Re: A 1/4 wave Tesla coil

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Skip,
         I'd use (a lot) more C and less L in the primary.

Regards,
malcolm

On 5 Feb 01, at 20:16, Tesla list wrote:

> Original poster: "Skip Greiner by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <sgreiner-at-wwnet-dot-com>
> 
> Hi All
> 
> I thought that some of you might be interested in a true 1/4 wave
> coil. Following is a complete description. This was designed and built
> to be 1/2 half of a twin. The second secondary is now under
> construction and will be added soon.
> 
> Secondary:
> Skeleton form made of 12 polystyrene 1/2" rods and acrylic spacers
> Size: 14" x 30" Turns: 240 Wire: #16 stranded PVC covered machine tool
> wire, 1/8" in diameter Wire length: 880'. This corresponds to about
> 280khz Free air resonance: 400khz Ctop: toroid 8" x 25" dryer duct
> with aluminum foil coating Ctop capacitance: ~22pf Secondary resonance
> with Ctop: ~280khz
> 
> Primary:
> Diameter: 19"
> 5 turns 3/8" copper tubing on 5/8" centers
> Capacitor: .021uf
> Primary resonance with cap: ~280khz
> 
> Primary/secondary system resonance: ~280khz 
> System Q: over 150 but measurement limited by my instrumentation
> K: Not measured at this time but expected to be .21 or higher
> Best coupling is obtained with top of primary about 1/2" above bottom
> of secondary
> 
> Power: 15/120 NEST
> Break: SRSG, 1800 rpm and 120 BPS
> Contact spacing: 0.2" total, so far but still working up to larger
> spacing
> 
> Performance:
> Operating frequency: 280khz
> Spark length with no breakout tab: multiple arcs 48"(+)
> Spark length with breakout tab: single arcs 60"(+), very, very thick
> Interesting note: With no Cop, arcs are close to 42" from top
> terminal, but coil is obviously poorly tuned and much corona around
> top turns of secondary.
> 
> This coil operates at the design frequency. There is no indication
> that any ion cloud adds capacitance to the system that might lower the
> operating frequency. This coil was designed basically using Medhurst
> and Wheeler formulae. No tuning was required after assembly except to
> phase the SRSG and to increase the coupling between primary and
> secondary.
> 
> Changing the primary turns only reduces the output length of sparks.
> Question to those on the list with experience: The output sparks are
> very thick and fat but only reach 60"(+). The coupling is as close as
> possible, just before racing sparks start, and changing the SRGS
> phasing only decreases the length. I would appreciate any suggestions
> to increase the spark length. John F., I know you have done much in
> this area and I would appreciate your comments in particular. Note
> also that the above indicated operating characteristics occur with
> about 100 volts input and additional voltage up to full line voltage
> seems to make little if any difference in spark length.
> 
> Skip Greiner
> 
> 
> 
>