298 PHILlPS TECHNICAL REVIEW VOLUME 18

need not be laminated. A short résumé is given of the piezo-magnetic quantities that are relevant in this connection, and isfollowed by an account of the generation of piezomagnetisvibrations and a descript.ion of one or two conventional formeof transducer. The most important factors in the generation ofacoustic waves are the electroacoustic efficiency and themaximum safe radiation intensity. For vibration frequenciesabove 20 kc/s the electroacoustic efficiency (measured at theoptimum frequency) is higher for ferroxcube than for metals,since there are no eddy currents and since, in the absence oflaminations, frictionallosses are very low. The maximum safeintensity can be at least 10 W/cm2 for continuous loading. Inorder to attain this high value, materials of good homogeneityand large saturation magnetostriction are required. Moreover,such materials require a high tensile strength; this may beachieved by suitable sintering techniques or suitable variationsof the chemical compositions, which renders them less porous.High values for tbe piezomagnetic coupling coefficient, the

mechanical Q and the magnetic Q enhance the efficiency andtherefore also the maximum safe intensity, since they make forsmaller thermal stresses at a given power. For pulsed operation,which avoids thermal stresses, maximurn safe intensities of asmuch as 15-20 W/cm2 can he expected.

In general the suitability of ferroxcube as a material foracoustic detectors is also determined by the above-mentionedcoupling coefficient.

Unlike metals, ferroxcube vibrators can be used in electricfilters, when the latter call for both a high mechanical Q (2000to 8000) and a high coupling coefficient. This application allowsonly a slight variation in the resonance and anti-resonancefrequencies with temperature. By adding cobalt this variationcan be kept within the desired limits (0.03%) for the requiredtemperature range (20-50 °C). The addition of cobalt likewiseimproves the coupling coefficient, which in this way can beraised to a value at remanence nearly equal to tha t of the bestmetals in use at present (0.25).

RECTANGULAR CATHODE-RAY TUBES OF HIGH ASPECT RATIO

For cathode-ray tube displays which are essen-tially long and narrow, e.g. special type radar("A" scan) displays, there is considerable wasteof equipment space when a circular-face tube is

621.385.832

used. Further, when several displays are observedby one operator, the distances between the individualdisplays are inconveniently large. A special tubewith a long and narrow rectangular face (bulb

Fig. 1. Glass lathe for joining the pressed screen and cone of the rectangular cathode-raytube bulb. The lathe contains eight stationary and four reciprocating burners. The latterare actuated by the large cam visible behind the bulb. The photograph shows the screen-cone joint during the rolling process.

1956/57, No. 10 RECTANGULAR CATHODE-RAY TUBES 299

periphery 156X 66 mm, useful screen area 125X 35mm, i.e. an aspect ratio 3.5 : 1), has been developedfor these cases. Tubes of this type permit of compactstacking and thus avoid both the disadvantagesmentioned above. Some manufacturing problemsnot encountered in normal cathode ray tube pro-duction had to be solved for these tubes; a numberof these problems will be briefly reviewed in thisarticle.

Since it is impracticable to produce a strongenough bulb of the required shape by the usualprocess of blowing, the bulb design was based on theuse of a pressed glass screen and cone. The depthof both screen and cone was chosen so as to permitsatisfactory pressing notwithstanding their flat,narrow form; the sides of both are slightly curved forincreased strength and slightly tapered for easyremoval from the moulds. These requirements set alower limit on the overall bulb dimensions for agiven useful screen area.

The joints between screen and cone and betweencone and neck (a length of standard 50 mm tubing)are made on a glass lathe of special design. Thislathe, shown in fig. 1, contains four reciprocatinggas-oxygen burners in addition to the usual statio-nary ones. The stationary burners alone would heatthe corners of the glass parts less than their sides,owing to the greater peripheral speed of the former.The reciprocating burners, which are actuated by alarge cam on te head stock of the lathe (see figure),increase the heating on the corners only, and pro-duce a uniform temperature round the edges of theglass.

The phosphor coating for the screen is producedby the well-known sedimentation technique 1). Forapplying the internal graphite coating, a specialbrush was designed whose head can be swept acrossthe flat internal surfaces of the bulb by manipula-tion at its long handle.

Electrostatic deflection is usually used in tubesfor this type of display. The electron gun, includingthe deflector plates, has to be sealed into the neckwith the proper orientation, i.e. with the directionof the scan (x-trace) accurately parallel to the longaxis of the rectangular screen. Setting of the gun inthe correct position is effected by means of a jig,making use of the fact that the x-trace deflectorplates deflect the electron beam in a direction per-pendicular to the axial slot of the "interplate shield"(the latter separates the two sets of deflector plateselectrostatically in order to prevent "cross-talk"

1) See the illustrations in Philips tech. Rev. 9, 339, 1947/48and 10, 306, 1948/49.

between x- and y-deflection 2)). The jig is shownin jig. 2 and the aligning procedure is explained inthe caption of the figure. By this method it has beenpossible to maintain a tolerance of ± 2° on the anglebetween the x-trace and the long axis of the screen.

