Chillicothe TelsaFest 2018 - 18.5 x 54 coil
Roger - That secondary is 18-1/2 in diameter and 58 in tall. There are ~ 648
turns of #22 copper with traditional inter-turn spacing of ~1/12 inch. The
spacing is to provide longer strike distance end-to-end of the single
solenoid-type winding and to give it a high-Q. I think the self-resonant
frequency is ~ 72 kHz (without top toroid). You may be able to power it
using your induction heater power supply with a little added capacitance at
the ground end.
The elephant stand primary form was originally wrapped with 10 turns of
expanded aluminum roof flashing with plastic lawn edging insulation. The
wooden box with four handles is full of glass sheets. Sheets of aluminum
foil were sandwiched in between the sheets of glass, with alternate layers
of foil protruding from one end or the other to form the multi-layered
capacitor. The foil was 1/2" from the other edges. The wooden "bushing" fits
over the 1/2" tin bronze electrode at the top of the coil. The rod has a
1/4"-20 thread into the coil. The two Plexiglas discs were for the second
generation rotary spark gap. I didn't bring the original spark gap as it is
still tucked away for later re-discovery. I originally set up a single
primary spark gap using scrap (industrial) water valve stem samples made
from silicon bronze. These electrodes got quite hot before I blew a fan over
them to quench the sparks during crossover (as this was purely an AC coil).
I hope you can light up this coil again. You see, it was wound using the
ringer assembly from a 1946 ringer-type clothes washing machine, back when I
was in school in 1979. The concrete form Sonotube was painted with Glyptal
Red Enamel and the wire was wrapped by hand. I set up a parallel 1/2"-12
all-thread rod with a Teflon wire guide and slowly hand-cranked the
all-thread once every time the coil rotated once (the index mark is still on
the end plate of the coil). The sticky part was I added Bullseye Orange
Varnish as I wrapped to hold the windings in place (but it mostly made the
turns want to slide around). Once all of the windings were in place, I
applied 4 additional coats of orange varnish over everything. With all of
the windings, there is ~ 3,138 ft of magnet wire (~ 6.1 pounds of copper)
with an overall resistance of ~50.6 ohms. 1968 ARRL Handbook formula gives L
= 57.646 milliHenrys.
I powered it using a 3300 volt, 1 amp plate transformer, but I had a hard
time setting the fixed gap for the low voltage of the supply transformer.
Rule of thumb is 10 kV (peak) per inch, but I was down around 3/16".
Please let me know what you find setting it up.
Thanks,
Dick
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