Amp issue (Tube gurus, help!)

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Antero, Aug 25, 2005.

  1. Antero

    Antero Member

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    So, my amp is a Silvertone 1484 (Twin Twelve), love it. I am, however, amp-tech-ly ignorant, and have no idea how to really fix my own problems.

    Other day I turn it on, get massive amounts of noise and hum and clicking (the clicking vanishes when I turn of the tremolo). I check the preamp tubes, one seems to be microphonic. Two days later I turn it on again - some hum, more than usual, but no MASSIVE NOISE. Swap the possibly microphonic tube with a Sovtek 12ax7... hum increases dramatically (and unacceptably! Screw you, Sovtek!). Switch it with another, hum's back down... not fixed, but ok for now.

    Try switching out the tremolo tube... no real effect. Blue glow from one power tube (I'm currently running a 5881 and a Silvertone 6L6 in one of the more laughable slapped-together power tube arrangements ever - yes, I should change it, no, I haven't had a chance). Now I still have clicking from the tremolo, still have more hum than before things went wrong, and still have no clue what is going on.

    Help?

    Update: Tried it out again. A LOT of hissing and crackling and static, still has that hum going on. Augh.
     
  2. Normster

    Normster Member

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    I'm not an amp guru by any stretch of the imagination, but that's exactly what my Blues Deluxe was doing. Turned out to be a bad power tube resistor. Unfortunately, I don't remember which one. :(

    The bad news is, you probably need to take it to a shop. The good news is, it's probably only a $50 repair. YMMV
     
  3. JerryP

    JerryP Member

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    Are the filter caps original still? I've worked on quite a few Silvertone amps and I usually find bad filter caps and drifted resistor values.
    Jerry
     
  4. Antero

    Antero Member

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    God, no idea. They could well be old enough to have given birth to me. :eek:

    Thanks for the thoughts, guys. I'll find a tech.
     
  5. Blue Strat

    Blue Strat Member

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    About the only thing you can do is clean the tube pins and sockets as per the FAQ on my site, under Resources, or replace tubes.


    Seeing a tech is a good idea.
     
  6. Antero

    Antero Member

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    Update: Ok, WTF.

    So, I try it out again today. Plug into the non-tremolo channel (still some clicking on the other). Everything's working fine - a little more human than usual, but nothing drastic. How mysterious. I start playing, everything seems fine - kick out some of "Sparks," it sounds about right.

    AFter about a half hour, though - HISSS CRACKLE STATIC STATIC BIZZ and it's getting louder. Well, says I, this is no good at all! I look at the amp, then flip the Ground switch forward and back once. There's a tiny pop, and the noise is gone - I keep playing as before.

    What in god's name is going on here? :confused:
     
  7. John Phillips

    John Phillips Member

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    STOP!

    DO NOT play through the amp again until you've had it checked out by a tech. It's possible that the increased hum and static noises are caused by a failing ground cap. If it shorts, depending on the position of the ground switch the chassis may become live and so will your guitar strings.

    This cap is often called the 'death cap' for exactly that reason.

    This is not a joke.


    You need to have the amp fitted with a 3-wire grounded power cord - anyway, even if it proves to be some other problem. It's possible that it's something else that's not dangerous (the ground switch itself, or something disturbed by the slight vibration of the switch being flicked), but don't take the chance.
     
  8. Antero

    Antero Member

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    That's most mysterious, because it DOES have a three-prong cord... :confused: I'll get it checked out. Thanks for the warning! I'd rather not go up in a shower of sparks! :eek:
     

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