[Ron Ramirez]

The rubber insulation used on the leads of this power transformer contributed to its demise, no doubt. I've seen many 1939 Philco models that had rubber insulation on the power transformer leads; with evidence that the rubber melted, then dried out, then flaked off, causing the wires to short together.

I would go ahead and replace it. The original specifications are:

High voltage secondary: 410 volts center-tapped (205-0-205 V), 42 mA.
Filament: 6.3 V, 2A.

You'll need a vertical mounting transformer, which is easier to find than a horizontal mounting transformer.

Either a Hammond HX-269EX or HX-269GX will serve as a replacement. I think I would go with the HX-269EX; its high voltage secondary is 380 volts center-tapped (CT), compared to the 450 volt CT output of the 269GX. Too much B+ could upset the circuitry of the TH-3; causing squealing/oscillations, etc.

You can buy Hammond transformers from Radio Daze.

http://www.radiodaze.com/