On one leg or two legs?

That's very interesting. So the amp with the more severe hum/buzz also has lower gain. It could be due to a lot of things, but I suppose the most likely culprit would be a tube. Perhaps before taking it back to him it would be worthwhile switching tubes between the two amps.

Regards,
-- Al

Al,
Yes, that's what I'll try tonight.

A bad tube can definitely cause a buzz and a bad electrolytic in the power supply can cause a hum. I would also think a leaky cap in the signal path could cause a hum.

You might want to send an email to BAT customer support and ask them.

You never answered my question. Do the amps have auto biasing? If you do not know for sure I would not just switch the tubes around.

Jim -- He appears to have answered that, at the end of his first post dated today.

-- Al

Amps are self biasing.
02-04-09: Maril555

Al,
Thanks I missed it on the first read.