Assembly and Installation Instructions for the


CDV-705 Clone Kit

For LENi and ENi Geiger Counters

Or as a stand-alone speaker for any Geiger system.

By GEOelectronics


The CDV-705 was a speaker option made contemporaneously with the CDV-700’s, back in the early 1960’s. Only a few hundred were ever made, and are much sought after today. This kit is a faithful reproduction of the circuitry of the CDV-705 and has been “updated” only in the sense that we use

all new,   modern components. A brief glance at the circuit might indicate an amplifier, but it is actually much more than that. A discrete component multivibrator is the actual description, and the subtle difference is that an amplifier alone would draw excessive battery current,. And more importantly would amplify background whine from the power supply in the CDV-705. This design eliminates both of those problems, and reduces battery drain to an inconsequential factor.

A circuit board is part of the kit, and we speak of the “top side” as the side with color-coded dots around certain of the eyeleted component holes. These dots also indicate the position and color of wire that connects the circuit board circuitry to the LENi, ENi or other Geiger Counter, as well as to the speaker and volume control. Place the circuit board on a flat surface in front of you, and position it with the yellow dots to the right.

With this orientation, familiarize yourself with the layout and hole numbering sequence as shown in Photo #1. Starting with the bottom row of holes, the holes are numbered in a clockwise manner in a logical sequence. We will refer to these numbers when explaining parts placement.

(NS) means place the part but do not solder it yet. Usually more than one component lead will share an eyeleted hole. (S) means solder the connection. “Bend dim. =” is the pre-form distance between wires in case you have a bending fixture or just want to measure and pre-bend the components manually.

Note: if you are following the circuit without benefit of the kit, use perf-board or any other suitable substrate to hold the parts, and follow the general layout and instructions.

All LENi’s were made with a compartment at the meter-end of the battery holder to accept this circuit board.

Please remember that LENi’s, Eni’s and some others are POSITIVE GROUND circuits. Numbered Holes


Circuit Board Assembly


First put all the jumper wires in into the correct holes, joining the various buss lines together electrically.  Photo #2 and #3 shows this step, for top and bottom sides. All jumpers except one are made of bare wire, as supplied in the kit. It is strung between the holes and bent over on the bottom side. Trim excess, leave just enough to hold it in place until it gets soldered along with other leads that share that eyelet. .

Front Side JumpersTop side of board:

Refer to photo #2

Put a zero-ohm resistor between #19 and #14. Approx ¼” of Teflon tubing should be placed on each lead before bending. Bend dimension for this part is .6 in. (NS)


Bare wire between #7 and #8 (NS)

Bare wire between #20-18-16 –10 ¾” of Teflon tubing on the part between 16 –10. (NS). All holes connected together in a “daisy chain”.


Bare wire between 2-3-4-5-9 (NS). All holes are connected together in a “daisy chain”


Bottom side of board:

Refer to photo #3


Back Side Jumpers

There are three jumpers on the bottom, all emanate from hole #22 and go to a single hole each going to a single destination. This style of jumper is called a “wagon wheel”.


From 22 to 15, Use 1 “ of Teflon tubing (NS)

From 22 to 6 use bare wire (NS)

From 22 to 1 use bare wire (NS)




Previously placed parts not shown for clarity.

Resistors and Capacitors


From left to right:


C1-.001 @50V cap between 21 and 19. No polarity issues. Bend dim. = .5”. (NS)

C2-.001 cap @50V between 17-12, use 3/8” Teflon tubing on each lead No polarity issues.

Bend dim. =. 5”(NS)

R3-27K ¼ W resistor ( red-violet-orange) Between 19 (NS) and 20 (S). Bend dim. = .3”

R2-150K ¼ W resistor ( brown-green-yellow) Between 17 (NS) and 18 (S) Bend dim. = .3”

R6-47 Ohm 1/4W resistor (yellow-violet-black) Between 15 (NS) and 16 (S) Bend dim=. 3”

R1-150K (brown-green-yellow). Between 14 (NS) – 3 (S). Bend dim. =. 75”

R4-820 Ohm ( gray-red-brown). Between 12-13 (NS). This component stands on end.

R5-27K (red-violet-orange). Between 13 (NS)-4 (S). Bend dim. = .6”

R7-27K (red-violet-orange). Between 11 (NS)-5 (S). Bend dim. = .5”






















Refer to photo #5.

Transistor Placement

Previously placed parts not shown for clarity.


Q1 and Q2 are placed along the top edge. These are both PNP transistors, p/n 2N3906.


There are 5 eyeleted holes across the top edge.

Q1 (2N3906) is to the left and is placed with the flat side facing away from the board center.


E-15 (NS)

B-17 (S)

C-19 (S)


Q2 (2N3906) share one hole (#15)with Q1, the center in the row of 5. The flat side of Q2 faces board center.


