so far ?Until the last month or so sales havebeen so very slow that we thoughtthat car radio was a thing of the past.Just recently, however, with thebetter weather and the introductionof some really good sets, there hasbeen a decided reaction in favourof radio in cars.

Not so Easy !In the past, many manufacturers

came to the conclusion that sellingcar radios was an easy thing, anda quick way of making a good profit.Consequently, instead of designingsets with special components tostand vibration, heat and the generalrough and tumble of motor -cartravelling, they used standard types.

Instead of the general publicrushing in as anticipated, there wasconsiderable apathy to buy receiverswhich were an obvious compromiseand sounded like the portablereceivers of the early days.

Even then some of the manu-facturers wondered why it was thatthe sales in America exceeded

conditions werenot borne in mind. Over thereeverything is in favour of car radio.Cars are much larger so that thespace beneath the facia board housesquite a large receiving unit.

Long distance freight vans andpassenger coaches, which makejourneys of 3,000 miles or so, areequipped with loud -speakers andheadphones. Americans have realisedthat radio at night helps to keepsleepy drivers awake, while on this

NOT A SPEEDOMETERThis is the Motorola remote control unitwhich fits on the steering column of a car.It is indirectly illuminated to prevent dazzle

side of the Atlantic the powers thatbe shivered in their shoes at the veryidea.

American car drivers are accus-tomed to make long journeys acrossthe continent so that a radio isalmost indispensable.

Companies are being formed inU.S.A. with the sole idea of makingcar sets for cars and not modifyingstandard sets.

Consequently these advantagesbacked by a good sales drive arebringing a large reward.

566

These points having been realisedby British set makers, we now havereal car -radio sets actually available.

In spite of the Government refus-ing to make any definite statementas to whether or not they will banradio in cars, the man in the streetis beginning to realise that there issomething in car -radio after all.

Snags OvercomeMost of the snags have been over-

come. Quality is good, range almostas good as the home set, fadingnegligible, and there is no ignitioninterference.

There are four firms in the fore-front with car -radios through sheermerit and attention to detail. Theyare Motorola, Philco, Lissen, andMajestic.

These four firms are in a positionto supply receivers that are equalto the finest in the world. Motorolahave concentrated on car -radio andnothing else. They were quick torealise that with a new toy the car -radio owner would be very criticalabout performance, and would com-pare it with the family set.

So Motorola decided that not-withstanding the poor aerial, vibra-tion, temperature, power supplyproblems, and ignition interference,their car -radio set would be as goodor even better than the averagehome receiver.

Self-contained OutfitA few words about these Motorola

sets. The Dual-" 6 " model is asingle unit receiver complete initself, as the radio -receiver chassis,loud -speaker, power pack and noise -filter system are all in one metalcontainer.

The remote control is fitted to thesteering column, and can be suppliedwith liners to fit any diameter steeringcolumn.

This is one of the few controls wehave tried with the aeroplane typeof indirectly illuminated dial. Inappearance it looks very similarto a speedometer except that it hasthree control knobs. Here againwe were surprised to find that inaddition to the usual tuner andvolume control knobs there was atone control.

Locking the Set !The knobs cannot be removed, so

there is no possibility of any of themworking loose through vibration.The receiver can be put out ofaction and locked by means of a Yaletype of lock and key. In addition tothe spark suppressor resistancesfitted in the engine, the radioreceiver is fitted with a specialnoise -filter system built into thereceiver as an integral part.

This removes all traces of back-ground noise and reduces thenumber of external wires veryconsiderably.

We noticed that the set could beremoved from its metal containerin a matter of seconds ; all connec-tions being made by sockets. Whenthe receiver is slid into the containerspecial pins make contact with thesockets.

Easily RepairedIn the unlikely event of a break-

down it can be removed and a newchassis put in its place in a veryshort space of time.

The Motorola receivers are allsuper-hets and designed to give6 -kilocycle selectivity, which is con-siderably better than can be claimedfor the average home set. A

Wireless Magazine. July 1934vibrator converter running off a 6 -or 12 -volt accumulator gives an out-put of 220 volts and is enough toensure excellent quality.

As car radio would be almostuseless without automatic volumecontrol, this point has been givenspecial attention. Their successcan be judged from the performance,for bridges, cuttings between hills,and shielding from large towns makeno appreciable difference to thevolume or quality.

All components usedhave been designed to with-stand a rise in temperatureup to 244) degrees, a pointnot likely to be reached innormal conditions.

The Dual Model " 6 " isintended to be fixed beneaththe facia board, but incars where this is not possi-ble the Twin 8 can be usedinstead. This can be fittedunder the running board,beneath the back seats, orto the dashboard above theengine.

The Twin 8 is really thelast word in receivers forcar use, and will bring infifty to sixty stations under the worstconditions.

Some idea of the automatic -volume -control efficiency can beobtained from figures supplied bythe makers. They claim that thevolume output is uniform with asignal input varying between 4 and500,000 microvolts.

The price of the Twin 8 is£26 5s., and the Dual 6 £18 18s.

Now for Philco. Philco decidedthat if car radio is to become uni-

HOW THE PHILCO TRANSITONE SET IS CONTROLLEDHere you see the radio control unit of the facia panel of the Hon. Peter Aitken's touringFraser -Nash car. The Philco set and loud -speaker are fitted underneath the facia

panel. The outfit does not take up much room

567

versally used in this country theprices must be comparable with thoseof the family set.

As a step in the right directionthey reduced the price of the Transi-tone Model 10-brought out lastyear-from £33 12s. to £16 16s., andat the same time improved it out ofall recognition.

This new model embodies fullautomatic volume control and four -point tone control. The whole unit

COVEPN UT$

BRAIDEDLEADNUT

OILMOLE

GENERATOR AND FILTER UNITThe generator and filter unit of the Motorola car -radio

set fits on to the dashboard of the car

is housed in a metal container lessthan 12 in. square. As it is fixedby only three bolts, installation is avery speedy matter.

A special Philco vibrator con-verter runs from the car accumulatorand supplies the required high- andlow-tension voltages so that thereceiver is on a par with a mains -driven set.

Last Word in EfficiencyTheir six -valve super -het circuit

is the last word in efficiency. Back-ground noises are kept down to alow level, while Continental stationscan be tuned in with the car travellingat high speed. A point that wenoticed was that the control knobscould be used without difficultywhen wearing thick motoring gloves.

The quality, with an output in theregion of 2,500 milliwatts, bearscomparison with the best homereceiver.

