Tips on capacitor and toroid design

The aluminum air duct tubing will work as a toroid, however, the surface is
still irregular enough to interfere with the electric field as compared
with a more expensive, smooth toroid.  If you are using air duct tubing or
dryer hose, you might consider making a final overall wrap with aluminized
mylar tape.  This will present a very smooth electrical surface, however,
due to the thin size of the alum. tape, you must use a discharge rod to
vent the discharge off your toroid.  A direct discharge from the smooth,
thin, tape surface will damage it.

Capacitor builders should consider Kapton over polyethylene or polystyrene.
 Kapton has a dielectric constant of 4.2 - 4.2 which allows very small unit
construction.  Another great feature of Kapton is it's operating
temperature max is nearly equal to Teflon --- over 500 degrees F. for
Kapton.  A typical design with Kapton dielectric will produce a 1,000 pF HV
capacitor element with an element size of only 2 x 2 x 1 inch.  Elements
are series-parallel connected to obtain proper value.  Kapton is
distributed by DuPont Co. -- consult your local library Thomas Register for
a rep in your area.

Another interesting application for Kapton sheets is to find a nice medium
size surplus air variable capacitor.  Now, attach Kapton sheets to the
metal blades with the Kapton sheets extending approximately 3 inches beyond
each blade.  Immerse in xmfr oil and your have a wide range variable
capacitor that can be connecting in parallel with your normal Tesla coil
capacitor for tuning while the system is running.  Just use a very long
nylon shaft extention on the capacitor shaft and adjust while coil is
running for dynamic tuning.  A lot easier than trying to construct a
variable inductor.