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  • December 20, 2025 at 2:47 pm #30105
    R_A_Ghosh
    Participant

    How to connect two gm tubes in parallel for increase sensitivity….. Any schematic?

    January 5, 2026 at 10:40 am #30172
    uRADMonitor
    Keymaster

    We did tests with many GM tubes in parallel. Here is one example: https://www.pocketmagic.net/city-air-quality/

    This increases detector capacity, so what you need to do is to adjust the compensation capacitor. It is explained here: https://www.uradmonitor.com/compensation-capacitor/

    January 5, 2026 at 10:56 am #30174
    R_A_Ghosh
    Participant

    What I did is to use an hvdc and two gm tubes with their separate anode resistors and cathode resistors and their respective compensation capacitor. Created two independent counter channels and finally added the counts per seconds.
    I used two LND7807

    January 5, 2026 at 1:57 pm #30175
    uRADMonitor
    Keymaster

    Sounds good! What HVDC did you use?

    Would love to see this setup, do you have pictures?

    What’s next in your project?

    January 5, 2026 at 2:34 pm #30176
    R_A_Ghosh
    Participant

    I used a small ac to ac 230v to 230v isolation transformer for mains isolation. Then used a full bridge diode doubler followed by a 68k 5w resistor in series with 200+200+100 V 5watt zener diodes to get 500V.

    Extremely low noise than a dc dc converter that disturbed my previous setups ….

    April 14, 2026 at 11:54 am #30195
    uRADMonitor
    Keymaster

    Interesting design, simple yet effective. Would love to see it should you post a few pics.

    April 15, 2026 at 10:35 am #30199
    R_A_Ghosh
    Participant

    Please see attachment for schematic. I will post image of the setup soon. Small transformer provides necessary isolation from mains though.

    April 15, 2026 at 10:41 am #30200
    R_A_Ghosh
    Participant

    check the image

    Attachments:

    1. hvdc-scaled.jpg

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