v72 Pcb Manual

drip electronics| 72 pcb build manual

attention|disclaimerthis project is presented as artwork, and is solely intended as such.

the photographs containing the telefunken logoare protected as original artwork and do notimply association with telefunken or itscompanies (including telefunken usa)

although this board can be assembled andbuilt into a functioning microphone pre-amplifier.due to the high voltages and possibilities ofhuman error , drip electronics | gregory lomayesvahereby assumes no liability for injury/damage/loss which might unintentionally occur.

proceed at your own risk.

dripelectronicscopyright 2008 gregory lomayesva

[email protected]

designed by gregory lomayesva

features :1. the pcb has been designed around the circuit and not the compo-nents. creating the shortest paths to each important connection

2. pcb uses 3 oz copper

3. a ground plane is used with the heaviest gauge of of copper possible . (also acting as a shield against emi) 4. the use of axial leaded SPRAGUE ATOMS or CDE tc series capacitors both revered for their sound and high ripple tolerance. 5. optional emi mod resistors

6. pcb is .93thick , less vibration ,better thermal dissipation excellent dielectric between layers.

7. input volume is controlled by potentiometer

8. tube heaters have dc reference circuit built into board (further protecting ac hum from entering the audio circuit)

9. gain boost can be selected with stepped atenuator (rotary switch) without pops or thuds. (feed back loop adjustment)

10. optional hi frequency roll off using rotary switch up to 12 positions (no pops or thuds).

11. the diode footprints are for hi performance hex / fred diodes (to-220)

19. most traces are 2mm wide on 3 oz copper (almost 20 times the needed copper)

20. direct input capable for guitars etc.

21. pcb mount lundahl transformers

22. optional grounding through standoffs

23. use of readily available ef-86 or ef-806 tubes

24. entire circuit is on one side of board (no overlapped traces)

25. same symmetrical design as the drip opto 3

26. insulated 5.08 screw connectors can be used for all connections

27. main circuit is true to the original design

28. heater traces on board (no heater wiring)

29. all pots/switches can be bypassed preserving the original signal path .

30. use of available power transformer (same version as LA2a)

31. heaters can be powered by a dc power supply

32. hi separation between powersupply and audio circuit.

33. most resistors and caps correspond to the original schematic giving you the ability to adjust and experiment with different values34 optional air mod for boosting hi frequencies.

13. optional output volume control using potentiometer

14. low cut (rumble filter)

15. on board fuse

16. resistor footprints are large enough for carbon comp.

17. tube heaters are on pcb (no wiring)

18. VU meter now works with the design.

Warnings|caution

It is important to cover a few safety tips and cautions before you begin.

1. This project has high voltages, at some places on a live board voltages can be upwards of +300v . It is not a terrible amount of current/voltage , and I have been shocked many times for foolish mistakes such as forgetting the unit was powered on while servicing it etc. Its enough voltage to remind you to never make that mistake again. For someone with a heart condition this voltage can be lethal.2. Once the unit has been powered up , the filtering electrolytic capacitors will remain with charge in them for a period after the power has been switched off. I found that a shock also is still possible for a few moments. 3. Never lift or remove the safety ground (chassis ground from AC cord). The board with proper wiring and ground layout will have minimal noise and hum , solving a hum problem by lifting the safety ground is wrong, often il legal and dangerous to you and others.4. Work off of an ac plug that is grounded to earth.5. If the fuse pops on the pcb or a circuit breaker , there IS something wrong , stop ,re check all connections and review your work. the fuse will only pop if there is a short or a miswired connection.6. Do not rush through the project with out reviewing your work several times . beware of solder bridges . sloppy work or impatience is dangerous to you and others.7. Be neat in your connections and wire runs, dont use more wire then is needed for each connection. if you cant be neat , dont bother with this project. Neatness promotes accuracy8. If the electrolytic capacitors are mounted in reverse , they can explode violently . REMEMBER THIS. CHECK EACH ELECTROLYTIC !.9. if you do not understand something fully that is not covered in this manual or are unsure about something. STOP. and ask a question either in the forum or through email. you will be helped.10. This unit is intended as a mono unit , and was not designed for anything but the rated power transformer.11. The use of a vented case IS necessary.12. always unplug the ac cord and tape the plug before servicing.

13. always use a small PLASTIC handle screw driver when adjusting the terminal blocks , THE SCREW CONNECTS DIRECTLY TO THE CIRCUIT !!

to start is simple , using the build order on the facing page , you will begin by placing all the components on the pcb,and solder them into place .

2 notes on soldering : always clean your tip of excess solder after eachuse , ALWAYS CHECK FOR SOLDER BRIDGES after each component is soldered.

whats great about the pcb is if all the parts are placed correctly .you will get identical results over and over.

only the power transformer will cause any variance in b+ voltage.but this can be adjusted by raising or lowering the value of r25.the ideal b+ voltage is between 260vdc and 275vdc , some people prefer260v and some prefer 275v , back in the 60s plus or minus up to 20%was ok , but with the advent of 1% resistors you can achieve more precisevoltages over and over. the pcb allows the use of 5.08 mm spaced insulated headers for yourconvenience in attaching wire to board , but i recommend soldering directly to the pcb for the power section and also the gain and reduction potentiom-eters .

be sure to take great care in double checking the values of the components you place , in most instances, the value on the pcb legend will be covered by the component once placed on the pcb .

if one component is misplaced or the wrong value is soldered , the entirecircuit can fail , damaging many other components .

after populating the board with all the components and transformers , you will place the board in its case and begin attaching all the wiresto the pcb ,

take great care and time in attaching each wire to the pcb . make sure each wire is not to short , but also not too long , leave a little slack in each wire so it can be either secured to the caseor like in the power section have enough room to allow for separation.

if you follow the instructions in the manual , your first power up should be successful , but always close the lid on the case when youdo this , for if you made a catastrophic error like soldering an electro-lytic back wards , it wont explode in your face.

info|build order1.) install transformers if using pcb mount2.) install tube sockets3.) install resistors and jumpers 4.) install capacitors5.) install _fuse clips and fuse6.) connect ground leads and solder tags7.) connect pots8.) connect switches | rotary switch (optional)9.) connect XLRs | ground lifts10.) connect ac section11.) connect vu meter12.) review your work13.) install tubes14.) power up 15.) pass audio test16.) trouble shoot if needed.

to start the project you will need some basic tools.depending if you have purchased a pre-drilled enclosure.or if you are fabricating your own case.

for basic assembly you will only need a few tools.solder/wire snips/needle nose pliers/wire strippers/screw driver and solder/hot glue gun.also a multi meter for testing connections and fine tuning voltages.

one of the most important tools will be your soldering iron .the radio shack 40 watt soldering iron is a great buy and works well.it is recommended to get a small 15w fine tip soldering iron for the delicate work of soldering the very close together pcbpins on the audio transformers.

however you will never regret purchasing a 200$ digital weller model as shown above.

tools:

always use a small PLASTIC handle screw driver when adjusting the terminal blocks ,

on some models

THE SCREW CONNECTS DIRECTLY TO THE CIRCUIT !! and can shock you even when the unit is off .

