Jcm900 1000volt Plate Votltage???

Discussion in 'The Workbench' started by Jared, Nov 1, 2016.

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  1. Jared

    Jared New Member

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    I have an old 1990 JCM 900 model 4101 EL34 valves. I have owned this amp for almost 20 years. About 10 years ago it blew a tube so I put the amp in storage thinking some day I will buy new tubes and bias it. Well that day has finally come.

    I went to measure the plate voltage to get my bias value, Pin 3 on all the EL34's are running at 1015 volts. I also measured off the transformer and it has the same voltage. I am pretty positive it should be in the upper 400volt range. Would anyone know what would cause this?
     
  2. Gunner64

    Gunner64 Well-Known Member Gold Supporting Member

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    Verify your meter is working correctly, and it doesnt have an internal fuse thats blown. Ive had it happen and got some pretty wierd readings..try another meter if possible.
     
    Last edited: Nov 2, 2016
  3. Jared

    Jared New Member

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    Yup thanks, I didn't even think of that. my meters switch to change settings was messed up.
     
  4. BowerR64

    BowerR64 Well-Known Member

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    So whats it reading now?
     
  5. ampmadscientist

    ampmadscientist Well-Known Member

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    If it really is 1015, the voltage taps on the power transformer primary are set wrong (probably).
    Other than that, the meter can be goofed up...
     
  6. Jared

    Jared New Member

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    After fixing my meter it reads a correct voltage of 470 volts.
     

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