Mica domino style caps from WW II onward (also known as transmitting
micas) are remarkably stable and efficient at RF (what they were made
for). Most of them are Mil-Spec. Most of the date codes on the ones
here are from the 1960s BTW, not the 1940s, although I would not
hesitate to use one from WW II.
They are $1 at any hamfest - typically found in junk boxes under a
table. Blow one up? $1 lost. They do not self-heal. I have only
shorted one - after about five years of use. I use them at 1500W in the
L networks for my 160 top loaded vertical and numerous other wire
antennas. I use them outside in the rain - don't even both to cover the
things. Most have current ratings that are around 5 amps but will do
much more. Loss at HF is negligible. You can feel them after a minute
of key-down, they are not even warm. Series and parallel applications
work out fine.
They have little in common with the Tesla application, which requires
1000-amp-plus pulses to be delivered at high rep rates, and loss factor
(ESR and DF) optimized in the 100-200 KHz region.
Try 'em, you will like 'em.
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