Dry Caps - How to (fwd)

---------- Forwarded message ----------
Date: Mon, 27 Apr 1998 20:59:24 -0400
From: George Huntington <ghunting-at-courant.infi-dot-net>
To: "tesla-at-pupman-dot-com" <tesla-at-pupman-dot-com>
Subject: Dry Caps - How to

My son and I have successfully built quite a number of dry caps for
tesla coils.  The best has been in use for over three years.  We are
switching to oil bath and poly caps for higher power, however.

Basic method::Materials

Dielectric - parrafin impregnated artists paper

Plates - very heavy aluminum foil

soak the paper in melted parrafin until all bubbles stop coming out of
the paper.  set paper aside to harden on a smooth, flat surface.

cut foil so that about 4cm extends out the side for electrical contact.
assemble cap.  use formulas in radio amateur's handbook for calculating

Assemble cap on a 1/4" acrylic plate supported underneath by a 3/4"
piece of plywood.  top of cap should also be a sheet of acrylic.  place
in a deep, flat bottomed pan and bake under a lot of pressure - 20 to 30
pounds of weight on top.  baking temp should be low - just enough to
slowly melt the mess.  usually takes about an hour or two to bake.

remove from oven and let harden - remaining under pressure.

after the cap has hardened, drill a couple of holes for 1/4" machine
screws on each side of cap - where plates stick out.  use an aluminum
strip and machine screws on each side for electrical connections.

after one more baking to thouroughly coat everything again and provide a
protective mass of parrafin aroung the cap, let set and cure for a day
or two.

break in slowly while listening for breakdown.  after a half hour or so
of break-in the caps are ready for service.

It is a messy, messy process, but the caps are servicable - but no where
as good as one's placed in an oil bath.