A

Two things I would check:
1. There may be a DC offset on the 1070 output.
2. Your left channel speaker may have problem.

This is not something that I've heard about before, so I'm not sure what the culprit might be. My first thought when hearing about an amp failure like that is wiring (particularly at the speakers), but the time between setup and event doesn't fit terribly well with that and the fact that the 1070's been hooked to the same cables and never blown up. You might want to give Outlaw support a call, though, just to see what they say.

a

DC on the output of a preamp will not effect a tube amp because tube amps are not direct coupled, at least to the power stage which is the only part which could draw enough current to blow a fuse.