MIKELAP
Headphoneus Supremus
Just flip it over and look on the volume knob side of the amp in one of the peep holes with a flashlight towards the side of the amp like picture .Mine is a 2012 model and it has a revision 2.0 board if its more recent i think its a revision 4.0
The searching took a while, but I found it: 4.0!Thx!
Still, for accessing the switches if I want to try different sorts of tubes in a possible future, I think it's easier to open it up, right?
I dont recommend opening it up its a pain the only thing you need to get is long jumpers and its going to be a breeze to change them to try other tubes