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Re: Museum Coil Revisited
Tesla List wrote:
>
> > Subject: Re: Museum Coil Revisited
> > Subject: Re: Museum Coil Revisited
>
> Subscriber: rwstephens-at-headwaters-dot-com Tue Dec 31 09:26:10 1996
> Date: Tue, 31 Dec 1996 03:57:13 -0500
> From: "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Museum Coil Revisited
>
<SNIP>
Robert Stephens wrote (in part) about his Medium Tesla Coil (MTC):
> This coil system is COMPACT! Everything except the supply
> variac is in the tower. This system is transportable, and is as very
> nearly plug-n-play as it can probably get. Not anything like the real estate
> hungry breadboarded models so common amongst many of the advanced coilers
> on this list (no insult intended guys!, I just added compactness to long spark
> length as an additional design parameter). Perhaps by rewiring and reversing the
> order of my primary tank and capacitor so that I can ground one side of the
> primary I can reduce my corona/ occasional flashing problem, and pick up some
> safety factor for the capacitor at the same time. I just hate to try
> to _fix_ something that ain't broke. This MTC works so darned well!
> You know Bert, you've seen it's 7kVA ballet on videotape!
Yes, it really DOES cook!!
>
> I do wish to buzz MTC higher than 7 kVA soon however
> and try to go for 4X the 50 inch resonator length in output spark
> length instead of the only 3X it presently does. I really think it
> can! I'd better try it soon though, Chuck Curran is up to something nearly
> identical in secondary resonator size, but sporting considerably more inductance
> and also thicker wire, and a significantly larger topload C. I don't want to loose
> my place. : ) Chuck, I haven't heard from you! : ) I spill my
> construction secrets to you trying to help, and you hide. Any hardware store
> merchants on this list in Chuck's area, be on the lookout for sales of heavy guage
> 200 foot extension cords! : ) Look out Gerry LaBine!
We haven't heard much lately about Gerry's experiment, have we... :^)
>
> >From here on, with any further increases in power I'm going to have to
> carefully watch the temperature of my stationary tungsten carbide pads on the
> rotary which are merely brazed onto their steel supports. I don't want to melt
> the brazing. These contacts are operated in high speed air blast
> from a vacuum cleaner blower with two small directed nozzles for
> cooling. So far this has worked faultlessly with the tungsten, but amazingly
> DID NOT previously when the contact material was mild steel and all
> other parameters including power level were identical! My contacts would go
> into thermal runaway, incandesce, and vaporize in a steady shower of sparks in
> the blast air stream. MTC's rotary break is run just like D.C. Cox's unit, without any
> series quench gaps.
>
> I posted my ideas on this a while ago, postulating that
> the tungsten could operate at a much higher surface temperature from the
> getgo without emitting a cloud of vapourized metal ions from its
> surface, thus preventing the thermal runaway effect. I believe a
> very micro-thin pool of molten surface metal instantaneously develops
> at the end of the switch arc with the steel contacts, and not so with
> the flying thoriated tungsten/stationary tungsten-carbide interface I now use.
>
Robert, there was some very interesting information buried in the one of
the articles you left me last week (from Glasoe and Lebacqz's "Pulse
Generators", Dover Publications, 1965) regarding rotary spark gap
materials, (pages 280-281). It turns out that tungsten has a much longer
life (by a factor of up to 20X) when run in an atmosphere containing
oxygen versus, say, pure N2 or some other non-oxygen bearing mixtures.
Their speculation is that the presence of oxygen forms a layer of
tungsten oxide that greatly reduces electrode wear! It sounds as though
if there's enough cooling (large enough electrodes and enough forced air
flow), air cooled tungsten (or perhaps tungsten or tungsten-carbide
tipped copper/brass) is the most affordable way to go.
> The bottom line is: There's an envelope here, and as a coiler/researcher never
> satisfied to sit on good, I am compelled. I _MUST_ push the envelope in an
> attempt for better, using good common sense and experiential judgement, or die
> trying!
>
> Happy envelope pushing without death or serious accident to you all.
> (Are you Chernoble scientists paying attention to this?!)
> rwstephens
Safe coilin' to you as well, and Happy New Year!!
-- Bert --