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Wednesday, September 5, 2012

DRSB-88 review

The russian DRSB-88 Geiger counter is maybe the cheapest Geiger counter you can afford. I received my unit just for under 20 euros including shipping from annakozub seller on ebay. It is a very small unit, only 13 x 3.5 x 3 cm, very lightweight and fits perfectly in your pocket. It's perfect as a first Geiger counter.

How it works?

The DRSB-88 Geiger is a classic detector based around a Geiger tube sensible to betas and gammas. Every time the tube detects a beta particle or gamma photon, the DRSB-88 sounds a click and a red neon bulb flash in red. It only has a on/off button so its usage is straightforward.

In practice

This small Geiger counter works nicely. I have carry it in my pocket for many months and it works nicely monitoring background radiation. Its clicking sound is very discrete but perfectly audible. I have carried it in my T-Shirt pocket and nobody detected its presence. Its small size tube do not gives too much background counts, around 2-3 CPM here where I live so it is very easy to check for radioactive objects, because you will detect soon the count increase. Just put them near the bottom of the counter, at the plastic window and listen. In this way I found my first radioactive object in my house: An old radium watch.

The sensible area in the DRSB-88. The Geiger tube is located just here

But my DRSB-88 died monitoring that watch. One day I put it near the watch and a few seconds later, it stopped to make sounds. Of course I replaced the battery, but it didn't come to life again. I opened the case just to check if can be repaired and I found this:


Inside the DRSB-88 case

Its construction reminds me to some radios in the 70s. There are three transistors all marked in russian and they all seems to be PNP types. There is also great amounts of wax over the circuit to prevent arcing. I thought I had bad luck with my unit, but some days later, I repeated the experience with the DRSB-88 from Alberto, EB4GLF. The same Geiger counter, the same radium watch and the same result: Another dead Geiger counter, but this time with another symptom: A fuzzy sound in the speaker and a constant turned on neon bulb.

I must admit I have not spent too much time in repair my DRSB-88 unit. All symptoms seems to indicate the oscillator in the DC-DC converter is too lazy to oscillate or even unstable, so there is no high voltage at the Geiger tube.


 DRSB-88 Geiger tube in detail (SBM-21). Grid square is 5mm in size.


I will try to repair it some day in the future. Maybe the first step is to try to get the electrical schematics from the PCB. It seems not to be very difficult, but it is a time consuming task. Another problem is the ferrite transformer. It has multiple wires and they are very delicate. Wax is another problem to get the schematics, I need to remove it to get all the traces and components... If I get success getting the schematics, I'll publish it here.

Finally

The fact that two units have die near an old radium watch, that showed around 120 counts per minute (around two per second, measured before failure) makes me think something is wrong with the DRSB-88 design. Maybe some component is working beyond its stress limits and died under high counting rates or simply the manufacturing quality is low and one must not to expect too much from it.

Nevertheless it is a nice device and I'll try to repair, or even improve. I only give you one recommendation if you own a DRSB-88 Geiger counter: Look for a moderated radioactive sample just to check your unit is still working fine, but do not abuse from it, or you can kill your unit.

2 comments:

  1. That geiger counter type is SBM-21 (SBM-10 has little higher length, and higher sensitivity - 9,6...10,8 vs. 7...8 pulse/uR)/

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    1. Yes, you are right! SBM-10's main body is 20mm long, and SBM-21 is only 16mm, almost the same size you can see in the photo. I'll edit the article.

      Thank you!

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