Lissen's,who introduced their firstcar -radio receiver at the last radioexhibition, have now brought theirone model right up to date to includeall of the latest ideas developedduring the past few months.

Actually they have two models,but both fundamentally the same.One is for 12 -volt and the other for6 -volt systems. The first model is

Wireless Magazine. Jtily, 1934

LISSEN CAR -RADIO CONTROLThis Lissen car -radio outfit is unique in that theswitching on the set is controlled by electrical relays

from the remote control unit

type 26006, and the second type26001, and both cost 16 16s.

The circuit is a complete departurefrom the more popular Americanpractice of using multi -valve super -

het receivers.

Straight-Not Super -hetLissen's are firmly convinced that

super-hets mean background noise,so they have pinned their faith to thereliable three -stage high -frequencyamplifier followed by diodedetection and intermediatelow -frequency stage with aspecial class -B output.

Dual -range iron -core coilsare used having a tuning rangeof between 200 and 520metres on the medium wavesand 830 to 2,100 metres onthe long. The whole re-ceiver is housed inside awatertight container with aneasily removable cover.

Illuminated ControlsAll operating is done from

the steering column. Theremote -control unit includestuner, volume and wave -range controls, as well as themaster on -off switch. Bothwave -range tuning scales areilluminated-the medium waves inred and the long waves in green.

A loud -speaker of the moving -coiltype is supplied in a " poke -proof "case, which can be fitted to the under-side of the facia board or to anyother convenient part.

Ample volume is obtainable fromall but the very distant stations, andon the locals an output of 2,500milliwatts is given.

A point, with which we wereimpressed, was the method ofswitching. Instead of the usualBowden wire arrangement, Lissen'suse a particularly effective electricalrelay system.

Yet another system isfavoured by the MajesticCo., who have produced asix -valve super -het receiverwith full automatic volumecontrol, tone correction,and provision for an addi-tional loud -speaker. Theloud -speaker and receiverare both housed in the samecase, which is fitted withbrackets so that it can bescrewed to the undersideof the facia board. Thissystem does enable thereceiver to be installed in

quick time.An aeroplane type of dial, fitted

to the steering column, is illuminatedand harmonises with the remainderof the facia board.

Remote control is provided fortuning, volume and master switch-ing. The receiver, when switchedoff, can be locked with a Yale -typelock and key. This Majestic setcosts £21.

After weighing up all of the

INTERIOR OF THE LISSEN CAR -RADIOThe Lissen car -radio set is contained in a strong metalcase which fits under the back seats of the car, or, in

fact, in any convenient place

evidence it doesseem as if theBritish manufac-turers are making avaliant and success-ful attempt to popu-larise radio in cars.

We do feel thata word from theGovernment on thelegal position woulddo a lot to put carradio either on oroff the wireless map.

As most of theresistance manufac-turers are now in a

568

position to supply the special noisesuppressor resistances for fitting inseries with the sparking plugs, thelast snag in car -radio is overcome.These manufacturers have conductedtests on the best value of resistanceto be used, and it is a simple matterto get maximum noise suppressionwithout affecting engine performance..

Dubilier, Erie, and other resist-ance manufacturers can supply thehome constructor with a deal ofinformation on the best valueresistance to use with different cars.

For the ConstructorThe home constructor should

remember that car radio receivers arenot difficult to make. In fact with alittle care quite effective four -valvereceivers can be made at home whichwill give good results, and cost ofconstruction is comparatively cheap.

We have experimented with aconstructor four -valve receiver usinga tuned aerial stage and an untunedgrid stage ; it gave excellent resultson the more powerful stations. Thesize of the cabinet was kept down toapproximately 9 in. square, and byusing a metal chassis and Catkinvalves the receiver was almostunbreakable.

Midget ComponentsCertain manufacturers are in a

position to supply midget tuningcondensers and midget dual -rangecoils, so there is no reason for thehome constructor not building, say,a super -het with single dial control.The necessary power supply can beobtained from the car accumulator,via a rotary or vibrator converterwhich gives an output of between200 or 300 volts at 50 milliamperes..

The car chassis is used as anearth connection, while Harbrocoloured cable can be tacked aroundthe car roof for an aerial.

" STRAIGHT " CAR -RADIO OUTFITThe Lissen car -radio set is the only British set that does not use asuper -het circuit. Three high frequency stages are used in a

straight circuit

THE

SHIELDED

UNIVERSAL

FOUR WAVERANGE COIL

(L.N. 5386)

PRICE

11/3EACH

(COIL WITH COVER REMOVED)

EXCLUSIVELY SPECIFIED

for the W. MALLIWAVE 312-2,100 metres without coil changing

1st Range - - 12-34 metres2nd Range - - 27-84 metres3rd 12. -mg - 2 0 0-5 5 5 metres

4th Range - 900-2100 metres

COMPLETE with self-contained switch,knot, coupler, extension switch rod, andaluminium cover

LISSEN COMPONENTS ALSO SPECIFIEDfor the "Two H.F. Portable" and the "SixGuinea A.C./D.C. 3." For the former one.0005 Mfd. Variable Condenser (L.N. 5103)price 2/6 and for the latter 4 Fixed Con-densers (Mica), price 2/6 and x Valve Holder(L.N. 739), price 1/3, are recommended.

Send a Postcard for literature describing allLissen products.

LISSEN LTD., Lissenium Works, WorpleRoad, Is'eworth, Middlesex.


CLIX4 - PIN5 - PIN7 - PIN

Chassis MountingVALVEHOLDERS

Specified for the"` W.M.' RADIOGRAM SUPER "

and invariably specified where-ver the modern chassis methodof construction is used.

4 -Pin 8d.5 -Pin 9d.7 -Pin li-CL I X. Thevalve holdersthat give perfectfull surface con-tact with ANYtype of valvepin.

7 -I ai

Write Joe e escripliveFolder "B"

L ECTRO-LI NX LTD.79a Rochester Row, LONDON, S.W.1

" We' e Fluxite and Solder, the reliable psi ;

Famous for Solderine, known everywhere'The Music WAS perfect t It something went wrong!WE came to the rescue hence laughter and song I"

See that Fluxite and Solder arealways by you-in the house-garage-workshop-anywhere where sim-ple, speedy soldering is needed.

ALL MECHANICS WILL HAVE

FLUXITEIT SIMPLIFIES ALL SOLDERINGAll Ironmongers sell Fluxite in tins: 9d., Sd.,Is, 44., and Is. Sd. Ask to see the FLUXITEPOCKET SOLDERING SET-complete with fullinstructions -7s. Ild. Ask also for our leaflet on

HARDENING STEEL with Fluxite.

