Gs5556 and Pawlowski6132 named probably the biggest don'ts.
If you get a tube amp that has a power on switch and a separate standby switch, be sure to follow the owner's manual and don't turn them on in the wrong order.
If you get a tube amp that has a power on switch and a separate standby switch, be sure to follow the owner's manual and don't turn them on in the wrong order.