Silverface bassman...the weirdest of problems...

Discussion in 'Amps and Cabs' started by Reyybarra, Mar 20, 2015.

  1. Reyybarra

    Reyybarra Supporting Member

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    Seems like everyone's taken a go at this problem..
    New tubes, tube trees, new speakers, biasing, just everything...

    When the amp fires up, Everything is great.
    As the amp warms up, weird sounds come out of it, if I hit the amp righ above the jewel light, or above the tranny, it sometimes goes back in, but most of the time, the horrible sound and signal drop stay.

    Anyone have any ideas? I feel like the only logical thing that it could be would be the transformer, but was wondering if any one may have had a similar issue at any time...

    Thanks

    Rey
     
  2. am-audio

    am-audio Member

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    These threads almost always end up with tons of conjecture and at least a few people making the correct recommendation of taking it to a tech...and I'd make the same recommendation. But with that said real world experience tells me that the rectifier and bias diodes on that little eyelet board below the jewel light have leads that develop small cracks and go intermittent and eventually open. Sounds like that or a bad solder joint could be the problem. Don't go poking around in there unless you know how to safely work on high voltage electronics.
     
  3. broken_sound

    broken_sound Silver Supporting Member

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    I've noticed something sort of similar with my drip edge (since converted to AB165 spec). Immediately after disengaging the standby this wierd buzzy hum comes out of the speakers and then goes away, it lasts roughly 1 second. I've always associated it with old caps flexing, maybe your front end needs some caps replaced? I'm no tech, but my two cents.
     
  4. drewl

    drewl Member

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    You have some type of intermittent problem. A tech would monitor the signal path and voltages while it is failing and should be able to determine the problem without too much difficulty.
     
  5. LordRiffenstein

    LordRiffenstein Member

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    Send it to Roy Blankenship in LA, he'll fix it for you and talk to him about his Bassman mods while you're at it!
     
  6. Blue Strat

    Blue Strat Member

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    ^^^ What they said. Unless you're qualified to "go in", there aren't a lot of things you can do.

    One thing you can do is clean the tube pins and sockets with some Deoxit or other spray electronics cleaner. This will often clear up intermittent problems and is good general maintenance.

    Good luck!
     
  7. mxvin

    mxvin Member

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    after its warmed up sometimes there is issues with the fiber eyelet board. Some are heavily wax coated and some are not. I have eliminated odd noise be reflowing the wax with a heat gun....be careful and use low heat. Or sliding a wide tongue depressor under the board to lift it from the chassis.
     
  8. Baxtercat

    Baxtercat Member

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    What they said^

    I too have slid sheets of plastic, polyethylene, whatever under the board to insulate and/or shut up the noise.

    These things are 40+ yrs old so moisture, warping, rust, etc. are a problem.
     
  9. Reyybarra

    Reyybarra Supporting Member

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    Totally appreciate everyone's input, I will be poking aroudn a little at stuff, (with one hand in my ya pocket hehe)
    I at first thought it was a blown transformer, since I think, the speakers in the original cab were wired for 8 ohms and the bassman is wired for 4. So after all these years I figured it had put too much stress on the transformer and it had given up...
     
  10. critter74

    critter74 Supporting Member

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    Wire has drifts somewhere maybe and is causing cross talk? I had my SF Bassman wiring harness redone as it was stock, and as many know, those could be quite the rats nest.
     
  11. bgoez

    bgoez Stratocasters are my downfall!

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    Chop stick and freeze spray. Stay safe
     
  12. btjguitarman

    btjguitarman Supporting Member

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    is it sort of a crackling sound along with a significant volume drop? I had a similar problem on mine that turned out to be a wonky solder joint going to one of the 6L6 sockets. It would happen fairly inconsistently and I'd pound on it down on the right side (which I believe was where the power tubes were) and it would come back on. Love that amp but what a disaster it was inside.
     
  13. paulg

    paulg Supporting Member

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    Here's a weird one. I worked on a Bandmaster that would cut out when it heated up. Turns out there was a blob of solder hanging off the bias pot that would expand when hot and intermittently short out. Weird things happen!
     

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