[NostalgiaRadioTime]

You can estimate the field coil resistance by looking at the voltage measurements on the schematic and the normal current draw of the tubes. The voltage difference between the 5V4G cathode and the 6K6G screen is 80 V (325V-245V). This is the voltage across the field coil.

The normal current draw of the tubes would be about 55 mA, so calculating by Ohms law,   80V/.055A= 1454 ohms.

So you are looking for a field resistance around 1500 Ohms.

The output transformer primary resistance should be around 400 Ohms. (15 V/.035A=428 Ohms) This is the DC resistance, not the rated load impedance which is  about 7500 Ohms.

Actually, most any output transformer for a 6V6, 6F6, 42, or 41 tube should work fine.

Many many thanks for that info!