[Reece]

Have the unit unplugged and the power switch turned ON. Take the unplugged plug (!) and clip the ohmmeter probes onto the prongs of the plug. Set the meter on lowest ohms. You are looking for some low ohms reading here, maybe between 3 and 10 ohms, exact number not important. The important thing would be that you don't see zero ohms or something really close to it. That would mean you had a shorted transformer primary, or that the .1 mfd. caps are shorted that are connected from each side of the transformer primary to ground. You can test across each of those also to check for shorts should get infinite ohms.

I'm betting that the power xfrmr. is OK and after the test above it's time to do the light bulb test as outlined before.

As to your output transformer, I think you can get along without one. The original circuit was meant to be used in a studio or similar "back in the day" with 500 ohm line output. You'll probably be connecting this to a home amplifier in mono mode, and it could be done with a resistor/capacitor circuit. In the bottom right hand corner of the blueprint schematic is shown the 76 output tube and the original transformer. If you could sketch and post what that circuit looks like now it would be helpful.
Thanks!
Reece