The AM Forum

This nice fixture was had at a vintage radio swap meet. It is part of a dielectric oil tester. What is shown is the top panel/cover of an oil-filled HV transformer (no longer present). The tap switch controls the primary, and the secondary voltage appears through the insulators. It is presumed that the primary AC line voltage is regulated.

The cup is to be filled with oil, and the micrometer sets the immersed ball gap spacing precisely. The voltage is then increased in rough steps with the tap switch until the dielectric oil arcs through, at which point the power is turned off and the gap widened until it no longer arcs under test. This way, the withsanding voltage is known in volts per inch with 0.001" accuracy.

Neat.

Wonder what the seals are?
Leather?
O rings?

All the coolest toys will someday end up at the "Bunker of Doom"

The seals are some sort of woven, heavily impregnated fiber washers, very thin. Due to age they may not seal well any more. I guess anything could be used as long as it did not change thickness enough over a long time to offset the calibration.

That bunker's getting full.. I need to have a donation party. Where I donate things to people with trucks. No scrappers need apply!