[RodB]

You can use an ohmmeter to measure the plug pins. Two of the pins should have about 1100 ohms; that's the power supply field coil across the filter caps (12 and 16 mfd). The other two pins are the output transformer primary wires and should measure about 450 ohms. If you trace the socket pins in the chassis, each of the field coil pins should run to the power supply 12 and 16 mfd caps. Each of the opt pins should run to an output tube plate pin.