# Re: 3/4 wavelength secondaries

Tesla List wrote:
>
> >From sgreiner-at-wwnet-dot-comTue Jul 23 21:59:58 1996
> Date: Tue, 23 Jul 1996 21:32:37 -0700
> From: Skip Greiner <sgreiner-at-wwnet-dot-com>
> To: tesla list <tesla-at-pupman-dot-com>
> Subject: re: 3/4 wavelength secondaries
>
> Thanks to Richard Hull, Robert W. Stevens, and John H. Couture for their
> answers to my query re the subject.
>
>
> I have snipped all of the above responses since they virtually reiterate
> the same ideas, ie., it should be possible to wind a 3/4 wave coil and
> make it resonate somewhere near its 3/4 wave frequency, taking into
> account its cself, etc.
>
> Richard, I want to do this if its possible. I understand it "should break
> out 1/3 of the way up the coil. If it is a standing wave, maybe it won't.
>
> John, I have my own home-brewed program to design coils. It does
> approximately what you suggest as far as satisfying the numerous
> applicable equations. It uses Wheeler and various other accepted
> equations for L, wavelength and frequency.
>
> Robert, I have a coil in which the wire length is "fairly" close to the
> 1/4 wave resonant frequency. This coil will put out discharges exceeding
> 36" from a 4.5" insulator on top with only a 1/4-20 screw for the top
> terminal. there is also a great amount of corona from the top several
> turns of the secondary. Driving power is a 15kv 120ma neon.
>
> Why did I bring this all up?
>
> I have tried to design and wind both 1/4 and 3/4 wave coils to be run
> with none or very little terminal capacitance with the idea that given
> the same energy delivered to the terminal capacitance, and using the
> energy equal to 1/2 cv^2...then decreasing the terminal cap should lead
> to increasing the voltage. Although its been a couple of years since I
> read Tesla's CSN, I believe he thought he was winding 1/4 wave coils and,
> if memory serves, he used very small terminal caps. I understand about
> corona and the fact that a toroid should build up the energy before
> breakout, but is that really how a TC works? I should not be able to get
> 36" discharges from a 1/4-20 bolt if that assumption is true.

> snip
>
> I would certainly appreciate any comments to this and I would especially
> like to hear from anyone who has built a 1/4 or 3/4 wave coil that comes
> in close to the correct frequency.
>
> Thanks for listening
>
> Skip,

Your math is correct on the given energy, higher voltage for smaller C
bit.  However, this math is thwarted by the reality of the matter in the
real world.

Let us say we have a fixed energy input.  Now, let us say that we have
50% more voltage available with no toroid, or removal of the load.  We
now use a bolt or very small electrode on the end of our coil.  We all
have seen what happens.  A vast shower of sparks, often hundreds, break
out all over the terminal or bolt in all directions.  The air break down
voltage of a bolt is about 15KV and a small 2" ball, about 60kv.  Thus,
as the Tesla coil's resonant rise builds to millions or billions of volts
it will break out way before this voltage is achieved or at 15 or 60Kv!!
The extra energy creates EXTRA SPARKS!!  Sparks which dissapate the
energy incredibly quickly as more and more fingers are added at the
BREAKOUT VOLTAGE.

True, given enough power, the ion cloud around even the most miniscule
terminals will be overcome by the energy.  This extra energy will expand
the spherical ion cloud and the spark length will grow even with a bolt
only electrode. But, my goodness,  we are stupidly making a large ion
terminal with brute power!!  There is absolutely no reason why a 20 foot
arc can't be made to issue from of a 1/4-20 bolt!  But Gee-whiz at what
power level and at what size of a coil would this happen!!  I don't want
to even imagine it!!!

A huge toroid or large top C absorbs and stores this energy as it is
being created by resoant rise.  The toroid's size and shape determine the
voltage of break out, say one million volts.  If you make a coil that is
not capable of generating one million volts, the spark will never occur
and RF radiation is all you get.  But let that 1 million volt mark be
reached and you will have a single, long, hot ribbon of flame releasing
all the stored energy in huge singular arcs moving slowly around the
coil.  We have all seen this too.  Am I right?!!!  If you haven't, then
you owe it to yourself to try it!  You will like it!  The spark return
from a giant toroided system using a given power input will always vastly
exceed anything from a system with little or no toroid.  This is just a
simple fact of physics and "the doing".

Tesla used small terminals in Colorado becasue that is all he had.  A 36"
diameter sphere is no small terminal, but compared to his system size and
power, it was vanishingly small!!

He learned quickly though from a long and tedoius group of daily
experiments with an elevated isotropic capacity in Colorado and didn't
repeat the Colorado "mistake" with Wardencylffe!  He planned and
constructed the largest regular formed terminal load ever created for his
tower.  His voltage would rise forever to incredible levels due to the
incredible storage capacity of his top terminal.

Finally, the voltage produced by a Tela coil is a function of the
resonator coil's inductance and the current injected into the base.  The
top terminal may load this a bit, but the value of the voltage created in
the system is not determined by the top C at all.  I hope this helps this