Zenith H-500 Transoceanic Quandry...

[Reece]

The tubes are in series: if one goes out they all go out, and right, you can't see them lit, they are so dim. It's been a while since I worked on one of these but I believe I put something between a 50 and 100 ohm 5 or 10 watt resistor in series with the new silicon diode to drop the voltage. The silicon rectifier drops less voltage than the old selenium does and needs the series resistor. Whatever value resistor it was, it put the voltage across the whole filament string right on the money per spec. I seem to recall it's supposed to be 8.6 volts or so? Sorry I don't have the exact value but there is some variance in thought. I'd suggest reading up across the net on power supply modifications specific to these sets.

What you can do once you figure out if you need a new tube is plug in the tube and put your voltmeter across the filament string and bring the set up on the variac. See if you've arrived at max filament voltage before you're at standard line voltage. With no series resistor, you will be, so you can try something about 75 ohms to start.