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Guitar amp re-capping

Discussion in 'Electronic Basics' started by Bearded Occam, Jan 3, 2008.

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  1. An old guitar amp is headed my way, solid state, maybe 50 Watts, maybe
    a couple decades old. One reads about the finite lifetime of
    electrolytic capacitors, so I have some questions:

    1. What are the actual failure mechanisms?

    2. Is there a convenient way to check an electrolytic?

    I don't want to replace more caps than necessary. One website suggests
    simply following the signals with a scope and verifying that the
    functioning of the circuit is consistent with functioning capacitors,
    and I will certainly do this, but am wondering if there are some
    tricks of the trade to know.

    Thanks in advance!
     
  2. Phil Allison

    Phil Allison Guest

    "Bearded Occam"

    ** But how many hours has it done??

    Bet it is only a tiny percentage of what a TV set usually does in 20 years.


    ** 99% pure bollocks.

    Forget it with a SS guitar amp.



    ....... Phil
     
  3. Eeyore

    Eeyore Guest

    The electrolyte dries out.

    Measure the capacitance.

    Not really adequate.

    Power supply caps are likely to be the main problem. Check for abnormally
    high ripple voltages. Also check for bulging cans and signs of leaking
    electrolyte.

    Graham
     
  4. Phil Allison

    Phil Allison Guest

    "Eeysore"

    ** Wrong.

    One measures the ESR and compares the reading with a similar, known good
    electro.

    A high ESR value indicates serious loss of electrolyte.

    The capacitance falls only much later in the failure process.





    ......... Phil
     
  5. Eeyore

    Eeyore Guest

    I've certainly seen examples of capacitance seriously degraded as a result
    of the 'bad caps' issue.

    Also, not everyone has an ESR meter by a long way. Any other suggestion in
    the absense of one ?

    Graham
     
  6. Phil Allison

    Phil Allison Guest

    "Eeysore"

    ** You can fabricate a simple ESR meter using an sine generator ( set to
    50kHz to 100kHz ) and monitor the output with a scope set to max
    sensitivity.

    Then just connect a co-axial output lead across the electro under test.



    ........ Phil
     
  7. Nice and simple. Good call. Lacking a real signal generator, I will
    try it tomorrow with a frequency in the audio band, using my PC as the
    generator and analyzer.
     
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