plate choke : lundahl LL 1667 / 5mA or sowter 9375B (with pcb pins)

audio input transformer : Lundahl 1636 pcb pinsaudio output transformer: Lundahl 1578XL pcb pins

audio transformers

pcb foot print for the LL1636 transformer

pcb foot print for the 1578xl transformer

it is important to place the audio transformers first , before any other components .

the pins are configured so you cant put them in backwards on the pcb.

the pins on the ll1626 are very close together and this is a good place to use a very fine tipped soldering iron.a good soldering iron is the radio shack 15watt. (fine tip)

you will need to inspect your work for solder bridges !

the holes of the footprint on the ll1636 are plated through please avoid solder flowing through and pooling on the other side creating a short.

the holes on the 1578xl pcb footprint are also plated through,so please use only enough heat and solder necessaryto make good contact with the pcb and avoid over doing it .

it is a good idea to place the transformers in their footprints and turn the pcb over on to a flat surface.

then while pressing down on the pcb , solder the transformers pcb pins.

another way is to solder 1 pin to hold the transformer into place then while pressing down solder a caddy corner pin.

you can re-heat these two pins to make sure the transformer is flat against the pcb surface , then solder all the pins.

once all the pins on these transformers are soldered , they are very difficult to remove , so be very carefulto get it right the first time .

ive damaged a transformer by overheating it to try and remove it from the pcb .

ideally it would be best to place the transformers in their footprints , then apply a small drop of hot glueon the sides of each transformer bonding it lightly to the pcb (do not put hot glue under the transformer).

then soldering the pins while the pcb is in an upright position ,this would help avoid solder flowing through too much on the 1578xl pins.

location for sowter chokeor use pads A and E if using lundahl 1667/5ma

location for 1578xltransformer

location for ll1636transformer

choke/audio transformer placement

lundahl choke : 1667/5mA

The LL1667 is an anode choke for tube amplifiers. The choke is built with two coils and are using a special audio C-core. The coils are made using a low capacitance coil winding technique. The two coil structure greatly reduces the risk of picking up hum caused by external magnetic fields from e.g. mains transformers.

pin 4

pin 4

pin 1pin 2pin 3to pad Ato pad E

bridge

to begin installation of your lundahl choke you will first need to jumper (bridge) two of the pins on the choke its self.if you look at the back of the choke there are four pins asillustrated below.

jumper pins 4 and 2 (it is best to use insulated wire)

you will then solder a wire to pin3 and then connect that wireto the pcb pad labeled E (plate)

then you will solder a wire to pin 1 on the choke and then con-nect it to the pcb pad marked A (b+) .

NOTE : once operational , this is a very high voltage area

using the lundahl choke 1667/5ma

connect to these padson the pcb footprint

the choke has mounting holeson the bottom of it for itto be screwed to the chassis.find the best location closeto the edge of the pcb near-est to the footprint to avoidlong wire runs.

using the sowter 9375b


the sowter 9375b choke mounts directly to the pcb ,

the choke has 4 pins , 2 of them are unused .

you will have to look at the choke pins and identify the two pins with small filament wire soldered to them .

the choke is marked with very small numbers on the black plastic base (very hard to see)

pin 6 is to be placed in the choke pad marked A (b+)

pin 10 is placed in the pad marked unused.

pin 15 is placed in the choke pad marked e(plate)

pin 11 is placed in the pad marked unused.

if in doubt or you can not see the numbers on the choke , use a multi meter set on resistance and ohm out each pin .

(meaning find the two pins that read an actual ohm value. two of the pcb pins are unused and will simply read overload)

pin 10pin 6

failure to place choke in the correct posi-tion will cause the unit not to function . and can cause damage to the other components.

note :picture is with choke already soldered to pcbhanging upside down

empty row of pin holders on this side

using alternate transformers | hook up information

it is possible to use alternate transformers other then the lundahls on the pcb .

for connecting an input transformer you will connect the output of the transformer to either pin 10 on the pcb , or you can connect it using the bypass pad marked + , which is probably best since hole #10 on the pcb input transformer footprint is unplated and you will have to solder from the bottomof the pcb . as far as grounding the input transformer , it is probably best to use a solder tag bolted next to the in-put transformer . but you can try using the padon the bypass pads marked as ground . this ground however is connected to the audio circuit ground and not the separate input gnd (you probably wont have a problem with this) its just a design rule of thumb i do, to always separate the input transformer gndand the audio circuit gnd.

as in the illustration above , you can see thatthe input transformer ground is clearly separatefrom connecting to the large plane audio circuitground .

it would probably be best if you connect the xlrpins 1 & 2 directly to the input transformer .

as to avoid rats nesting the area with random wire runs.

to output capacitor

use this to ground transformerleads

once again you should wire the output xlr directly to the transformer.

unused

using alternate transformers | hook up information

diode foot prints

diode|location

NOTE : the diodes are one way devices , they must be placed In the proper direction or damage to other components may occur. Diodes are very sensitive to electrostatic charges.

NOTE : when powered ,some of the highest voltages and amps Occur at this area on the pcb.

take notice of the arrow symbolin between the diode foot-prints.use this to match up to the schematic of your chosen semi-conductors.

the cathode is the square padthe annode is the circular pad.

Bulletin PD -2.382 rev. D 12/00

Ultrafast, Soft Recovery DiodeHEXFREDTMHFA06TB120

-55 to +150

A

C

1

W

Parameter Max. UnitsVR Cathode-to-Anode Voltage 1200 VIF @ TC = 100C Continuous Forward Current 8.0IFSM Single Pulse Forward Current 80IFRM Maximum Repetitive Forward Current 24PD @ TC = 25C Maximum Power Dissipation 62.5PD @ TC = 100C Maximum Power Dissipation 25TJ Operating Junction andTSTG Storage Temperature Range

Ultrafast Recovery Ultrasoft Recovery Very Low IRRM Very Low Qrr Specified at Operating Conditions

Benefits Reduced RFI and EMI Reduced Power Loss in Diode and Switching

Transistor Higher Frequency Operation Reduced Snubbing Reduced Parts Count

Features

DescriptionInternational Rectifier's HFA06TB120 is a state of the art ultra fast recovery diode.Employing the latest in epitaxial construction and advanced processing techniques itfeatures a superb combination of characteristics which result in performance which isunsurpassed by any rectifier previously available. With basic ratings of 1200 volts and6 amps continuous current, the HFA06TB120 is especially well suited for use as thecompanion diode for IGBTs and MOSFETs. In addition to ultra fast recovery time, theHEXFRED product line features extremely low values of peak recovery current (IRRM)and does not exhibit any tendency to "snap-off" during the tb portion of recovery. TheHEXFRED features combine to offer designers a rectifier with lower noise andsignificantly lower switching losses in both the diode and the switching transistor.These HEXFRED advantages can help to significantly reduce snubbing, componentcount and heatsink sizes. The HEXFRED HFA06TB120 is ideally suited for applicationsin power supplies and power conversion systems (such as inverters), motor drives, andmany other similar applications where high speed, high efficiency is needed.

