Mark, yes, the wave change switch is missing (I assume it should be next to the tuning coil?) if you want the rest of the chassis, drop me a pm.
Many thanks for the pointers on PL36 used for audio - complete with circuit diagram and 55v grid bias. One of them has indeed gone to air. While there are strong arguments that this could be an amplifier, I have sympathy for ac/hl's argument on sparse components. I will take the transformer off the chassis to try to work out whether it is a meaty PP output transformer (for which I have no use and would need to rehome) or a mains transformer (which would be useful to me)...
I'd like to try to use the PL36s SE, the graphs seem to suggest that strapped triode and with lowish anode volts there is a usably straight part of slope.... But it will be down to experiment rather than calculated design