Carvin X-100B -- is this a tube problem?
I'm relatively new to using tube amps -- mine's a Carvin X100-B. (I like it a lot!) I bought it used "with new tubes" (4 6L6 and 3 12ax7). I have not replaced the tubes in the year or so since the purchase. I always play on the dirty channel with the lead drive all the way up and the master volume about 3 or 4. Recently I have noticed two things:
1. An intermittent wind-like noise, like someone blowing across a microphone. More noticeable at lower playing volume.
2. Pretty regular syndrome (at any volume) where the sound suddenly loses brightness, volume, and gets a little muddy. Sounds like the sound has receeded into the back of the speakers (Legacy 2x12 cab w/ V30s). Most often after some time (15min at least) the sound comes back to near normal.
I use good cable and there's no obvioous problem with the input jacks. I would be grateful for any advice. Thanks!