Absolute Maximum Ratings

VR = 1200VVF(typ.)* = 2.4V

IF(AV) = 6.0AQrr (typ.)= 116nCIRRM(typ.) = 4.4A

trr(typ.) = 26nsdi(rec)M/dt (typ.)* = 100A/s

* 125C

TO-220AC

1

BASECATHODE

2

3

CATHODE ANODE2

4

ANODE

CATHODE

HERE IS THE SCHEMATIC FOR A HEXFRED DIODE (1200V 6AMP)HFA06TB120

it is important to remember that the metal plate on top of the fred is also the cathode , and high voltage travels through it , avoid this area once the unit is active, also a short time after the unit is turned off.

most of the time the letteringon the diode case will face this side (double check)

parts|diode|info


route all cables along edge of board .

cable routing diagram

rotary switch|feedback network|info

feedback network

the feed back network on the pcb controls the gain (boost) and frequency response (hi cut) of the unit.there are a few options that the pcb is capable of , you may either use 2 multi- position rotary switchesone to adjust the amplification (gain boost)and one to control the frequency response .also the ability to bypass both switches and keeping thecircuit as found in the original unimpeded.

optional drip 2 pole five position rotary switch pcb.works with mouser part # 105-SR2612F-25-18S (shorting)

originally this pcb was designed to compensate for thechanges in frequency response as the resistance in thefeedback loop was altered.

it is designed for a 2 pole five position rotary switch.5.08 headers can be used for the pads 1&2 and pads 3&4.

its an easy alternative to the following pages on manually building an attenuator set up.

drawback is you only get five positions of gain bost orfrequency adjustment.

one side of the pcb is designed for mica capacitors toadjust the frequency response of the unit. (hi cut)

and the other side is designed for resistors to adjustthe resistance in the feedback loop (boost).

you can use two separate pcbs and only populate one sideof the pcb leaving the other side blank.

giving you the ability to separately control the frequencyresponse and a separate control of the boost (feed back resistors).

example for gain boost only :

populate the resistors and solder them into place ,keeping in mind that position 1 is the lowest setting and position 5 is the highest.

then connect 1 wire to pad 2 (pole) and one wire to pad 1(labeled gain). then twist these wires and connect them to the pads on the main pcb marked 1&2 in the feed back section .

example : for frequency response (hi cut) only.

populate the selection of mica caps that best suits your desiredtone . (see following pages for values)keeping in mind position 7 is the lowest setting and position 11 is the highest setting .place capacitors in footprints and solder.

then connect 1 wire to pad 3 (pole) and one wire to pad 4 (ring),twist and connect them to the pads on the main pcb marked 3&4 inthe feedback section of the pcb.

gain side (larger foot-prints for resistors)

capacitor side (for mica caps)

connect to gain pads 1 & 21=ring2=pole

connect to frequency pads 3&43=pole4=ring

feedback sectionon main pcb

capacitor side(hi-cut)

resitor sidegain (boost)

assembly :

the rotary switch is placed on the side of the pcb that is blank.

AUTO COMP MODE :

the pcb will also work as one unit , controling boththe frequency response and the gain boost.

in this format the resistors and capacitors are paired togeather alowing you to have a pre selected frequencyresponse for each step of gain boost.

the resistors are paired with the switch positions as follows :

position 1 / resistor 1 with capacitor 7position 2 / resistor 2 with capacitor 8position 3 / resistor 3 with capacitor 9position 4 / resistor 4 with capacitor 10position 5 / resistor 5 with capacitor 11

connect gain 1&2 to the main pcb in the feed back net-work section pads 1&2

connect freq 3&4 to the main pcb in the feed back net-work section pads 3&4

pin a

pin c

installing the switch to the pcb :

it is very hard to see the numbering on the back of the rotaryswitch , its a good idea to highlight the letters with a sharpieand also number the side of the switch so you can double check the alignment with the pcb .

be very sure about the alignment because its almost impossibleto de solder it from the pcb once soldered.use a multi meter to test your positioning if needed.

it is possible to place the switch in reverse ! pay attention

simply align the switch with pin a up and pin c on the bottomand then place the pcb on top of the switch (silk screened side up).

solder into place.

pin 1

pin 7

place pcb on top of switch / silk screen up

switch side of pcb

RING 1 POLE 2

building your own rotary switch

frequency responseto rotary switch 3 is pole4 is ringor for fixed place cap here

gain (boost)to rotary switch 2 is pole1 is ring

for fixed gainplace resistor here

to use fixed freq response jumper this and omit cap.

pads are spaced 5.08 mmfor use of a 4 positionterminal block.

p = poler = ring

materials :1 \ shorting type rotary switch capable of 200v minimum 12 POSITION OR 6 POSITION / 1 POLE

2 \ 2 six inch pieces of 24-22 gauge wire

1 \ piece of bare copper wire 18-24 gauge 3 INCHES LONG

12 OR 6 RESISTORS BETWEEN 10K AND 500K

NOTE : when powered ,this is a high voltage area

original schematic for the v72 feedback network

as you see two resistors in series read 80k +5k = 85k

and the two caps in parallel total 90PF

these or the normal factory set values.

switch resistors :

you will use these resistors for the gain boost switch.

this switch can be bypassed with a fixed value on the pcb.

values for 12 position rotary switch: (2 watt is best .5 watt is minimum)

1 10k 2 22K (la2a size gain)3 68k4 90k (original value)5 100k 6 150k (tube mics )7 200k8 220k (general use )9 280k (guitar direct in)10 330k 11 400k (dynamic mics)12 500k

it is recommended to adjust these values to your needs .and to experiment ,the higher the resistance , the more gain.

220k seems to be perfect general area .

500k up gets noisy but do experiment.

solder 1 resistor to each leg of outer pins

building gain boost switch | DIAGRAM 2

polesolder 1 wireto this point.this wire is poleconnect to pad 2 on the pcb

connect 1 wireto ring with solderthis wire is ringconnect to pad 1 on the pcb

bypass gain (boost) rotaryswitch control|fixed value

leave this blank

place fixed valueresistor here .(2watt is best)

copper wire loop

resistors aresoldered to loop madefrom copper wire

ring

pole

hi-cut rotary switch

frequency responseto rotary switch 3 is pole4 is ringor for fixed place cap here

this switch controls the frequency responseof the unit . it acts as a selector to roll off the highfrequencies.

it can be very helpful in some applications .

you will build the switch same as you built the rotary switch with resistors , only substituting the resistors with mica caps.

a six position 1 pole SHORTING rotary switch is good for this area .

attach a wire to the pole of the switch and connect it to pad #3 on the pcb .

then attach a wire to the ring of the switch/cap assemblyand connect this wire to pad #4 on the pcb as shown below.

12 positions is a little much , but the switch can be adjusted to have fewer positions by adjusting the metal stopper.

you might use a meter to ohm out the switch positions as not to accidentally put the order in reverse.the far left position of the switch should be the position for the lowest value cap . (with the shaft facing you)

on some shorting rotary switches you can adjust the number of stops.

use 300-500v mica caps / ceramics are lesser quality but will work (500v is best)

p = poler = ring

1. 2pf (very little cut)2. 10pf3. 30pf4. 50pf5. 60pf6. 80pf (original value)7. 100pf8. 150pf9. 200pf10. 300pf11. 400pf12. 500pf (under water)

NOTE : shorting type switch must be used

place a capacitor herefor fixed value.bypassing selector switch.

bypass frequency responsecontrol (hi-cut)|fixed valueor mica trimmer

jumper this witha piece of wire

VARIABLE CAPACITOR :

it is possible to use the arco 465 variable trimmer as used in the la2 project.

this would allow you to forgo the rotary switch , but still have the ability to adjust the brightness of theunit, (you must adjust while the unit is off and un-plugged)

simply solder one lead to each side of the mica trimmer and install as shown in the diagram on the left page.

