#1
So I bought a B-52 At-112 February of last year, and it has been having some odd problems. When I turn it up pretty loud. It gets this weird screeching noise. I am pretty sure it isn't feedback because I have delt with it before. My bandmates describe it as like a demon screeching noise. It kind of modulates in pitch, I have turned my noise gate up as it was happening and that didn't do anything, but when I have the noise gate up high, the weird noise doesn't happen, but it affects my tone. The noise isn't constant and rising like your normal feedback, just at a constant loud volume, kind of like a scream echoing. We practice in a small room, I recently upgraded tubes. I have a noise gate and eq plugged into the front and a delay and chorus pedal into the effects loop. I have the footswitch plugged in also.

So I would like to know if any of you have experienced this problem before, and how to fix it, or also how to just tame feedback in general. Thanks.
#2
Well, you should first narrow down the source of the problem.
Try a different guitar and a different cable just to be sure that the problem isn't originating there.

However, this problems sounds like you have a bad tube. I've had this problem twice in the past (on two different amps). In both cases, changing out the tubes fixed the issue. It could also be possible that one of your tubes has become harmonic. To test this, with the amp turned on, gently tap on your tubes with the eraser side of a pencil. If you hear any change in your tone, then its definitely a bad tube.

It has been my experience that "combo" amps require more frequent tube replacement/changes as most of them share the housing for their tubes with their speaker cabinet. This means that the tubes are under more stress then in an amp "head".
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Last edited by theraven871 at Aug 23, 2010,
#3
Quote by theraven871

However, this problems sounds like you have a bad tube.

This was my first thought. One of the pre-amp tube to be specific. I think the power tubes die more quietly, but the pre-amp invokes the demons
Water which is too pure has no fish - Ts'ai Ken T'an
#4
Did this problem begin before or after the tube change?

If after, then almost certainly a bad preamp tube.

If it occurred BEFORE the tube change:

- Try cranking the amp up to the volume where you experience the feedback WITHOUT the guitar being plugged into the input.

If no feedback, try a different guitar.

If it still oscillates, it sounds to me like a leaky capacitor. Since it only occurs at high volumes, it could mean that a capicitor somewhere is breaking down at higher voltages. Likely a coupling cap, but that's not to rule out a filter cap, either.

If it gets to this stage, take it to a tech.
Tastes like chicken, if chicken was a candy.