[TCML] VTTC New Grid Coil Geometry

[Dr. John W. Gudenas]

Greetings John
The pancake grid coil, on initial experiments, seems to be a very  
stable arrangement.
I did find that I could reduce the number of turns on the pancake so  
that the variac could be cranked up higher before  the voltage was  
sufficient to oscillate.
This is a minor advantage as you can run up the plate voltage without  
hitting the grid with too much voltage. As with all VTTC tuning was  
critical. Simply
using the reduced size toroid improved performance greatly. I won't  
know exactly how improved, until I get the thing on a lower bench, but  
when you have been around these VTTCs it isn't hard to see improvement.
However, the sound and spark quality was consistent with the standard  
arrangement. I don't need a staccato controller yet and digital  
pictures verify the sword like sparks. What is amazing are the bright
white power arcs and I am not sure yet how long they get. This coil  
has no metal except for wires & toroid and is five feet away from the  
power supply and oscillator, however, the tank capacitor is adjacent  
to the coil with short leads.

It keeps the coil away from me ( reduce RF burns) and other  
surrounding elements that act as stray capacitance or antennas. My  
next run will use an HV twisted pair for the grid leak leads.
There is much yet to learn, especially understanding the coupling  
Physics of the three coils.

One thing, you are right on. It looks really neat and clean with the  
hidden grid coil and flash over is eliminated.

Incidentally, thanks for spinning all the different size toroids. Due  
to your efforts I have accumulated a set that stacks like a toroid  
christmas tree.
Regards
John W. G.

John W. Gudenas, Ph.D.
Professor of Computer Science

On Sep 17, 2008, at 4:31 PM, futuret at aol.com wrote:

> Dr. John,
>
> I used a still different grid coil arrangement on my 36" spark Tesla  
> coils.
> Both used flattish primaries.  The grid coils were very close to the  
> secondary
> and were solenoid coils only 1" high and about 1/2" wider diameter  
> than
> the secondary.  The grid coil was in the same plane as the primary  
> (in a
> sense).  The
> grid coil consisted of two layers of winding, about 19 turns total of
> 18awg pvc insulated wire.  I raised or lowered the grid coil to adjust
> things.  These coils were very tricky to adjust, and they never gave
> swordlike sparks, they always gave fuzzy sparks.  I don't know if the
> arrangement offered any real advantage or disadvantage overall.
>
> Then on my TT-27 VTTC, I attempted to use a flat primary and
> put the grid coil along the outside of the primary.  This worked
> very poorly.
>
> I like your idea of a hidden grid coil.
>
> Cheers,
> John
> -----------
>
>
> -----Original Message-----
> From: Dr. John W. Gudenas <comsciprof at ameritech.net>
> To: Tesla Coil Mailing List <tesla at pupman.com>
> Sent: Wed, 17 Sep 2008 12:01 am
> Subject: Re: [TCML] VTTC New Grid Coil Geometry
>
>
> Over the past two months I have been experimenting with a different  
> grid coil geometry.
> On my dual 833A coil I fabricated a flat pancake coil out of 14 awg  
> wire for grid feed back. The inner diameter is approximately the  
> same as the primary solenoid.
> It has 24 turns and is placed 1" under the lowes
> t secondary winding. The whole arrangement is covered by a phenolic  
> disc and presents the appearance that the grid coil doesn't exist.
>
> With this geometry I have changed the coupling association that  
> exists among the three coils. I haven't as yet determined the exact  
> relationships, albeit it works great.
> The coil required some tuning changes that were accomplished by  
> reducing the secondary self capacitance with a smaller toriod and  
> minor adjustment of the grid leak resistor.
>
> I use two identical plate transformers 2800 volts @ 280 ma in  
> parallel through a doubler. I need to lower the coil as it power  
> arcs around 24" to the floor joists above. I suspect continuous 30"  
> corona at full variac.
> I have no time now to work on it as I ended up on the University  
> Personnel Committee deciding tenure issues.
> As far as I know this is a different approach to grid coils. Flash  
> over is completely eliminated and I suspect (but have not proved)  
> there is greater magnetic coupling to the primary.
> Bert Hickman was over a few weeks ago and saw the prototype. When  
> things settle down I'll put up some pictures.
> You have. I believe, a new alternative now. Let me see what you  
> folks can do with it.
> Regards
> John W. G.
>
> John W. Gudenas, Ph.D.
> Professor of Computer Science
>
> On Sep 16, 2008, at 9:14 PM, S&JY wrote:
>
>> SNIP+++++++++++++++++++SNIP