[FullRangeMan]

Thanks Dave.

[Russell Dawkins]

Actually, it's the amp. I switched the left and right and now the other driver squeals with feedback. What could that be? bad tube?

At least by this point, having done this, you can be certain it's not the speakers that are at fault, so it doesn't matter how 'ancient' they are.

[windupman]

At least by this point, having done this, you can be certain it's not the speakers that are at fault, so it doesn't matter how 'ancient' they are.

Yes, it's definitely not the speakers. I've tried switching the preamp tubes and it still screeches out of the same channel. The odd thing is that it works fine for a few seconds - maybe even 30 seconds sometimes - and then it starts with the feedback noise.