[rghines1]

Adding up all the filament voltages comes to 106. Assuming a typical mains voltage of 122 VAC, leaves 16 VAC across the resistor. Assuming a nominal 150 mA for the filament string, the varistor wattage would be 16VAC x 0.150A = 2.4 watts and a resistance of 16/.150 = 106 ohms. The schematic appears to be showing a hot resistance of 100 ohms for the varistor. Curious if you could measure the voltage drop across the varistor. Also would interested in the mains voltage and the filament voltages across a tube such as the 35C5. If you really want to pick it apart, break the filament string circuit also to get a current reading. Makes for a good ohm's law exercise. The varistor at 2.4 watts will burn your finger. Richard