silverface concert lead lets out horrible squeal

[cooldude666]

ive got a silverface concert lead that used to sound awesome, but one day I turned it on an it sounded funny. quiet, squashed, like something was holding back the current. A few minutes later smoke was pouring out of it, now when I turn it on it just lets out a horrible high pitched squeal. I don't see any charring on the PCB to indicate where the smoke was coming from, I'm sort of guessing the OT is fried but how should I go about solving this and ideally getting it running again. I'm interested in solid state amps so I'm kind of invested in fixing it so I can learn a lot more.

[loudthud]

There is a power amp input jack on the back of the amp. Does installing a cable in that jack eliminate the squeal? That would mean that the power amp is ok and the problem is in the preamp. If you know anything about solid state amps, you would know that virtually none of them have an output transformer. The Sunn Concert amps have an interstage transformer to drive the power transistors. They do go bad and are very expensive to replace.