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crackling sound in fender tube bassman

Discussion in 'Amps and Cabs [BG]' started by jamesonellis, Mar 17, 2006.

  1. jamesonellis


    Nov 12, 2004
    got a '76 fender bassman, sometimes it makes a sound like slowly crumpling paper. this seems to happen most while the amp is on and i am not playing.i.e. shortly after i stop, in quiet passages or if i leave it on standby a long time.at this point it is slightly annoying but not catastrophic, so i am reluctant to let go of it for repairs.could it be somethig simple+obvious i can fix myself?
  2. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    It could be something as simple as just cleaning the pots and jacks, but your amp is also about ten years past due for changing and upgrading the power supply capacitors. I'd do so immediately.
  3. Harpo61


    Dec 15, 2000
    Tampa Bay
    The caps usually start leaking my guitar player has Bassman 50 that we had replace the caps and works fine we are both good with a sodering iron if you not a good tech should be able to fix for not to much
  4. billfitzmaurice

    billfitzmaurice Commercial User

    Sep 15, 2004
    New Hampshire
    Owner, Bill Fitzmaurice Loudspeaker Design
    Working with high voltage power supplies isn't recommended for those who don't know what they're doing. Also, capacitor technology has changed greatly in the last 30 years, a qualified technician would be aware of that and would not use the original values but would upgrade them to the largest values that will fit in the tank.
  5. jamesonellis


    Nov 12, 2004
    thanks for the response but where does that leave me?change to caps w/ new values,who has a curcuit diagram which incorporates the new values?(if that is what you are talking about),also , i have not owned the amp it's whole life, who knows what has been done to it in the past.
  6. Philbiker

    Philbiker Pat's the best!

    Dec 28, 2000
    Northern Virginia, USA
    No offense intended to anyone who posted before me.

    How long has it been since you replaced the tubes?

    Sounds like the tubes are going. Nothing more complicated than that. There's a reason that people like solid state amps. BTW my tone amp is a '67 bassman.
  7. Tubes don't make ANY noise in standby. He most likely has a capacitor probelm.

    You need to get this amp to someone who knows how to repair it. Your tubes are most likely completely fine.
  8. WalterBush


    Feb 27, 2005
    Yuma, Az
    Full disclosure, I'm a certified Fender technician working in a music store that carries Fender, Yamaha, and Ibanez products among others.

    A qualified technician will know what's going on inside the amp, will know where to get schematics if they don't already have them, and will know what cap values will work best with your amp, whether they just do a straight a replacement or a slight modification. They will also be able to tell what has possibly been modded over the years, or whether it's all original.

    And yeah, it sounds like a leaky capacitor to me, as well.
  9. tornadobass

    tornadobass Supporting Member

    Nov 20, 2000
    Iowa City, Iowa
    The good news is that other than tubes or transformers, most other parts to be replaced are fairly inexpensive. Labor will likely be the largest cost, but an experienced tech will have a good idea of what to do and won't mess around getting it fixed.

    I've been learning this stuff and have repaired two Bassmen...a 100 and a 50...in the past few months. An experienced friend has been a good help. To get an idea of what's involved, take a look at the Hoffman Amps site where he runs through the basics needed to update a Fender amp. link

    On one Bassman, a resistor was broken over a power tube socket, but just managed to touch when cool and keep things going. On the other a different resistor over a power tube socket was burned up and the tube sockets weren't able to keep the tubes in place.

    I'd guess that we'd like to suspect tubes because that's the easiest problem to fix, but between aging electrolytic capacitors and random broken parts, things are likely to be more difficult than just plopping in new tubes (and then there's re-biasing when plopping in the tubes!).

    As others have said, these amps aren't something to just dig into without knowing what's going on.
  10. jamesonellis


    Nov 12, 2004
    i checked out hoffman, and in the 'oddball noises' section he describes a crackling sound as the 1/2 watt plate resistors burning up. a relatively common problem and simple fix. that is an excellent site btw.

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