When a filter cap goes bad....

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Randy, Sep 17, 2008.

  1. Randy

    Randy Member

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    What happens? Does it go all at once or slowly? Does a slow death equate to a corresponding degradation of tone? When it's completely failed, will the amp cease to work?

    I ask because I just got a used amp and it sounds terrible. I've owned this model before and know what it should sound like. This one is muddy and farty with no definition. I took a look at the filter caps and low and behold, saw this;

    [​IMG]

    Other then the horrible tone, the amp seems to be working OK. So is this filter cap the likely culprit? Since the amp still works is the cap just part of the way to total failure? What happens then, sparks and explosions and stuff? :huh
     
  2. SatelliteAmps

    SatelliteAmps Member

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    Caps can explode, with a bang, sparks, and smoke. Bulging caps are on their way out quickly. Muddinesss, lack of definition, overall poor tonal response are all indicators of bad filter caps.
     
  3. John Ward

    John Ward Member

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    The bulging cap is on the way out and should be replaced. It is worth it just to avoid the smell and mess that it will make.
     
  4. noctilux1

    noctilux1 Member

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    What replacement caps would you use in an old 50 watt plexi marshall---and where would you get them from?
     
  5. Dave C

    Dave C Gold Supporting Member

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  6. HipKitty

    HipKitty Silver Supporting Member

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    We've had excellent experiences with the JJ's and F & T's.
     
  7. SatelliteAmps

    SatelliteAmps Member

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  8. AL30

    AL30 Member

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  9. PRNDL

    PRNDL Member

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    In this case, it looks like there was a problem with the liquid inside, which has melted and bubbled over to cause the bump. The cap has enough liquid inside to work, but it's not evenly distributed. With enough heat, the liquid will explode and cause a nasty mess.

    It's best to replace both of those blue caps (since they're from the same manufacturer and year), and the other two while your at it.
     
  10. skipm45

    skipm45 Member

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    Some electrolytic caps have a "pressure relief" vent and allow the electrolyte to blow out in the event of a failure (and some don't). The bulge definetely indicates a problem.
    +1 on replacing both
    +1 on JJ Tesla or F&T
    Another source..
    www.tubedepot.com




    Skip
    www.skipzcircuits.com
     
  11. Dexter.Sinister

    Dexter.Sinister Still breathing Gold Supporting Member

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    I use F&T. Get those out of there, Randy.

    DS
     
  12. golson

    golson Member

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    How do you tell if Orange Drop capacitors are bad since they are sealed.
     
  13. tmac

    tmac Goldmember Gold Supporting Member

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    When they start smokin' & drinkin' and running with the wrong crowd. :p

    Seriously, just checking for leaking current or maybe the pots are scratchy or other clues.
     

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