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Tube Amp Gurus: DIY Question

Discussion in 'Amps and Cabs [BG]' started by Kelly Lee, Apr 3, 2006.


  1. Kelly Lee

    Kelly Lee Yeah, I'm a guy! Supporting Member

    Feb 17, 2004
    Marana, AZ, USA
    I was wondering if I could replace the input gain and output level pots myself without having to drain the capacitors?

    The pots on my Quatra need to be replaced and I have the soldering skills to do so. The pots are mounted to the chassis and not on a PCB. The caps are towards the rear of the amp.

    Can I do this without killing myself? I was planning on sending it in to British Audio Service but for the cost of shipping and the parts and service it just really wouldn't be worth it for two pots. Thanks.
     
  2. Have you tried a shot of DeOxit? If the pots are just noisy, that usually will cure them, and there is next to no risk. All you have to do is get the spray straw to the pot opening near the solder posts and squirt it in and run the pots through several full rotations.
     
  3. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    The caps self discharge in a reasonable amount of time, so if you just leave it off for a day, they should be good. Also, there won't be any high voltage on the pots anyhow, so you would be doubly good. I also suggest that you try cleaner (as per PBG) first . . . , and if that fails, go ahead . . .

    - Tim
     
  4. Kelly Lee

    Kelly Lee Yeah, I'm a guy! Supporting Member

    Feb 17, 2004
    Marana, AZ, USA
    I have tried cleaner and it hasn't helped. Not that brand but another one I have used for years with good results.
     
  5. MeYHymN

    MeYHymN Habitual User

    Nov 7, 2004
    Charleston, WV
    True caps can hold power for long time, as long as your not working on the power amp section it shouldn't matter. It's when you start working in the power section you need to start discharging caps. FWIW, always keep one hand in your pocket and dont drop the screwdrive and you should be fine :D
     
  6. jz0h4d

    jz0h4d

    Apr 26, 2005
    Don't try it! If you can't figure out how to safely drain the caps you have no business inside a tube amp.
     
  7. dood

    dood

    Dec 9, 2004
    UK

    Agreed. A day is MORE than enough for any caps to drain. Blimey, I used to work on CRT monitors and they would be fully discharged when I came back from lunch ;o)

    You'll be safe to do the work. If you are happy soldering, no probs. make sure you get the correct value of pot though! Solder the wires into the same places from old to new.

    Good Luck!
     
  8. If you don't know what you're doing inside a tube amp, this may be your last post.

    Capacitors do have the potential (no pun intended) to hold a charge for a surprisingly long time.

    Why not just take the chassis (carefully) to a local electronics repair shop and have them drain the capacitors for you. Then you can poke around all you want.
     
  9. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    Only out of a circuit. In pretty much any application, a hour would be a stretch, and overnight is pretty much guaranteed safe. There are voltage divider networks all over tube gear that bleed the supplies down pretty quickly - measure one sometime if you don't beleive it.

    Oh, and your high falutin' tech, who probably barely made it through high school, will do nothing more than to put a screwdriver with an insulated handle across the caps to discharge them. Not something I would be inclined to pay more than about $.25 to someone to do . . . .

    - Tim
     
  10. No resistor to ground?
     
  11. tadawson

    tadawson

    Aug 24, 2005
    Lewisville, TX
    Most folks don't bother - too much like work, and no real advantage. Besides, the resistors to ground are already in the amp . . . . as I say, wait a breif period, and discharging is a moot point.

    - Tim
     

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