'63 Showman Transformer Hum/Vibration

Discussion in 'Amp Tech Center' started by Faceman, Dec 11, 2018.

  1. Faceman

    Faceman TDPRI Member

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    I recently finished bringing a 1963 Fender Showman back from the dead and I used all the original transformers. All voltages check out perfectly but when I power the amp on (in standby) I can hear the power transformer humming and vibrating like a high voltage power station. It vibrates the chassis and when I turn off standby, I get a little pop and the buzz is transferred through the output to the speaker. It's not overly loud and I can play through it on a gig fine without it effecting the sound. That said, I'm concerned...

    Any advise? Maybe re-pot the PT?
     
  2. clintj

    clintj Friend of Leo's

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    It may be normal, depending on how loud it is. The phenomenon is known as magnetostriction, and is the magnetic field in the coil causing the laminations to vibrate. Same effect will cause some OTs to put out audible sound when bench testing on a dummy load.
     
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  3. robrob

    robrob Poster Extraordinaire Ad Free Member

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    Verify all the bolts on the transformer that hold the laminations together are tight.
     
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  4. wanderin kind

    wanderin kind Tele-Meister

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    usually the lams are varnished pretty good on the Shumacher (EIA code 606 stamped on bells)

    more likely is a loose coil,

    those transformers were wound as layered paper (no nylon bobbin) then the coil is blocked to the core by a wood wedge, as the coils stretches, it can become loose, simple plan is to take off end bells and give the transformer a wedgie,
     
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  5. schmee

    schmee Poster Extraordinaire

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    I had one rectifier tube that hummed a lot for some reason. Sounded fine, but made the amp vibrate just a touch, not a lot. The Showman is SS rectified, but one wonders if a diode/diodes is bad or something?
    By "bring it back from the dead" ... by any chance was it water damaged?
     
  6. Faceman

    Faceman TDPRI Member

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    It appeared to be water damaged. It was the same one I posted on that rusted chassis thread. Thing sounds amazing, just an annoying hum. I did find a broken transformer bolt so I am sure that isn't helping matters. I will replace that bolt and see what happens.
     
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