Re: Home-brew Capacitors

Tesla List wrote:
> Original Poster: Bill Fuller <wfuller-at-home-dot-com>
> Hi all,
> I have some 500pF 30KV "doorknob" caps. Does anyone have experience with how
> well this type holds up in TC use? I will be using a 15KV-at-120mA NST setup.
> Should I consider using them in a series/paralell configuration of 16
caps to
> get a .02uF, 60KV rating. At ~$10 a piece I would prefer to use just a
> parallel
> arrangement to keep the cost down.
> Any recommendations from you experts out there??
> Bill Fuller


These type capacitors will work... for a while at least. Unfortunately,
the evaporated silver "plates" tend to be quite thin, and may be
"disappear" under the repetitive high currents seen in the tank circuit,
causing a continuing reduction in capacitance over time. They also tend
to be rather lossy, and they also tend to change their capacitance as
they heat up. They ARE better than salt water caps, but not nearly as
good as PP or LDPE caps. You'll definately need to run them in
series-parallel in order to drive them off a 15 KV source. 

However, to get a 0.02 uF 60 kV cap out of these, it would actually take
80 caps in a series/parallel configuration. At $10.00 each, you could
instead buy a genuine, much better performing, polypropylene pulse cap
from Plastic Caps or on the surplus market and have significant money
left over...

-- Bert --