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Pro Reverb Voltage Issues

Discussion in 'Amp Tech Center' started by bblumentritt, Dec 29, 2020.

  1. bblumentritt

    bblumentritt Tele-Afflicted

    Posts:
    1,978
    Joined:
    Dec 3, 2012
    Location:
    Austin, Texas
    Here's one for you...

    Guy brings a Pro Reverb type amp in for service, says one 6L6 won't light. Sure enough, with the power on and in standby, there's no light on one power tube.

    I pull the two 6L6's and sure enough, one the dead one pin 2 to pin 7 is open. Okay... new tube time.

    Or so I thought.

    Go to test voltages....

    With no power tubes, the PT is putting out about 525VDC... should be about 460-480... but here's the bias tap is -120V, and that's before the 470Ω bias dropping resistor.!!

    With the power tubes in, the plate voltage drops to 318VDC with like -150V at the bias junction. Should be 440V at the plate and -51V at the bias point.

    It's a standard 325-0-325 V, 370 VDC @ 200 mA (DC) with 50 V bias tap.

    My first thought is bad tranny...

    Thoughts?
     
  2. bblumentritt

    bblumentritt Tele-Afflicted

    Posts:
    1,978
    Joined:
    Dec 3, 2012
    Location:
    Austin, Texas
    Open heater on one power tube... blown HT fuse.

    Fixed.
     
    dan40 likes this.
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