On Sun, 27 Sep 2015, Noel Chiappa wrote:
> From: drlegendre
> I'm not sure what you're describing. Can you link to a pic of one of
> these caps?
http://www.electrical4u.com/images/glass-capacitor.jpg
These are hermetically sealed ceramic and are non-polarized. The glass
encapsulation made them more expensive so they were usually only used in
high reliability, aerospace, military, etc type applications. There are
also similar sized axial ceramics which are epoxy dipped which are not
hermetically sealed.
One downside is like glass encapsulated diodes, you have to be careful to
support their leads at the capacitor's body while forming to avoid
cracking their glass shell. Also like with glass encapsulated diodes, they
should be covered with clear heatshrink if the board will be conformal
coated.
As for wound foil capacitor types, they sort of have polarity. In audio
and other noise sensitive applications, the outside foil end of the
capacitor should be connected to ground or the lower potential side of the
circuit. You also can't go by the black band printed on new manufacture
parts as it does not actually indicate the outside foil end (they are
printed randomly). When I briefly mentioned these before, someone pointed
me to this video which goes into more detail.
https://www.youtube.com/watch?v=BnR_DLd1PDI
