So a while back I purchased an ENGL Powerball, and when i received it, channel 2(the high gain channel) had an oscillation problem that rendered it useless. Recently, I decided to try and get by playing metal via turning the gain on the first channel all the way up, at which point the amp promptly displayed similar symptoms.

The sound of the feedback/oscillation/whatever it is, sounds differently depending on the amount of gain and the EQ settings. Turning on the bright and bottom switches affect it also. When increasing the gain, the sound turns from a loud mid frequency hum to a shrill squeal. I took it to a tech, but he couldn't figure out what was wrong with it.

I tried replacing the preamp tubes with known working ones, which had no effect. However, I didn't have any other 6L6's to change the power tubes. I would assume, however, that this is something a tech would check? I really don't have money to spend on the tubes right now, so is there any way to figure out if they are the cause without having to buy new ones for it to possibly not even be the problem?

EDIT: The amp produces this feedback even without a guitar plugged in, and no matter what cab I connect to it or what cable I use to connect it.
Last edited by aildeokl at Aug 14, 2010,
It sounds like to me that your pick-up might be extremely microphonic.
Have you tried to use a different guitar with it?
Does it do it at low volumes?
Unfortunately no, the amp is no longer under warranty.

And as stated in the original post, the amp produces this oscillation even without a guitar plugged in.
Try swapping in some known quality preamp tubes. Often times a weak preamp tube in a high gain setup can send the amp to the shitter. Just a suggestion before you start ripping the amp apart and dumping money into it.
Sorry, I thought i included this but evidently I didn't. I'll edit it into the OP in a sec.

Swapping the preamp tubes with known working ones was the first thing I did, before I even considered calling a tech.

EDIT: No edit necessary, it was already in the OP.
Last edited by aildeokl at Aug 14, 2010,