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Re: An internal primary

Original poster: "K. C. Herrick" <kchdlh@xxxxxxx>

My thanks to Steve for the excellent advice. When I get to the point this time where I'm actually concerned about maximizing the spark...that'll be the day!

At least, I did make a sstc work at one time--and I'd conceived a rather cockamamie primary apparatus for it. Looking back, I'm amazed that it worked as well as it did (for a while, at least, until I "improved" it too much...).

Ken Herrick

Tesla list wrote:
Original poster: Steve Ward <mailto:steve.ward@xxxxxxxxx><steve.ward@xxxxxxxxx>

Hi Ken,

Just a comment on what you wrote:

> I take note of a "Rev. Sci. Instrum." article cited some time ago on the > List, "Greater voltage gain for Tesla-transformer accelerators". It > concludes that the optimum k, primary:secondary is ~0.55.

Of course, .55 is impractical to achieve in reality.  From my
experience, my DRSSTCs like about .25 for the coupling for best
results.  Basically increase it to the point where it starts to flash
over at full input power, then reduce the K just enough to stop the
pri/sec arcing.  This is where i arrived at the .25, that seemed to be
about the max possible when pushing a secondary to 3X its length in
spark output.

As I read it
> (perhaps imperfectly; I can't wade thru all the math), one determines k
> using 2 measurements of the secondary's Fr: when the primary is shorted and
> when it is open; here, "wsc" and "woc". The formula is k =
> sqrt{1-(woc/wsc)^2}. Once k is realized, then tune the primary circuit for
> two Fr's differing by a factor of two--and presumably then run the coil at
> the lower of the two. When & if I can get it all up & running, I'll shoot
> for that.

Well, programs like Java TC calculate K pretty well as far as i know.
But really, just position the primary coil experimentally. Like i
said, higher K is usually most efficient at getting the energy into
the secondary (otherwise it just goes back to the filter caps, and
some is lost as heat of course).

To start you may want to tune the primary to the Fo of the secondary
(not the lower frequency caused by the frequency splitting due to
primary coupling).  You are somewhat guaranteed for it to "work" with
that tuning.  You will then find that tuning the primary lower and
lower will lengthen the sparks as you increase your power input.
Eventually you will tune so low that it doesnt even break out, then of
course you tune it back up a bit ;-).  If you dont detune the primary,
your spark length will hit a "brick wall" and the streamers just WONT
get any longer after a certian voltage applied to the driver.  It all
makes sense once you build one and see it for yourself.

Its great to see that you're still at it at the age of 77!  I wont be
surprised to find myself building tesla coils when im retired... but
im getting a bit ahead of myself, i need to finish college first!

Steve Ward