(replacing the fixed cap with the leads from the trimmer)

direct in | for guitars etc.for adding a direct input for guitars you will needthe following material .

1 panel mount (mono) 1/4 phone jack (radioshack part # 274-280 works great) (radioshack part # 274-0252 will work also)

1 piece of shielded wire aprox 3-4 long 2 conductor w/ foil shield and shield wire,

direct in hook up (location)

5.08 spaced pads forconnecting + of the phono plug / gain potpin 2

for hook up you will solder the shield wire to the ring connector

and the insulated conductor wire to the tip connectoron the phone plug.(instead of clipping one of the conductor wires since you only need one , just strip and combine them )

tip

ring

shieldwire (GND)

insulated conductor

+

connect the ends of this wire to the location for GAIN 2as shown below on the legend .you will piggy back them into the connector with the wires from the potentiometer (pin2)

take notice as the insulated conductor wires go to the pad marked + and the shield wire goes to the pad marked GND.

this is a really great spot for insulated terminal blocks.

+

a transformer balanced direct in is said to give a better signal.jensen transformers make some great transformers for this .

to xlr input socket pin 2

to pcb pad xlr pin 2

switches|low cut filter|info

spst switch

1-2uf cap

1 uf for pop vox2 uf for rock vox

following this diagram you can add the low cut filter1uf is the traditional cap.but you can adjust this to suit your needs.

GND TO CASE

TO XLR SOCKETPIN # 1

.01/200V

1 MEG OHM RESISTOR

SPDT SWITCH

1 2 3

XLR INPUT GROUND LIFT

xlr connectorsin some situations when interfacing your unit with other equipment a ground lift is helpful in eliminating many different types of unwanted noise or hum often associated with ground loops and interference.

the circuit here illustrates how to create a ground lift switch for the back of your unit .

materials :

1 spdt switch (1/4 inch threaded)1 .01@200v(400v best) poly pro capacitor1 solder tag (lug)1 1/2 watt 1meg ohm resistor1 xlr socket 3 pieces of 22 gauge insulated wire

xlr connectorsground lift | drawing 2

NOTE :it is recommended to install thisfrom the get go , thus eliminating needless troubleshooting due to interfacing conflicts.or the notorious pin 1 problems.

ground to solder tag next to xlr socket

ground to solder tag next to xlr socket

XLR INPUTXLR OUTPUT

You will use 2 chassis mount xlr sockets.One female which you will use for inputand one male which you will use for output.(In the photo , male is on the left)

There are many degrees of quality thatyou can get for these , try to buy thebest you can afford . The audio circuitof the unit begins and ends here.(switchcraft and neutrik are some good brands to consider)

illustrated here are the pinoutsfor the xlr sockets if viewed fromthe rear (solder side)

input

output

NOTE : before you install , identify each pin on the socket with a marker , write the number on the side of the socket . this will insure proper placement of each wire.

gnd to case

xlr in circuit with lift/cutnetwork

1

2

3

2

3

1

xlr out circuit with liftnetwork

2

3

the pad marked shld isfor when using shielded wire. under most circumstances shielded wire is not needed.

potentiometers

gain pot hook up (location)

5.08 spaced pads for connecting pins 3 & 1of the potentiometer

5.08 spaced pads forconnecting pin 2 of the potentiometer

shieldedwire

1 2 3

gain potentiometer hook up schematic

1 2 3

for these connections , it is essential to use 2 conductorwith foil shield and ground wire.

22 gauge is recommended as it is more manageable to work with.

please route the gain cable around the left side of the pcbto the pot , use enough wire do the cable sits along the bottom corner of the case .

routing the cable over the pcb is not recommended.

using this pcb gives you the ability to use a main volume control.for this you will use a 100k / 2 watt pot with an audio taper.linear taper pots are too quick in their response and make it hardto dial in smaller amounts of gain .

the gain pot acts as a large resistor in between the signal coming from the input transformer and the beginning stage of the amplifier circuit.

there are some effects on the signal , the pot tends to cut a little high end from the overall frequency of the signal going in to the amplifier circuit , but this can be overcome with some mods found after this section.

gain pot|wiring|info

NOTE :i have wired this incorrectlyand coincidentally lost one of the coils on the input transformer.make sure you do this right !

to gain 3

to gain 1

to gain +

to gnd

1

2

3

shield wire(gnd)

shieldedwire

for alps 100k pot

NOTE : the numbering format on the alpsis actually the normal numbering formatfor most pots. the numbering format onthe pcb is in reverse to this3 2 1 format , PLEASE USE THIS DIAGRAMTO CLARIFY THIS MISTAKE

ERRATA :

input gain potentiometer | bypass

if you choose to for go using a potentiometeryou will simply connect a length of shielded wire. you can com-bine the insulated wires on both ends connecting them to the pads marked with a + symbol, and use the shield wire to in-terconnect the pads marked withthe ground symbol

note:by bypassing the gain pot , you can still control the over-all amplification using the boost attenuator.

output pot| hook up

output volumecontrol pads

this pot will be helpful in controlling the volume when using the direct in . (the direct in bypasses the inputgain control pot )

hooking up the output pot is a pretty straight forward task.using 22 gauge shielded wire using the diagram in the middle of this page , connecting the shield to pin 1.

youll want to use the same size of pot as you use on the input volume control.

the recommended value is 100k audio taper 1/4 to 2watt(2watt is best)

to bypass this pot , simply do not connect a pot to the pads and jumper the footprint on the pcb la-beled bypass next to the output pads on the pcb. pin 3 is gnd

shielded wire

3 2 1

shield

shield

3 2 1

drip air mod

POLEto pot pin 3

RINGto pot pin 2

heres a nice mod to add to the gain INPUT pot , it will bleed more high frequencies past the potand directly into the amplifier section.

simply build another SHORTING rotary switch as for the feedback loop frequency response switch.

except choosing the values of the mica caps from the chart below.

potentiometers depending on brand will react differently to the values of capacitors you choose .

as where on some alps blue series, 500pf will put the signal atalmost a perfect flat frequency response. (if using a 2pf inthe feed back loop.)

on a pec 100k pot 150 pf puts the frequency response at flat(if using a 2 pf in the feedback loop)

so if you want the hi frequencies to go up , then select a range of mica capacitors above the capacitor that makes the signal flat.

a good selection for a 6 position rotary switch would be :

for a pec/mil grade

150pf (flat)200 pf300 pf400 pf500 pf600 pf

for an alps blue :

500pf (flat)600pf700pf800pf900pf1000pf (.001)

to install :solder the wire from the pole to pin 3 on the gain pot

solder the wire from the ring to pin 2on the gain pot

you will piggy back them on top of thewires already soldered into place .

do not solder to the bareshield wire (ground)

leave this wirealone !

drip air mod litethe lite version of the air mod is simply a toggle withone leg of a mica cap soldered to each post of a spst switch (same type of switch as the one used for the power on/off switch)

choose your cap to suit the size of hi frequency boostfrom the previous page.

it is better to keep the mica cap legs very short as withthe wire connecting the pot to the switch .this will avoid any out side emi from getting into the circuit.

a .001 (1000 pf) might work best if using this setup.

