CD V-700 Mods

  This is my “LENi”, an Electro Neutronics CD V-700 model 6b modified by George Dowell (A.K.A. K0FF, GeoElectronics).  George is the founder of the GeigerCounterEnthusiasts Yahoo group.  In his words:


 “The Electro-Neutronics CD V-700 model 6b has had a bad reputation for 40 years. On the other hand, the Lionel CD V 700 model 6b is regarded by many as the best circuit ever. Surprisingly, of all the variations in CD V 700's I have seen, including Victoreen's various models, and the Antons, there is no circuit more similar to the Lionel's than the ENi! At least it is similar enough to make a logical transformation that is really significant electronically, but easy to do.  In my opinion the physical layout of the ENi is better than that of the Lionel, so the merger of the Lionel circuit concept into the ENi mechanical layout really does give the best of both worlds.


By performing the simple and inexpensive K0FF LENi mod, you can create a Lionel clone from an ENI.”


CLICK HERE for George’s instructions on modifying the Electro Neutronics CD V-700 model 6b into a LENi

George Dowell’s “LENi”

David Prutchi’s “CDV-700 Pro”

  This bench Geiger Muller Counter was built using a surplus Anton CD V-700 model 5 board (kind courtesy of Lee Frank).  Power is provided from a 12VDC adaptor via a 5V-output DC-DC converter.  A Veeder-Root Type A103 totalizer is connected directly across the headphone output.

CLICK HERE for a redrawn schematic of the original ENi CD V-700 model 6b circuit [PDF].

CLICK HERE for a redrawn schematic of K0FF’s LENi showing the portions of the circuit that need to be modified.  My part numbers are somewhat different than George’s (because I kept the original ENi part numbers as a basis).  This schematic also shows modern replacements for the various parts [PDF]

The “CDV700 Pro” is based on K0FF’s LENi, but adds the following features:


· Preamplifier to make it compatible with scintillation probes (GM tubes can still be used)

· Selectable, regulated bias voltage (900V or 1,200V) for connection to GM tubes and photomultiplier tubes.  A blinking indicator warns of the high voltage selection.

· Noise-reduction circuitry eliminates hum.

· Internal piezo clicker.

· Power input jack saves batteries when powered from car or AC-operated power supply.

· 8-digit digital counter.


To build your own CDV-700 Pro, start by modifying an Electro Neutronics CD V-700 model 6b into a LENi per George Dowell’s instructions, with the exception that the Zener-diode chain should be constructed per my schematic diagram.  Then, build the preamplifier circuit on a small piece of perfboard. CLICK HERE FOR DETAILED INSTRUCTIONS [3MB MHTML]  [1.7MB PPT].

CLICK HERE for a schematic diagram of my “CDV700 Pro”  [JPG]  [PDF]

The ENi CD V-700 model 6b is first modified into a LENi.  A plastic battery holder is used to make space for the preamplifier circuit.  The Zener diode board allows selection between 900V or 1200V output.

David Prutchi’s Scintillator Probe for the “CDV-700 Pro”

  Nibble-out a 68mm x 33mm rectangular hole on the enclosure bottom to accommodate the Veeder-Root A103-000 Totalizer.  This module is a compact, self-contained counter.  It displays counts on a supertwist LCD with .47" (12mm) high digits.  An internal 3-volt lithium battery eliminates need for external power. The reset button is on front panel.  If you need to take your CDV700 Pro to rough places, don't’ worry— the A103’s front panel is rated NEMA 4/IP65. 

  The CDV-700 Pro can be connected  either to a 900V Geiger Mueller tube or to a 900V or 1200V photomultiplier-based scintillation probe. The CDV-700 Pro has an internal preamplifier which makes it possible to detect low-amplitude pulses related to low-energy gamma interactions with the scintillation crystal.  The GM probe on front is a DT-106 with a LND5979 GM tube (got it from

  In my home-brew scintillation probe, a surplus 8” long x 2” dia NaI(Tl) crystal is coupled to a Photonis XP2102 photomultiplier tube. The PMT tube is wired following Charlie Thompson’s recommendations. The complete assembly is wrapped in optical-black cloth and placed inside a thick cardboard tube closed using PVC caps. CLICK HERE for Schematic [PDF], CLICK HERE [3MB PDF] for detailed instructions.

  My CDV700 Pro has a blinking LED next to the probe connector.  This indicator warns users against connecting a GM probe when the bias voltage is set at 1,200V.

  You will need a high-impedance probe to measure the voltage at the CDV700 Pro’s probe connector.  This 10X high-impedance probe is built with a string of 9 10MOhm resistors inside the body of a ballpoint pen. CLICK HERE for Charlie Thompson’s schematic.

The CD V-700 is not a “Geiger Counter” because it doesn’t count!  The CD V-700 uses an analog integration circuit to provide an estimate of the short term dose rate (mR/hr or more correctly, clicks per minute).  Self-contained counter and timer modules used for industrial machinery are now widely available.   My counter/scaler uses a Veeder-Root A103-000 Totalizer and an Eagle Signal A103-008 Preset Timer for counting, timing and scaling the clicks at the headphone output of any CD V-700.  This makes it possible to reliably measure even low-level radiation sources.  CLICK HERE for the schematic of this add-on for the CD V-700.

David Prutchi’s Digital Counter/Scaler for the CD V-700

David Honig’s free “CDV Counter” program turns a PC into a "scaler" for the CDV-700 Geiger Counter or other pulse-source. That is, it detects, counts, and logs pulses (clicks) in a PC's audio line input.  So with a cheap CDV-700 and any Win95 or later PC plus soundcard, you can integrate counts over any length of time.  This combination is capable of much finer low-rate measurements than the analog CDV-700 meter can provide. 



David Honig’s CD V-700 Digital Counter/Scaler PC Emulator

  CDV Counter displays total counts, Counts Per Minute (CPM), and milliRoentgens/hour (mR/hr) integrated over a user-selectable time period. By repeating measurements CDV Counter can graph activity over time. Measurements can be displayed over the Internet in a Web Browser. Cosmic rays can be detected by feeding 2 CDV700's into both audio channels.

© 2005 David Prutchi.  All rights reserved.

  My digital counter/scaler is shown connected to an unmodified ENi CD V-700 model 6b.  It can be connected to virtually any CD V-700. 

I don’t want to compromise the security of our country.  If you are a government agent (FBI, CIA, DEA, FDA, FAA, etc.) and find material in these pages that you find objectionable, please contact me so that I can rectify the situation.

Corner of Geiger and Oppenheimer.  Our summer address in Israel is simply inspiring!*