Nuclear Radiation

Science Summaries

Here is a photo of the Civil Defense Victoreen CD V-700 Geiger Counter that I purchased on eBay. This device detects gamma and beta radiation.

The top of the Model CD V-700, Model 6B, is shown for identification purposes. The schematic is a JPEG, so you can download it, and print it out.

1. Nuclear Radiation Detection Summary - for general information
2. Geiger Counters Summary - for descriptions and pricing
3. Geiger Counter Data Compared - for sensitivity comparisons
4. Ludlum Radiation Product Summary - detection devices and probes
5. Victoreen CDV-700 6B Detector Summary - True Geiger Counter (antique)
          1. CD V-700 Photograph
          2. CD V-700 Schematic
          3. CD V-700 PC Board Photo
          4. CD V-700 Ion Chamber Survey Meter Evolution
6. Victoreen CDV-715 1A Detector Summary - Ion chamber detector (antique)
7. Victoreen CD V-750 5B Dosimeter Charger - Charges CD quartz dosimeters
8. Uranium Ore Summary - common types of radioactive ore

This is the 6A schematic that was in the bottom of the unit. It is incorrect. These units have been banging around for over 40 years. Many bottoms have been switched around, due to battery corrosion in the lower case. My Geiger Counter is a 6B, and the schematic on the bottom is a 6A. When I was tracing the circuit, this drove me nuts, until I figured out what had happened. The annoying schematics do not give the Model #. This is a horrendous oversight in the documentation world. But then, the manufacturer never figured that the bottoms from 4 other types of radiation detectors would be switched around like crazy, over a 45 year period.

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This 6B is the correct schematic for my unit. Note the circuit changes from the Model 6A.

The unit was DOA. Step 1 was to pull the PC board, and start checking things. Rather than take the time to make a tedious drawing, I simply took a photo, so it is easy to re-solder the wires back afterwards.

I spent 10 years as an electronics technician, and 20 more as a semiconductor engineer. Many problems can be found simply by visual inspection, if you know what to look for, and this case was no exception. I measured the two diode junctions of the 2 transistors in the unit, and they looked fine. But close inspection revealed that the leads of the transistors were NOT SOLDERABLE when the unit was made. Four of the 6 transistor leads were tarnished beyond belief, WHEN INSTALLED, 44 years ago. The result was that over time, the lousy solder joints ceased being electrically connected. Not only can the tarnished leads be seen by inspection, but the solder did not form a proper fillet. The solder did not "wick-up" the leads, resulting in an extremely poor solder joint. Historically (1960's), some transistor leads were NEVER properly plated with an easily solderable alloy, and many were plated with nickel, which hates to be soldered.

For proper soldering, the leads of a device must be "tinned". That means that they have had a shiny coat of solder applied to the surface, BEFORE any attempt is made to solder them into a circuit. This was certainly not done here. My solution was to remove the transistors, and score the leads by squeezing and pulling on them with a small pair of serrated long nose pliers, until you see bare metal. Then tin the leads, and reinstall. Worked like a champ.

This must be done carefully, as the transistor pads are too small, and the holes are way too big. Use a perfectly tinned soldering iron, and retract it quickly after the melt, or the traces will lift right up. I'm an expert at this stuff, and two pads lifted off the board anyway - I must be losing my touch.

WHAT'S the point? The point is that there are many thousands of units out there, which were probably assembled with the same "un-solderable lead" transistors. Not to mention the "piling on" of excess solder, which masks the poor connections underneath. I removed a lot of solder from various joints with a "solder-sucker", so I could inspect the underlying wires.

My next move was to install a piezoelectric transducer from Radio Shack, so I could listen to the clicks. I removed the obsolete headphone connector, added two drops of super glue, and 2 solder joints, and I had sound! Pretty cool.

Here is a summary of Model Numbers, with corresponding dates of production. Anton, Chatham, Electro-Neutronics, International Pump, Lionel, Nuclear Measurements, and Universal Atomics GM units are included.

Note

1955

Nuc. Meas.

2-1.5V, 3-45V

Detects gamma and beta radiation

Typical eBay Price "As Is" = $25
Typical eBay Price "Working" = $50


"As Is" means "Probably is Bad"
"Working" means the device currently detects radiation. Some people say the device is "working" if the meter works. This is NOT an accurate description.

All models from Model 5 forward utilize the #6993 GM tube in the probe. The Electro-Neutronics Model 6b is considered the best of the bunch, physically. They (ENi) are used to create the LENI Geiger Counter, a custom, enhanced unit which can be purchased on eBay.

Victoreen

2-1.5V, 3-45V

Int. Pump

2-1.5V, 3-45V

Chatham

2-1.5V, 3-45V

Univ. Atom.

5-1.5V

Anton

5-1.5V

Anton

5-1.5V

Victoreen

4-1.5V

Victoreen

4-1.5V

Victoreen

4-1.5V

Lionel

2-1.5V

Elec. Neut.

4-1.5V

100

40

50

100

120

300-710

Information provided by Oak Ridge Associated Universities

Although the author has tried to be as accurate as possible, errors are possible.

I could not find the information shown above. So, I made this CDV-700 Geiger Counter radiation detector schematic web page, to help myself understand the technology, and to fix my broken unit. I hope that it helps you.

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