Thanks for the replies. The specs are 120 ohms cold and 6 ohms hot. I do not know what the current rating is (it does not say on the schematic) but it about 7/16" in diameter. I didn't see anything like that in the Digi-Key catalog but will check again.

It is in series with the 155 volt power supply so I would imagine that it has to be a fairly high current one.

I tried a circuit with a positive temp thermistor - it didn't work and would up magnetizing the face of the picture tube so I had to manually degauss it...

It would be great if I could locate a set of OEM Heath parts!