Channel switching volume drop

[jpatt2]

My tube amp has never given me any trouble before, but I noticed yesterday that when I switch channels, Channel 2 has almost no volume, even when I crank it. Channel 1 still makes my ears bleed, and even though I keep channel 3 clean, that works just fine too. I made the mistake of turning it on without a speaker hooked up and let it warm up on standby for about 15 minutes like that, but as soon as I realized I was getting no sound, I shut it right off. Any potential causes? Any help would be greatly appreciated...If it helps, it's a Mesa Triple Rectifier (which I love the tone I get with bass, oddly enough).

 

[BassmanPaul]

Swap the pre-amp tubes one at a time between channel 1 and 2. If one change makes the low volume on channel 1 change out that tube.

 

[Bassmec]

Swap the pre-amp tubes one at a time between channel 1 and 2. If one change makes the low volume on channel 1 change out that tube.

Yup to the failed pre amp tube, if the original poster did not attempt to run the amp out of standby with a signal other than for a few seconds, Then he probably did no damage or very little damage to his tubes and output transformer by not connecting the cab.
A mesa triple rec makes a great bass amp, recorded an album with one as a bass amp not so long ago.