bf champ plate voltage

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Pencho, Dec 20, 2009.

  1. Pencho

    Pencho Member

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    I'm almost finished with the work on a 66 vibro champ I got a few monnths ago. I did a cap job, 3 prong cord and replaced the plate resistors to fix some crackling. I added a 1k/5w ceramic screen resistor and replaced the cathode resistor with a 5w ceramic 820 ohm (and 50uf/50v bypass cap). The amp sounds great and I'm happy with it. I only play with single coils and p-90 like pickups and don't get breakup until 8 on the volume, which I think is normal?

    What is the highest plate voltage you would want to see? My plate voltage is 414 and I think the dissipation is 14.1 which is right at the limit. 414 pin3, 414 pin4 and 30.8 across the cathode resistor.

    I'm thinking about swapping the 1k screen resistor for a 2w/2k and wrapping it up. Should I be concered about the 414 plate voltage?
     
  2. phsyconoodler

    phsyconoodler Member

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    You need to measure your plate voltage from pin three to the cathode(pin 8),not to ground.
    No,the plate voltage is not a concern.A class A amp will normally be biased at 100% disipation anyway.
    If it sounds right to you,you're done.
     
  3. Pencho

    Pencho Member

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    Thank you phsyconoodler!
     
  4. SatelliteAmps

    SatelliteAmps Member

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    You could have also just done the math instead of remeasuring. The plate to ground voltage plus the cathode to ground voltage will give the same result as reading between the plate and the cathode. When people read to ground, it is usually used as a reference point.

    Some people prefer to keep one lead clipped to ground, so when they measure anything in the amp, they never have both hands on hot leads. Can't electrocute yourself with only one hand inside the amp.

    As far as limits, there are plate voltage limits to all tubes. In most tube manuals, recommended plate voltages are about 450v for a 6V6GT, but there is at least one manual that shows how to push it up into almost 700v.

    Your Champ should never get that high, so there is no concern there.
     
  5. Pencho

    Pencho Member

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    Yes, I'm one of those who doesn't like both hands in there. All of the measurements I listed were from ground. 30.8 from ground to the cathode resistor and 414 from pin3 to ground. Thanks again, sounds like the 414 is no problem.
     

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