Runaway Click readings from R_Source

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geigerguate
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Joined: Sun Mar 09, 2014 11:10 am

Runaway Click readings from R_Source

Post by geigerguate »

I got my unit up and running with no trouble and set the proper voltage using a 1g resistor. The unit seems to detect my radioactive sources just fine, but if I leave the source near the counter for more than 20 seconds the clicks seems to continue to increase until the unit itself is left with a full alert squeal/ full red LED. When I remove the source the counter continues to whine full blast/full red LED until I shut off power. When I power it back on after about 5 seconds it continues to whine full blast with led shining brightly. If I remove the batteries it seems to reset itself and goes back to normal. It's kind of like a drifting resistor type reaction if that makes sense.
Is there an alert feature that sounds if there are too many counts? I tested with mutiple R-sources including radium, thorium, and uranium. Even my Vaseline glass will cause the unit to runaway. My primary geiger counter shows accurate readings for my sources so I'm not exactly sure what the issue is. Perhaps a bad sbm-20?

Thanks for the help!
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mightyohm
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Re: Runaway Click readings from R_Source

Post by mightyohm »

Hello,

It sounds like your tube is breaking down (avalanching). Try lowering the HV adjustment (VR1).
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