1. Chrome Dinette

    Chrome Dinette Member

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    I have an amp that has MOV's going from plate to ground on two of the power tube sockets. I assume this protects the tubes from some sort of spike.

    Is there any detriment to this?

    How long does it take an MOV to go bad and can it be tested?
     
  2. donnyjaguar

    donnyjaguar Member

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    The MOVs are there to protect the tubes and transformer from arcing when the amplifier is run without a load. I've seen them on amp's that are running the tubes very hot and hard to get maximum power. The 90Watt Traynor bass amps using 2xEL34 come to mind here. The failure mode of an MOV is a short circuit and thus usually blow the main fuse (assuming it hasn't been replaced with tin foil). :) I think MOVs age pretty well so if the amp is working I'd leave them in there. As for how it affects sound, well you can remove them and find out for yourself. Just don't detach the speaker while you are testing... ;)
     
  3. Chrome Dinette

    Chrome Dinette Member

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    Great, thanks. No tin foil here, though I did blow a fuse the other day(it was a fast blow that should have been a slow blow). When I opened up the amp c to check for burnt parts, I remembered the MOV's.

    Everything works fine, so they didn't fail.
     
  4. AdmiralB

    AdmiralB Silver Supporting Member

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    MOVs, or diodes? I've never seen an MOV anywhere in an amp other than across the two legs of the AC supply.

    I've also never seen an MOV fail into a short; they've always blown up and gone open.
     
  5. Chrome Dinette

    Chrome Dinette Member

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    They are definitely 2000 volt MOV's. I have seen diodes in other amps/as a mod suggestion.
     

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