UK Mains Voltage

  • Hi there from a new member.

    I have just finished building a madamp G3.
    On testing I have found that my house voltage is 250vac.
    The heater voltage is 6.6 which is fine.
    Br1 is 232vac.
    All vdc readings are high and I would like to know if it is ok to use.

    Thanks in advance.
    Geoff.

  • Hi Geoff,
    while the heater voltages for all three valves and other voltages for V1 and V2 are no issue, the anode voltage and the resulting power dissipation for V3 is too high with 250V AC Primary. The 6N6P is specified for 8W (two systems) but your voltages result in approx. 10,5W which wouldn't destroy the valve immediately (theses russian valves are pretty robust) but will will shorten it's lifetime. So you should change the kathode resistor R20 to a higher value to shift the operating point to a safe area. I would just replace it with a 390 Ohms / 2W resistor and measure again the voltages at V3. The formula to calculate anode dissipation is P=(Ua-Uk)*Uk/Rk (Ua is measurement #17, Uk is #18, Rk your new value of R20).
    Happy to see your results :)
    Martin

  • Hi Martin.

    I have swapped resistor for a 390ohm 2w as suggested.

    Having checked the readings at several different times I get the following variances at home.

    The home power supply has varied between 244v and 255v on my meter.

    This results in a variance of between 8.42w and 8.7w depending on the input voltage.

    Although much improved, is this now considered useable or should I go further?

    Thanks,
    Geoff.

  • HI,
    Has taken a while (family).

    Have just done measurements. 06:50hrs

    1. Wall socket start 244

    16. V3-1. 283
    17. V3-6. 284
    18. V3-3. 11.97
    V3-8. 11.98

    20. Wall socket end 249

    Thanks,
    Geoff.

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