Description: Czechoslovak army radiation indicator.
Manufacturer: TESLA or Czechoslovak army
Made in year(s): late 50s-early 60s; 1962 was my model
Country of origin: Czechoslovakia
Status: Not available
The Indikátor beta-gama, tranzistorový, IBG-58-T (“Beta-gamma indicator, transistorized, IBG-58-T”) is an army radioactivity indicator used in the former Czechoslovak People’s Army (ČSLA). This was a primitive Geiger counter with just optical and acoustic indication, i.e. with no metering device equipped. It has been designed to be worn on the neck of a soldier, with a pushbutton momentarily turning the machine on, indicating and checking for unsafe radiation intensity levels (0.1-1 R/h). I have got it back in 2009 for a price of 10 EUR including shipping; it was one of my first items that I’ve bought through an auction.
As you can see, the circuit is pretty straightforward. The inverter runs from a single 1.5 volt D cell and there’s a single germanium NPN switching a transformer (flyback topology), again very similar to my 380V circuit tester. The small iron-cored transformer’s secondary gave circa 130V~ at a few hundred Hz, 150-300Hz if I remember correctly. This went through a voltage multiplier, which gave 400 volts on the output. Just a note, the two diodes in the schematic were actually 500 volt 2 mA selenium rectifiers; something considered new at that time.
Before going to the Geiger tube, a special glow lamp, called a corona stabiliser at that time, was used to limit the maximum voltage to approx. 440 volts. The Geiger-Müller tube (a Soviet STS-5, the predecessor of SBM-20) went through a series of calibration resistors, which changed the amplitude of the final signal. This signal charged the capacitor across the second glow lamp, which was used for indication purposes; when it was charged with enough voltage for the second glow lamp to strike momentarily, a loud pulse was heard in the headphones. And that’s it…
In fact, this meter did not indicate every pulse from the Geiger-Müller tube. The few-megohm calibration resistors were pre-set so that the final glow lamp would blink randomly at radiation levels above 0.1 up to 0.5 R/h. Above 0.5-1 R/h, the blinking should change into a permanent shine, and the occasional audible “ticks” to static.
Accessories included were the meter itself, an instruction manual/log book, some neck straps, a battery compartment “screwdriver” and last but not least – 4000 ohm high impedance headphones for acoustic indication, dating back to either WWII or early 1950s…
This device sure is rare nowadays, since it has been completely phased out of service in the mid 60s. But I did not want a cool army-green paperweight, so I did some hacks to convert it to a normal Geiger counter, which would indicate every single pulse with proper piezo-speaker and LED indication. It was a success (check the video), but the exterior did not look very well. Finally, I have got a hold on better army Geigers and in the end I have even made my own Geiger counter, too.