VR1 - getting ticks at full counter clockwise ?

[hlain]

First, I really enjoyed building this device! Instructions are fantastic and the PCB and case are beautiful. Thanks!!

So per the instructions, turn VR1 fully counter-clockwise, power on the unit, and slowly turn til you hear ticks. I hear ticks at the fully counter clockwise position... should I be turning this to 9 o'clock position then? That is first ticks sound position + 45 degrees? Does this set the voltage? I could get the 1 giga ohm resistor to measure and then dial VR1 that way with my multimeter to target 400V?

One other question, why are so many of these geiger tubes sourced from Ukraine?

Thanks!

Hans

[mightyohm]

Hans,

Glad you are enjoying your kit!

It's not unusual to hear clicks with VR1 fully counterclockwise. In this case I would set it somewhere between 9 and 12 o'clock.

VR1 sets the high voltage. You can use a 1 gigaohm resistor and a DMM to check and set the voltage to 400V. Make sure your DMM has a 1 Megaohm input impedance. https://ea4eoz.blogspot.com/2012/09/one ... probe.html

I'm not sure the history on Soviet geiger tubes but I suspect there was a large buildup during the cold war and especially following the Chernobyl disaster. This may explain why there are still so many new old stock surplus Soviet tubes today.

[hlain]

Will do and thanks!

[mightyohm]

You are very welcome. Let me know if you have any more questions!
Enjoy your kit!