Installing the resistors is easy , I recommend a resistor bendingtool, this will speed up the process and keep the resistors looking neat and straight.Most of the resistor bends will all be the same size.

resistors

NOTE :DO NOT USE 1/4 watt resistors! however tempting this might be . the voltage in some places on the circuit near or overlap the operating range of them.

the pcb allows for many different types of resistors to be used . you will want to use 1/2 watt resistors.

most all of the resistors on the main circuit correspond tothe original 72 schematic , allowing you to adjust and experimentwith different values if you are a more advanced user.

the footprints on the pcb allow for carbon comp or metal film resistors.

carbon comp tend to be more noisy , but their tone is very desired.

metal film are very quiet and have fantastic tolerances of up to 1% accuracy.

since this is a vintage design tolerances of upto +/- 10%are acceptable , however please try to stay as close to the specified resistors according to the bill of materials and the footprints on the pcb .

part # :1/2 WATT +/- 10% SO GET THE NEAREST VALUE

r12/1.25K mouser part # 273-1.24k-rc (1.24k)R11/425K allied part # 895-0306 (430k) / mouser part# 273-430k-rcR13/50K allied part # 895-0184 (49.9k)R14/800K mouser part # 273-806k-rc R15/800K mouser part # 273-806k-rcR16/200K allied part # 895-0289R19/50K, mouser part # 71-cpf249k900fke14 (49.9k)R21/3MEG mouser part # 293-3m-rcR23/200K, mouser part # 272-200k-rcR24/80K, allied part # 895-0272 (80.6k) mouser part # 273-80.6k-rcVU/3.9K mouser part # 273-3.9K-RC500 OHM mouser part # 71-cpf1500r00fke14680 ohm optional emi mod \ mouser part # 273-680-rc560 ohm optional emi mod \ mouser part # 273-560-rc

2 / 1 meg resistors for gnd lift \ mouser part # 660-MF1/2LCT52R105J

2WATT : (dale cpf series is a good choice)(1/2 WORKS TOO)

1K /2W, mouser part # 71-cpf21k0000fke144.7K /2W mouser part # 71-cpf24k7000fke1410K /2w mouser part # 71-cpf210k000fke14 22K /2W, mouser part # 71-cpf222k000fke14220K /2W, mouser part # 71-CCF02-J-220K

VOLTAGE ADJUST

resistors|VOLTAGE ADJUST|info

WHEN USING THE USA BUILD ALLIED 6K88VG TRANSFORMERYOU SHOULD NOT NEED TO ADJUST THIS RESISTOR .

if using transformers other then the 6k88vg you will have to adjust this resistor to compensatefor more or less resistance depending on how much voltage the alternate transformer has .

275 volts is ideal (measuring on the left side of the resistor)

r29/A and r29B can also be adjusted to achieve the nominal voltage at r25

test pointfor 260v-275v

resistors|emi mod|info

change r12a to 580 ohm change r12b to 680 ohm

iec socket gnd (middle pin)

hi voltagecenter tapred/yellowUsa build

main power gnd

audio gnd

input xfrmergnd

electro staticshield (grey)

star ground the star ground will be 4-6 solder lugs (solder tags).bolted to one leg of the transformer in the patternas shown in the diagram , either forming a cross or astar. (this bolt must be extremely tight)solder the following to this location.

1. pwr/gnd2. audio gnd3. input gnd4. iec plug gnd5. electrostatic shield from pwr xfrmr6. high voltage center tap from pwr xfrmr

it is very important to grind the paint off the case before mountingthe solder tags to case.

note :often it is good to mount the audio gnd / input gnd to a sol-der tag at the base of the input xlr socket.but try the above first.

parts|capacitors|infofor the project you will use two types of capacitors ,electrolytic which are one way components that must be aligned in the proper direction OR THEY MAY EXPLODE !and non polar type caps that can be placed in any directionplease take note of the electrolytic , and use caution.

positive +

you can use sprague atom series or the cde tc series capacitors .

cde (mallory) tc series axial electrolytic capacitorshave a very high ripple current capability.

however you can use any axial electrolytic you like .even xicon caps will work.

the original circuit uses all 8uf electrolytic capacitorsbut uses a full wave bridge as the main rectifier.

the full wave center tap diode configuration was chosen to take advantage of available off the shelf power transformers.

the pcb does work with this all 8uf cap arraignment.and for more advanced users i do recommend experimentation.

however the power supply was adapted from the la2 seriescompressor and works very well with the design.

i would recommend using the stated electrolytic capacitors on the pcb legend.

since the transformer is overrated by almost 3 times over the needed amount of power ,

a larger size capacitor is recommended for the pi filter.

i have had successful results with using all 40uf for the power supply.

just as well using all 10ufs for the filter section.

you can also adjust the pi resistors to match the original circuit

by replacing r29A / r29B with 2.5k @ 1-2 watt resistors.

r25 will need to be adjusted up or down depending on yourtransformer voltage 240-0240 or 250-250 or 260-0-260.

the foot print for r25 can fit many types of resistors buy the best you can afford for r25 / r29a / r29b

electrolytic capacitors|power supply notes

first filter 40uf

second filter 40uf

third filter 40uffourth filter 10uf

circuit filter10uf to r15/r16

first resistor

second resistor

third resistor

pi-filter|info

drip pcb translation :

r26 on schematic is r29a on pcbr27 on schematic is r29b on pcbr25 on schematic is r25 on pcb

c36 is first filter on pcbc37 is second filter on pcbc38 is third filter on pcbc35 is fourth filter on pcb

#6 | 10uf@450v #5 22uf-100uf @450v

#3 40uf@450v

#1 40uf@450v

#4 10uf@450v

#2 10uf@450v

electrolytic capacitor placement PAY ATTENTION TO THE POSITIVE SYMBOL ON EACH FOOTPRINT !

optional first filter 40uf@450vpositive side

optional first filter 40uf@450vnegative side

optional first filtering stage capacitor placement

illustrated are the location of pads for the option to install an additional filtering capacitorto the first stage of the pi-filter.it is important to use shrink tubing on the leadsof this capacitor as not to have exposure to the high voltage positive side lead.it should be mounted on top of filtering caps 1 & 2.

output cap2uf@400v

.001@400v .022@400v

.05@400v

optional filtering cap..1@400vUSE ONLY IF EXPIRENCING RF PROBLEMS

non electrolytic capacitor place-ment

the following caps are non-polarand can be placed in any direction.

c33 output cap 2uf @400vc32 .022@400vc31 .05@400v (.047 works too)

unnumbered cap .001@400v

x-cap : 0.1 @ 400v use polypro.(this cap is optional and mightonly be used if having rf problems)

c33 is a very important cap , please try to use the highest quality cap you can here .

solen is a great choice.

the higher ther quality of caps the higher the quality of performance.

un numbered cap

c33

c32

c31

x-cap

1 / .05 @ 250-400v (400v recommended) sozo or solen are a good choice. or use a .047 if using orange drop . 1 / .022 @ 450v mouser# 75-715P600V0.022 (orange drop) solen or sozo work great here.

