New Tesla Coil!

This was originally written on 6/15/95 but apparently has not
been seen by the Tesla group due to my ongoing mail problems.

I would like to report on a newly completed Tesla coil project by
Ryan Jester. Ryan, age eighteen,  has been working since late
winter on a Tesla coil for a grade in his electronics AND
independent study class. Ryan worked on the project components
with the assistance of his father, George, who is a machinist at
Washington University here in St. Louis. Neither has had any
previous experience with Tesla systems, high-voltage projects, or
high powered oscillators.

I provided design assistance, a demonstration of the required
equipment, and answered an occasional question. Ryan had access
to my Tesla texts, spark gap plans, wiring diagrams, etc., that
are available for download from my local BBS and the ftp site
where our material is archived. Everything else was left to Ryan
and his father to work out.

Ryan called my at about 6pm on Saturday, June 3rd, to ask a
question on toriod discharger construction. He informed me that
he had completed two homemade rolled capacitors and had assembled
a cylinder spark gap, the secondary coil, and the primary coil
form. I asked him when his last day of school was and he
indicated that he had to present the project by Tuesday, June 6.
I offered to go to his house to assist in the final assembly,
wiring, and testing.

On arriving at Ryan's house I found all of the major components
had been constructed with exacting care. With the assistance of
Ryan's father George, we fell upon the task of completing a small
toriod out of aluminum ducting used in the engine compartments of
the venerable VW Bug. Ryan slapped a couple of coats of poly-
urethane on the plywood primary coil form, and I reworked the
ground and air terminal leads on the secondary coil.

With the aid of 1500 watt electric heater we quickly cured the
polyurethane on the primary coil form. Using all three sets of
hands we rough wound the primary coil out of a single 60 foot
length of 3/8-inch o.d. soft copper tubing, ending up with 13-1/2
full turns in an inverse conical section. The primary angle of
inclination is 30 degrees.

The secondary coil is wound on a 29 inch length of polyurethane
sealed PVC, thin wall, drain pipe. The measured outside diameter
of the coil form is 6.25 inches. The winding is 26 inches long,
approx. 962 turns close wound with No. 22 AWG enamel covered
magnet wire. The coil is finished with several coats of
polyurethane sealer over the winding, and the coil form is capped
at both ends and hermetically sealed with two plexi end plates.
There are no holes drilled into the coil form, and nowhere is the
winding allowed to enter inside the coil. The aspect ratio of
this coil is 4.16:1. The approx. calculated frequency of this
coil is 260 kHz bare and probably 240 kHz with the small toriod
discharger. I was altogether impressed with this construction.

The two capacitors were rolled using 16-inch wide strips of low
density 60 mil polyethylene sheeting for the dielectric and 14-
inch wide strips of aluminum roof flashing for the plates. The
capacitor rolls were placed in tanks constructed of the same 6-
inch PVC drain piping used for the secondary coil form, and the
tanks were filled with about one gallon of pure mineral oil each.
The tanks had been pumped down with a vacuum pump to assist in
the removal of trapped air. The capacitors both measured .022
microfarads each and were all ready to hook up and fire.

The spark gap was a simple cylinder static constructed according
to the GIF schematic I provided. Cooled with airflow provided by
a 5-1/4 inch muffin fan, this gap was built using seven sections
of hard copper water pipe mounted inside of a short length of the
same PVC drain pipe used elsewhere. The electrodes are gapped at
.028 inches and are mounted with 1/4 inch brass hardware that
serves as connections to the tank circuit.

After some final assembly taking about three hours, we set the
coil up and wired the tank circuit. We began to test the all new
system with a single 12 kV 30 mA neon power supply controlled by
a 7-1/2 amp Powerstat by Superior Electric. I placed the two caps
in series for .011 microfarads capacitance and used only three of
the available six gaps in the cylinder static gap. With the
variac set to input about 30-40 volts into the neon we were able
to get the tank circuit to pulse. The capacitors did not outgas
at all due the previous pumpdown, and with the primary coil
tapped all of the way out on the last turn we were getting a
fluorescent tube to glow gently several feet away. I was able to
pull a few inches of spark from the discharge terminal with the
end of the tube.

We gradually increased the number of gaps and the input voltage
until we obtained a fair tune with the primary tap set at around
11-1/2 turns out on the primary coil, and were getting about a
foot of spark off the discharge terminal. We called it a night.

The following day I returned with my wife and nine year old step-
son, as well as another neon which we placed in parallel for a
total of 60 mA -at- 12 kV. After an adjustment made to loosen the
coupling a bit by raising the secondary about two inches, the
coil was tuned and functioning perfectly; producing nearly three
feet of spark and corona. We were even able to conduct a simple
experiment using a counterpoise before we retired for a snack of
cake and whipped cream provided by Mrs. Jester.

I wish Ryan the best of luck on getting the project re-assembled
at school for a demonstration and lecture. Tesla coil projects of
this caliber are rare for young adults in school, and I feel
honored to have been able to assist in what is clearly an A++
project. This coil also looks like a hands-down science fair
winner should Ryan be able to enter the project in local
competition. I would like to thank Ryan and his father George
publically for the interest they expressed in my work, and in
allowing me to be present when their project was fired for the
first time.

Richard Quick

___ Blue Wave/QWK v2.12