[Arran]

1. All 5 wire-wound resistors, 50K, 100K, 250K, 500K have run away to the values that are anywhere 30-100% up.
Wow. Granted, I have no experience with these that are 80 years old but the resistors I did not expect to behave like so.

Need to buy those.


2. Also, the tapped resistor last section (1-2) of 1.4K that ties the 71A filament's Power Xfmr winding center-tap to all other Xfmr centertaps was just opened.
I even think I know why - the output stage probably smoked, as the output audio Xfmr primary, one half, was fried, and so was one of the tubes. There was something catastrophic, so the current probably burned that 1.5Kohm section.

Once I put an external 1.4K resistor there, the speaker came alive, and I clearly hear a reasonably loud scratch when I rotate the volume (the antenna attenuator) var. resistor.

I wonder what else's in stock for me, but I will start with resistors.

I want to buy "authentic" parts, so what do you tfhink of "Philcorepairbench.com"?

Wire wound resistors do not drift, they either go open or some of the turns may short out which would reduce the resistance not increase it, you may be thinking of body-end-dot code carbon resistors and yes they can drift 30-100% upward in value. As far as I know nobody sells authentic resistors for these sets, to have authentic looking resistors you would have to take a modern resistor and cast in plastic resin to look like an old B.E.D "Dog" bone style resistor.
Wattages can be tricky to figure out but most carbon resistors aren't any more then maybe 2 Watts in size, the vast majority of the small ones will be 1/2 Watts, the medium sized 1 Watt, and the larger size 2 Watt. Sometimes you can figure it out the wattage by where it is used, grid bias resistors can be as low as 1/4 watt, cathode bias resistors usually 1 watt for example, plate resistors can be as low as 1/2 Watt for a single tube, voltage dividers are usually wire wounds but in sets with a fixed bias supply they can use a series of large carbon resistors from 1 to 2 Watts. If you had the factory data it would likely have a parts list to tell you exactly what they used.
May I suggest using your voltmeter here? There should be B+ going into the center tap on the primary of the output transformer, then each leg should be going to the plate pin of each of the #71A tubes. There should be an audio interstage transformer in the amplifier circuit as well, the primary has one end connected to the B+ circuit and the other connected to the plate of the first audio tube, either a type 27 or a 56 tube. The secondary of the audio interstage transformer should have the center tap grounded or connected to B- somehow, the two legs of that transformer should be connected to the grids of the #71A tubes. The resistor between the center tap of power transformer winding © and B- is either for hum control or for tube bias, it would be unrelated to whether the output transformer primary was open because the output transformer is in the plate circuit.
So the plates of the #71As should be getting 200+ volts B+, the plate of the 27 first audio tube should be getting something maybe 20 volts less, so if those are getting B+ everything ahead of them is working. There are no voltage divider resistors ahead of these points, just a filter choke, and the output transformer primary in the case of the 71As, and a choke, the speaker field coil, and the primary of the interstage transformer in the case of the 27 tube.
The volume control is in the antenna circuit as you noted, turning it may result in scratching noises but that does not necessarily mean that everything after it is working. See if you can find a voltage chart and then check all of the voltages on each pin of each tube, if anything is missing or way off then check the resistors, capacitors, and coils connected to it or in line with it.
Regards
Arran

P.S Here is a voltage chart and schematic located on another web site, it may be enough to get you by:

http://www.nostalgiaair.org/PagesByModel...029582.pdf