[Elecraft] Re: tube amplifiers and polypropylene capacitors

[BMW]

Polypropylene caps are useful for two main things:

1) circuits that rely on repeatable charging/discharging characteristics
(such as analog to digital converters, sample & hold circuits and active
filters), due to their good dielectric absorption properties (i.e., they
don't "re-charge" after being discharged as bad as some others)

and

2) high voltage circuits, due to their high voltage ratings.

They are great replacements for paper caps in boatanchor radios. They are
not as useful in other modern ham applications because of their size. C0G
and NP0 disk ceramics are smaller and do the job nicely. Poly caps also have
a linear, negative temperature coefficient, which makes them good for
temperature compensation in LC circuits.

I don't really know of any reason to use them in audio circuits over
ceramics or bipolar electrolytics (depending on capacitance value needed).

Brian, W0DZ