Home Forum Hardware DIY KIT1 v102 – Unit voltage on GM tube is too low

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  • #3044
    tuxik
    Participant

    Hello,

    recently i soldered unit on custom PCB and i am not able to tune voltage at GM tube – there is only 250-270V. I changed MPSA42, inductor, but problem is still here 🙁 On first stage of voltage pump is 127V (at second diode). Any idea where problem may be ?

    Thanks

    • This topic was modified 4 years, 5 months ago by Radu.
    • This topic was modified 4 years, 5 months ago by Radu.
    #3045
    tuxik
    Participant

    Photo of voltage on display

    Attachments:
    #3047
    Radu
    Keymaster

    I’ve seen this before, and the problem was related to the inductor. Try getting 2.2mH inductors from a different source, or ,as a quick dirty hack, put two 2.2mH inductors of the kind you have now in parallel.

    We might get over this by changing the frequency the inverter operates at – drop me a mail so I can send you a test firmware that uses a lower frequency (that might get noisy).

    #3053
    Radu
    Keymaster

    I also sent you by mail versions of the firmware configured for lower inverter frequency (down to 6.5KHz). Please test them and let me know if it helps.

    #3679
    jon
    Participant

    We tested a lot of transistors from different sources. The best Voltage/Duty ratio, we got it with the transistor (T2)
    http://www.reichelt.de/BF-299/3/index.html?ACTION=3&LA=446&ARTICLE=5464&artnr=BF+299&SEARCH=bf299
    BF 299 :: Transistor HF NPN TO-92 300V 0,1A 0,625W
    and
    http://www.reichelt.de/L-XHBCC-2-2M/3/index.html?ACTION=3&LA=446&ARTICLE=138556&artnr=L-XHBCC+2%2C2M&SEARCH=2.2mh
    L-XHBCC 2,2M :: Festinduktivität, axial, XHBCC, Ferrit, 2,2 mH

    best regards.

    #3682
    Radu
    Keymaster

    Perfect, thanks for the update!

    #6866
    tuxik
    Participant

    Hello all,

    i have build another uradmonitor, but problem with low voltage is here again (same as on first piece 3 years ago) – and voltage is extremely low.

    I lowered down frequency of oscillator, but no change occures.

    Some ideas ?

    Thanks,

    #6879
    tuxik
    Participant

    Sorry, my failure 🙂 Two of transistors was misplaced, everything is now ok

    #28406
    Outsider
    Participant

    Tuxik, could you please elaborate on the problem? Ițm having the same situation here (15V on LCD, 8V measured across the tube).
    Thank you!

    #28419
    Wolferl
    Moderator

    Hi Outsider,

    What do you mean with “15V on the LCD”? That seems totally wrong. Nowhere on the LCD module should be a voltage greater than 5 volts!

    Cheers,
    Wolferl

    #28420
    Outsider
    Participant

    Hi Wolferl!

    My mistake… I meant the internal voltage measurement is 15V, as it is shown on the LCD.
    The LCD is powered at 3V (2xAA batteries).
    I have replaced the small axial inductance (2.2 mH, 32 ohms) with a larger, ferrite-core one (2.2 mH, 3 ohms),
    but the voltage remained the same.

    #28463
    Outsider
    Participant

    While I’m waiting for help for compiling/modifying the firmware for my STS-1 tube (practically identical to the SI1G already defined in the code), I’m troubleshooting the high-voltage stage. I’m using firmware made to work with the SBM-20 tube while I have a STS-1 version, but I don’t think that is the reason for having such a low voltage – 15V on the tube!
    I took some measurements with the oscilloscope. Could it be the MPSA42 transistor? Or the 2N2907 transistor?
    The coil is a quality 2.2 mH, very low resistance, not the green version that looked like a resistor.
    Any ideas? Can someone measure same test points on their units?

    #28468
    Wolferl
    Moderator

    Hi,

    You can’t measure at M3 directly. It has a very high impedance, a multimeter or an oscilloscope probe loads the voltage down so much. You would need a voltmeter with a input resistance of 100 MOhms at least to get meaningful results. And you’d need to measure not at M3 (anode) but on the cathode of the diode. You can instead use scope or multimeter across R4 and multiply the reading by 214 to get the real high voltage value.
    That M1 measurement looks weird. It has only 2,7 volts peak-peak. That should be more like 3.3 to 3.6 volts. Frequency looks good.
    What you can try: with the KIT1 turned off, check the resistance of the connection R3 to R3 (the 2 10Mohms resistors) to ground. It must read 10 MOhms.

    I hope I can find some time for your firmware tomorrow.

    Cheers,
    Wolferl

    #28469
    Outsider
    Participant

    The low 15V tube voltage is also displayed on-screen (KIT1 screen, not multimeter).
    I have measured R3 to ground: 8.5 Mohm. R3+R5 to ground: 17.2 Mohm (with the tube in circuit).
    I suppose M1 has only 2.7V because I use 2xAA batteries to power the kit.

    #28472
    Wolferl
    Moderator

    Hi folks,

    Since I had my KIT1 apart, I took some measurements with the scope for comparison.
    The yellow curve (lower trace, 2 volts per division vertical, 20µs per division horizontal) is the PWM output of the MCU. We see it is running at about 50% duty cycle, which is good.
    The green curve (upper trace, 1 volt per division) is probed at the cathode of diode D7. We see some ringing when the current in the inductor is turned off.
    That’s normal. HV is 380 volts (displayed).
    If you have no ringing, you have no high voltage spikes. Loading the collector of the MPSA42 with a 10Mohms probe completely kills the HV (duty goes up to 90% which is the maximum).
    If you probe there, be careful, there are 200 volts peaks present! Do not kill your scope 🙂

    I have the original parts for transistors and inductors as the kit came from factory.

    The only thing I modified are:
    R3 is 47Mohms instead of 10MOhms
    R4 is 220kohms instead of 47kohms
    That yields the same divider ration of 213.
    These modifications creates less load on the high voltage and reduced current consumption dramatically, plus reduces stress on the parts.

    Cheers,
    Wolferl

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