Changing speakers, draining caps

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Crazyquilt, Jun 8, 2006.

  1. Crazyquilt

    Crazyquilt Guitar Dad Silver Supporting Member

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    No, this is not the name of Ang Lee's newest rock & roll kung fu blockbuster.

    I'm just wondering, because I'm planning on pulling the chassis of my Swart AST to swap the speaker, if I need to drain the caps first. Obviously, I'm not going to be purposefully poking about inside the chassis, but fumbles happen. I don't even know if I should rest it on the "open" side or the knob side. I was planning on pulling the tubes out, just so I don't accidentally knock one.

    I've changed speakers before, just never had to pull a chassis to do it. And, while my hair is curly, I'd rather not make it any frizzier. I'd rather be overly cautious than foolhardy.

    Thanks.
     
  2. hasserl

    hasserl Member

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    Not being familiar with that amp, can you drain the caps before pulling the chassis? If you have to pull the chassis to get to the filter caps to drain them, than what is the use. Just pull it and set it down out of the way. Typically this is not an issue, just be careful and don't stick your fingers inside the chassis while you're pulling it. How you set it down depends on how it is constructed. Most amps have the transformers on one side of the chassis, often these are tall enough to keep it from resting on the tubes. You may need to block it up with some scraps of wood or thick styrofoam. Or, you could flip it over and set it down on the open side. You'll find out when yuou get it out.
     
  3. Crazyquilt

    Crazyquilt Guitar Dad Silver Supporting Member

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    I'll take a look at the Mitchell tube amp book & see what it says in terms of ways to drain caps, and try & figure if any of them are applicable. Going from the appropriate pin of V1 to chassis, at least, is doable; the tubes are on top of the chassis, and fully open/easily accessible (kind of like a Fender chassis, but upside down.)

    Judging from the way the chassis is constructed, the most logical way seems to be to put it down on the open side; the bottom is angled to allow the speaker to fit (which the following photo doesn't show.)

    [​IMG]

    Thanks again.
     
  4. Guinness Lad

    Guinness Lad Silver Supporting Member

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    I thought you discharged the caps by turning the amp off in this sequence, main power first while the amp is on and running then the standby after about 30 seconds. You should normally hear the volume die out if your playing the guitar. This should be your caps discharging.
     
  5. Crazyquilt

    Crazyquilt Guitar Dad Silver Supporting Member

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    Harry, check out the thread on discharging caps -- the consensus seems to be that, while that dissipates a chunk of the charge, it still leaves enough to damage the amp, and several folks noted that the charge can regenerate. Bottom line was that the strategy was deprecated in favor of various others involving jumpers & a multimeter.
     

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