Hey thanks, that sounds only too familiar. Got my rig end of October as well. Maybe they share the same bad batch of tubes ... As I am essentially a newby (stopped playing for 30 years ... and things have changed!) I was not able to pick up on sound issues (or may not have them), but I do definitly have a weird buzzing, rattling sound on specific notes at medium to loud volumes. Weeks ago, I took all the backing boards off and reseated the tubes and the issue went away unless I used very high volumes, but now its creaping back in ... and I started wondering how to approach this. As I said, with little experience on current amps/speakers and how they should behave at higher volumes, I was not so sure whether I am just a nit-picky amateur or whether there was really something not quite right. Will have to get back on to this ... although I have to say I'd rather play ;-) and at bed room levels I barely notice a hint of the problem.
Thanks again for the feedback. I feel much better equipped to do more checking and/or describe to a service guy what's going on. I would have never guessed at the tubes and was pretty sure that there was a mechanical issue with the speaker or some component mounting. Maybe 1 or more of the tubes' base is a little out of spec and does not seat snug. Certainly worth having it checked out if another reseating does not help.
I just stumbled on this thread - I was trying out a DT-25 at a dealer last night, but forgot to ask a few questions. What brand of tube is supplied with the DT-25 from the factory, and where are they made? Also, is there a need to re-bias the amp when adding new tubes?
I just had a brainstorm, dudes: Somebody should create an amplifier that uses digital models of tube amplifiers instead of actual tube hardware, then you'd never have to deal with issues like that. Oh wait. Nevermind.