Is the ringing coming from one channel or both? If one channel try swithcing the tubes to the opposing channel and see if the ringing moves.
Do you hear it in both channels? If so for it to be a tube it would most likely be one that services both channels. I'm not familar with your amp but a single tube serving two channels is not uncommon, they have two sections.
Ringing is most often associated with the small tubes, try them first.
In my experience ringing in power tubes is not common except for a headphone amp I use :-), so it is possible, but again it would usually appear in only one channel.
Do you hear it in both channels? If so for it to be a tube it would most likely be one that services both channels. I'm not familar with your amp but a single tube serving two channels is not uncommon, they have two sections.
Ringing is most often associated with the small tubes, try them first.
In my experience ringing in power tubes is not common except for a headphone amp I use :-), so it is possible, but again it would usually appear in only one channel.