FNIRSI GC-01: GM tube version question

[dobrishinov]

Hello,

First, thank you for the great firmware!

I recently got the FNIRSI GC-01, and when I opened it, I noticed it's using the Geehy APM32. That’s great since it provides more memory for storing data points, from what I’ve seen.

I just need confirmation about the tube—it's quite small, around 50mm. I also noticed connectors on the board for a larger tube. Is the current tube an HH614? (Attached images bellow)

How good is its sensitivity? Would you recommend upgrading to a different tube, or is this one sufficient?

Regarding the settings, I should select J614, correct? Do I need to adjust the dead time and background compensation for optimal performance?

Thanks in advance!

[Gissio]

It’s indeed a J614/HH614. It’s about five times less sensitive to background radiation than the larger J321.

It's ok for detecting gamma radiation, but requires a longer averaging period. For beta radiation (electrons) the J614 is quite insensitive.

[dobrishinov]

Thank you for your response.

So, does this mean the device isn’t performing well with the current tube? Should I adjust the dead time and background compensation for optimal performance, or is that not necessary?

What would be the best tube to use? If I replace it, is it enough to simply update the tube selection in the conversion factory settings, or are there other adjustments needed?

I'm a bit confused about the different tube versions. I know the SBM-20 is a good option, but it's quite old and expensive.

I’d appreciate your advice! 😊

[Gissio]

Plato’s Republic is also old, but definitely worth reading!

If you are new to radiation, I recommend reading the field guide at https://github.com/Gissio/radpro/blob/main/docs/field-guide.md . For additional insight, explore relevant forums or consult https://grok.com — It’s an excellent resource!

[dc1rdb]

My unit had the same tube when I got it from Amazon and I replaced it with a J321 for better performance.
I noticed that R38 is not populated on your board (same as on mine). You need to be careful when experimenting with different tube voltages via the HV profile menu to not exceed the maximum voltage for the installed tube.
I soldered a 400V zener on the R38 pads (actually two 200V in series) to limit the tube voltage. Then I set my custom HV profile to 5kHz and 2.75% which gives me enough reserve at higher count rates.