3 / .1 @ 400v POLY PRO / axial works best mouser# 75-715P400V0.1 (orange drop)

1 .001 @ 400v mouser# 75-715P600V0.001 (orange drop)

1 / 2 uf @ 400v poly pro. output cap/ NON ELECTROLYTIC1 / 1 uf @ 400V poly pro (250V MIN) for low cut / NON ELECTROLYTIC

capacitors/non electrolytic

Many people use the orange dropVariety of caps, either the 716 or the 715 series.They are reliable polypropylenecapacitors often used in guitar amps,and the sound of them is liked.they will need to be the 600v range.

The codes to identify them are :

102J : .001 cap104j : .1 cap223j : .022 cap (.022 replaces the .02)

parts|vu.When it comes to meters , sifamis the way to go hands down.

shielded wire is not necessary .but it is important to twistthe +/- wire very tight .

twisting with a hand drill helps.most meter terminals are markedwith a positive and a negative .simply connect the +\- pcb padsto the correct terminal on the meter.

VU METERHOOK UP

ROUTE WIREALONG EDGE OF PCB

depending on your vu meter , tracking may not match your mixing board .

you can adjust the meters calibration on the pcb by adjusting the VU resistor on the pcb . under most circumstances the 3.9k works great.

if not , one option to add to the back of your unit is a100k pot using only pins 1 and 2 each pin attachedto one pad on the pcb footprint (omitting the 3.9k).

this will allow you to calibrate the meter using the pot , and dial in the perfect match.

unused1 2 3

power transformer hook up area

power transformer | hook up locationpower switch

red/red500v ac

green/green6.3v ac

black/blackac in to transformer

greyshield to gnd

red/ylwhi volt center tap to gnd

green/ylwlow volt centertap

the small grey wireis the electrostaticshield (6k88vg model)ground this wire

star ground

twist tightin pairs

Power transformer :

the circuit requires a transformerof 250-0-250 volts centre tapped @ 40 milliamperes and a secondaryof 6.3 volts center tapped @ 2 amps.

(this transformer is overrated and could actually run 2 pcbs.)

The primary can be the USA 110v or the European 240v

The allied electronics 6k88vg transformer works very well for USA builds , It is center-tapped and has minimal noise and hum.

please use a transformer with a center tap inorder to take advantage of the dc reference circuit on the pcb

sowter makes a more expensive power transformer for both USAand European voltages. Im sure this is a fantastic transformer builtto the highest standards.

but the hammond 369jx will also work very well for both usa and international builders.

do not mount the power transformer inside the case !out side the case is best.

it is important to take note that on the AC connection BLK is the fused side ,

high voltage connection

low voltage 6.3 v@2 amps minimum fused AC enters

the transformerfrom here.

power groundconnect to star gnd(use thick wire)

optional power switchlocation.

xcap AC mains rffiltering cap.(optional)

take note of thearrow .reference the fredmfgs schematic for proper placementof freds

transformer connections :

now you will begin to hook up the various transformer leads to theircorresponding pad on the pcb.

it is often a custom that builders twist the pairs of wire as illustratedin an attempt to help reduce noise or hum associated with overlappingwires of different voltages.

this is very important that you do this .twist the pairs so tight , that they almost contort.

as in the diagram , it is clearly marked on the pcb where each of thesewires go , I.e x-black means transformer-black

there is no polarity issue here , so either lead of correspondingcolor can be placed on either pads named for it.

NOTE : please pay attention to the instructions in this area. incorrect wiring of this section can highly damage the components on the pcb, as with possible electrocution and injury to you.

here in this picture it shows how to wire the power transformersection of the pcb . notice how the wires are all separated into pairs and that there is space between them . take care in this area layout not to cut the transformer wires tooshort , but also do not leave them to long as to flop around . separation is very important ,noise and hum can be introduced in this area if the wires are squished together.when connecting the wires to the board , strip only a minimal amount of the wire to avoid short circuits.

correct wayof attaching wire to board

incorrect wayof attaching wire to board

if using 5.08 terminal blocks , strip only enough wire to be placed inside the terminal block . it is best to tightly twist the exposed wire after it has been stripped , and then lightly tin the end with solder.this will help prevent small strands of wire from separating and causing a short.

transformer mounting

there are a couple options in mounting your transformer

option 1 is to grind off the paint on your case where eachleg meets the case (chassis) insuring the transformer is grounded to the case .this option has worked very well for the drip opto pcb usingthe same transformer.

option 2 is to mount rubber bushings or gasket materialin between the feet of the transformer and case helping to quiet the natural hum of a mains transformers.

option 3 is to just mount the transformer with very tight bolts.

all 3 work .

you can do option 3 , and if there are problems , then proceedto option 1.

PLEASE MOUNT YOUR TRANSFORMER TO THE FURTHEST CORNER OF THE CASEAS TO AVOID INTERFERING WITH THE AUDIO CIRCUIT.

its not recommended to mount your transformer in the case unlessyou have a separate compartment for it .

sowter 0295 schematic

drip pcb translation

red (hi voltage)

red (hi voltage)green (6.3 v)

green (6.3 v)

green/yellow (lv center tap)

red/yellow (hv center tap)

shield (ground)

alternate power transformer :

alternate power transformer :

for usa / international builds (universal primary) :

hammond 369jx 250-0250 @ 60mA |[email protected]

international transformer

dc reference circuit

dc reference circuit:location

dc reference circuit:lv ct tap : LOW VOLTAGE CENTRE TAP (6.3V)

i prefer to use this last once the unit is assem-bled and running .

but i find this circuit in conjunction with groundlifting circuits ensures the most quiet interfacing with other gear .

use 2 watt resistors in this area.capacitor should be in the 450v range

22uf is a start i often use 100uf to ensurea very smooth dc reference to the heaters thuspreventing 50hz hum in the tube heaters.

please use caution in this area and reference your transformer schematic if using anything but the al-lied 6k88vg (usa).on this transformer , the 6.3v center tap will be GREEN/YELLOW

other transformers will use different color wires so double check.

it is important to connect the LOW VOLTAGEcenter tap wire ONLY.

attach green/yellowlow voltagecenter taptransformer wire

NOTE : the electrolytic cap has an arrow and minus symbol to denote that the lead on that side of the radial cap is NEGATIVE. take note of the plus symbol on the cap footprint

you will use one radial leaded electrolytic in the dc reference section of the board ,

positive symbol

IEC power socket (type c14 chassis inlet)For your power cord , you will use theIEC style inlet , since the fuseis mounted on the pcb , you willnot need the fused version .