FLUXITE LTD., Dept. 332Dragon Works, Bermondsey St.,

FOR ALL REPAIRS!

17

"TM

569

im PORTA NT.-Aliscellan"as C°""ent,. P""Kits, Finished Reccivees or Ames-., r, for Cash, C.O.D., or B.P. on our own sustem of EasyPayneents. Send us a list of your wants. We will quote you byreturn. C.O.D. orders value over 10/- sent carriage and postcharges paid (GREAT BRITAIN ONLY).

SIX GUINEA A. C./D. C.KIT "A" Author's Kit of First Specified parts less valves andcabinet. Cash or C.O.D. Carriage paid, 13/0/0. Or 12monthly payments of Sill.

KIT " B "As for Kit "A," but In-cluding set of first speci-fied valves. Cash drC.O.D. Carriage paid,15/12/6. Or 12 monthlypayments of 10/5.

KIT "C"As for Kit "A," but in-cluding set of specifiedvalves, cabinet, andspeaker. Cash or C.O.D.Carriage Paid, 17/0/0.Or 12 monthly paymentsof 12/9.

KIT -BITS You pay the Postman. We pay postcharges on all orders over 10/. GREAT

BRITAIN ONLY.1 Peto.Scott Ch_ssis 12 in. by 9 in. by 21 in. With £ a. d.

metaplex top ..1 Peto-Scott Cabinet type No. x141(117 .. 12 8

I Set of 4 Tungsram V,,heq as specified .. 2 12 6

PETO-SCOTT Moving Ccil

SPEAKER ExclusivelySpecified

Power or Pentode. Cash or C.O.D.Complete with Inputtransformer. '2,500

0111118. Send to -day.Limited quantity only. Carriage Paid.

Or 2(8 deposit and 4 monthly payments of 4/.

/-

"W.M "RADIOGRAM SUPERRECEIVER KIT

Comprising Author's Kit of First Speified partsfor Receiver Portion only, less valves and Cabinet.Cash or C 0 D. Carriage Paid,Or £1 deposit and 11 monthly £8:18: 6payments of 15/9.

AMPLIFIER PORTIONComprising Author's Kit of First Specified partsfor Amplifier Portion only, less valves.Cash or C.O.D. Carriage Paid

1Or 11 deposit and 11 monthly 2:13:0payments of 23/3.

COMPLETE KITComprising Receiver Kit and Amplifier Portion Kittogether with specified valves and Peto-Scott Adapts -gram -de -Luxe Cabinet.Cash or C.O.D. Carriage Paid. g35 : 7:0Or 19:7:0 deposit and 11 monthly payments of 62/

PETO- SCOTTADAPTAG RAM -DE - LUXEA splendid cabinet specially de- EXCLUSIVELYsigned for the "W.M." Radiogram SPECIFIEDSuper. Soundly constructed inWalnut -faced ply -with beautifully Cash or C.O.D.contrasting inlays. Ample record £6 : 10 : 0accommodation.Or 12 monthly payments of 12!-. Carriage and packing

5/- extra.

ALL WAVE -3KIT "A" Author's Kit of First Specified parts, less Valvesand Cabinet.Cash or C.O.D. Carriage Paid g5:5:0Or 12 monthly payments of 9/6.1 Peto Scott Cabinet, Type E.N. 17/8

PETO-SCOTT CO. LTD.77 CITY ROAD, LONDON, E,C.1Telephone : Clerkenwe/1 9406/7West End Showrooms:62 High Holborn, London, W.C. I

EST. 1919


AMERICA'S 831 -FT. AERIALThe aerial mast of WLW, America's new 500 -kilowatttransmitter. The mast is insulated from the ground,

for it is itself the aerial

AUSTRIAVienna Experimental, a 3 -kilo-

watt station which was regularlyworking on the long waveband beforethe Lucerne Plan came into opera-tion, has again made its appearancein the ether. It can be heard everyMonday, Wednesday and Saturdayon 1,255 metres (239 kilocycles) fromabout 2000 B.S.T.

CZECHOSLOVAKIATests are being carried out by the

old Prague-Strasnice station (3 kilo-watts) in the early morning hours on249.2 metres. It will be known asPrague No. 2, and when overhauledand brought up to date will providean alternative programme for lis-teners in the Czech capital.

As most of the Central Europeanpowers now possess a short-wavetransmitter for the relay of theirradio programmes overseas, theCzech Ministry has drawn up plansto install suitable apparatus atPodebrady, near the capital. Thenew station would combine the dutiesof a relay for transmissions to theU.S.A. with those of a public wire-less telephony service.

01 THE CREST

OF THEWAVESRadio News From All the World

By JAY COOTE

EGYPTThe old fortress of Ras -

el -Tin, at the mouth ofAlexandria harbour, hasbeen selected as the siteof the 1 -kilowatt stationdestined to provide thatcity with a relay of theCairo programmes. Thetransmitter will work on267.4 metres.

FINLANDIn order to do away with a number

of smaller relays, the Finnish Broad-casting Company has secured govern-ment financial assistance with a viewto the installation of a 150 -kilowattstation to replace the present Lahtitransmitter. Engineers are nowexploring the country in the hope offinding a more favourable central sitefor the new station.

JUGOSLAVIAA proposal has been put forward

by the Jugoslavian authorities toconstruct a new broadcasting stationin the Slovene town of Maribor (pre -War: Marburg), which is situatednear the Austrian border. Its aim isto counteract the transmissions ofGraz which, during the past fewmonths, have assumed a politicalcharacter.

LITHUANIAKlaipeda, a port on the Baltic

better known perhaps under itsformer name of Memel, is to bethe site of a new broadcasting trans-mitter destined to relay the Kaunasprogrammes. It has not yet beendecided whether or not to replace

570

the station in the capital, but if sucha course is carried out the 7 -kilowattplant would be transferred to anotherpart of the country to work on 222.6metres (1,348 kilocycles).

POLANDWork on the new Mokre high -

power station is being hurried for-ward and every effort is being madeto get the transmitter ready by theend of this summer. The studioswill be installed at Torun (Thorn).

It is expected that the new stationwill take over the Poznan channel.

SPAINAccording to a recent report, the

Spanish Government appears to haveagreed definitely on a completereorganisation of the broadcastingnetwork and will not delay a start onthe new scheme. It has been decidedto endow the capital with a super-power station, working on the chan-nel allotted in the long wavebandand, in addition, to erect in theprovinces six medium -wave stationsvarying from 40 to 60 kilowatts.

