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skydiverman
USA
17 Posts |
 Posted - 08/22/2025 : 11:20:08
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I have an older GMC 500+ (v2) and then also a newer circa 2023 500+ - just realized the high range tube on the newer one isnt a SI3BG or a tube at all, its a daughterboard with shrinkwrap on it.
while I can try to believe that its some kind of high range counter, all the details I have on what the right multiplier for the SI3BG are therefore inapplicable. for the older one i'm using the 2.024 which aligns generally with the 2.08 geigerlog uses and not the 5. something GMC uses. but what about this new thing - surely it cant also be exactly 2.0x? I saw a thread about this from years back but never conclusion.
thanks!
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| Reply #1
skydiverman
USA
17 Posts |
Posted - 08/22/2025 : 11:22:46
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| Follow up Q - i suppose i'm making an assumption that the primary tube is a M4011 still - is that even true? |
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| Reply #2
Kaninbjerget
Denmark
28 Posts |
Posted - 08/26/2025 : 08:56:24
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Interesting. Either a PIN detector (semiconductor) or a scintillator...
Semiconductors are not that sensitive so they might be a good candicate for a high range detector. |
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| Reply #3
Kaninbjerget
Denmark
28 Posts |
Posted - 08/26/2025 : 11:26:58
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Now I look closer.. It seems all components are there for the 2nd high voltage supply. The board is also connected to where tube larger Russian tube would be. And I really think Russian is the keyword here. Using a newly sourced is naturally out of the question for the time being.
Which leads me to think it can be small chinese tube such as J707 which looking at the shrink wrap doesn't seem that implausible. The daughter board is then simply an easy way of avoiding to have to redesign the board to accomodate yet another tube - or to use the boards in stock and just make the relatively small change in the next batches - why throw out good boards when it's easy to fit alternative avilable tube? I'm not aware that J707 should be UV sensitive but shrink wrapping it could be an easy way of stabilizing it - just like the larger is stripped down. Such choices are quite common in the manufacturing industry - seemingly identical products differ more than what appear at first. Some times it's because of cost reduction - other times because of availability of components. Whether the new tube is better... Well if it's less sensitive then it should be able to go higher - and at those high values where the small tube come into play ultimate accuracy doesn't matter that much in deciding how fast you need to get out of somewhere.
The reason for the (unshrunk) shrinkwrap on the larger tube is simply because black painted tubes doesn't seem to be made anymore and to mitigate the UV sensivity... I like to have spare parts of a few crucial parts - such as tubes - in my prepping inventory. Also one day you might drop a geiger and instead of waiting a month for a tube to arrive you simple swap it and order a new one.
As for the default values.. Just look in the settings. If you've messed with them a simple factory reset should bring them back. |
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| Reply #4
ullix
Germany
1214 Posts |
Posted - 08/26/2025 : 23:16:58
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The second, black-wrapped tube is possibly a J707. If so, you find more details in the GeigerLog manual, in chapter "Appendix K – Tubes".
https://sourceforge.net/projects/geigerlog/
One cannot say with certainty, as GQ tends to change tubes without telling.
This also applies to the first tube, which is supposed to be a M4011, but could be any other cheap glass tube, which fits into the holder (even if barely so). As example, a J305 had been found in lieu of the expected M4011, which had been stated as tube in the specifications.
More data on tubes in my article GeigerLog-Calibration Guidance.
https://sourceforge.net/projects/geigerlog/files/Articles/GeigerLog-Calibration%20Guidance-v1.5.0.pdf/download
And even more in folder "Supporting documents"
https://sourceforge.net/projects/geigerlog/files/Supporting%20Documents/
I have no idea what its sensitivity is, but it is largely irrelevant anyway :-). GeigerLog uses its default of 2.08 CPM/(uSv/h) for all "2nd tubes".
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Edited by - ullix on 08/26/2025 23:27:32 |
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GMC500+ new tube - what multiplier
