Tube Amp Technical Question

I have a pair of Wright Sound Mono 10 amps. Recently, I heard some static out of one of the amps, and now, although I don't hear static anymore, one of them produces significantly lower output than the other (about 5db measured with a sound level meter). I tried swapping all the tubes between the two amps, but it made no difference; the amp with the reduced output before the swap still has the reduced output after the swap. Anyone have any idea what could be wrong?
If the biasing is manual, did you check it? Otherwise, it sounds to me like you will need to contact the manufacturer about this one.

Thanks for the thought; the amp is auto biasing.
I recommend calling George. I'm sure he can help. He's quite generous with his time if you get him on the phone. Good luck, Mark
Yeah, thanks. I have spoken to him before; he is quite helpful once I got a hold of him which wasn't that easy.