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Common Table of Geiger-Müller tubes

You can edit this page of the wiki without login to add or update the table. Just use the edit button at the top of the menu on the left.

This wiki page should serve as a common place where we can note/compare/discuss our reference conversion settings to have a more reliable data basis for our calculations and equivalencies.


Name Type A/B/G Voltage R10a Conversion Factor Compatible Notes
LND 712 Tube A/B/G 500V ? 0.00233? - -

Frieseke & Hoepfner

Name Type A/B/G Voltage R10a Conversion Factor Compatible Notes
FHZ 76V Tube -/B/G 500V ? 0.000233? Philips/VALVO 18550 1r/h
FHZ 74 Tube -/B/G 500V ? 0.00233? - 50r/h
SBM-20 0.00277
SI-180G 0.00321


2016/12/28 14:50


what do I get with the above conversion factor * count → mSv?

Do I subtract the dead time per count from the measurement time?

Can you show the calc of counts to the usual representation nSv / h?

I have the FHZ 76V tube ;-)

Grüße aus Landshut


2016/12/28 18:10

Yeah, I don't know why, but there is very little actual/credible information about it out there on the net. We've tried to collect and verify what we could and came up with convert-cpm-to-usv-h. In tests, comparing with other counters at LDR, the equivalency results were pretty much the same.

uSv/h seems to be the base for most formulas in use out there, so we've simply adopted it; other magnitudes derive from there.

When in doubt - use the source, luke:

(edr = equivalent dose rate)

Any updates, corrections and more insight are always welcome.

2016/12/31 00:19

Hi Chrono, I find a verified measuring station from “Bundesamt für Strahlenschutz” right in my area. The factor is one shift diffrent –> to µSv/h x 0.000233 or nSv/h - x 0.233 ralphi

2017/09/10 06:32

Ah, totally missed that, which tube was that?

2017/09/07 12:37


is there a known value for R10a for the sbm20 tube? I don't have access to a gigaohm resistor right now, and thought that someone maybe knows the value. Also, do I always need an additional resistor on the anode of the tube? I am somewhat confused…

Thanks for this great resource,


2017/09/10 06:28

Hey Timo,

so far, no R10a value for a certain tube has bubbled up to my knowledge. It was just implemented to accommodate for future, larger productions, where a specific known working board/tube configuration could be replicated easily. If I ever find the time, I can try to measure the values of the trimmers for my tubes as an indication.

If you're in trouble setting the HV, you can also work slowly and work by ear. So far all of my modules were emitting a certain switching “feep” when they were in working voltage range and it stops completely when you're “overdoing” it and voltage breaks down. Having a test source nearby would be the other option to dial it in.

As for anode resistors: I haven't tried without it yet.

2017/09/11 12:18

Hej Chrono,

Thanks for your answer.

I was thinking about eyeballing it, but I was super worried about “blowing up” and damaging one of the tubes. How big is the danger of doing that?

I´m planning to use either an SBM20 or the SI1G, because I have a specimen of each.

Concerning R3: It should be possible to add another one of those 4.7mΩ smd resis in series to R3 to get closer to the 10mΩ anode resistor, right?

Thanks again for you help,


2017/09/11 13:01

I wouldn't worry too much about it, so far they've been pretty robust and even cranking up to the trimmer's limit had no effect on the tubes. At some point the HV just collapses. Also, if you don't want to get a gig-ohm resi, you can always hack around by taking a couple of the highest value resistors you can find at hand, and put them in series. It'll not be precise, but I think I left a calculation example in the hardware section to get a ballpark figure.

Have a look at:

PiGI in long-term test harness on the Bench (all the wires are just for testing:)

You can see that, additionally to R3 on the board, there is a TH resistor connecting the anode to the pad. You want that resistor to be as close to the anode as possible. I've no personal experience with your tube types, so your mileage may vary.

Is that a personal/hobby project or are you doing something university related with it?

2017/09/13 15:49

Ok, that makes me a little more relaxed, thanks. Is it okay if the gigaohm-resistor is only a 0,25w one? I would be able to get one of those relatively cheap.

This is for a uni-project, I want to use the PiGi as an entropy source for an electronics project. Also somewhat of a hobby-ish project, for I am just interested ;)

Thanks for your help, Timo

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