Thyrite question

The three orange cylinders on the back of the front shelf of the "drawer" unit. I will assume they are some sort of resistor. But what the heck are they and what do they do? And is there a way to bench check them. When
I ohm them out I get varying values. Thanks Daryl

They are voltage variable resistors. Supposed to be basically open for low voltages, or line voltages (a little more leaky at line voltage).

If the voltage goes above line voltage, they are supposed to effectively decrease in resistance and shunt away spike voltages.

When voltage comes down, their effective resistance goes up again. It is a non-linear function of voltage, at some voltage resistance really dives.

I don't know what you are measuring as far as resistance, but they should be a few megohms at meter voltage, maybe a few hundred K to a meg at line voltages.

The exact spec varies with the part.

They are an old version of the disc zinc oxide "tranzorb" etc that you see in lower cost computer surge limiters. But thyrite lasts longer.

As far as what they do, they keep inductive spikes from puncturing insulation and causing arcing in the C16J etc tubes.

Suddenly changing currents could turn the armature or field into an ignition coil, generating several thousand volt spikes.

Today, these proprietary GE Thyrite® devices would be replaced by MOVs.