An agreement has been reachedin respect to the fifty -odd privatetransmitters, which have been in-stalled during the past three years.They will be allowed to carry on theirbroadcasts providing they do notcause interference.

UNITED STATESAt Carlstadt (New Jersey) a new

2.5 -kilowatt transmitter with thecall sign WNEW has been recentlyinstalled; it works on 240 metresand is on the air from midday until5 a.m. B.S.T. daily.

THE "W.M." RADIOGRAM SUPERContinued from page 509

It will save a lot of trouble if theholes for the connections are markedin pencil with the small letters asindicated on the blueprint.

With regard to a suitable loud-speaker for use with this radiogramophone, we have indicated avery good model in the list of parts.This is of loiv-resistance type, butincorporates its own input trans-former. On the other hand, if itis desired to use several loud-speakers externally it is better thatthe transformer should be placedinside the set and leads taken directto the speech coils.

About Loud -speakersThe position therefore is that if

several loud -speakers are to be usedthe internal transformer on thereproducer can be cut out and theleads from the speech coil takendirect to the Ferranti transformer.On the other hand, if only aninternal loud -speaker is to be usedthe Ferranti transformer can bedispensed with and the input trans-former on the loud -speakeremployed.

We have not sufficient space atour disposal this month to give areport on the set's performance.This will appear, with a list ofstations, in the next issue.

THE ALL -WAVE BATTERY THREE

Continued from page 561

that the receiver oscillates quitefreely over both short wavebands.With a long aerial the condenser willhave to be almost fully out of mesh,but with an indoor or moderatelyshort aerial considerably more capa-city will be required.

Except that the tuning is so verymuch sharper, and that the set mustalmost be on the point of oscillation,no trouble should be experienced intuning in a large number of short-wave stations.

In the beginning, it is perhaps anadvantage for the inexperiencedoperator to keep the receiver oscillat-ing all the time. When some high-pitched chirps are heard, this indi-cates the carrier wave of the stationand all you have to do is to decreasethe reaction until the carrier isresolved into a signal.

Slight readjustments of the tuningcondenser should then bring in thestation at good volume.

[ Wireless Magazine. July 1934

THUNDER STORMS ARE COMING !

0 LT'PE RCOLATIVEEVER -DAMP

EARTH

KEEPS DAMP AND

DROUGHTIN HEAT &EFFICIENT

'6

Fit the new GARD Automatic to your aeriallead-in and your aerial is safe from the fiercestlightning flashes. No need to worry with GARDfitted-no need ever to switch off. Forgetlightning, enjoy your radio throughout thestorm, GARD permanently safeguards yourset-your home itself-for the trifling cost oftwo shillings.EVERY GARD IS FLASH -

TESTEDFrom all Dealers or post free

from sole manufacturers.

The First and Finest entirelyself-contained

UNIVERSAL A.C.-D.C.SHORT-WAVE ADAPTOR

kill! UNIVERSAL HIGH VOLTAGE RADIO LTD., 28-29 Southampton St., LONDON, W.0.2.

BRING NEW LIFE TO tiYOUR OLD RECEIVERThousands of Readers have been looking for an eco-nomical method of making practically a NEW SETfrom their OLD ONE. An excellent way, botheconomical and yet highly efficient, is to CONVERTby use of the Ostar-Ganz Universal High VoltageValve. Converted sets can be used on Any Mainswithout further alteration.It Don Not Matter whether your present set is aHome -constructed or Commercial one, Battery orMains, we are prepared to convert it into a mostup-to-date UNIVERSAL A.C./D.C. RECEIVER, andguarantee you excellent results, for the nominalcost of Only 10/- per valve holder, plus cost ofOstar Ganz Valves. Write to us for further details.

'Phone Temple Bar 4985.

Can be used on either A.C. or D.C. withoutany alteration, and also on any mains from100-250 volts. Simple to connect. Just plugthe unit into the mains, connect the aerial toadaptor, and take another lead from top ofadaptor to aerial terminal of receiver.Suitable for all wavelengths between 12 and85 metres.

PRICE 15 Ss. Od.Complete. Fitted with the fatuous Ostar-Ganz High -voltage Valves. Adaptable toany Mains Receiver.

571

p


Notes and al otttngs/T is certainly a pleasure to see

good use being made of theSpectrum Portable at Llandudno.

The photograph, reproduced at thetop of this page, was taken at HappyValley and shows Charles Wade'sConcord Follies Concert Party enjoy-ing a bout of dancing to HenryHall's band during an intervalbetween performances.

As you can well imagine, theSpectrum Portable with its QP21output valve gives plenty of volumefor dancing in the open air. Thisfine portable was fully described inthe April, 1934 issue of "Wireless.Magazine." It is a three-valver witha screen -grid high -frequency ampli-fier, detector and twin -pentode valvesequence and is entirely self con-tained. A moving -coil loud -speakeris used.

There are plenty of fine days tocome this summer and, if you wanta set for outdoors, you will find theSpectrum a first-rate outfit. Thosewho require a larger portable shouldread the report on the " TwoH.F." Portable published in thisissue.

.Talking about concert parties,

readers who live in the South ofEngland will be interested to knowthat they can meet many broad-casting favourities on the pier atWorthing this season.

Worthing's show is called Radio

Mirror, and the cast includes suchwell-known favourities as LeonardHenry, Beryl Orde, Clarence Wright,who at one time conducted the SavoyOrpheans, and the famous EightStep Sisters.

Holiday news reminds us about thefloating radio showroom which willbe cruising around the NorfolkBroads this summer. C. W. Willmott,a Norwich dealer, has hired a largemotor cruiser having three cabins.One he has fitted up as a showroom,another has service gear and a bat-tery charger and the third is fittedwith a receiver and transmitter sothat people on the cruiser can keepin touch with head office.

The Glow of Light, as the boat iscalled, has been fitted out with theco-operation of the MarconiphoneCo., and carries a large figure of a" Marconi Man " on the prow.Such is enterprise

.The H.M.V. show train is con-

tinuing its tour of the country'sprincipal towns during July. Wegave full details of this railway radioexhibition last month, but in caseyou missed the details the showtrain consists of three special car-riages in which are an up-to-dateexhibition of H.M.V. sets and gramo-phones.

