[Vlad95]

And now for the sad, but fortunately resolved, issue: audio transformers.
As I already wrote, the original transformers are clinically dead.

         
   
   

To find a suitable replacement, I examined the output transformer of my working Philco-20A, which has a completely identical audio amplifier output stage and the same 8-ohm speaker impedance. With the speaker unplugged, I applied 3 volts to the output and measured the voltage at the tube anodes. The result was about 60 volts. This means the required transformation ratio for each anode is about 20. Therefore, a suitable replacement would be a 120 + 120 volt to 6 volt line transformer. And I found one at a very reasonable price—only about $11. It's a Jameco Reliapro 9W TR4820-91-R Power Transformer.

   
   

https://www.jameco.com/z/TR4820-91-R-Jam...BEbDF7kXTv

Primary winding: 115+115V, 9W.
Secondary winding: 6+3V, 1A.

   

This transformer is suitable for the output transformers as is, and only the primary winding will be used as a phase-inverter autotransformer (FIAT).

         

An additional 10kΩ resistor and 0.1μF capacitor for the modified circuit were built into the casing, resulting in the connection of the transition transformer remaining exactly the same as in the original circuit.