[trinescope]

So far every vintage style transformer I have unwound has been constructed of the same materials; enameled magnet wire, some sort of thin, wax coated paper between winding layers, and kraft paper covering the outside of the winding assembly. It's the wax paper layers that get burnt through, creating a carbon path and a winding short when the enamel on the wire fails after age and there is enough voltage stress to cause an arc. Voltage pulses in the vertical output stage can reach up to 2KV or so. Modern single build magnet wire insulation is good for 700V, and Kapton tape for 7KV/mil; these are what I have used so far in my transformer rewind projects. I'm sure Zenith had a few failures at most when the sets were current, these failures are occuring decades after most of these sets were retired by their original owners.