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TESLA, CW


 RE> Have you had any experience driving coils with high freqs    
 RE> instead of the cap discharge type circuits?

Yes I have. This is a very efficient method of exciting a coil.
There is a book in print, and a very good magazine article on
driving coils with solid state (read real cheap) oscillators:

> MODERN TESLA COIL THEORY
Duane A. Bylund, 1990, Tesla Book Co., no ISBN or Lib. of
Congress No, paperback 142pp. Duane has developed very powerful,
efficient, and reliable, solid state oscillator circuits for base
feeding Tesla resonators. These solid state driver and coil
designs are excellent for lighting bulbs and for conducting
experiments with wireless power transmission through ground
currents. The book is also chock full of Tesla math and theory,
and includes chapters on spark gap and tube coils, sections on
waveforms, grounding and counterpoise experiments, multiphase
coil systems. This is a must have book for any serious coiler.

> October 1992, Popular Electronics pp 69-71, Fun With Tesla 
> Coils, by Charles D. Rakes 
This article builds a small solid state coil using a driver
oscillator which base feeds the HV HF Coil. The project uses
a 567 tone decoder IC, a few resistors, caps, and a power supply 
to drive a small coil to light bulbs etc.. The secondary is wound
on a piece of 4" PVC, looks simple and inexpensive (~$80.00). My
archives contain a self extracting program (TESLABLD.EXE) that
gives detailed instructions on building this project.

 RE> After digesting Tesla's patents and desiding for now not to  
 RE> build a HF alternator, I have taken a 250 watt switching     
 RE> power supply from a car audio amp to use. It is currently    
 RE> running at 22 khz, but I'm making the freq variable, prob    
 RE> from about 10khz up to about 30khz or so, depends on how the 
 RE> toroid holds up in the supply. I'm rebuilding my previous    
 RE> coil attempt now, after discovering all the things I did
 RE> wrong...so I will drive it with this supply to start off.

 RE> Just wondering if you had any direct experience with this    
 RE> type of coil, and/or helpful advice that you always seem to  
 RE> have handy.

I can refer you to the two sources above which detail exactly the 
project you are looking at. Though it may seem strange to you... 
Tesla knew very well the problems of coupling efficiency and
frequency stability in the "standard" 1/4 wave Tesla coil driven
by a spark excited tank circuit. He was also very aware that
capacitor Q and tank circuit performance had to be excellent
in every aspect: high performance, low failure. He knew this to
be a requirement before the Tesla coil could become commercially
acceptable as a means to transmit power. These same factors are
the bane of modern coilers seeking exceptionally good spark.

By 1896 Tesla understood perfectly the many advantages of base
feeding the coil with frequency stabilized RF current. This
pregression led up to his achieving tremendious VSWRs at Colorado
Springs and Wardencliffe. These systems are absolutely beautiful,
and are fully thought out (and tested) in every possible
combination. The documentation exists both in his patent record
and in his notes published later. The true depth of the story is
still mind boggling:

The simple 1/4 wave coil hits it's theoretical maximum efficiency
at 50% when driven from an inductively coupled tank circuit. This
applies whether the tank operates in damped or CW mode. The coil
(electrical resonator) is limited in it's resonance by both the
magnetic influence of the primary/secondary field flux, and the 
equalization of energy between coils. When the spark gap opens,
you cannot have more energy in the secondary coil than you have
in the primary; therefore 50% of the input energy remains in the
primary coil/tank circuit. 

Tesla was already adept at using HF alternators (all new RF
technology he developed) at base feeding coils, and had already
gone yet another step forward with the development of isochronous
electro-mechanical RF oscillators patented in 1893. These
isochronous oscillators were powerful enough by the time that
patents were in place that they could provide frequency
stabilized RF current to the field windings of very large HF
alternators. Combined with rigorous steam pressure regulation, he
was able to deliver several kilowatts of extremely stable CW RF
to the base of his coils in 1893.

By 1898 Tesla had developed the Magnifier circuit. This circuit
used the more powerful tuned capacitor discharge for the pro-
duction of the RF energy. But unlike the simple 1/4 wave coil of
earlier, the end resonator was removed from the influence of the
primary/secondary field flux. The end resonator or "Extra Coil"
allowes energy induced into the secondary to be removed by tran-
smission line. The 50% efficiency barrier disappears. 

In the Magnifier circuit, the primary/secondary are completely
reconfigured. The two coils are extremely tightly coupled, the
break rate is mechanically increased, and the secondary coil is
forced to resonate at the 1/8th wave harmonic as opposed to the
natural 1/4 wave. In essence, the primary/secondary (with driving
oscillator) becomes a very high powered narrow band signal
generator. The HF RF current from the signal generator is base
fed into the extra coil (free resonator) some distance away where
it is allowed to resonate unrestricted from the primary/secondary
field flux. Even a buck amateur can get 70% efficiency if a few
attentions to details are observed.

I think you understand how this would relate.

Richard Quick


... If all else fails... Throw another megavolt across it!
___ Blue Wave/QWK v2.12