We are using the 6AF11…it’s a Compactron with two triodes and one sharp cutoff pentode. It’s definitely not a common tube to use in audio amplification. It was originally designed for video amplification in TV circuits, but we’ve found it sounds great in a guitar amp. I love using obscure tubes in guitar amps because of the unique tone you can get with them, and it’s fun to repurpose something that probably would never be used anyway…there’s not many working tube TV’s around anymore, but there are are plenty of these tubes left.
No! Sorry. We laid our hands on a warehouseful of these peculiar tubes and designed the amp around the tube. If the tube ever fails, replacements are not hard to find; and of course you can always get one from us. But you must use the same Compactron 6AF11.