Neozap.com - Ex USSR DP-5B Geiger Counter Review

ДП -5В Счетчик Гейгера Oбзор
DP-5B Geiger Counter Review

See also:ID-1 Dosimeter Review

Origins
Specs
Box Contents
Geiger Counter
Probe
Batteries
Accessories
Reliability
Other Info
Summary

Origins
I bought this geiger counter from soviet army stuff. The first counter I bought came with a broken microammeter (the scale needle), but Soviet Army Stuff kindly shipped me a replacement free of charge. The Geiger counter cost roughly $75 USD.

Specs
More specs can be viewed at The Civil Defence Museum The Geiger counter has two tubes and can register from very low mR/h readings to 200 R/h. See this link for more details.

Box Contents
The DP-5B Geiger counter comes in a wooden box with metal corners for added strength.
DP5Bboxcontents
The box contains:

> One DP-5B Geiger counter
> Case
> Screwdrivers
> Spare bulbs (wrapped in cotton wool)
> Headphones (very clever design so that one could wear them with a helmet or fur hat)
> Telescopic probe holder
> Plastic probe covers
> Straps
> 12/24V external power supply cable.
> Manuals (with service history and circuit diagrams)

Geiger Counter

Geiger Counter
This version has a green plastic case, although sometimes the DP-5B is pictured with a faux wood case. The case is very solid, with plenty of waterproofing. The counter sits inside a plastic case that has a holder for the probe as well as spare batteries. Overall the design is simple – the pictures speak for themselves. Simple is good in military hardware as it reduces the chance of a break.

DP5B Scale
This is the scale removed from the device. It appears to be a semi log scale with a separate reading line for each GM tube in the counter. For example, if the Geiger counter was set on the 200 setting, then one would read the R/h from the bottom scale.

You can see the settings available on the counter, with the first position of the dial being ‘off’, the second position ‘battery test’, the third ‘200 R/h (bottom scale)’ and from then on multipliers for the top scale (mR/h).

The switch on the left is for two small light bulbs below the scale. These provide quite good illumination at night. Additionally, the scale and selector switch back plate glow in the dark and glow brightly for a few hours.

Probe
The probe is made of metal and is quite solid. It contains two glass GM tubes, so one should still be careful not to drop it. You can clip the telescopic handle into the back of the probe (so that you could assess fallout levels, especially beta radaiton) and so that you can keep distance from the radiation source. The probe also has a beta window that one can open to allow beta radiation in, or to block it off and register only gamma radiation. The bump on the side of the probe contains a beta source. Rotate the shield until the test source is over the beta window to test the dial/headphones (on my counter the test source reads 15 mR/h).

DP5B probe

I have read that the probe is waterproof, but one would do well to wrap it in plastic or latex rubber (use a glove or condom) to prevent accidental short circuits or rust.

Batteries
The batteries are a strange Russian design. All the device needs are three 1.5 volt batteries (one for the lamps and two for the counter). The current draw seems to be extremely low so it’s no big deal to use smaller batteries than the original Russian design. I use AA size batteries.

batteries
Because AA batteries are shorter and thinner than the original Russian ones, I created some tube adaptors for them. Simply get some piping that fits the batteries you want to use (I found some old stuff in the workshop) and increases their diameter, and a bolt to increase the length by about 7 mm. Then cut the shaft of the bolt & hot glue it into the tube, making sure that it articulates well with the battery and with contact.

DP5B battery adapter

Now all you have to do is slide your AA battery in an it will fit and work perfectly in the device. You can see that they are not pretty, but do fit perfectly and won’t fall out. Try not to get confused by the fact that it now looks like the battery has two positive terminals!
It is important not to bend the contacts, as you will be unable to fit the 12/24V external power plug into the device.

Accessories
The counter also comes with straps to hold it, a screwdriver and some headphones. You could make your own headphones – it is a very simple circuit with two holes for contacts.

Box base

Box back

Reliability
The units are fairly rock solid. Having two tubes is advantageous as there is some overlap between their ranges (if one was to break). If the microammeter was to break (which controls the scale) you would still be able to hear the radiation counts ‘clicks’ on the speakers. In this sense, the redundancy is good. Construction is solid, and I think the device would survive heavy rain and a bit of physical abuse without breaking. I am confident that they are a lot tougher than modern digital geiger counters.

In terms of accuracy, it is hard to know if the counters are still calibrated correctly. The scales that I have tested have been self referentially correct (that is, the same reading is obtained from the same test source repeatedly, and, is the same regardless of the multiplier setting) but it is unknown as to whether it detects, say, gamma radiation correctly. Hence, I would suggest either testing the device, or, using it to detect the presence but not the strength of radiation.

Other Info
The circuit inside is very simple and can be followed even without a workable knowledge of the Russian alphabet.

DP5B circuit

The components are simple and could probably be replaced if need be. The microammeter is solid, but if it breaks you will be unlikely to be able to replace it as:
10 microamp ammeters are very rare and expensive, and, the scale is designed for this ammeter only.

Summary
This device is cold war relic, but still has a functional use today. It is well worth the money and will stay operational for many more years. Components which may die are the capacitors (but this will take a little more time) and the transistors. The transistors are glass and would be very nearly impossible to replace as spares are hard to find.

For the price you can’t go wrong & at the worst it is an interesting museum piece. Highly recommended.