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 2.GQ Geiger Muller Counter
 Voltage adjustment GMC-300+ V7 board		  New Topic  Reply to Topic
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vikisonline

Canada
3 Posts
Posted - 06/27/2019 :  17:25:56  Show Profile  Reply with Quote
I have a GMC-300+ and it says V7 on the board inside.

I bought this with the hopes of using other tubes in it,
but it seems like there is no pot to adjust the voltage any more?

Is there a way to still change the voltage by soldering resistors maybe?
I was hoping to put an SBT-9 in it or maybe some LNDs (though LNDs require much much higher voltages)
Reply #1

Geo-Johnny

Austria
161 Posts
Posted - 06/28/2019 :  05:37:58  Show Profile  Reply with Quote
quote:
Originally posted by vikisonline

I have a GMC-300+ and it says V7 on the board inside.

I bought this with the hopes of using other tubes in it,
but it seems like there is no pot to adjust the voltage any more?

Is there a way to still change the voltage by soldering resistors maybe?
I was hoping to put an SBT-9 in it ...


Exactly this problem I have with a GMC 320 + V5. On the board is also V7 and no potentiometer for the high voltage. It would also be interesting for me how you could realize the conversion to a SBT-9 counter tube? Pictures would be very nice too?
Geiger Counters: GMC320+V5 & GMC500+
Geiger Tubes: M4011; SI-3BG; SBT-9; LND712; SBM-20
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Reply #2

vikisonline

Canada
3 Posts
Posted - 06/28/2019 :  07:18:25  Show Profile  Reply with Quote
I chose the sbt-9 because its voltage requirement is very close to the original m4011. I'll let you know if it works with no modification, I should have it in a week or so.

But ideally I should be able to adjust the voltage :(. All the older models had this capability, not sure why it was removed.

Without that sbt-9 might work, same for the 20 tube. but the better lnds will never work at these low voltage.
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Reply #3

Geo-Johnny

Austria
161 Posts
Posted - 06/28/2019 :  08:23:22  Show Profile  Reply with Quote
Thank you. We will look forward. Maybe there is another user who has already realized the conversion from the M4011 to the SBT-9 tube.
Geiger Counters: GMC320+V5 & GMC500+
Geiger Tubes: M4011; SI-3BG; SBT-9; LND712; SBM-20
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Reply #4

EmfDev

2250 Posts
Posted - 06/28/2019 :  12:01:05  Show Profile  Reply with Quote
On the new hardware unfortunately there's no way to adjust the voltage anymore. Our engineer said that this new hardware is more reliable than the old.
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Reply #5

Geo-Johnny

Austria
161 Posts
Posted - 06/28/2019 :  12:15:18  Show Profile  Reply with Quote
I am confident that we will find a simple hardware solution to match another counter tube such as the SBT-9. Good things take time.
Geiger Counters: GMC320+V5 & GMC500+
Geiger Tubes: M4011; SI-3BG; SBT-9; LND712; SBM-20
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