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 2.GQ Geiger Muller Counter
 Problem (deteriorating?) M4011 in a new GMC 500+
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Lutz123456

Canada
5 Posts

Posted - 05/29/2021 :  11:18:29  Show Profile  Reply with Quote
Hi, I just got a new GMC 500+ and after setting up WiFi and connecting it to the GMCMap.com, I noticed that over 12 hours the background was slowly creeping up from 15 to 30 CPM. The default firmware setting suggests 410V on tube 1 (likely the nominal middle of the plateau of the M4011). One day later I noticed >2000 CPM as background! This can only happen as a somewhat triggered self-discharge in the tube. So I lowered the tube voltage to about 360V (36.67%) and I got my 15CPM background back and it seems okay for now. The ACPM still creeps up but to a much lesser degree. I also found the voltage when "strikes" are starting to occur at around 320V (according to the firmware, never really measured it - which I will do soon). So, now I am wondering if I got a bad or prematurely deteriorating M4011 tube? How can I tell. My useful plateau range seems to be now from 320-380V - after that the tube just seems to start self-discharging on the first "strike" it gets. Does anyone have any idea or perhaps knows how fast GM tubes can deteriorate like that? It could also be that the voltage readout of the firmware (2.25) is bogus. Can a GM tube actually get damaged when using a too high voltage, despite the fact that there is a ~10MOhm in series? Also, does anyone know where one could get this black M4011 tube? I checked AliExpress and Ebay - but only the transparent ones seem to be available.

Any help is appreciated, thanks in advance!

Thanks !!
Reply #1

EmfDev

1438 Posts

Posted - 06/01/2021 :  12:34:00  Show Profile  Reply with Quote
Hi Lutz123456,

It is possible that the tube voltage has drifted. Can you please turn on the Tube 1 and 2 CPM display under Main Menu -> Init setup -> Tube Settigngs -> Tube 1,2 CPM Display. This is to check it is not tube 2 that is increasing in CPM. If lowering down the voltage work, then it is the voltage that is drifted.

For now we have stock of the black M4011 tube. You can order by contacting support@gqelectronicsllc.com
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Reply #2

Lutz123456

Canada
5 Posts

Posted - 06/02/2021 :  14:16:42  Show Profile  Reply with Quote
Thank you for the reply. I always had tube 1 and 2 display on. The tube 2 merely causes any counts, maybe 1-5CPM. Its clearly not causing the increase. I'll attach a screen shot of how I have set it it up running for 4 days now with 359V on the display. If I make it to 395V little less than nominal, it goes into >140000 CPM (see picture). To take this last photo which took like 30s and going back to 359V it does not turn back to 15CPM but 35CPM. There is definitely something wrong with the M4011 and it goes worse...



Thanks !!

Edited by - Lutz123456 on 06/02/2021 16:12:40
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Reply #3

Lutz123456

Canada
5 Posts

Posted - 06/02/2021 :  14:23:56  Show Profile  Reply with Quote
Trying again to post the pictures...




hope it works this time. I will contact your support.
Thanks again
Lutz
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