Readers can visit the show, but

572

Entertaining the entertainers ! Here isthe famous "W.M." receiver, theSpectrum Portable, providing dancemusic for a concert party at Llandudno

they must get tickets from theirlocal H.M.V. dealers.

Here are the places and dates inJuly on which you can visit the train :Edinburgh, July 2 and 3 ; Newcastle,July 4; Sunderland, July 5; Mid-dlesborough, July 6 and 7; Scar-borough, July 9; YOrk, July 10 ;Hull, July 11 and 12 ; Leeds, July13 and 14; Bradford (ForsterSquare), July 16; Huddersfield, July17 ; Doncaster, July 18 ; Grimsby,July 19 ; Sheffield, July 20 and 21 ;Derby, July 23 ; Nottingham, July24; Leicester, July 25; Northamp-ton, July 26; Cambridge, July 27and 28; Norwich, July 30 and.

Ipswich, July 31.

Philips Lamps has just installed aninteresting self -timing device incor-porating a photo -electric cell relayat the new Welsh Harp GreyhoundTrack. The apparatus is so arrangedthat the winning dog itself stops thetiming watch.

The release of the dogs from thetrap starts the stop watch, which isconnected with the photo -electriccell. As soon as the nose of thewinning dog interrupts an invisiblebeam at the finishing line, the photo-electric cell stops the watch.

To prevent any misrepresentationthe service engineers of Electricaland Music Industries, Ltd., havebeen provided with an identificationcard on which is the engineer'ssignature and photograph.

We are asked to remind dealersand set owners to ask every serviceengineer calling upon them to pro-duce his card before being allowedindoors to " put the wireless right."If you don't, you may be the looserof money or of other valuables.

Decca has sent us two samplerrecords for dealer use to introduceto listeners-or should we say gramo-fans-four new albums of selectionsfrom the classics. There isn't spaceto tell you the contents of thesealbums, but we can say that theyhave been arranged and chosen byChristopher Stone the inimitable.

The four albums contain tip-topclassics. You can get full detailsfrom your dealer or from the DeccaRecord Co., Ltd., of 1-3 BrixtonRoad, London, S.W.

We understand that supplies ofBritish -made Tungsram valves willbe available in the autumn. The newfactory, which is being built atTottenham, is making excellent pro-gress.

McMichael Radio, Ltd., has hadfive sets approved by the CentralCouncil for School Broadcasting foruse in schools. The sets passed arethe Lodex Five, Duplex Mains FourPortable, A.C. and D.C. models ofthe Supervox and the new super -hetmains set.

New moving -coil loud -speakersare always an interesting news itemfor the home constructor. Good -mans (Clerkenwell), Ltd., are in thenews this month for they have justbrought out a new reproducer whichthey claim to have a double bass peakat 40 and 75 cycles and dippingslightly at 50 and 100 cycles to avoidhum troubles.

It is also claimed to reproducenotes with a frequency as low as 25cycles and as high as 7,500 cycles.They are available with all values offield winding and cost 35s. By theway, they are of the energised type.

We have heard a lot about newfactories to cope with the ever grow-ing radio business. Cossors' areputting up a huge new factory atHighbury, a photograph of which ison page 493.

Another firm who are extending isAerodyne Radio, Ltd. Aerodyne arebuilding a new factory at Tottenhamwhich will give an additionalfloor space of between 50,000 and60,000 sq. ft. It is hoped to havethis new factory in full operation bynext September.

The public-address engineers ofthe Marconiphone Co. will beat theirown record for a day's work thismonth. No fewer than five largeinstallations will be in use in variousparts of the country on July 18.In all there will be 129 loud -speakersand fourteen microphones in use onone day.

Following the successful inaugur-ation of the new Marconi broad-casting station at Cape Town, theAfrican Broadcasting Co. has decidedto install two more high -powerstations, one at Grahamstown andthe other at Pietermaritzburg. Theywill be identical to the Cape Town

Wireless Magazine, July, 1934

transmitter and will be manufac-tured at Marconi's Chelmsfordworks,

One more thought about the holi-days ! The General Steam Naviga-tion Co., Ltd., has installed superradio gear for microphone announce-ments and music broadcasts on itspleasure steamers, which run dailythroughout the summer betweenTower Pier, London and Southend,Margate, Ramsgate and Clacton.

On their new steamer, RoyalEagle, the gear is a de -luxe job givingan undistorted output of 35 watts,which is fed into eight Epoch super -

cinema moving -coil loud -speakersplaced in various parts of the ship.

Two are mounted in special baffleboxes on deck, two are in the ship'sglass -enclosed lounge, and the re-maining four in the dining saloons.

The ship's current of 100 voltsD.C. is used for driving a largerotary converter which gives avoltage of nearly 1,500 volts neces-sary for the two Ediswan ES75output valves.

Public address enthusiasts whotake a trip to the sea via LondonRiver, will gladly be shown the" innards " of the installation by theofficer in charge. -

Short Waves with theSeventy-seven Super

MANY hundreds of " W.M."readers who built the Seventy-

seven Super, described in the Dec.1932 issue of " Wireless Magazine "will be interested in a converterbeing used by a Kingsbury reader tobring in short-wave stations.

The circuit is reproduced herefor the benefit of readers who wouldlike to try their hand with short-waves on this set.

Recommended ConverterMost constructors will be able

to build the recommended con-verter from the circuit diagram. Theconverter is connected to the Seventy-seven Super in the ordinary way, butit must be borne in mind that theset must be tuned to a long wave-length.

The best wavelength will be foundby trial; our Kingsbury corre-spondent states that a wavelength of1,000 metres gives the best results.

Regarding the results to beobtained he says that " W3XAL canusually be heard in the adjoiningroom at splendid volume and freefrom excessive fading. In fact, thisstation with Pittsburgh, Springfield,Boston and Schenectady give resultsequal to most of the Continentalstations heard on the broadcast wave-bands."

He goes on to say that he con-siders this combination of Seventy-seven Super and converter equal tothe best short-wave commercialreceiver, irrespective of price.

573

People who have doubts about theentertainment of short-wave listeningwill be keenly interested in thisenthusiastic listener's opinion ofshort-wave entertainment. He saysthat " short -waves are definitely of

TO HT+SNORT 220V.WW1

ocrOf view.

.0001".

ON SET

TO'EARTN"ON 6ET

2

EARTH

Circuit of the short-wave converterrecommended for use with the Seventy-

seven Super by a Kingsbury reader

splendid entertainment value with agood super -het such as a convertedSeventy -Seven Super.

