GQ Electronics Technical Support Forum Active Users: / Visits Today:
Highest Active Users:
GQ Electronics Technical Support Forum
Home | Profile | Register | Active Topics | Members | Search | FAQ
Username:
Password:
Save Password
Forgot your Password?

 All Forums
 GQ Electronics Forums
 2.GQ Geiger Muller Counter
 GMC-500+ High CPM - Dead tube?

Note: You must be registered in order to post a reply.
To register, click here. Registration is FREE!

Screensize:
UserName:
Password:
Format Mode:
Format: BoldItalicizedUnderlineStrikethrough Align LeftCenteredAlign Right Horizontal Rule Insert HyperlinkInsert EmailInsert Image Insert CodeInsert QuoteInsert List Spell Checker
   
Message:

* HTML is OFF
* Forum Code is ON
Smilies
Smile [:)] Big Smile [:D] Cool [8D] Blush [:I]
Tongue [:P] Evil [):] Wink [;)] Clown [:o)]
Black Eye [B)] Eight Ball [8] Frown [:(] Shy [8)]
Shocked [:0] Angry [:(!] Dead [xx(] Sleepy [|)]
Kisses [:X] Approve [^] Disapprove [V] Question [?]

   Insert an Image File
Check here to include your profile signature.
    

T O P I C    R E V I E W
Bazooka Posted - 05/02/2022 : 11:34:16
My GMC-500+ have started showing unreasonably high CPM on the first tube. I've had it for a few years so far, and initially everything was fine.

Some time ago CPM1 started going off the charts: the usual background range is 10-20 CPM, and CPM1 now fluctuates between that and couple thousand. CPM2 is 0 to 5 at the same time.

I haven't changed any HV settings prior to this.
Resetting to factory defaults didn't fix this.

Is tube #1 dead? Any chance this can be fixed with a firmware update?

Thank you.

Device revision 2.23

4   L A T E S T    R E P L I E S    (Newest First)
ullix Posted - 05/21/2022 : 23:36:45
quote:
... it does not depend on the tube but on some electronics problem.

This may well be the case, but we won't know until we know what the true voltage is to either determine that this is the cause or exclude it.

I believe the anode voltage of the two tubes is the same, and cannot be set individually? To measure you need a decent DVM and a 1 GOhm resistor.

If you don't know how to do it or do not have the equipment you can take some "iterative" approach:

Whatever the setting of the voltage setter is, reduce it to half. If then you don't get any counts, keep increasing the voltage step-wise and check counts at each step. The background should be near 20 CPM - anything from 10 to 30 CPM is likely ok.

If you have no better radioactive source, get Potassium. It can bring some CPM=100. It may be in your household already. For details see "Potty Training" https://sourceforge.net/projects/geigerlog/files/Articles/

Make yourself a nice cup of hot chocolate. But before you prepare it, measure the counts from the cocoa powder ;-)
EmfDev Posted - 05/10/2022 : 09:51:57
@ullix is right, you may need to check if the voltage is still in the working range. You can try to decrease the tube voltage percentage by 5-20% to see if there is any improvement. But I most likely the tube needs to be replaced. Still need to check the voltage though because if it is too high, you do not want the new tube to die faster, or not work properly.
ullix Posted - 05/02/2022 : 23:30:48
A new tube won't help if for any other electronic(?) defect the voltage has gotten out of hand.

There were quite a few reports recently about high anode voltage. Surely can't hurt to measure voltage.
Senketsu Posted - 05/02/2022 : 15:31:59
It seems to me that the GM M4011 counter is to be replaced (it has discharges that are not extinguished). You can do such a repair yourself in a simple way - by purchasing the GM M4011 glass counter

GQ Electronics Technical Support Forum © Copyright since 2011 Go To Top Of Page
Generated in 0.12 sec. Snitz's Forums 2000