Re: Doorknob Caps

Subject:  Re: Doorknob Caps
  Date:   Mon, 9 Jun 1997 20:17:46 -0700 (PDT)
  From:   "Edward V. Phillips" <ed-at-alumni.caltech.edu>
    To:   tesla-at-pupman-dot-com

"When I first started building Tesla coils door knob capacitors were
all over the place and cheap! But they never seemed to perform well
in a tesla coil they would also get rather hot implying there were
large power factor losses."
        Have been using 3000 (marked 4000) Sprague "doorknot"\
filter capacitors (make that 4000 mmfd) capacitors here for a
couple of years, on a coil running with a 12 kV, 60 ma transformer.
Work quite well, as SERIES resistance is low, but they sure do
heat up and also the capacitance decreases at high temperature.
Haven't blown any since I watched the run time.
        Main comment is that even filter capacitors seem to work
and the sure are small and convenient.  There are much lower
loss ceramic capacitors available, but they are much bigger and
very expensive.