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Top capacitance


From: 	Per Niva[SMTP:pna-at-pp.gellivare.se]
Sent: 	Tuesday, August 26, 1997 7:21 AM
To: 	Tesla List
Subject: 	Top capacitance

Malcolm Watts wrote, concerning discharge terminals
on top of the secondary:

> 
> [...snippage...]
>
> This has been researched in more depth on the builder's list and was
> first seriously experimented with by TCBOR. The main advantage to a
> large top-C is to give a large instantaneously available source of
> energy to strengthen streamer ionization. We are talking about the
> top terminal aren't we?

Yes, we are. This reply helped clear some things up inside my
coil-constructing head. I thought along the lines that the top-C
was there mainly for it's role in the LC oscillator of the
secondary circuit. Then, if I get this right, it is a good thing
to have such a large top-C as possible. This must be determined
from how much effect you could put into your primary tank?

So, this coil I'm currently constructing would use a primary C
variable up to around 10nF. The secondary would be about 500' of
#24 wire on a 3" OD HDPE pipe (not the black stuff) ~= 600 turns.
This would give a resonance frequency in the unloaded secondary
coil of slightly above 850kHz. With top-C some 6 or 7pf it would
drop to around 600kHz. This means I'd have to tap the primary at
the 6th turn.

But the right thing to would be to rise the top-C to just about
as big as my transformers could drive? Looking up some toroid
tables I found somewhere... 800-1000 watts, that would allow
maybe 15pf of top-C. Is there any way to calculate this? 15pf
of top-C would bring down the resonance freq down to around 
430kHz. Then I'd have to tap the primary at the 8th turn instead.

The 4" coil with a 15pf top-C would lower the resonance freq
down to about 360kHz. This is even better then? If I have too
big top-C, would that mean that sparks would not break out?


Interested, but somewhat confused,

Per

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