Before sealing the glass foot carrying the gun intothe neck of the cathode ray tube, the foot must be

Fig. 2. Jig for adjusting the electron gun in the tube neck sothat the direction of the x-trace is parallel to the long axisof the rectangular screen. The screen end of the bulb is posi-tioned unambiguously on a heavy casting whilst the neck restsin a semi-circular support: these two locations provide a re-ference plane defined by the axis of the tube and the long axisof the face.· At the nominal position of the interplate shieldof the electron gun assembly is a bracket painted with a whitereference line (broken to allow space for the tube neck). Theline has the same width as the interplate shield slot and islocated in a plane perpendicular to the above-mentioned refer-ence plane. The gun assembly, which fits tightly in the neckin order to prevent its vibrating out of position in subsequenthandling, is moved up the neck by the mechanism seen in thelower right part of the photograph, until the interplate shieldis at the position of the reference line. The gun is then rotateduntil the shield slot is seen in the same straight line as thereference line. The x-deflection will then be parallel to theformer reference plane and hence to the long axis of the screen.

2) .J. de Gier and A. P. van Rooy, Improvements in theconstruction of cathode-ray tubes, Philips tech. Rev. 9,180-184, 1947/48.

300 PHILlPS TECHNICAL REVIEW VOLUME 18

brought up to about 200 oe. This is usually, donebefore insertion: of the assembly into the neck, butsince the aligning operation cannot be made witha hot foot, the pre-heating for the tubes describedmust take place with the gun and foot already in'place. This is accomplished by a hot turret of steelplaced around the stem. Nitrogen is passed up thestem of the foot into the bulb to prevent oxidation.of the gun eomponents. The nitrogen is pre-heatedin order to avoid cracking of the hot foot.

Conventional methods are used in the further,manufactiH~ng processes' such as pumping, ageing,etc., The most important characteristics of the tube~re the following: 'final anode voltage 5 kV, nominalscreen current 10 [lA with .a grid drive of 17.5 V,totallight intensity 0.15 candela (owing to the useof a willemite fluorescent screen of very high effi-, ciencyjj. nominal deflection sensitivity in .the x-direction 0.19 mm/V, in the y-direction 0.21 mm/V.The line' width when scanning nearly the whole '

screen area (describing an ellipse of 100 X 30 mm)with optimum overall focus and nominal beamintensity is 0.5 mm. This good definition, which waspart of the specification for, the radar applicationsof the tube, was obtained by a special design of theelectron gun: the undeflected spot size was reducedby a high cathode loading, a high first anode voltage(1800 V) and a long focussing anode (cf. the articlequoted in 2)); the deflection astigmatism was dimi-nislied as far as possible by using relatively longdeflection plates with a rather large separation.Striking a suitable compromise between length andseparation of the plates was facilitated by the verylimited scan in the y-direction. The relatively large.deflection-plate assembly called for a neat mechani-cal construction in order not to increase the requiredtube neck diameter beyond the value of 50 mmmentioned above.

F. G. BLACKLER *).

") Mullard Radio Valve Co., Ltd., Mitcham (Surrey), England .:

FLOODLIGHTING OF THE DUTCH NATIONAL WAR MEMORIAL IN AMSTERDAM

A National War Memorial situated in the DamSquare in Amsterdam was unveiled by Queen J ulianaof the Netherlands ill May 1956.

The illuminàtion of tlie 22 metres high columnwith its statuary a:r~dthe low wall that serves asbackground is effected by means of 30 spot-lightsdisposed on the roofs of neighbouring buildings.Thi~ arrangement of the sources of light is in accordwith the wishes of the sculptor John Rädecker andthe.architect Dr. J. J. P. Oud, that the characterof the monument seen by day, be as far as possiblepreserv~d when the monument is illuminated bynight.

To ens_ure'reasonable intensity of illumination atthe unavoidably large, distances involved (40 to100 metres), it was necessary to concentrate asmuch as possible of the light from the spot-lightson to the object. On the other hand,' the highluminous intensity of the light beams could not 'beallowed to interfere with traffic in the busy squarenor could light be allowed to shine into the windows

- of t~e buildings opposite, so that the light beams'had t.o be strictly confined to the object to be flood-lit. In vi~w of the slender form of the object itprove~ that the problem could b.!i solved simplyand economically by using high-pressure mercury-vapour lamps. ,

The lamps used' are 'of the HPK 125' W type.

628.974.6.064: 725.94: 621.327.534.2

The diseharge is concentrated in the axis of thetube, and is about 30 X 1.5 mm in size; the meanbrightness of this very elongated source is 640 stilb.The vertically disposed source is projected on thecolumn of the monument, with a magnification ofseveral hundred times, by means of a sphericalmirror. The mirror has a sealing cover-plate whichhas horizontal flutes to elongate the image, of thelight source in a vertical direction, the source bcingless slender in shape than the monument. Weakerlight from the outer edge of the discharge and fromthe quartz wall, whieh wóuld pass wide of themonument, is intercepted by screens of ceramicmaterial which are fitted close up against the dis-charge tube to avoid penumbrae. The Hf'Kvtypelamps were chosen with an eye !o this requirement:in this type of lamp the discharge tube is exposedto the air 1) and not niounted in an external enve-lope as in normal HP or H,PL lamps. To. ensure thatthe screens remain precisely in position when thetube is renewed, the construction shown in the dia-gram (p. 302) is employed.The, luminous flux produced by the ~.o spot-

lights with their total power of about 4 kW isapproximately 140000 lumens; the luminance' of themonument is 10 cd/m2.

1) See: W. Elenbaas, Philips tech. Rev.18, 1~7-172,1956/57.