JCM800 Low Plate Voltage

Discussion in 'Amps and Cabs' started by Wagster, Sep 28, 2008.

  1. Wagster

    Wagster Member

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    My 84 2204 is reading low on the plate voltage.Anywhere between 370-400.What causes it to drift?I'll check it a few minutes later and it's a different reading.I'm using GT EL34M's.

    Thanks,
    Billy
     
  2. skipm45

    skipm45 Member

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    Are you taking a measurement at idle or with a signal applied?
    At idle, B+ should be steady, with signal applied, it will vary somewhat.


    Skip
    www.skipzcircuits.com
     
  3. Wagster

    Wagster Member

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    It was w/o signal applied.What's the best was to check B+?I was using pin 3 of the o/p tubes.
     
  4. skipm45

    skipm45 Member

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    Yes, pin 3 to chassis ground.
    is your rectifier output voltage fluctuating?

    Skip
    www.skipzcircuits.com
     
  5. mmorse

    mmorse Member

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    That's typical for earlier 800s. I have an '83 and mine reads around 370. My '89 2550 read around 425. I wouldn't worry about it.

    As far as the drift goes, can't help you there.
     
  6. ebsbert

    ebsbert Member

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    How stable is your AC mains voltage? The B+ will drift as the mains voltage drifts.
     
  7. Wagster

    Wagster Member

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    Found the culprit.I had a EL34 and KT77 in there.......oops!I biased it up to 47v and put in the KT77's.My plate voltage is 370.It now thumps like a mofo :dude
     

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