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 2.GQ Geiger Muller Counter
 SBM-20 vs M4011

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T O P I C    R E V I E W
and_kom Posted - 09/30/2012 : 01:47:05
Can anyone confirm that russian tube SMB-20 is more sensitive than m4011 tube?
8   L A T E S T    R E P L I E S    (Newest First)
ullix Posted - 05/26/2019 : 01:06:40
You find a comparison between an SBM20 and a M4011 here:,sbm20,m4011

My Conclusion:
Overall, the SBM20 has the same background as the M4011, but is 40+% more sensitive to counts as long as the source has a strong beta component. Whether the difference extends to gamma is not known and cannot be told with these experiments.

I think the installation of a SBM20 into a 300 housing, while possible, is not worth the hassle!
Franglish9265 Posted - 05/25/2019 : 10:46:05
I recently verified that the SBM-20 outperforms the M4111 tube. I read 500 cpm from my vaseline glass cat paperweight, with an SBM-20 tube, but only got 370 to 400 cpm from the M4111 tube, under the same conditions.
Nudnik Posted - 05/21/2015 : 02:40:56
Originally posted by ska

The real problem is find a good sbm-20 tube, It's really tricky.

GM tubes are not degrading by age. A 50 year old but unused russian tube will still work as specified. You probably need to remove corrosion from the contacts, depends on the storage conditions.

GM tubes degrade by detecting.
and_kom Posted - 10/06/2012 : 08:48:19
I am from Ukraine (ex. USSR) and it's not a big problem to find SBM-20 there. It costs 10-15$ in average there...
I've got one today. First tests showed it seems to be ok.
ska Posted - 10/03/2012 : 05:16:55
The real problem is find a good sbm-20 tube, It's really tricky.
and_kom Posted - 10/03/2012 : 02:26:52
Found some tubes info:


SBM-20 - The quintessential Russian tube. Lower priced, and more sensitive to beta and gamma than most. This is still one of my favorite all around beta gamma tubes. The STS-5 is pretty much the same tube and may be cheaper.
M4011 - Glass tube made (new) in China. Claimed to be more sensitive than the SBM-20. Although I once got high readings, it now seems similar to the SMB-20. I'm not overly impressed - especially at it's price. IMO the claims for it's sensitivity are exaggerated.

The comparision shows that SBM-20 is slightly sensitive than m4011.


Initially, the M4011 appeared to be more sensitive than the SBM-20. However, I couldn't repeat this result. I'm not sure what happened - something with the tube? To rule out any change in the counter, I simply changed tubes to the SBM-20 and repeated the SBM-20 test, which was consistent with the previous results. I have no choice but to revise my previous results with what are now more consistent readings. The tubes operating range is 380-450V, and I ran the tube at 450V for the test above. (In the dark, you can see a faint orange glow inside the tube when it's firing.)

ZLM Posted - 10/02/2012 : 22:05:41
Both SMB-20 and M4011 are in same sensitivity range.
ska Posted - 09/30/2012 : 06:55:20
According to my tests, SBM-20 is actually more sensitive in slightly radioactive object, but I'm still looking into. I'm searching for more slightly radioactive objects.

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