Troubleshooting help- YCV40

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Paul Conway, Jan 24, 2012.

  1. Paul Conway

    Paul Conway Member

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    Hi guys

    Recently re-tubed the amp after a power tube died. Now, I get about 45mins play out of it before a massive drop in volume. Any thoughts?
     
  2. 900z1

    900z1 Member

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    the power tube failure may have partially taken out a plate load resistor at the same time as the tube failed.

    If you have experience working inside the chassis, look for an intermittently working resistor on the plate pin of the power tube socket of the tube that died, otherwise take it to a tech and tell him a tube died, etc...

    did you replace the phase inverter tube when you replaced the power tubes ?
     
  3. phsyconoodler

    phsyconoodler Member

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    Those amps use a mosfet for the standby and the circuits do fail.It will need a tech who knows how to check.
     
  4. Paul Conway

    Paul Conway Member

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    I think my tech disconnected the standby because it died and he didn't feel it was necessary.
     
  5. Jerry Glass

    Jerry Glass Member

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    There are also two transistors (Q4 & Q5) that limit the peak current of the power tubes by increasing the bias voltage as the tubes draw more current. Those are also subject to failure, particularly since a power tube has failed. When these transistors fail, the bias voltage goes way up putting one or both sides of the circuit in cut-off. If they were thermally damaged, it could be intermittent as you are experiencing.
     
  6. Paul Conway

    Paul Conway Member

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  7. Prairie Dawg

    Prairie Dawg Member

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    I don't know how you'd disconnect the standby in these amps. There's an IC, a diode, and a FET transistor that runs things. When a power tube croaks it takes out the FET.

    Yorkville's got pretty good technical support and there is a service manual for these things.

    http://judyboxamp.blogspot.com/2011_11_01_archive.html
     

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