" One can hear the programmes,and for the long-distance fan thereare dozens of stations to investigatewhen one bas time to spare. Werarely fail to hear the stock exchangereport and the Kiddies Club fromBoston, followed by the ' SingingLady ' at full loud -speaker strength.'

Such a recommendation shouldconvince those who believe thatshort-wave listening is not so thrillingas is frequently suggested.

Wireless Magazine. thity, 1934

YOU CANNOT GO WRONG IF YOU USE A

And here are over 50 moreto choose from-

CRYSTAL SET (6d.)1931 Crystal Set AW3084 Station Crystal Set AW427

ONE -VALVE SETS (Is. each)Easy to Build One ._ AW304Portable Short-wave One ... AW354A.B.C. One-valver AW387Short-wave On e-valver AW429

TWO -VALVE SETS (Is. each)A Two for 7 Metres (D, Trans) WM295A.C. Quality Gem (D, Trans) .- WM3I2The Companionette (D, Pen-A.C./D.C.)... WM358

SPECIAL HALF-PRICE OFFERBlueprints of the following " WirelessMagazine " sets described in thisissue are obtainable at the specialprice, given beldw, if the coupon onlast page is used before June 30, 1934.

Six -guinea A.C./D.C. Three (SG, D,Pen), WM364 ... ... 6d.

All -wave Battery Three (SG, D, Pen),

" WM " Radiogram Super (8 valveA.C. Super -het) WM366

" A.W." Iron -core Two (D. Trans) ... AW395"A.W." Iron -core Two with Q.P.P. . . AW396Big Power Melody Two, with Lucerne Coils

(SG, Trans) AW338AB.B.C. National Two, with Lucerne Coils

AVV377ALucerne Minor (Det, Pen) AW426Home Station A.C. 2 (D, Pen) ... AW374B.B.C. National Two (D, Trans) AW377Melody Ranger Two (D, Trans) ... AW388Consolectric Two (D, Pen) A.C. , AW403Lucerne Minor (D. Pen.) ... AW426

THREE -VALVE SETS (Is. each)C.B. Three (D, LF, Class -B) WM333Duo -tuned Three (SG, D, Pen) ... WM34IA.C. Transportable (SG, D, Pen) ... WM347All -wave Three (D, 2LF)

.

... WM348"W.M. " 1934 Standard Three (S.G., Det,

Pen) _. WM351Emigrator (A.C. set : 14-500m.) (S.G., D.,

Pen) ...£3 3s. Three (SG, D, Trans) ... WM354

Heptode Super Three (A.C. Super -het) ... WM359Iron -core Band -c as; Three (SG, D.QP 21) WM362James Push -push Three (SG, D, Q.P.P.) (1/6) AW378Everybody's Home Rad iogram (SG, D,Trans) AW38 IHome -lover's New All -electric 3 for A.C.

mains (SG, D, Trans) ... AW383Our Up -to -the -Minute Three (SG, Wes-

tector, LF, Trans) ... AW384Class -B Three (D, Trans, class B) AW386A.C. Triodyne (SG, D, Pen) ... AW399Home -built Coil Three (SG, D, Trans) ... A'A4C4

Calibrator de Luxe (SG, D, RC, Trans) ...All -metal Four (2 SG, D, Pen -A. C. Mains)Self-contained Four (SG, D, LF, Class B)...All -progress Four (Battery Super -het)Merrymaker Super (A.C. Super -het)1934 A.C. Quadradyne (2SG, D, Pen) ...Lucerne Straight Four (SG, D, LF, Trans)Universal Merrymaker (A.C./D.C. Super-

h:t)"A.C. Melody Ranger " (SG, D, RC, Trans)

"A.W." Ideal Four (2SG, D, Pen)2 H.F. Four (2 SG, D, Trans)Lucerne Major (256 SG, Trans) ...

111

ElEach blueprint shows the posit on of each compo-nent and every wire and makes construction asimple matter. Copies of " Wireless Magazine"and of "Amateur Wireless" containing descrip-tions of most of these sets can be obtained atIs. 3d. and 4d., respectively, post paid. Indexletters " A.W." refer to " Amateur Wireless"sets and " W.M." to " Wireless Magazine" sets.Send, preferably, a postal order (stamps oversixpence unacceptable) to "Wireless Magazine,"Blueprint Dept., 58-61 Fetter Lane, London, E.C.4.

Fan and Family Three (D, 2LF) AW4I0f5. S.G.3 (SG, D, Trans) ... AW4I 239/- Lucerne Ranger (SG, D, Trans) ... AW422Penta-quester (S.G., D, Pen) . AW43 I

FOUR -VALVE SETS (Is. 6d. each)Calibrator (SG, D, RC, Trans) ... WmM330003

Table Quad (SG, D, RC, Trans) ..." Words and _Music.: Radiogramgram...(2

D, Trans)"Words and 'Music " Radiogram de Luxe

(SG, D, RC, Q.P.P.) _ ...WM307aHome Short -waver (SG, D, RC, Trans) WM31Empire Short -waver (SG, D, RC, Trans) ... WM313

WM3I6WM329WM331WM335WM345WM349WM350

AW380AW402AW42IAW433

FIVE -VALVE SETS (Is. 6d. each)New Class -B Five (SG, D, LF. Class -B) -. WM340Class -B Quadradyne (2 SG, D, LF, Class -B) WM344James Short-wave Super (Super -het) AW328Simple Super (Super -het) AW340The Etherdyne (Super -het) ... AW4061934 Century Super (Battery super -het) AW413

SIX -VALVE SETS (Is. 6d. each)1932 Super 60 (Super -het) WM2691932 A.C. Super 60 (A.C. Super -het) ... WM272" W.M." D.C. (Super -het)... WM32IJames Class -B Super (Super -het with iron -

cored coils) ._ WM326Welcome Portable with class -B output stage WM325Connoisseurs' Super (A.C. Super -het) WM334James Super Straight Six (2 SG, D, LF,

Push-pull) WM339Lucerne Super (battery super -het) ... WM355

SEVEN -VALVE SETS (Is. 6d. each)Super Senior (Super -het) ... ... WM256Seventy-seven Super (A.C. Super -het) ... WM305Q.P.P. Super 60 (Super -het) WM3I9

PORTABLES (Is. 6d. each)Town and Country Four (SG, D, RC,

Trans) ... WM282Everybody's Portable (five -valve Super -het) WM291Welcome Portable (six -valve Super -het) ... WM322Spectrum Portable (SG, D, QP2I) WM357"Two H.F. " Portable (2SG, D, QP2I) WM363General-purpose Portable (SG, D, RC,

