Bad Tube? Which one?

call Mark at Rogue.

I would not even play it until you talk to him, it could be a bad cap or resister.

Just to be safe imo...

Can you isolate the problem to one side or the other? If so, move the output tubes to the other channel and see if the problem moves with the tubes. You can do the same for the small signal tubes if needed.

Always a good idea to keep some spares on hand for these types of investigations.

Tom6897 is right. When you own tube equipment you should always have a spare set of tubes on hand.

I'll 3rd what Tom6897 and Rrog said.

A spare set will come in handy when:

1. Things go bump in the night. I just had a tube rectifier develop a short. Replaced the fuse and rectifier and was good to go.

2. Diagnosing. My 2a3 amp was sounding a little flat. Tubes measured ok and I could bias them properly. Put in a new set of 2a3's and all the life came back.

Even though your KT90's bias "a perfect 35 mA" they may be tired although gambling, I would bet on one or all of the 12's. Get a new set of them first, they're cheaper.

I do have a spare matched quad of KT90's. I'll call Mark at Rogue and also get some spare 12's.

So I guess I should have mentioned that my CDP is also a preamp. The issue was the volume on the CDP was turned up all the way and was clipping the input to my amp. I can't take credit for figuring this out. It was my amazing local salon owner that made me aware of this as being a possibility. I'm still ordering spare tubes because the pain of one week without music was worse than passing a kidney stone (been there). Thanks for all the input.