[Ron Ramirez]

Yup, I was right about the ballast...it can be plugged in two ways. In the 115 volt position the radio operates through two jumper wires inside the ballast. In the 230 volt position, two resistors (resistance wire inside the ballast) are placed into the circuit to drop the voltage.

I was looking over the 42-761 schematic. I see it uses two 25L6 output tubes in push-pull, and a 25Z5 rectifier. Lower output power than the AC-only 42-760.