Re: my friends coil

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <teslalist-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:

 > Original poster: "Rodney Goolsby by way of Terry Fritz 
<teslalist-at-qwest-dot-net>" <jeronimo-at-bright-dot-net>
 >
 > My friend is having some trouble with his first coil.  It was a small
 > "Budget Coil" wound on a piece of pre cut 2 in. diameter
 > acrylic.  Unfortunately it could only be 12 inches tall and he used extra
 > 24 awg wire to make it.  It have between 500 and 600 turns,

About 550 turns. Not much. L2=2.35 mH, a small inductance. C2 self=4.4
pF.
With a 6" sphere with 8.5 pF, C2=~12.9 pF.

 > powered by a
 > 12/30 NST. Capacitor is a "Geek Group" MMC style cap rated -at- .015uf 20kvdc.

Making L1*C1=L2*C2, L1=2 uH, a small inductance. Assuming a solenoid
with
5" of diameter (r=6.35 cm) and 2.5" of height (6.35 cm), you need about
3.9 turns. The structure has a coupling coefficient of 0.183. The coil
will operate close to mode 5:6, transferring energy in ~3.5 cycles of
914 kHz. The frequency looks quite high, due to the small L2.

 > Spark gap was a simple static gap adjustable between 6mm and 25mm.

Use a multiple gap, with multiple small spacings in series. Works
certainly better.

Primary
 > 7.5 turns, .25 in. copper tubing, .25 in. spacing, vertical.

Height?, diameter? (I assumed 2.5", 5".)

 > Top load: 6 in. diameter sphere.

Add a breakout point (better a small sphere) to see big streamers.

 > I'm still working on my first coil, so I'm pretty
 > inexperienced.  I tried doing my best to help but it only managed to get
 > 2.5 in. sparks. He and I are both hoping for more help here on the list, so
 > we would appreciate any help offered.

With careful calculation of the inductances and capacitances, the
system works immediately without need of any tuning.
And it's more instructive than to just assemble the coil and try to
tune it.

Antonio Carlos M. de Queiroz