JVM205 Head Screech

Jim DeSclafani

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when i turn on my JVM205 head ,after about 5 minutes , a screeching sound comes out last for 5-10 seconds, then the volume drops about 2 notches, and get alittle muddled, anyone else have suggestions before i start buying things that might not work, im thinkind preamp tubes?. starts out fine . then this happens and happens on both channels
 

Leonard Neemoil

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when i turn on my JVM205 head ,after about 5 minutes , a screeching sound comes out last for 5-10 seconds, then the volume drops about 2 notches, and get alittle muddled, anyone else have suggestions before i start buying things that might not work, im thinkind preamp tubes?. starts out fine . then this happens and happens on both channels

Welcome to the forum.

Does it screech with the volume all the way down?
 

scozz

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Do you have spare tubes lying around?

Something like 70% of tube amp issues are with the tubes, I would try swapping out the preamp tubes one at a time first.

If no luck, I would then change out the pair of power tubes with a matched set. Failing that, off to the tech it goes, because changing tubes is the extent of my amp knowledge, lol!
 

Jim DeSclafani

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That would lead me to think preamp microphonic. Does it do it with volume off and gain low? A micro tube needs to have gain and volume.
So the latest!! Last nite clean green channel went out , but only thru back end, FYI I’m running a GT1000 with 4cm . Curious if that has something to do with it , I always ran it with clean green , now that doesn’t work, but will work if I switch to any other channel
 

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