Greetings fellow radiation nerds!
Recently I managed to acquire an old, vintage, Polish Geiger counter from the early 70s, the DP 66M. What makes them a very interesting is the fact that they can measure anything from background to extremely high levels of radiation and they are really affordable costing as low as 50 euros/bucks on the used market!
My first impressions.
I got my unit from a warehouse, this meant it was stored in really bad condition. When it arrived, I had to clean it few times in order to get the dust off and remove unbearable smell of mould. If that wasn’t enough, batteries that were inside of this unit have leaked into battery compartment resulting in me not being able to remove the batteries! Luckily these units are fairly simple to disassemble and I managed to remove old battery compartment with a help of a hammer and replace it with a new one that I have build myself from a PVC pipe. Finally I managed to fire this guy up and luckily the unit was working fine, however calibration was way off, so I had to calibrate it. This Geiger counter uses military version of the same tube that is inside my Terra-P Geiger. This meant that I had a relatively good reference point for calibration. I used samples of pitchblende and uranium glaze from my collection in order to calibrate the unit (please note, this is not “professional” way to calibrate Geiger counter, but for the home use, I think it is more than enough). After cleaning, repairing and modifying my DP 66M, it was finally in a working condition and I could start measuring stuff with it.
How does DP 66M perform?
Despite being old unit from the 1970s, DP 66M still holds it ground and pushes modern digital Geiger counters to the test. There are 8 positions on the rotary switch. I did find it confusing at first so I made a table for you guys on how to read the measurements correctly.
W= Device is off
K = Battery check (needle should be reaching red K on the meter, if it is not, you need to change batteries)
200 R/h = use scale on the meter that goes up to 200. This is your reading in R/h
5 R/h = Multiply your reading from the 0-5 scale on the meter by 1. This is your reading in R/h
0,5 R/h = Divide your reading from the 0-5 scale on the meter by 10. This is your reading in R/h
50 mR/h = Multiply your reading from the 0-5 scale on the meter by 10. This is your reading in mR/h
5 mR/h = Multiply your reading from the 0-5 scale on the meter by 1. This is your reading in mR/h
0,5 mR/h = Divide your reading from the 0-5 scale on the meter by 10. This is your reading in mR/h
Now if you are little bit up to date you probably know that mili Roentgens are no longer used and have been replaced by Sieverts. Luckily it is relatively easy to convert mR to uSv, 10uSv is around 1mR. Here a table with the readings but in Sieverts
200 R/h = use scale on the meter that goes up to 200 and multiply you reading by 10. This is your reading in mS/h
5 R/h = Multiply your reading from the 0-5 scale on the meter by 10. This is your reading in mS/h
0,5 R/h = Multiply your reading from the 0-5 scale on the meter by 1. This is your reading in mS/h
50 mR/h = Multiply your reading from the 0-5 scale on the meter by 100. This is your reading in uSV/h5 = Multiply your reading from the 0-5 scale on the meter by 10. This is your reading in uSv/h
0,5 mR/h = Multiply your reading from the 0-5 scale on the meter by 1. This is your reading in uSv/h
The range on the unit is very impressive, from 0mR/h to 200R/h (0 – 2 Sv/h). This means you will most probably never run into 3,6 Roentgen situation. There are two other switches on the unit. The one on the left side with “KAS” written above it is used to reset measurement/zero the meter. This is helpful when you are measuring different samples and you don’t want to wait for the needle on the meter to drop down. Second one with OŚW. written above it, turns on a small lamp that allows you to see the measurement during the night or when there is little to no light.
The meter on the DP 66M is made out of glow in the dark material which makes reading the measurement in the dark easy. Unfortunately, due to the age of the geiger the glow does not last long so I would not rely on it.
Bonus feature of the DP 66M is its ability of charging (zeroing) DKP-50 personal dosimeter. To do that simple unscrew cap and insert DKP-50 dosimeter, then use potentiometer to “zero” reading on the dosimeter.
Different DP 66 models.
Let’s start with the most basic version, the DP 66. The main differences between DP 66 and DP 66M are different external probe designs (they are still identical on the inside) and better quality components on the M (military) model. Also the DP66 measures in mili roentgens, roentgens and in CPM (0 – 1 000 000 CPM) while DP66M measures in mili roentgens and roentgens. Third variation is the DP66M1. It is identical to the DP66M except that the DP66M1 can be powered by an included power cable without needing adapter like the other models.
What to look for when buying DP 66M?
If you are considering buying DP 66M (or any other model from DP66 family), make sure you got some basic DIY skills and you are capable of doing some minor repairs. It would also be good idea to get in contact with a seller before buying and making sure that there was no battery leakage (like in my case) or any other problems with the unit in the past. Most units had their Strontium-90 check sources removed when they were decommissioned from military use, however some units can still have them. If you find one that has it, lucky you! In terms of price you can find them in “unknown condition” for as low as 30 euro/dollars on European used market. If the unit is in good working condition the prices might be higher, ranging from 40 to 70 euros/dollars (in states, prices can be higher). Anything above that I would consider a rip off unless it’s made out of gold.
If you are in the market for a Geiger counter that won’t break the bank and has Cold War vibe, I would highly recommend the getting DP 66M as long as you got some basic DIY skills just in case if the unit needs few mods or repairs. I hope you enjoyed this review of the DP 66M Geiger counter. If yes please feel free to subscribe to my blog and let me know in the comment section what is your your experience with Cold War Geiger counters!