Newbie EL84 Plate Voltage questions ?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by rreiser, Mar 23, 2015.

  1. rreiser

    rreiser Supporting Member

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    Is 375 volts on the plate somewhat high for EL-84s ? The voltage coming out of the transformer is 330v but at the tubes its 375v. Not sure why the increase is so great. EZ81 rectifier tube. Thanks
     
  2. Blue Strat

    Blue Strat Member

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    How are you determining that you have 330V out of the transformer?

    375V is high-ish according to EL84 specs, but not out of line in a guitar amp that's ignoring the tube specs. IOW, it'll work as long as you're not running the idle power of the tubes at 150% or higher...also not uncommon in guitar amps (with short lived EL84s).
     
  3. Kyle B

    Kyle B Supporting Member

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    The 330V you're reading is (probably) AC. The 375 you read is (probably) DC. DC Rectified voltage is 1.4x the AC value.
     
  4. Blue Strat

    Blue Strat Member

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    I was thinking that until I got 462V rectified DC. There's something else going on with the 330V number.
     
  5. swiveltung

    swiveltung Member

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    Not uncommon for plate voltage to run real high in a lot of those amps. My Z Ghia was into the 435v range.... or something like that.
     
  6. rreiser

    rreiser Supporting Member

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    Yes , 330v AC right off the power transformer , after the EZ81 390v dc on the plates. We are trying a 10 watt 270k resistor on pin 3 of the EZ81 going to the filter caps and initial tests are positive but its too late to crank right now. It seems to be less strident of a sound , warmer and fuller.
     

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