AW35I

AMPLIFIERS (Is. each)10 -watt A.G. Amplifier WM36010 -watt D.C. Amplifier ... WM361Universal Push-pull Amplifier ... AW309"A.W." Record Player (LF, Push-pull) ... AW3I 9Battery -operated Amplifier AW362" A.W.'s " Push -push Amplifier ... AW376Class -B Gramophone Amplifier ... AW39IUniversal A.C. Amplifier (3 -valve) AW4I IFive Q.P.P. Output Circuits AW3 15

MISCELLANEOUS (Is. each)A.C. Short-wave Converter ... WM353"A.W." Trickle Charger ... . AW352Plug-in Short-wave Adaptor ... . AW382Experimenters' D.C. Mains Unit ... AW430Experimenters' A.C. Mains Unit ... . AW432Add-on Band-pass Unit AW359Plug-in Short-wave Alapae: . AW382

You can always rest assured that if you build yourset with a .147.M." full-size blueprint, it will wor

f.rst time and wor.; well !

574

This useful article in the July issue of TELEVISIONtells you how you can use your present set fortelevision and so save the cost and trouble of aseparate receiver.The following are some of the other contents ofthe July issue:-

LOOKING IN WITH A STATIONARYMIRROR DRUM.

A RECEIVER FOR SCREEN PROJECTION.FACTS AND FIGURES OF PUBLIC OPINION

ON TELEVISION.

HOW TO MAKE A VALVE VOLTMETER.OPERATING THE KERR CELL FOR THE

BEST RESULTS.TELEVISION AND THE STAGE.THE FREQUENCY BAND PROBLEM IN

TELEVISION.

JULY ISSUE NOWON SALEPRICE 1L

SUBSCRIPTION

RATES

Post paid to anypart of the world :

3 months, 3 66 months, 6/9

12 months, 13 6

The ONLY Publication entirely devoted to TELEVISION

iWirelessMagazine. July, 1934

A FOUR -FOLDTRIBUTE !

The W.M. RADIO -GRAM SUPER

SPECIFIES POLAROne Star Minor 4 -gang with Semi -Circular

Drive 1-180 degrees

The W.M. ALL -WAVE THREE

SPECIFIES POLAROne Compax .0005 and One Compax .0003

The W.M. SIX -GUINEA A.C./D.C. Three

ARSPECIFIES POLTwo Compax .0005

The W.M. TWO H.F. PORTABLE

SPECIFIES OUROne Compax .0001

SENO FOR

COMPLETEPOLARCATALOGUE

POLARSTAR -MINORFOUR GANG

with Semi -Circular Drive

Trimmersplated keel frame.

rommers operated fromtop. Sections matched within

the°rlogrreilaytete

scale

rveeur

4 V.afgronly 25/-

POLAR COMPAXA low priced variable con.,7emerfor tuning or reaction where airdielectric is not essential..0005, .0003, .00015, .0001 and 216

WINGROVE & ROGERS LTD.188/189 Strand, London, W.C.2

Phone Temple Bar 2244. Works Old Swan, Liverpool.

When replying to advertisements, please mention " Wireless Magazine

575

X15255


BLUEPRINTCOUPON

Valid only until July 31,1934 (or until August 31,1934, for overseas readers)

1C0" -NN"--;;FOR ONE BLUEPRINT ONLY

If you want a full-size blueprint ofany ONE of the sets constructionallydescribed in this issue for half price,cut out the above coupon and send it,together with a postal order, toBlueprint Department, WIRELESSMAGAZINE, 58-614Fetter Lane, Lon-don, E.C.4.

This coupon is valid for a blueprintcf any ONE only of the following setsat the prices indicated

SIX - GUINEA A.C. / D.C. THREE(page 519), No. WM364, price 6d.,post paid.

ALL -WAVE BATTERY THREE (page557), No. WM365, price 6d., postpaid.

" W'.M." RADIOGRAM SUPER (page503), No. WM366, price 9d., postpaid.

INFORMATIONCOUPON

Valid only until July 31,1934 (or until August 31,1934, for overseas readers)

C

If you want to ask any questions,cut out the above coupon and send it,together with a postal order for Is.and stamped addressed envelope, tothe Information Bureau, WIRELESSMAGAZINE, 58-61 Fetter Lane,London, E.C.4.

Note that not more than twoquestions may be asked at a timeand that queries should be writtenon one side of the paper only.

Under no circumstances can ques-tions be answered personally or bytelephone. All inquiries must bemade by letter so that every readergets exactly the same treatment.

Alterations to blueprints or specialdesigns cannot be undertaken : nor canreaders' sets or components be tested.

If you want advice on buying aset, a stamped addressed envelopeonly (without coupon or fee) shouldbe sent to the Set Selection Bureau,WIRELESS MAGAZINE, 58-61 FetterLane, London, E.C.4.

THE SIX -GUINEA A.C./D.C. THREE

Continued from page 523

Then before the set is tried out forthe first time, the mains droppingresistance-fitted to the top of thechassis-must be adjusted to corre-spond with the voltage of yourdomestic supply. Three tappingsare provided, covering all suppliesbetween 200 and 250 volts.

Operating the set needs very littleexplanation. It is switched on bythe toggle switch, on the back of thechassis, you will remember, and thewave -change switch is set for eitherthe long or medium waves as desired.

Tuning the SetThere is only one knack of tuning

this set, that is, if it can be called aknack. The two tuning dials shouldbe turned almost in step and theaerial -input control adjusted to getthe required degree of selectivity.To get the utmost selectivity, theaerial -input control should be setas far to minimum capacity as possibleand the reaction control advancedtill the set is on the verge of oscilla-tion.

One word about the cabinet. Thecabinet we have specified is well madeand is very reasonable in price. Wehave not included the price of thecabinet in the six guineas, because,no doubt, some readers may have acabinet in stock or they may preferto buy a more expensive one to fitin with some particular home fur-nishing arrangement.

About the Test ReportThat this outfit lives up to the

fine reputation of " W.M." sets isborne out by the independent testreport that appears on page 524.Some thirty-five stations were loggedin a short test.

There is no need for us to pointout to readers that every " W.M."set undergoes thorough tests, bothin the laboratory and independently,before details are published." W.M." has a great reputation andit is going to live up to it !

