[Arran]

Given the era this was built I would check the primary of the audio output transformer, I would also check the plat load resistor of the first audio tube for either being open or greatly increasing in resistance, though the latter problem I haven't encountered in a Philco. These sets had the audio output transformer mounted to the chassis, and whilst that wasn't an issue in itself, for some reason the transformers have a high failure rate. I'm not an engineer but I have wondered before whether it has something to do with the "screen gid inversion" setup they used in the audio output stage, whilst this set has a ninth tube that they are only using it as a detector, not a phase invertor, so it's basically a 41-280 with a tube stuffed chassis.
Regards
Arran