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Thread: Recapping Peavey Mark IV Bass Amp?

  1. #1
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    Recapping Peavey Mark IV Bass Amp?

    Do you recommend to providenly change all electrolytic capacitors in my Peavey Mark IV Bass amplifier?
    I opened up the chassis for cleaning purposes and wonder if this wasn't a good idea.
    The amp seems to work properly, just to mention that.

    Is there any possibility to adapt the transformers primary voltage from formerly 220V to 230V or 240V, since mains voltage was raised in Germany some years ago?
    I think this could protect transistors and electrolytic caps.

  2. #2
    Old Timer J M Fahey's Avatar
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    Personally I wouldn´t, unless actually needed; others may differ.
    As of creeping up voltages, they rise but not dangerously so, still within tolerance, and there´s not a practical way to adjust that, unless power transformer is an "Export" type with 220/230/240V taps .
    Some are wound that way, but I guess Peavey is happy with "universal" 2 x 120V>1 x 240V windings.
    Juan Manuel Fahey

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    This leads me to some other questions.
    How can I determine if a electrolytic cap actually needs to be replaced until it's broken dead short?
    And how can I tell whether I have an "Export" power transformer and if, how have the taps to be rewired?

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    I would not recommend recapping unless there is problem with the amp or there is obvious leakage of the electrolyte or damage to the capacitor. Don't fix something that is not broken.

    I have repaired a few of those Peavey amps and even though they are old the capacitors seem to check out fine. All except the big blue 5000uf/55v filter capacitors. I have had a few of those caps that were bad. I found them with an ESR meter.

  5. #5
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    I wouldn't re-cap either. I also use an ESR meter to give an indication of cap health. Rising ESR in a cap gives a clue that the cap is ageing and its resistance will only increase further.

    Many of the amps here in the UK are running off a mains supply that can be 248v or higher. Sometimes off a 220v or 230v primary transformer. They do this year-in, year-out. You need to check the schematic to see what the arrangements are for your particular amp. Unlike a tube amp, SS amps transform the voltage down so a 5% or so increase in supply isn't so drastic.

  6. #6
    Old Timer J M Fahey's Avatar
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    Courtesy of Enzo who published the schematic, here is the power transformer wiring showing "USA only" and Export versions.
    The former is 120V only; the latter has 3 taps: 120V, 220V and 240V .
    The black wire always goes to mains Neutral, while mains Hot is connected mains>switch>thermal breaker (the metallic fried egg shaped thingie bolted to heatsink, to cut power OFF if overheated) > Fuse > 1 of three coloured transformer wires: Blue, Grey or White meaning 120V, 220V or 240V respectively.

    So check which wire is actually used, other two might have ends taped or, in some amps, may go to "unused" terminals , simply to have them "somewhere" safe and not floating around.

    Schematic shows that "usually" amp is shipped with the 220V tap connected (Grey wire) since in the 80´s Europe was mostly 220V too, 240V was meant for UK, but voltages have been creeping up all over the World so nowadays the 240V tap might be a better match ... but check what do you ¨*actually* have first

    And post what you find.

    peavey-400bh-supply.gif
    Juan Manuel Fahey

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