Re: Am I missing something here?...

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

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

I have a 4500/22 NST (actually not sure what its application is - probably
not an NST) and I have worked on your very problem.  A couple of things come
to mind.

The resonant match capacitor (Cres) of your xformer is 10.6nf so your
running at 4nf is definately smaller than resonance and your BPS is probably
around 500.  I bet most of your power draw in dissapated in the sparkgap.
My experimentation has agreed closely with Terry Fritz's derivation of using
about 1.57 x Cres for a LTR cap value for static spark gaps.  This will get
you close to 120 BPS.  With your low number of primary turns and low Cp,
your primary resonant frequency is high (probably close to the self
resonance of your secondary with no top load).  In order to increase the
number of turns on the primary to something more resonable (maybe 8-10
turns) and use a LTR cap of 17nf, you will need to increase the top load
capacitance to lower the secondary resonance to match the lowered primary
resonance.  I used a 3x11 inch toroid mounted about 4.5 inches (measured to
the center plane of the toroid) above the top turn of my 3.5x18 inch
secondary in order to lower the resonant frequency down to about 200KHz.
The toroid will also allow the field gradient to reach farther out from the
breakout point (see recent post by Paul Nicholson under the thread: spheres
vs toroids) and allow longer streamers.

Your NST has a 100VA rating and with a static spark gap, your maximum power
draw will be about half of this rating (with proper Cp value).  So 1.7 x
SQRT(50watts) is about 12 inches.  I measured 11 inch streamers (to free
space) with my 100VA rated transformer.

A multisegmented spark gap with cooling,  MMC caps, and an aspect ratio of
5:1 vs your 6 or 7:1 ratio will probably improve things as well.  The 3
biggest improvements I can think of is to increase the Cp value to 17nf, add
a top load to allow 8 - 10 turns of primary, and add cooling to your spark
gap.  Be sure to have the terry filter and safety gap with the safety gap
set appropiately (see previous posts on this subject).

Hope this helps,

Gerry R.
Ft Collins, CO


 > Original poster: The MCP <ejkeever-at-comcast-dot-net>
 >
 > Alright, I've setup the coil as described and even though I've confirmed
 > through an oscilloscope that it's resonating, I still get nothing even
 > beginning to approach the claims that it will shoot 17 inch sparks.
 >
 > I've the the 5000/20 NST attached to two 2nF/40Kv doorknob caps in
parallel,
 > for a total of 4nF. From there, I have a single static spark gap which is
two
 > .5 inch copper pipe elbows which are basically impaled on screws and
 > rotatable, and the primary coil which is 4 turns of .25 inch copper tube,
 > with turns averaging 1 to 2 inches apart (It's a little messy right now,
just
 > sitting on the floor bare) which tunes when tapped around 2.5 or 3.5 if I
add
 > the third doorknob cap (Whew - I'd get marked down for a runon if this
were a
 > test).
 >
 > The secondary coil is 26 gauge copper magnet wire wound around a 3 inch
ABS
 > plastic form, about 18-20 inches wound. One side is connected to a wire
 > running to an earth ground, which is a steel rod pounded about 1.5 feet
into
 > the ground, the other (since I don't have any real topload) is ~10 inches
of
 > wire from the end, wound into a little coil .75 inches in diameter.
 >
 > This arrangement produces streamers going about 3 inches into the air, and
 > going maybe another half inch to anything you get close enough. I haven't
 > taken exact measurements, but it doesn't take a ruler to realize that this
 > coil is NOT generating foot-long sparks.
 >
 > Where am I going wrong? Do I need to ground the primary equipment to the
same
 > earth ground as depicted in some schematics?
 >
 > On a rather ridiculous side note, what would happen if one were to take
the
 > 5000 kilometers of wire necessary to make a coil that would have a natural
 > resonant frequency of 60Hz and drive a primary by simply hooking it
directly
 > into the mains? Or if you were to go a step further and connect it to the
 > cross-country 340Kv lines?
 >
 >