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Some interesting observations ....



I have built tesla coils on and off starting way back about 1972 and just
recently got back into the hobby. One of my biggest problems was not knowing
how to build rf chokes to prevent feedback through the NST and destroying it.
Until recently, all the tesla plans I ran accross involved showing me how to
build chokes using a full page of mathmetical symbols that resembled egyptian
hieroglyphics than anything else. I used the plans from sciencefirst because it
had choke winding instructions in terms of "Wind X guage wire over Y length of
wooden down of Z length. 
 
I built a tesla coil according to plans gotten from
<http://www.sciencefirst-dot-com>http://www.sciencefirst-dot-com but the results were
not as advertized but I did get about 6" streamers and similar sparks. The
thing was supposed to produce 18" sparks. It also had some design problems such
as instructions that resulted in a plat capacitor that had ONE sheet of plastic
between the sheets at the junction where a bare ends of the plates came into
contact with the next plate. I emailed this and other corrections to them and
hopefully, they have revised the plans with an addendum.
 
Unfortunately, I took the coil with me on a trip to Reno so I could show some
friends and I stayed in Best Western there and I returned to find that someone
on the cleaning staff was fiddling with it and despite six coats of spray on
accrylic, the first half foot had come loose apparrently from someone trying to
force the end cap off and look inside. It was a total birds nest of tangled
wire and I was so distraught and frustrated. I ended up having to cut off six
inches of my primary with a saw!!!
 
The primary was 1.5" by 40" of #29 wire. I had a small 8" toroid and this
configuration did not produce any output but it did produce nice 8" streamers.
 
Well, after reading about fine advice such as sanding off the lettering from
the PVC and using thicker shorter secondaries, I built another primary from two
spools of awg #29 I had. I did a very microscopic splice. tried an end to end
solder but the joint broke immediately. I spliced about a 32'nd of an inch
together and sanded it down so there was no bump sticking up. This made for an
interesting coil since the wire was different colors. I hadn't noticed. This is
all wound on a sanded 3" pvc form and I ran out of wire after winding about 2
feet.
 
Just got done installing it into the tesla coil and got the following results
....
 
At one tuning setting, output was rather dissapointing being only an inch and a
half at most. The interesting thing was at this setting, the toroid emitted
lots of 4" streamers! So at this setting, the toroid seemed to act as an
accumulator.
 
Further tuning found a spot where the streamers from the bolt was about 6" to
8" as well as producing nice 6" minimum streamers from the toroid.
 
The thing that has me a little mystified is why did the first coil with the
thin secondary produce such long streamers but NO toroid spark break out but
the more shorter squat secondary could produce such short streamers but nice
output from the toroid?
 
My guess is that the two were operating in two separate modes and that the
shorter secondary allowed the toroid to act as an accumulator of sorts. If this
is so, what was the first coil doing?
 
Another question is is there a formula for relating streamer length to voltage
output? I kind of doubt this because it would probably have to take into
account the size and shape of the top terminal whether it be a bolt or a
toriod.
 
Another interesting thing was that when I got a tubular florescent light tube
close to the coil sparks jumped from the coil to the light and I felt my hear
start to stand up on end from accumulation of static electricity. Woo Hoo!!
 
Well, I promptly built a grounded Jesus stick so I could draw sparks without
touching it anymore. No point in risking RF damage or an arc from the primary
to the secondary as I touch the unit.
 
The circuit is two capacitors in series with both ends of the primary winding,
chokes between these and the nst, the primary is also center grounded.
 
I am getting up to 12" sparks. I know this is a little small but since I live
in an apartment complex, I really don't need bigger louder sparks and it isn't
bad output for a .3 amp 9kv NST system.
 
One lesson learned is NEVER leave your tesla coil in a motel room. It might be
too big to steal but it sure isn't something you want some idiot trying to take
apart or actually operate. I figured things would get stolen but I never
dreamed someone would actually damage my tesla coil.