Good-All Type 623 capacitors

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

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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.

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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?

Update:

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I finally got around to slicing one of these open. 

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

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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.

© Steve Byan 2011-2016