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Thread: Hum in my BF Bassman

  1. #1
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    Hum in my BF Bassman

    Hi - nice forum!

    Hoping someone can help me troubleshoot my 64 Bassman. Will start a low, dull hum that reminds me a bit of a refridgertor running every so often -- especially when stomp boxes are in use.

    Also, tends to kick in when I flip the standby switch on; or right when I power off (then of course goes away because the amp shuts off).

    So, any ideas? I have RCA Blackplates in there, and they sound good. Is it the caps you think? They were supposedly fine when I bought the thing a few months ago. But who knows.

  2. #2
    Forum Member Nigel's Avatar
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    I'm not an amp expert (although I play one on the internet) but you might want to try swapping out the preamp tubes one at a time with a 12AX7 that you know is quiet. If you don't find a noisy tube that way it may very well be a cap.

  3. #3
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    aging caps

    My 64 Bandmaster aquired hum over the years because the large paper caps will slowly degrade. At some point, all of these will need to be changed. NOS may last 20 yrs but new designs will outlast all of us.

  4. #4
    Forum Member Casey4s's Avatar
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    It seems to sound to me like a bad power supply cap(s). It would be a good idea in an amp that old to replace ALL of the electrolytic caps. The parts are not that expensive.

    Casey4s

  5. #5
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    Tim C.'s Avatar
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    The filter supply capacitors would be my first suspect.

    Tim C. :)

  6. #6
    Forum Member Nigel's Avatar
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  7. #7
    Da Green Fuhrer
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    Caps! No doubt.

  8. #8
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    Hi. Thanks for all of the replies. Yes, it appears to be the caps -- all will be replaced within the next week. Thanks again.

  9. #9
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    If the amp still has it's original caps, then I'd say it's high time for a cap job. Start with replacing all the electrolytics in the power supply filter, including the bias filter cap. See if that fixes the problem.

    Alternately, it's not unheard of that a tube may have a heater-cathode short, which would induce hum.

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