Bugera 2x12 combo is buzzing

[Deathmachine]

My Bugera combo amp is making a constant buzzing. Is there anyone that can give me some advise on how to fix it. I love this amp and I don't wanna replace it

[pdf64]

1st supect is a bad tube - use a 'known good' 12AX7 that you can use to sub in to each suitable tube socket in turn.
Circuits with elecated cathode voltage, such as phase splitter and cathode follower, are more suseptible to heater-to-cathode insulation failure.
Maybe the heaters have lost their ground reference, eg blown resistor.
Pete.

[Enzo]

Turn ALL the controls to zero. Does the hum remain or does that make it quiet?