Shit, I go poking around the Crack to see if I can find any loose connections that might have explained the right channel going out last night (which would come back if I pushed on various spots on the amp or tubes), and when I set it back up, I'm now getting a low-pitched, quiet hum. There regardless of tubes, volume, input connections, etc. Most likely scenario is that the connections need reflowed, but this thing looks like a PITA to work with given the speedball upgrade, huge caps, and given whoever built this did a sloppy job of it. Sweet! (Will pay good money if someone wants to take a look for me, seriously. I don't have much time for this.)