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Re: More info on mica caps (was Re: .062uf 20,000 volts cap on Ebay)
> > I had to jump in on this one as well. Sangamo mica caps (sometimes)
> > if you are lucky, do hold up to repeated abuse at (or above)
> > nameplate ratings. I must take exception that mica caps (in general)
> > are lossy. Quite to the contrary! They are very low loss: (look
> > up the dielectric loss tangent of ruby mica in any CGC Handbook.)
> > Mica caps are possibly the very best, at being low loss and high
> > effeciency; espececially with respect to size and weight, not
> > to mention low dielectric heating cooeficients, even at many MHz
> > of operating frequencies. They are, however, *much less forgiving*
> > then extended foil type capacitors; especially the poly-pro family.
> >
> > In my more then 25 years of work with this type of capacitor I
> > submit the following (rated best to worst.)
> >
> > #1) Cornell-Dublier
> > #2) Aerovox (now mfr. under a different name.)
> > #3) Sangamo
I have been using an 0.006 ufd, 30 kV DC Sprague transmitting mica for
about 20 years, usually in connedtion with 15 kV, 60 ma NST's. While
it's a little smaller (electrically, its enormous physically) than I
would like it works like a champ, doesn't get hot after running for
about as long as I think I dare before the neighbors or police start
knocking on the door (15 min or so), and doesn't get warm at all. I
have a couple of Murdock 15 kV, 0.001 ufd molded micas from pre-WW1
which still work. They were sold in modules of 0.001 ufd and the user
apparently bought as many as he could afford. Also have a couple of
aluminum-cased Navy 0.004 ufd, 15 kV transmitting micas, circa 1917,
which are also OK and work well for small coils. As long as you don't
overvoltage them, mica's are about the best capacitors you can get, and
have been used extensively in "wireless" service for almost 100 years.
Ed