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.
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.