Re: Thorated vs Pure Tungsten
To Steve, Terry, Malcolm, all.
I neglected to mention in my earlier post, that the old faithful,
(well, not that old, really) Home Depot, stocks polished and
lacquered spherical brass balls, with a turned single small
mounting pedestal, which is drilled and tapped (8-32 n.c. I
believe,) and these would make absolutely *excelent* discharge
balls, not only for a Tesla Coil safety gap application, but also
on a Marx generator (of moderate size.) The pedestal part is
about 0.500" across its circular flat face, with the hole in
the middle, and it stands out from the curvature of the ball by
about 0.375". The ball itself, is about 1.25" o.d. They cost about
$3.00 each, so in small quantities, they may well be considered as a
viable alternative, to all the pains and trouble of heating up
ball bearings, drilling or soldering, etc. The Home Depot units
can be found in the section of the store that sells drawer pulls,
handles, and knobs. (Happy hunting!)
Of course, for larger (and more powerful applications,) you can
"step up" to the hollow-spun copper float variety, as sold through
McMaster-Carr. I use these as well. (Please see www.ttr-dot-com,
Model 13M pictures.) When you see a pix. of a guy who looks
like he's been out in the sun too long, wearing a sweat band and
leaning over a large capacitor bank, look for the adjustable safety
gap made from two 2" dia. hollow copper spheres. These units
are not expensive, and are easily polished on a drill press or
lathe. They work very well for high power, high tank circuit
charging voltage applications.
For large quantities of brass balls, there are several suppliers, who
make lamp parts, who will sell in bulk quantities. But they will
deal only with bonified businesses, not private individuals.
Regards to everyone on the List.
> Date: Wed, 16 Jun 1999 18:11:46 -0600
> To: tesla-at-pupman-dot-com
> Subject: Re: Thorated vs Pure Tungsten
> From: Tesla List <tesla-at-pupman-dot-com>
> Original Poster: Steve Roys <sroys-at-umaryland.edu>
> Tesla List wrote:
> > Original Poster: wysock-at-ttr-dot-com
> > To Terry (specifically) and All,
> > Please reconsider your design for a "safety gap." I worte to you
> > before, about using either brass or copper sphere electrodes,
> > for this purpose. They can either be solid machined pieces, or
> > hollow-spun units. The solid pieces are needed where you are
> > operating at a.c. input levels above about 5 Kva. The "ball gap"
> > offers a very well defined E-field stress line model, between the
> > two electrodes, assuming that they are polished and very smooth
> > and of a constant radius of curvature.
> Keep your eyes open at yard sales and flea markets for old brass doorknobs
> - they're
> already nicely curved, have a decent radius of curvature, look spiffy, and
> work just
> great as safety gaps. In addition, they're already threaded so it's easy
> to mount
> them and attach your wires to them.
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