NOTE :

DO NOT USE POWER CORDS DIRECTLY WIRED TO THE PCB!This practice is dangerous and under no circumstancesShould you do this.

wiring : NOTE : NEVER DISCONNECT THISGROUND !

if looking at the IEC socket from the back as shown in the illustra-tion , you will always connect the pcb pad marked AC black to the pin on the right.this is very important.

the bottom pin is con-nected to the star groundat the transformer leg.

this ground is knowas the safety ground

never lift or discon-nect this ground underany circumstances.

you must twist the two ac wires very tight.

twist

AC IN PADS

star gnd

connect blackto this side

optional powerswitch location

part

s|tu

be|i

nfo

the pcb is designed to work with ef86 and ef806 tubes . the decision to use these vs the original ef-804s was based on availability , simply there are not a lot of them to go around. the ef-86 has the same characteristics as the ef-804 and are con-sidered the same tube with a different pin out.

please have your tubes tested for microphonics and noise.i have had great luck with the rft brand , but tubes arevery subjective and their tone can be a matter of induvidual taste.

tube rings and dampers can help the microphonic tendency ofof the ef86 also some have the ability to dissipate heatprolonging the life of the tube .

tung-sol has developed the new ef806 with gold plated pinsand is said to be a lower noise tube and is sold as a superpremium ef-86.

ef86

ef 804/s do not work on this pcb becausethey have a different pinout.

parts|fuse|infoThe fuse is a 250v 400mA(.4 amp) SLO BLO mouser no# 576-0313.400HXP

The clips used to attach the fuse to the pcb are littel fuse : 3AG PC clipmouser number 576-01220083honce installed fuse should snap right in.

NOTE : take notice of the direction that you mount these clips .for they have a notch on each sideif placed wrong the fuse will not fit.

solder fuse clip here solder fuse clip here

if using an iec socket with built in fuse holder.its not a bad idea to still use this fuse as added insurance for safe operation.

NOTE :

under no circumstances should you operate this project withouta fuse in place. (by bypassing or jumping this connection)

if your unit keeps popping fuses SOMETHING IS WRONG.

simply check all your power connections , and component placements .

fuse location

The tube sockets are a very important part of the project,Try to use hi quality ceramic pcb mount sockets.molded plastic will work , but often have poor contactwith the tubes.Sometimes compressing the metal contact in the socket itselfwill help insure a good connection.

You will need two 9 pin sockets (12ax7 size)

place tube sockets in their footprints on the pcb , solder into place

parts|tube.socket|info

tube socketlocation 1

tube socket location 2

NOTE :

some tube sockets have bigger pins and will not fit all the waythrough the holes in the pcb .

two options :

a. grind the pins on the socket with a dremel so they do fit.

b. align the pins on top of each designated hole/pad , press down and solder . (the pads are plated through , as long as they are soldered to the pads , a connection is made.)

power switch (spst)

the power switch now has a place for a snubber network on the pcb.

CDE part number : 104M06QC100 (.1 cap in series with a 100r 1/2 watt resistor) use the 600v version to ensure safety.

simply install the snubber and solder , this will help eliminateany popping transients at shut down of the compressor.

here a 5.08 screw header works great.

NOTE : it is absolutely essential to twist the wires together from the power switch to the two pads labeled pwr SW otherwise noise or hum may be introduced into the audio circuit.

if you choose not to use the cde snubber , here is an alternate method of creating one .

parts|misc|info

This project will require the use of solder tags for very importantConnections like the individual grounds and the transformer starground.

Please use these or something compara-ble.

These connections are some of the most important of the project .

pre-bent solder tags with an addedlock washer teeth are best,they help insure a solid contact.

solder tags :

NOTE : if your case is painted , you will have to dremel or sand away a small area to attach the solder tags, clean solid contact to metal is important.

Depending on the configuration you chooseyou use , you will need to purchase4 knobs for :

1: gain2: boost3: output4: hi cut5: AIR mod

You can select these on basis of your personal aesthetic, molded plastic works great here.

NOTE : Knobs often have shaft size requirements , so be sure to check this to match your pots and rotary switches.

Knobs

Standoffs 8 standoffs are needed to elevate thepcb above the case floor.

a minimum of 1/4 inch is required.

WirePlease use at least 22 gauge wire for theVarious connections used in this project.(24 gauge would be the minimum allowed)

jumps :there are a few jumps on the board , with these you will simplybend a piece of 24 GA wire like a resistor and solder theminto position.

a standard 0.7 jumper will work also.

you should elevate each jump so it is about 1/8 from thesurface of the pcb .

lamp

the pcb has 2 locations for a 6.3v AC lamp 1 for the meter and one for the on light .

often it is a good idea to install a temporary lamp on the inside to help avoid accidental shocks while servicing or trouble shooting .

v72 pcb | bill of materialsmono series with lundahl transformers ver 1

drip electronics

V72 Pre cases offered by :

[email protected]

1 resistor bending tool speedy bend lead formermouser#5166-901

1 mallory (CDE) .1/150r @600v quencharc snubber networkmouser part # pt#539-104MACQRL150 . (will use one for power switch pop control (aka rc network snubber)z

1 / .05 @ 250-400v (400v recommended) sozo or solen are a good choice. or use a .047 if using orange drop mouser part # 75-715P400V0.047 . 1 / .022 @ 450v mouser# 75-715P600V0.022 (orange drop) solen or sozo work great here.

3 / .1 @ 400v POLY PRO / axial works best mouser# 75-715P400V0.1 (orange drop)

2 / 10uf@v450v electrolytic Allied Stk#: 852-9089 (cde mallory tc72) Allied Stk#: 507-0192 (atom TVA 1705 450V)

2 / 40uf @ 450v atom electrolytic (for power section) mouser#75-TVA1908-E3 (500v version) (450v minimum) for cde(mallory) use tc78 40uf@450v (allied electronics)

1 .001 @ 400v mouser# 75-715P600V0.001 (orange drop)

10UF @ 450v Radial mouser part # 647-UVZ2W100MHD

22UF @ 450V radial or use 100uf radial for better DC reference 22uf mouser part # 647-UCA2W220MHD6 100uf mouser part # 647-UPW2W101MRD

1 / 2 uf @ 400v poly pro. output cap mouser part # 75-V730P205X9400 allied part # 613-0571

1 / 1 uf @ 400V poly pro (250V MIN) for low cut mouser part # 75-V730P105X9400 allied part # 613-0573

capacitors/non electrolytic

capacitors/electrolytic

note : using the highest quality parts will yield a higher quality machine , however the pcb will work well with standard quality parts.

some of these mica caps are spares , but will be needed for fine tuning (500v is best)

1 /120pf mica capacitor 300-500v 1/ 100pf mica capacitor 300-500v1/ 90pf mica capacitor 300-500v 1/ 40pf mica capacitor 300-500v 1/ 2pf mica capacitor 300-500v

RESISTORS :1/2 WATT +/- 10% SO GET THE NEAREST VALUE

r12/1.25K mouser part # 273-1.24k-rc (1.24k)R11/425K allied part # 895-0306 (430k) / mouser part# 273-430k-rcR13/50K allied part # 895-0184 (49.9k)R14/800K mouser part # 273-806k-rc R15/800K mouser part # 273-806k-rcR16/200K allied part # 895-0289R19/50K, mouser part # 71-cpf249k900fke14 (49.9k)R21/3MEG mouser part # 293-3m-rcR23/200K, mouser part # 272-200k-rcR24/80K, allied part # 895-0272 (80.6k) mouser part # 273-80.6k-rcVU/3.9K mouser part # 273-3.9K-RC500 OHM mouser part # 71-cpf1500r00fke14680 ohm optional emi mod \ mouser part # 273-680-rc560 ohm optional emi mod \ mouser part # 273-560-rc

