loss of volume and gain channel on channel

[will9999]

Was playing around in the basement before work and noticed that channel three didn't quite sound right it's almost like
It lost some gain and volume. Also I found when I turned the treble knob it would fix it for a while but it would go back to sounding anemic after a few minutes. Any thoughts?

 

[miqueas92]

Chan's 1 and 2? what about them?

First thing, change your power tubes. If you have a set you know are good, put them in.

Being that its just Ch. 3, could be a pre. Check the power's first though.

Mick