I've used prototyping pcb boards sold on Ebay by various Chinese sellers. You can find them by searching "prototyping pcb board tube".
They have footprints for several 7, 8 or 9 pin tube sockets, size 150x200mm barely enough to assemble all the power push-pull amplifier stuff, thickness 1.6mm makes them too flexible and fragile to cracking.
Images of prototyping boards with KT88 Williamson ans floating paraphase /push-pull attached.
Extra terminals soldered on board used to switch between penthode, UL, triode and CFB modes, turn GNFB on and off, and attenuating RC networks. Very handy to tweak and debug amplifier.