RE: 70kv system questions

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "John H. Couture by way of Terry Fritz <twftesla-at-uswest-dot-net>" <couturejh-at-worldnet.att-dot-net>


Jonathan -

The 70 KV TC shown in my Tesla Coil Construction Guide is about the simplest
and cheapest TC that you can build. However, it does have its limitations.
When changes are made in the components the tuning must be carefully
checked. You can do this by using the JHCTES Ver 3.2 online computer program
shown at my website

    http://home.att-dot-net/~couturejh/

Make sure that the inputs actually represent your coil's parameters because
some of the parameters have a large effect on the tuning. The program does
all the calculations to keep the TC system in tune when you make changes.

I suggest that you actually measure the the capacitance of the primary
capacitor or have a radio ham do it for you. You can check the ignition coil
by connecting it as shown in the wiring diagram except do not connect
anything to the high voltage terminal. When the power is on and the relay is
operating you should get a small spark from the HV terminal to a grounded
wire. There is high voltage present that can give a mean shock so be
careful.

I used a 2 inch diameter door knob that worked good for the secondary
terminal. Please let us know how you are doing.

John Couture

-----------------------


-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Tuesday, April 03, 2001 8:12 PM
To: tesla-at-pupman-dot-com
Subject: 70kv system questions


Original poster: "Jonathan Peakall by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <jpeakall-at-mcn-dot-org>

Howdy All,

I am building a small coil, a 70kv system from John Couture's book. I am
having some trouble getting it to break out, and am hoping for some
advice.

System:

150 watt 120/12vdc power supply
Ignition coil wrested from a '62 Falcon
Potter and Brumfield 12v relay, # K10P-11D15-12
470vac, .068uf and 50v 1000uf caps
Bolt and acorn nut style spark gap, mounted on plastic cutting board
material
12 turns #12awg auto wire wrapped on a 3" x 5" form (Book calls for 5
1/4")
Aprox. 468 turns of 24 gauge insulated magnet wire on a 13 1/4" x 3 1/4"
form (Book calls for 3")
4 x 7.5kv .001 uf caps hooked together with two in parallel and two in
series to theoretically produce .0025 uf.

I was having trouble finding the correct size forms (I live in a town of
368, so the hardware scene is a little limited) so I went ahead and
coiled as listed above. As well, I coiled the secondary out of what I
thought was 24 gauge (I had the wire I laying around from a radio
project), but then when I measured an inches worth, it became apparent
that I would need a longer form that the book called for, so I figured
it must actually be 22 gauge. As it would take days for me to get more
wire  I went ahead and wrapped it anyway. Today I got some definite 24
gauge, and it measures out the same as what I have already wrapped. Hmm.
I don't have a capacitance meter (ordered one, not here yet) so I can't
verify the hillbilly primary capacitor system.

I have tried a number of discharge sphere configurations, from a 1"
brass door knob,  2" and 2 1/2" aluminum foil covered balls and a copper
toilet float. I have tried insulators from 1/2" to 3". I have also tuned
the spark gap and primary coil. I have raised and lowered the secondary
relative to the primary, and spaced the primary wires a little, which
seemed to help. Regardless of what I do, all I can get is a little
corona from the bare end of the secondary coil wire, or 1" to 2"
streamers to a metal object.

My primary suspects:

Are the coil dimensions too out of whack to work?
Is the 22/24 gauge thing a big deal?
Spark gap is a little erratic. Is this a huge factor? (Making a new one
already)
Any way to test the ignition coil with a VOM? It *was* still running the
Falcon...
Primary caps are obviously suspect. Do my numbers add up in the first
place?
Relay sounds a little different after some use. Have been doing fairly
short runs, but it has gotten a little hot once or twice.

Anyway, thanks for any and all help.

Jonathan Peakall