2 / 1 meg resistors for gnd lift \ mouser part # 660-MF1/2LCT52R105J

2WATT : (dale cpf series is a good choice)(1/2 WORKS TOO)

1K /2W, mouser part # 71-cpf21k0000fke144.7K /2W mouser part # 71-cpf24k7000fke1410K /2w mouser part # 71-cpf210k000fke14 22K /2W, mouser part # 71-cpf222k000fke14220K /2W, mouser part # 71-CCF02-J-220K

switch resistors :

you will use these resistors for the gain boost switch.

this switch can be bypassed with a fixed value on the pcb.

values for 12 position rotary switch: (2 watt is best .5 watt is minimum)

1 10k 2 22K3 68k4 90k (original value)5 100k 6 150k (tube mics )7 200k8 220k (general use )9 280k10 330k 11 400k (dynamic mics)12 500k

it is recommended to adjust these values to your needs .and to experiment ,the higher the resistance , the more gain.

220k seems to be perfect general area .

500k up gets noisy but do experiment.

optional hi cut switch (12 position rotary):

this switch is optional , and can be bypassed with a fixedvalue on the pcb.

12 positions is a little much , but the switch can be adjusted to have fewer positions by adjusting the metal stopper.

use 300-500v mica caps / ceramics are lesser quality but will work (500v is best)

1. 2pf (very little cut)2. 10pf3. 30pf4. 50pf5. 60pf6. 80pf (original value)7. 100pf8. 150pf9. 200pf10. 300pf11. 400pf12. 500pf (under water)

note : these switches may be bypassed to preserve theoriginal feedback loop as in the original design.but you will need at least one resistor and one mica cap for use on the pcb.

862-0706 CD15FC621J03F 620 300 862-0553 CD15FC681J03F 680 300 862-0554 CD15FC751J03F 750 300 862-0707 CD15FC821J03F 820 300 862-0539 CD15CD010D03F 1 500 862-0540 CD15CD050D03F 5 500 862-0541 CD15CD100D03F 10 500 862-0624 CD15CD100J03F 10 500 862-0625 CD15CD150J03F 15 500 862-0542 CD15CD180J03F 18 500 862-0635 CD15ED200J03F 20 500 862-0626 CD15ED220J03F 22 500 862-0627 CD15ED270J03F 27 500 862-0543 CD15ED300J03F 30 500 862-0704 CD15ED390J03F 39 500 862-0705 CD15ED430J03F 43 500 862-0495 CD15ED470J03F 47 500 862-0628 CD15ED510J03F 51 500 862-0546 CD15ED680J03F 68 500 862-0496 CD15FD101J03F 100 500 862-0630 CD15FD121J03F 120 500 862-0497 CD15FD151J03F 150 500 862-0547 CD15FD181J03F 180 500 862-0631 CD15FD201J03F 200 500 862-0548 CD15FD221J03F 220 500 862-0709 CD15FD251J03F 250 500 862-0633 CD15FD271J03F 270 500 862-0710 CD15FD301J03F 300 500 862-0498 CD15FD331J03F 330 500 862-0499 CD15FD471J03F 470 500 862-0551 CD15FD501J03F 500 500 862-0711 CD15FD511J03F 510 500 862-0712 CD19FC682J03F 6800 300 862-0718 CD19FD511J03F 510 500 862-0556 CD19FD821J03F 820 500 862-0634 CD19FD102J03F 1000 500 862-0557 CD19FD122J03F 1200 500 862-0558 CD19FD152J03F 1500 500 862-0560 CD19FD302J03F 3000 500 862-0561 CD19FD332J03F 3300 500 862-0716 CD19FD392J03F 3900 500 862-0562 CD19FD472J03F 4700 500

allied electronics mica cap part numbers

part# mfg part# pf value voltage

1 bag of 0.7 / 3M insulated jumper wires violet for all jumps (optional or just use wire)

1 VU meter sifam (same vu as the la2a)meterdistributor.com or sifam.com

10 / 5.08 spaced 2 position screw terminal blocks (for attaching wire to board ) (side entry screw on top)



2 SPDT toggle switches for ground lifts (radio shack)2 SPST TOGGLE switch for low cut and power switch1 spst if using the air mod lite

2 100k ohm potentiometers must use AUDIO TAPER / 2 watt (1/4 watt will work) / alps blue velvet or conductive plastic works best.

2 / 12 position SHORTING rotary switches 1 for boost selector 1 for hi cut. (non shorting will NOT work!) mouser part # (alpha) 105-SR2612F-12-38S

1 / 2 pole 5 position rotary switch (shorting) if using optional drip switch pcb / mouser part # 105-SR2612F-25-18S (shorting)

XLR sockets1 xlr in socket (chassis mount) mouser :mouser# 568-NC3FP-11 xlr out socket (chassis mount)mouser :mouser# 568-NC3MP

parts and supplies :

10 solder tags (lugs) Terminals LUG LOCKING TINNED#4 mouser#534-7311 (for #4 screw size) mouser#534-7330 (for #8 screw size)

6 1/4-1/2 stand offs with screws.(to mount pcb to case) radio shack # 276-195 20.6 mm (13/16)

1 panel mount (mono) 1/4 phone jack for direct input (radioshack part # 274-280 works great)

power transformer :(uses same transformer as the LA2a)

usa build :allied transformer 6k88vg (250-0250 40Ma CT / 6.3v 2a CT ) (recommended) :allied part #: 227-0113

sowter part #: 0295 (for Teletronix )

european build :sowter part #: 0208 (for Teletronix )

1 IEC power plug IEC C14 mouser#161-R30148

1 power cord to fit iec plug

1 .4 amp slo blow fuse (standard size) mouser part#576-0313.400HXP

2 fuse clips for mounting fuse to pcb mouser : P/N 01220083H |desc : 3ag pc clip (littel fuse , fuse clips)

2 hexfred rectifier (diode) mouser#844-HFA06TB120PBF

power section :

usa/canada use K&K audio (note for drip v72 pcb)

plate choke : lundahl LL 1667 / 5mA or sowter 9375B (with pcb pins)audio input transformer : Lundahl 1636 pcb pinsaudio output transformer: Lundahl 1578XL pcb pins

audio transformers and choke :

tubes :2 ef-86 (these tubes can be microphonic , so have matched and tested if possible) ef806 tubes by tung-sol work also / RFT is one of the better tubes.

note : pcb will not work with ef-804 tubes because they have a different pin out then the ef-86 tube.

tube sockets :2 nine pin (12ax7 size) ceramic pcb mount tube socketstriodeelectronics part#:#9pincerpcgoldtubedepot.com part#:SK-9PINPCG

note : both the lundahl and sowter chokes work very well

wire :aprox 3 feet of foil shielded 2 conductor (plus ground) wire 22GAaprox 4 feet of 24-22 gauge hook up wire for the assorted connections.

coming soon

v72 Pcb Manual

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Transcript of v72 Pcb Manual