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Just a brush

Taylor, Chris CC wrote:
> 
> I have just recently completed building my first coil and fired it up
> last night. To my utter disappointment all I got was a big racket from
> the spark gap and little else.
> 
> I have a 15/30 neon with a six element spark gap and a plate poly
> capacitor, (20 plates 10x8" with an 80 mil poly dielectric, theoretical
> C=0.0085 uF). I haven't got around to placing the cap in an oil bath yet
> and it doesn't arc unless the gap separation is very large, the cap then
> arcs around the edges and I shut down and reduce the gap separation.
> Would the cap be providing 0.0085 uF without the oil bath, I can't see
> why not, it is my understanding that the oil is only used to provide a
> better insulator than air around the cap.
> 
> The coil also has a 1/4" copper tubing primary with 15 turns spaced at
> 1/4" in a saucer configuration, (30 degree). The secondary is 22 ga
> transformer wire on a 2.8" PVC pipe with 840 turns, (22.5" long).
> 
> All I seem to be able to get from this baby is a small brush discharge
> from the tip of the secondary wire, (primary optimally tapped at turn
> 5). I have also built an 11 x 3.5" toroid which when attached does not
> produce any discharge.
> 
> My questions to the lads are;
> 
> What sort of diagnostics can I perform to point me in the right
> direction for larger discharges.
> 
> Have I missed anything, I have used a number of the circulating formulas
> to roughly size various components.
> 
> The coil is working but just doesn't seem the be very efficient. The
> lowest turn on the secondary is in line with the inner turn of the
> primary, do I need to lower the primary to get better coupling.
> 
> Is my secondary too long for efficient coupling, (H/W ~ 8.5) I have read
> this may be a bit large.
> 
> The addition of the torus increases the resonant frequency, do I
> increase or decrease my tank capacitance as the secondary frequency
> increases and how do I adjust the primary tap as the secondary resonant
> frequency increases.
> 
> Any help would be greatly appreciated and will speed me on my way to
> coilers nirvana.
> 
> Chris Taylor
> Perth, AUSTRALIA