I'd look at what's happening at the plate of V2B, where it feeds V3A's grid, and on thru V4. As well as V2A, who's plate and cathode voltages are low. That's where your DC voltages are not matching the nominal published values. I'd also be looking at the bottom of the PCB for solder joint fractures thruout the PCB. If typical Ampeg mounting practices, the front side of the PCB is supported by the pot PCB solder terminals, where I always find radial fractures. If there are connectors where we see all of those symbols where the tube plate/grid/cathodes pass thru the schematic rectangles, I'd look there too. So many of the faults I find on Ampeg SVT tube gear is mechanical in nature.