I'm not an amp tech but I can follow basic instructions. Before I take it to someone thought I'd seek help here first.

I have an FM50 that is about 1.5 years old that blew a fuse. Tried replacing the fuse but it made a loud hum and blew again. Put new tubes in, replaced fuse, and sound is passing and amp is quiet. This is all at low volume so I'm thinking nothing is wrong. Stuck a meter on the tubes to bias and the left tube (looking in from the rear) is at about 37mv. Checked the right tube and nothing. I swapped tube position (left to right) and still whichever tube was on the left checked ok and the one on the right read 0.0.

When the amp is turned on in standby both tubes glow orange where they should on the inside of the tube. When I switch from standby to operate only the left tube glows blue.

Any ideas about what I should look at or check first would be greatly appreciated.

Thanks