Freaky frequency

Subject:  Freaky frequency
  Date:   Tue, 17 Jun 1997 08:20:08 PDT
  From:   "Erik Hennix" <mr_white-at-hotmail-dot-com>
    To:  tesla-at-pupman-dot-com

Hi everyone!

I've been getting some strange results while tuning my
coil. I'll first state the specifics of my system.

Secondary coil: 
11cm PVC pipe wound with approx 810 turns 
of 0.6mm magnet wire. About 37 turns per inch.
Sealed with clear plastic laquer.

Primary coil.
Cone shaped with 60 degrees banking and 15 1/2
turns of 1/4" soft copper tubing. The hypothenuse being
22.5cm in length and the inner (lowest) turn 15cm in

Vertical plate type made of polyethene and aluminum foil
and immersed in motor oil. I've measured the capacitance
(using line voltage and a mA meter) to 0.022uF.

Power supply:
Two 3920V 50mA neons in series giving 7840V 50mA (390VA). 
Puny -I know.

Spark gap:
RQ style cylindrical gap with 5 electrodes spaced as wide
as possible with a 17W cooling fan.

RF Ground:
Three metal rods 65cm in length 1.5cm in diameter 60cm in
very wet soil. Connected to base of secondary via a 50cm
long heavy cable.

And of course a line filter, RF choke, safety fuses.
BTW line frequency here in Sweden is 50Hz

While tuning I've been getting the longest spark using a
metall ball, 2cm in diameter, as a discharge terminal. With
this the coil tunes at 15 1/4 turns. I also tried using a
7.5cm sphere which reduced the spark length considerably.

This seems very strange to me since I've calculated the
inductance of the primary coil to about 57.5uH. With
0.022uF of capacitance this should give a frequency of
about 142kHz. 

141kHz for a 2cm sphere?!!
That can't be right.

What's going on here? 
Is there something wrong with my calculations?
Maybe the the input power is too low to produce long sparks
from larger discharge terminals.

Hope someone can help me out here.