[Arran]

Not correct on the B+ voltage, for some reason they chose 67-1/2 volts for the B+ on this set rather then 90 volts like most battery sets do. I have the same model but it's a little more neglected, the back is missing, also one of the battery packs must have been left inside and sprung a leak as there is a rusted area on the back of the chassis. I wouldn't be surprised if either your set or mine still worked if power was applied, short running times, low voltages, and no heat tends to make the caps, resistors, and wiring last a lot longer. I would even consider restuffing the original caps as there are only four of them in there, it's not too hard with a toaster oven and a glue gun. The service info for this model is in my 1940 Philco service manual.
Regards
Arran