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mmc
United Kingdom
8 Posts |
 Posted - 03/21/2012 : 10:28:12
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I have a GMC-200, brand new and unmodified in any way. Switching on the unit works fine and it detects background radiation normally.
I obtained a gas mantle saturated in Thorium to test the counter, its about 1.35uSv/h.
When the sample is placed on top of the GMC-200, the clicks become more frequent as expected. Anywhere between 60 seconds to 5 minutes may go by, then suddenly the light will stay on and the speaker will produce static like an AM radio.
Do I have a defective tube? |
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| Reply #1
ZLM
1261 Posts |
Posted - 03/21/2012 : 11:17:20
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I think that is normal as long as it stops after you removed the radiation source.
If the sound does not go away after you remove the source, check the tube voltage with your multimeter. Just in case the voltage is off. With a good multi meter 1000V range, direct measure the two tube-ends shoule be about 210V. |
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| Reply #2
mmc
United Kingdom
8 Posts |
Posted - 03/21/2012 : 11:19:38
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| Its not stopping when the radiation source is removed. I will check the voltage now. |
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| Reply #3
mmc
United Kingdom
8 Posts |
Posted - 03/21/2012 : 11:31:55
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Well, this is interesting. I got a reading of 88V. The potentiometer full range is 28V - 110V. Nowhere near the 210V you suggest. Was this an error?
I am getting the same issue with the voltage up high. I also noticed an orange glow along the length of the wire inside the tube when this happens. |
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| Reply #4
mmc
United Kingdom
8 Posts |
Posted - 03/21/2012 : 12:09:21
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I pulled out the tube and reinserted it, it seems to be working fine now. I will test it for a while and see if the issue reappears.
I think the tube was inserted the wrong way round, but I'm not 100% certain. |
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| Reply #5
ZLM
1261 Posts |
Posted - 03/21/2012 : 15:03:39
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Your voltage meter is not good enough to measure the high voltage. A standard multi meter is 11M ohm resistance. But you one seems too low. You need a higher grade multi-meter to measure the Geiger Counter Tube voltage.
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| Reply #6
mmc
United Kingdom
8 Posts |
Posted - 03/22/2012 : 03:29:02
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| Its a cheap multimeter, so I'm not surprised. It seems to be working fine this morning, so I will keep testing it over the next few days and see if the original problem returns. |
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GMC-200 - Constant Light and Static Noise
