I think there were a couple things going on with the hum... The first night we were getting everything ready to fire up for Andy, Tom, Levi, Martin, etc.... We go to plugin the guitar, no guitar cable!! All I had was a 5' speaker cable! It worked, but was noisy as hell, as you can imagine.
Tom ended up coming back another night and we actually had a real cable. His guitar, more than others still picked up a crazy hum in the room, also worth noting he has only single coils. This hum was also evident, though to a much lesser degree, with humbuckers. There are some florescent lights both in and below the room where there are parking spaces. The only thing I can figure is there was some hum induced from those. Unplug the guitar and it's silent. I demonstrate this at some point in a video, though I'm unsure which.
Sure can! The bias points allow you to easily measure the bias current with any DC voltmeter. The bias pot is on the top of the chassis, so no need to remove it for anything except service. Also the bias range allows you to dial in any tube without flipping any switches.
All our amps come standard with "bear claw" style retainers, so you can't use big base tubes (KT66, KT88, 6550, etc) without removing the retainers, or asking us to install spring retainers instead. We'll also ship with any tube you like, but most chose to keep the stock 6L6GCs.