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Re: Tube Type Tesla Coils

Subject: 
        Re: Tube Type Tesla Coils
  Date: 
        Wed, 19 Mar 1997 11:09:00 -0500
  From: 
        "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
    To: 
        Tesla List <tesla-at-pupman-dot-com>


> Date:          Wed, 19 Mar 1997 00:20:58 -0600
> To:            tesla-at-poodle.pupman-dot-com
> Subject:       Re: Tube Type Tesla Coils
> From:          Tesla List <tesla-at-pupman-dot-com>

> Subject: 
>             Re: Tube Type Tesla Coils
>        Date: 
>             Wed, 19 Mar 1997 12:17:43 +1200
>        From: 
>             "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
> Organization: 
>             Wellington Polytechnic, NZ
>          To: 
>             tesla-at-pupman-dot-com
> 
> 
> I don't think there should be any great surprise about this....
> 
> > John,     I seem to remember hearing that the Corum's (or maybe their
> > students), did this with a tube coil.  If I remember correctly, they
> > were
> > able to acheive a quite low, maybe 1.5 or so VSWR, and they said the
> > coil did
> > perform best at lowest VSWR.  I don't remember where I heard this story.
> 
> A VSWR approaching 1 implies maximum power transfer to the load
> impedance from the source impedance (Y-N)?  It does also imply that 
> the line is terminated in Zo at each end also I would think.
>     Using a Smith Chart graph to match a transmission line is fine 
> where the source and load impedances are known exactly but those 
> results fly off in the breeze when either changes as they do in a TC 
> situation. I think the fact that Rgap varies with current in the gap 
> system makes the use of Smith Chart totally invalid for a spark gap 
> coil, sparking secondary or not because the resonator feed impedance 
> must vary as Rgap varies despite the fact that the resonator base is 
> grounded (Y-N)? It can't be very useful to us because it is valid 
> only when the primary is not coupled and the secondary is not 
> sparking, regardless of the energy content of the secondary 
> (assuming static losses = dynamic losses).
> 
> Other opinions/answers welcome as always,
> Malcolm
> 
> 
Malcolm,

I think the case of a non-pulsing vacuum tube T.C. (a true C.W. high
voltage 
source drivn from a filtered, full-wave rectified D.C, power supply) in
the
discharging state where 
you have a brush of corona off a sharp terminal, or a flare off a 
smooth radiussed terminal, may well represent a fairly steady load 
impedance to the H.V. generator. Under this condition it may be 
possible to actually set upome metering and determine a meaningful 
VSWR measurement.  As I seem to recall GL commented some time ago,
maximum streamer activity would probably occur when the Z of the
secondary
matches the load impedance of the surrounding air.  In this case the
VSWR
should be at a minimum I would think.  I've noticed a distinct voltage 
clamping effect by ionized atmosphere while doing direct connection 
capacitive divider H.V. probe measurements of these beasts.  Voltage 
soars with applied power into the tube oscillator until corona is 
formed, then the ionized atmosphere hard clamps the voltage and 
continuing increases of power do not raise the voltage, the corona 
just gets larger, longer and fiercer.  The atmosphere acts just like 
a big gas filled voltage regulator tube.  In tuning up one of these 
beats you have to tune for favourable power processing in this loaded 
state or the machine will fall on its face at relatively low power 
near the corona breakout event.  That jump from no-breakout to 
breakout is quite a dramatic change in parameters for a coil system 
for sure.

rwstephens