Conrad Johnson Premium 12 - Noise when turned on

I would get a new 6550 from C-J. Not sure if you have the GE or Svetlana, they now use Svetlana though. You should be able to isolate it to which monoblock first. That narrows it down to 4 output tubes, once you figure which mono it is coming from. Take the new tube, put it in place of one of the four, and fire the amp up. If it persists, put the original tube back in it's slot. Then repeat this procedure, inserting the new tube in place of the second original tube. Then , same for steps 3, and 4 if necessary. Hopefully, it's just a tube. Nice amps BTW. Keep us posted.

Had an even simpler thought. Once you have isolated which mono, use a 6550 tube out of the amp which is OK. This way,
you won't order a tube you don't need. I would order it anyway just to have spares though. It's been a while since I had my 8A's. Normally a red light indicates a bad tube.
However, in this case it just may be a noisy one. I always loved the Premier 16 combo w/ my 8A's.

Thanks Fjn04. I will find time to do the exercise. Hopefully its just a bad tube.

Sounds like a tube may be ready to go bad. If the tube was already bad the amp should have blown the plate fuse which is indicated by the red light on the top of the amp chassis as mentioned above. You should try to isolate the problem quickly before the fuse blows. Once the fuse blows you will have to replace the fuse before swapping tubes around and then you must figure out which tube is going/has gone bad before the fuse blows again. I just went through this with my Premier 12’s and at $15 a piece each time you have to replace a fuse it can add up very quickly.

BTW, I use the Premier 16 with my 12's....GREAT combo.