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Twin AB763 filter cap question

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  • Twin AB763 filter cap question

    Would you dare to run 22uF @ 500v caps where the schematic shows 20uF@525v? They came in a customer's amp that has no PS issues, and I don't want to sell him something he doesn't need.
    It's weird, because it WAS working fine.....

  • #2
    What is the actual voltage?

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    • #3
      Schematic says 460, so even if it were 30v high the 500v cap is still enough.
      Education is what you're left with after you have forgotten what you have learned.

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      • #4
        Well then, 460 is OK on a 500 volt cap. Although as you know, the closer it comes to max, the shorter the life of the cap will be.
        So, it may last 10 years instead of 20.
        You could suppose that the rating was 525 to make it last longer.
        As has been said, Fender amps last a really long time, very reliable.

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        • #5
          The 500v rating on the caps are "working voltage" ratings. The 500v cap is designed to be used at 500v.Tha caps also have a surge rating that is higher voltage to accomodate surge voltages such as at power up.
          Education is what you're left with after you have forgotten what you have learned.

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          • #6
            Some AB763 can hit 530vdc on the plates, this will be taken care of by the series caps at the B+ node, but I'd check voltage & if necessary install 2x series 47uf 450v caps at the screen supply node, each cap bypassed by a 220K 2W resistor. With modern axial caps, you can usually fit the 2 in space left by the old, single, Mallory. 500v rated caps will be fine for PI & preamp nodes.

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