Good-All Type 623 capacitors

I've been working on re-capping the audio chassis from my Voice of Music 307 portable stereo phonograph.


It had these unusual capacitors in it: Good-All Type 623, in 0.1 µF at 200 VDC  and 0.047 µF at 400 VDC values. At first I thought they were wax paper capacitors, but they are coated with some very hard encapsulant, possibly epoxy. 

I can see a few frozen drips of the encapsulant. They are rock-hard and are amber-colored. The capacitors were clearly coated by dipping them into the encapsulant.


The ends even look somewhat like beeswax. They look like they are some kind of slightly porous white ceramic underneath the encapsulant.

I tested them with my just-restored Simpson Capacohmeter. They test fine on the insulation resistance test, but show a little leakage on the pulse test (though I'm not very familiar with the pulse test yet, so it may well be instead a fault in the Capacohmeter). I think I could have left them in the circuit rather than replacing them.

Anyone know what's inside these capacitors? How were they made? Are they usually still good, like mine?



I finally got around to slicing one of these open. 


They are definitely metalized film capacitors. Probably Mylar (polyester). 


The metalization is so thick that the film behaves more like aluminum foil than Mylar.

These Good-All type 623 capacitors are good quality film capacitors. I could have left them in the circuit.

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