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 2.GQ Geiger Muller Counter
 GMC-080 high cpm		  New Topic  Reply to Topic
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boz123

USA
2 Posts
Posted - 04/12/2013 :  18:21:24  Show Profile  Reply with Quote
Im having a problem with high cpm of 350-400 cpm when my area is about 47 cpm. I put in a russian geiger muller tube SI-3bg Nos I also had to desolder and move the clamps closer together to fit the tube I then installed jumpers from the original clamp positions to the new clamps. I also need to know where to check the tube voltage...across the tube or somewhere else...
Reply #1

ZLM

1261 Posts
Posted - 04/12/2013 :  19:26:27  Show Profile  Reply with Quote
350-400 CPM is not a correct value. I think it is related to the tube or the voltage not matching your tube specification.

If you have a 10-11M ohm internal resistance multimeter, then you can use 1000V range to check the voltage between the tube. For the 380-500V voltage, the actual on you meter should be 160-220V.

To get exact voltage, you need to serial a 1G ohm resistor on you probe and then do the math calculation.
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Reply #2

boz123

USA
2 Posts
Posted - 04/12/2013 :  20:02:51  Show Profile  Reply with Quote
Thanks ZLM for your answer Im a nooby to electronics when I first installed the tube the cpm was nonstop I turned down the voltage pod all the way and now im measuring 200volts and getting 350-400 cpm. do I need a different tube? do you know which tube I need? they said most tubes would work figures Id get the wrong one....thanks fo any help you can give me.
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Reply #3

ZLM

1261 Posts
Posted - 04/13/2013 :  08:01:42  Show Profile  Reply with Quote
The fully tested tube is M4011. Otheres may work too as long as you adjust the voltage to the tube requirement. Too high voltage will damage the tube.

If you use M4011, then you need set the voltage on 170-180V if you measured the voltage directly from a 11M multimeter on tube two sides.
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Reply #4

Frank

USA
39 Posts
Posted - 10/10/2013 :  15:48:04  Show Profile  Reply with Quote
Is this with the tube installed and powered up, measuring across the tube ends?
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Reply #5

ZLM

1261 Posts
Posted - 10/12/2013 :  14:44:34  Show Profile  Reply with Quote
yes.
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