E-15 (S)

B-14 (S)

C-12 (S)


Q3 and Q4 are NPN transistors, p/n 2N3904. Both flat sides face away from board center.


E-11 (NS)

B-13 (S)

C-10 (S)



E-9 (S)

B-11 (S)

C-8 (S)








Now inspect the whole board. There should be 4 transistors, 6 resistors lying down, one resistor standing up and two capacitors. All holes should be soldered by this time except the ones with colored dots. We will now install the wires into those holes and solder.

Tap-Off Points


Red dot- hole # 1- Insert and solder one end of a  6” piece of red Teflon insulated wire (S). This is the POSITIVE 3V lead that goes to the Geiger Counter board RED tap-off point, see picture of CDV700.



Red dot- hole #22. No external wires hooked up to this if the board is used in a LENi. Just solder it closed (S). The extra terminal is used on stand-alone speaker boxes that have their own battery supply.


Black dot- hole #2- insert and solder a 6” piece of black Teflon insulated wire.  This is the NEGATIVE power lead that goes to the Geiger Counter board BLACK tap-off point.


Violet dot- hole #21.

 Insert and solder one end of a 6” piece of violet Teflon insulated wire (S). This lead is the PULSE input and connects the Geiger Circuit board VIOLET tap-off point.

If a volume control is to be used, remove the existing violet wire and “PHONE” jack from the LENi. This panel hole will be used for the volume control.














Volume Control Installation as provided in the kit: If no volume control is used, skip this step.

Volume Control KnobBackside of Volume Control


Remove the “PHONE” jack and its violet wire. Keep the rubber washer for reuse. Mount the volume control potentiometer into the hole thus vacated. Place the rubber washer on the threaded shaft so that it is on the inside of the chassis. On the outside, secure the threaded shaft collar with a lock washer and nut. Secure the knob on the shaft.

Looking at the back of the volume pot, the left and center terminals are used. Electrically this is a simple variable resistor placed in series with the yellow lead from the circuit board hole #7 going to the speaker.



Yellow dots- Speaker output leads. Holes #6 and #7 Insert one end of an 18” piece of Kynar insulated wire into each eyelet and solder (S) (S).


FOR NON-VOLUME CONTROL USE: Run each of the two yellow wires to a speaker terminal and solder. No polarity issues. Run the wire through a solder-lug strain relief at both ends to protect the speaker and circuitry should someone remove the battery box and pull on the wires.



Run the yellow wire from hole # 6 to a speaker terminal. No polarity issues but do secure the ends mechanically with provided clips. Run the yellow wire from hole #7 to the center terminal of the volume control (S). Run another piece of yellow wire from the left side terminal (S)  (as viewed from the rear) to the unused speaker terminal (S).



This completes the assembly and installation. Slow pulses from the Geiger should be audible as loud natural sounding clicks in the speaker, one click per event. Faster pulses are perceived as an audio tone, still one cycle per event, and will track up to very high rates. SPEAK2ME power is automatically switched along with the LENi, and its use will not appreciably affect the battery life.












The supplied 32-Ohm, thin profile speaker is best installed in the battery case, left side front as viewed by the operator. A hole just smaller than the speaker should be cut or punched in the battery box wall. Three screw holes (top, +/- 120 degrees) allow mounting via metal brackets, also supplied. A yellow plastic speaker grill waterproofs the set while letting out most of the sound.   Cut to fit, and then glue the supplied yellow plastic speaker cover in place before mounting the speaker. Secure the yellow speaker wires mechanically by wrapping them around the cutouts in the speaker frame. The other end is secured with the supplied metal clip, which should be attached to the battery holder with one of the existing mounting screws.

If you are not comfortable around metalworking machinery, I can make the hole for you, and even assemble and install the whole project in your LENi or ENi. Your free first annual tune-up would be a good time to add the SPEAKE2ME to your LENi.


Internal 705Speaker Mounting Detail


In order to have enough clearance between the main Geiger Counter circuit board and the speaker, it

may be necessary to notch out a small area near the board’s edge to provide a clear channel. There are no circuit traces in that area to worry about.


Useful modifications for the advanced experimenter.

Try placing an LED (supplied in kit) across the speaker wires for a flashing pulse indicator. The long wire lead from the LED goes to hole# 6, the shorter lead to hole#7. In this way the LED is unaffected by the volume control.


Reach inside the volume pot with a needle or other small tool to scrape away the conductive layer attached to the unused terminal. This effectively provides an OFF function for the audible clicks, and at the same time, allows the pulses to be routed to another circuit for further processing, as in a scaler, LED etc via that unused terminal Now you know why the instructions have you wiring the volume control in a manner opposite conventional practice!


Howl and Buzz Eleminator






UPDATE: Images Inc has produced a PCB for this project:




 PCB%20Layout                                        Have Fun


George Dowell