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Does this make sense? Power tube shuffle fixed crackling channel.

Discussion in 'Fisher' started by Lo-Fidelity, Nov 4, 2018.

  1. Lo-Fidelity

    Lo-Fidelity AK Subscriber Subscriber

    Messages:
    994
    Location:
    Houston
    I was having intermittent crackling on the right channel of my 500c. I have just replaced the left channel OPT and have the unit vertical on the bench so I am able to see the output tubes while running the unit.

    I finally noticed that the crackling was coming from the V11 tube as I could see slight flickering inside the tube. The tube appeared to be just slightly more orangish than the others.

    I swapped V11 and V10, and there was a little improvement. Checked the pin 5 ground resistors
    V11. 367mV
    V10 421 mV
    V9. 275
    V8. 306

    Thought I'd swap V10 and V8 to try and balance this mess out a little.

    Well after that swap there is not crackling from either channel for the last 90 minutes or so.

    Any idea what's going on here? I am afraid as soon as I put it back into service it will start crackling again.
     

     

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  2. E.Man

    E.Man Super Member

    Messages:
    1,229
    Location:
    Bega Valley, Australia
    Moving the tubes cleaned the pins/sockets?
     
    RUmad and Lo-Fidelity like this.
  3. sKiZo

    sKiZo Hates received: 8642 Subscriber

    Yup ... the pins oxidize quickly due to hot/cold cycles. Pulling the tubes can break the glaze enough for a better connection, but a pipe cleaner just dampened with D5 or iso alcohol is the better way to go. Any octal sockets should also be re-tensioned every time you pull a tube, as the fingers tend to spread - not so much a problem with novals ...

    If you still have problems, next step would be to re-point the solder on the socket connections.
     
    Lo-Fidelity likes this.
  4. Lo-Fidelity

    Lo-Fidelity AK Subscriber Subscriber

    Messages:
    994
    Location:
    Houston
    I think you guys must be right. Been listening continuously since the first post without any issues.
     

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