[Arran]

The so called "Usual Battery" set with 1.5 v and 90 volt batteries didn't really come onto the market until 1939 or so. The Philco model 623 is from 1936 and using two B+ voltages and C- voltages was not all that common. They are not really that complicated to get running, the battery eliminator kit that antique electronic supply used to sell (maybe still does) is more then sufficient to run one of these.
If you are a little better at home brewing you can make supplies out of scrapped parts, probably one of the easiest things to use is a power transformer from a 1940s through 1960s radio-phono combo units as they have most of what you need, 5 volts, 6.3 volts, and a 350-0-350 high voltage winding. I've also read about people using a pair of low voltage transformer connected back to back like joernone did on you tube.
I don't know how much of a hurry you are in but our own Bob Andersen also has a Philco 623 that he is planning to restore and needs to build a power supply for, maybe you could wait and see what he come sup with?
Regards
Arran