High pitched squeal from amp

[Brian_SG]

Lately whenever I have my amp on for about 5-10 minutes all of a sudden a very loud, very high pitched squealing sound comes out of it. I'm at school right now with now way to really take it to a shop, but I plan to as soon as I get home. My question is does anyone have any idea of what it could be? I'm hoping i can figure out the problem and just fix it myself. Thanks for your help.

[ggunn]

Originally Posted by Brian_SG

Lately whenever I have my amp on for about 5-10 minutes all of a sudden a very loud, very high pitched squealing sound comes out of it. I'm at school right now with now way to really take it to a shop, but I plan to as soon as I get home. My question is does anyone have any idea of what it could be? I'm hoping i can figure out the problem and just fix it myself. Thanks for your help.

My first guess would be a microphonic tube. Power it up and tap on each tube lightly with a pencil. If that's what it is then when you hit the problem tube you'll hear it ring.

[TelePaul]

Originally Posted by ggunn

My first guess would be a microphonic tube. Power it up and tap on each tube lightly with a pencil. If that's what it is then when you hit the problem tube you'll hear it ring.

That's good advice. Just to add to that, it's normal to hear the tap through the speaker but a bell sound is bad. I'm guessing this is a relatively recent thing for you? The only other thing it could be would be your pickups - might need to be dipped in wax, but thats pretty rare AFAIK.

[clovermountain]

how old is the amp? when was the last time it was retubed? my bet is the tubes. not to mention if you've never done it, once you do you'll hear a world of difference provided you use good tubes. also, be sure to use the same type of tube. if you amp uses 12AX7G then use those. if it uses 6L6s then use those. don't switch to EL34 unless you know what you're doing and get it rebiased correctly. as far as brand goes, i like Groove Tubes, then JJ.

[dementedchord]

he didn't even say it was a tube amp... though thats most likely if it is a tube amp (microphonic tube)... any oscillation in an amp is caused by feedback... whether it's inside a tube or not... other areas of concern are tone control circuits and nested feedback loops (especially in solidstates)... most likely it's a cap thats changed value over time... look for electrolytics that are starting to ooze or the top might be bubbled up...

[clovermountain]

Originally Posted by dementedchord

he didn't even say it was a tube amp... though thats most likely if it is a tube amp (microphonic tube)...

my bad, i've been using tube amps so long now that i forgot other types even exist. i've never heard a solid state amp that i like. that statement may prompt others to give me examples, but it's just my opinion.

[Brian_SG]

Yeah, it is a tube amp. I haven't retubed it yet and its probably time to do that. I'm looking at replacement tubes and it'll probably be around $100 to replace all, not too happy about that haha. But we'll see what happens after that.

[ggunn]

Originally Posted by Brian_SG

Yeah, it is a tube amp. I haven't retubed it yet and its probably time to do that. I'm looking at replacement tubes and it'll probably be around $100 to replace all, not too happy about that haha. But we'll see what happens after that.

Why would you want to replace them all? If you find a microphonic preamp tube, just replace the one that's bad. Power amp tubes you'll probably want to at least replace in pairs, but check the preamp tubes first.

[dementedchord]

tap them lightly with a pencil... when ya get one with alot of snap/crakle/pop... thats the culprit... though ya might want to check the sockets to rule that out as well...