We want readers to rememberthat we are always pleased to hearabout the results-good or bad-that they get from " W.M." sets.Any remarks about the set's per-formance are always of great help tothe Technical Staff in the design offuture sets. And do not forget thathalf a guinea is paid for every photo-graph of a " W.M." set published. CI

INDEX TOADVERTISERS

A Page

Automatic Coil Winder andElectrical Equipment Co.,Ltd... ,. 487

B

British Blue Spot Co., Ltd.Cover iii

CColumbia Graphophone Co.,

Ltd... .. 483

FFerranti, Ltd. Cover iv

Fluxite, Ltd. .. 569

GGramophone Co., Ltd. .. 490

Graham Farish Ltd. .. 571

K

Kebtex Radio 485

LLectro-Linx, Ltd., .. .. 569

Lissen Ltd. .. .. 569

PPartridge & Mee, Ltd. 485

Peto-Scott Co., Ltd. .. 569

R"Radio Pictorial" Cover ii

Radio Resistors Ltd. .. 485

S

Smith (M/A), Ltd. .. 489

TTelephone Manufacturing Co.,

Ltd.

" Television"

489

575

Tungsram Elect. Lamp Works(G.B.), Ltd. Cover iii

UUniversal High -Voltage Radio

Ltd. 571

WWestinghouse Brake & Saxby

Signal Co., Ltd.

Wingrove & Rogers ..

487

575

Wright & Weaire, Ltd. 487

El

Printed for the publishers, BERNARD JONES PUBLICATIONS, LTD., 58-61 Fetter Lane, London, E.C.4, by The Sun Engraving Co., Ltd., London and Watford.Colonial and Foreign Agents : AusTRALIA-Gordon & Gotch, Ltd., Melbourne (Victoria), Sydney (N.S.W.), Brisbane (Queensland), Adelaide (S.A.),Perth (VV.A.), and Launceston (Tasmania). BELGIUM-W. H. Smith & Son, Ltd., 71-75 Boulevard Adolphe Max, Brussels. CANADA-Gordon & Gotch,Ltd., Toronto. FRANCE-Messageries Hachette, 111 rue Reaumur, Paris, 2me.; W. H. Smith & Son, Ltd., 248 Rue de Rivoli, Paris. HOLLAND-Meulenhoff & Co., Amsterdam. NEW ZEALAND-Gordon & Gotch, Ltd., Wellington, Auckland, Christchurch, and Dunedin. Sole Agents for Sum

AFRICA-Central News Agency, Ltd. (London Agents : Gordon & Gotch, Ltd.) Printed in Great Britain. July, 1934.

576

The BLUE SPOT "STAR"

Cabinet Loud Speaker

is

SPECIFIED

EXCLUSIVELYfor the W.M. ALL -WAVE "THREE

because it is the best Moving Coil Speaker obtainableand the " Wireless Magazine " designers require thevery best for a set of this kind.The Blue Spot " Blue Star " is specified solelybecause its performance and construction are betterthan anything previously known.The wonderful reproduction of the higher frequenciesimparts a realism to reception which will be arevelation to you if you will get your dealer to giveyou a demonstration.A fully descriptive catalogue is sent post free onrequest.

CABINET SPEAKERas specified

98'Chassis Only

704

nil 6RITIfIl FIVE II CIDMPANY LID15L,,E SPOT HOUSE 94,9e ROSDNIAN STREET ROSEBERy AvettuE LONDON E CI

Tel.: Clerkenwell 3570. 'Grams : Bluospot, Isling, London.Distributors for Northern England, Scotland and Wales : H. C. RAW -SON (Sheffield and London), Ltd., Sheffield; 22 St. Mary's Parsonage,Manchester; 177 Westgate Road, Newcastle-upon-Tyne; 37, 38, 39

Clyde Place, Glasgow. Tungsram Electric Lamp Works (Gt. Brit.), Ltd., 72 Oxford Street, London, W. ITAS/Tu.50

Mention of the " Wireless Magazine " will ensure prompt attention

Wireless Magazine. July, 1934j

You know that love duet they were doing fromCzechoslovakia ? Some Tungsram valves reproduced itwith such fire that a listener's whiskers have beenscorched in Wigan! .

WIRELESS MAGAZINE SPECIFIES

TURMAN UNIVERSAL VALVES

(AC & DC COMBINED IN ONE!)A valve that is far better thanthe ordinary D.C. type and evenbetter than an A.C.; yet worksas either! Tungsram's supremeachievement ! No need foralterations if your supply changesfrom D.C. to A.C. ! No needfor a transformer ! " WirelessMagazine" exclusively specify fortheir SIX GUINEA A.C. D.C.THREE H.P.21I8 (14/6), R.2018(10/6), P.P. 2018 (17H, andV. 2018 (10/6).

There's a Tungsram for every radio need

TUNGSRAMVALVE S

iii


A Ferranti Transformer has NO equal !

He e are the three special insulating formers with theirmoulded -in pegs for external connection anchorage. Notethe air -spacing for windings, and the absence of paper, cot-ton, other hygroscopic material which causes breakdown.

The completed AF5-neat, compact, without

an equivalent.

These are the wound formers-three and a half miles ofwire in an AF5! Winding is done by compressed airturbine driven machines-thus avoiding all trace ofmechanical stress which is inseparable from directdriving.

It is true to say that every part of a FerrantiTransformer is an engineering masterpieceinvolving expert design, experienced choiceof material, and meticulous care in work-manship.

As an instance, take only the windings ofan AF5. (A similar structure is employedin nearly all Ferranti Audio and OutputTransformers.) The accompanying photos telltheir own story; the captions give interestingdetails.

Add fo these points the fact that FerrantiTransformers were the first to give goodresults even in the early days when thecharacteristics of valves made quality repro-duction far more difficult than it is to -day,

and you will know just why FERRANTI Trans-formers are the first choice of expert radioengineers.

FERRANTITRANSFORMERS

PRICES:AF3 Ratio 1/3.5

Inductance 220-60 HenrysAF5 Ratio I;3.5

Induccance 260;80 HenrysAF6 Ratio 1 7

Inductance 50190 Henrys 30/'AF7 Ratio I

Inductance 400:100 Henrys 304f'AF8 Ratio I 3.5

Inductance 20/45 Henrys loAF10 at 8/6 is 01 similar, though not identical,

Structure.

Write fo, List

FERR t NTI Lid HOLLINWOOC,, LANCASHIRELondon : Bash House, .1-0dwych, W.C.2

CIRCUIVOU CAN I - World Radio History

Documents

Transcript of CIRCUIVOU CAN I - World Radio History