Oudin Coil vs Tesla Coil

From:  Thomas McGahee [SMTP:tom_mcgahee-at-sigmais-dot-com]
Sent:  Friday, March 20, 1998 11:15 AM
To:  Tesla List
Cc:  acmq-at-compuland-dot-com.br
Subject:  Oudin Coil vs Tesla Coil

> From:  Antonio C. M. de Queiroz [SMTP:acmq-at-compuland-dot-com.br]
> Sent:  Thursday, March 19, 1998 12:40 AM
> To:  Tesla List
> Subject:  Re: Oddball Oudin Coil
> Gregory R. Hunter wrote:
> > The device I described in the original post uses the re-wound core and
> > interrupter from a T-Model induction coil as a kicker.  However, the
> > 75kV business end of the thing is a self-resonant, multi-layered air
> > core winding excited  by a copper tube primary & operating at much
> > higher frequency than any induction coil.  Brent Turner's book has a
> > good description & schematic of an Oudin coil.  If you're interested
> > in the original article, it's available (scanned) at:
> > http://www.noah-dot-org/science/x-ray/index.html
> Note in the circuit diagram (fig. 231) that the primary circuit has a
> too high series resistance for a Tesla coil (the rheostat), and is 
> -disconnected- from the power source when the current through it is 
> maximum. The input voltage is just 110 V. Too low for a Tesla coil.
> This is the operation of an induction coil, not a resonant transformer.
> There is no oscillation (other than parasitic, low Q) in this circuit.
> What the tube receives is a series of high-voltage pulses, one at each 
> interruption of the primary current.
> Antonio Carlos M. de Queiroz
> http://www.coe.ufrj.br/~acmq

Sorry, but the above explanation is not entirely correct. True,
the Kick Coil itself is indeed a form of self-induction coil. 
Its purpose is to step the 110 volts up to several hundred volts. 
When the Kick Coil pulls in the interrupter there is a fairly 
large peak voltage produced, and this is stored in the capacitor. 
When the interrupter re-connects, it connects the CHARGED capacitor 
to the primary in such a way that it now forms a classic resonant 
circuit. BTW, the official name for that secondary thing is 
"the Resonator". Sound familiar?

The inclusion of the rheostat by Mr. Harry D. Simons was a mistake on
his part, and when I visited with him in 1965 I pointed out that fact
to him. He included it simply because he found that it gave him a small
degree of control over the output. Hey, what works, works!

Tuning this kind of Oudin coil was often done by fiddling around with the
interrupter mechanism, when in fact it SHOULD have been done by tapping the
primary. That is how I accomplished it in all the Oudin coils I ever made...
I ran taps out at each full turn, and one set of quarter taps out at
the end where the secondary connected to the primary. That allowed me to
tune within 1/4 turn.

The Oudin coil really *is* a resonant air core system. The type described
above uses the Kick Coil as the power source, much as we use a neon 
transformer. The spark gap is replaced by the interrupter (which does
double duty as the Kick Coil vibrator...), and the capacitor, primary
and secondary are all classic Tesla coil items. For the record, the main
difference between a classic Tesla coil and a classic Oudin coil is that
the Oudin coil has one end of the secondary directly connected to one end
of the primary. That, folks, is truly a minor difference.

The resonant frequency of a multilayer coil tends to be quite low
by TC standards, but it is still a "resonant" frequency. The
multilayer Oudin coils can put out a fair amount of useful current.
The Oudin coil does not "have" to be multilayer. If any of the coilers
on this list have ever connected the bottom of their secondary
coils to their primary coil, then they inadvertantly transformed
their beloved Tesla coil into the much-maligned Oudin coil.
Shame on you!!! :)

I might add that historically the Oudin coil has been implemented as a
multi-layer secondary device, but Tesla's early devices also employed
multiple layers. Tesla often employed the Oudin connection scheme in his
coils designed for therapeutic applications. So, even Tesla built
Oudin coils. Oudin just happened to get the patent on this **particular**
connection scheme. But please, just because the thing is called a Oudin
coil, let's not assume that it is not "really" a Tesla coil.

Hope this helps.
Fr. Tom McGahee