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Magnifier Driver coil design

Original poster: Steve Ward <steve.ward@xxxxxxxxx>

Hi Guys,

Im looking for a bit of advice from experience here.  Im looking at
converting my large DRSSTC (10-11' sparks at the moment) to a
magnifier design.  But there are a few questions i cant seem to answer
on my own, and i think might primarily depend upon experience in the

What governs the size of the driver (secondary) coil?  I realize that
it must process many kW of power and must also step up the voltage to
adequately impedance match with the base of the tertiary coil.  And
how many turns seem to be adequate here?

Has anyone attempted couplings greater than .6?  I would like to get
the highest coupling possible.

Is there any general rule for inductance ratio between the 2ndary and
tertiary windings?  Colin mentioned 1:2, but that seems quite high and
perhaps un necessary.

I have come up with a tenative design, maybe someone can comment.  The
design goal is to achieve 12' sparks.

Primary: 20" diameter, .5" cu tube, 9.5 turns, .4" spacing, solonoid
winding fasion.

Secondary: 12.2" diameter, 16.5" high, 155 turns of 14awg solid THHN
(thats 500') with a 20"x4.5" toroid on top (corona shielding).  The Ls
is 4.05mH and its Fr (loaded) is 415.5khz.

Tertiary:  8.1"x24" winding of 30awg.  1950 turns, 226mH and loaded
with a 36"x4.5" toroid.  Loaded Fr is 47khz.

I might move up to 28awg with a longer winding (36"), but if i can
push the winding to 5-6X its length, then i would rather go with the
24" winding.  If all else fails, i still have my 8"x45" coil with
26awg.  My goal was to make things more compact so it fits in my car!

Note that i must operate in sub 50khz territory due to the solid state
driver.  45khz is my target frequency, my thinking is that the driver
inductance and capacitance will lower the 47khz by a bit.

So does this design look plausable?  The coils all seem sorta small
for the spark lengths im after, but ive seen other magnifiers that
push several X coil length in spark length, though i believe at the
expense of a very large driver coil.

If i dont get any responses, then i will likely build it and see for
myself as an experiment.  The fact that its a DRSSTC could throw some
of the maggy "rules" out the window as has happened somewhat with
2-coil systems.


Steve Ward