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Re: Tesla/Marx generators.

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> From: Tesla List <tesla-at-poodle.pupman-dot-com>
> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: Re: Tesla/Marx generators.
> Date: Wednesday, February 12, 1997 1:25 AM
> 
> Subscriber: MALCOLM-at-directorate.wnp.ac.nz Tue Feb 11 23:16:06 1997
> Date: Wed, 12 Feb 1997 09:09:23 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: tesla-at-pupman-dot-com
> Subject: Re: Tesla/Marx generators.
> 
> Hi Daniel,
>             You pose a good question IMO:
> > RE;
> > another thing that made this Tesla coil somewhat unconventional was the
> > fact that the resonating capacitor was connected directly in parallel
with
> > the primary of the Tesla coil.  The Marx multiplier would dump a nice
big
> > bunch of energy into the L/C primary circuit, and then the primary
would
> > happily ring away until it was hit again by the next dump of energy.
Note
> > 
> > But how could the Marx generator, or any other HV source charge the
> > resonating cap if it's directly connected to the primary? The DC
resistance
> > of the primary, only a fraction of an ohm, would surely prevent, (or
short
> > out,) any potential applied. It's my understanding that the purpose of
the
> > gap is to electrically separate the primary from the cap so that
charging
> > can take place to a certain value. When the gap fires, it's the
equivalent
> > of a switch closing and that's when the show begins.
> > 
> > Facinating phenomenom! Comments?
> > 
> > Daniel Hess
> 
> The secret is in the high impedance of the primary coil at *very* 
> high frequencies. According to a piece in Sargent and Dollinger's 
> book "High Power Electronics", spark propagation is on the order of 
> 10^-8 s in a typical spark gap (compare that with the sine period at 
> the resonant frequency of the coil). I have built Marx banks that 
> actually use this trick. By replacing the normally used resistors 
> with chokes, you can speed up recharge times, eliminate power loss 
> that normally occurs with the resistors and still get much the same 
> output.
> 
> A bit off-topic,
> Malcolm

Malcolm,
I don't think your remarks are off topic at all. A Marx circuit not only
*can* be used to drive a fairly high powered Tesla coil, it *has been
done*. It is one method that allows lower KV fairly high amperage
transformers to be converted to something with higher KV. Because the use
of coils instead of resistors allows them to have fairly fast recharge
times, you can use this method to dump some very high amounts of energy
*very often* into a tank circuit.

It also is one way to get the power delivered to a tank circuit that is not
just coupled through the spark gap. This allows the primary tank circuit to
ring in a more natural way. To put it another way: in the conventional
Tesla coil the primary and the capacitor actually only form a resonant
circuit during the time the gap is conducting. In this other form of the
circuit, the resonant components are *always* connected in parallel.
Therefore they can continue to resonate even after the gap has
extinguished. Whether this is something good and desireable depends on what
you are trying to accomplish. If you *want* the tank circuit to ring down
for longer periods, then this is at least one way to make that happen.

Fr. Tom McGahee