FNIRSI GC-01: Changing the tube

[webrex2000]

I need help as I'm new to this kind of upgrade. I have a FNIRSI GC-01 with j613 tube and I want to use a j321. The pcb has the spots for the clips and I found a tube on aliexpress. Few questions: firmware upgrade must be done before or after changing the tube? Hobby solder is good for the clips? I understand the voltage for the j321 can be adjusted with new firmware using HV am 'i right? Seems i do not need to remove or add any resistor. Thank you for your help and sorry for my English.

[alfmck]

I did that for me. If you made firmware updates to Radpro, initially HV will be 700-850V, which is too high for J321, but not critical. So, you have to come to settings, Geiger tube, HV profile, custom profile, OK, and set PWM frequency let say to 5 kHz and PWM duty cycle to 1.5-3.0%. After that you can change the tube.

[alfmck]

Yes, but the temperature has to be about 400 degrees. I had to do clips by myself.

[webrex2000]

I found a j321 in aliexpress with clips included..... 400 degrees the solder..... I hope I can do it

[webrex2000]

What about the old tube... Just cut the wires and thats' it right?

[webrex2000]

Hi i just updated the firmware and changed to the j321 tube, I used custom Hv profile you suggested but I have 91 volts on the tube, is this normal?

[alfmck]

To measure HV on the tube you should use 1GOm resistor, subsequently connected to voltmeter. In order to set right HV, simply try to increase duty cycle step by step and observe the average number of counts per minute. It should be 20-24 CPM, depending on the place you live. And you asked about old tube - I suggest leaving it, parallelly connected to J321.