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Re: Single 833A VTTC

Original poster: "Steve Ward" <steve.ward@xxxxxxxxx>

Hi Cameron,

Very interesting (and impressive!) results.  It seems like you just
found a sweet zone for the coil.  I might have to think on this
feedback coil positioning issue... interesting indeed.  I dont think i
ever positioned my feedback coil so high, maybe only 3" at most.  The
usual issue was arcing from the secondary to the winding.  I never had
the chance to scope out a VTTC to really study its operation in detail
(particularly the feedback part).  I still have a pair o 833C's
waiting for a use ;-).  So many ideas, so little time...

I had plans to make a solid state and vacuum tube integrated system.
The tank circuit would look like your typical VTTC, but the grid drive
would be solid state.  The idea was that it could give more control
(and perhaps some insight) over the feedback loop.  Pulse width, bias
and drive voltage, and phase relationship could all be finely
controlled to produce best results.  I also intended to build a multi
kW plate supply using transistors and ferrite transformers (like
newere microwave ovens use).  But this would be roughly equivelant to
a plain transformer power supply.  It would probably not be reproduced
by many (if any) other coilers.


On 8/11/06, Tesla list <tesla@xxxxxxxxxx> wrote:
Original poster: "Cameron B. Prince" <cplists@xxxxxxxxxx>

Hi again,

One other thing I wanted to share with you all is my recent success with my
VTTC. John Freau, Steve Ward and Christopher Hooper have all helped me very
much and I certainly learned a lot from them. John asked me to share the
results with the list because I may have stumbled on to something that might
help everyone achieve higher efficiency with their VTTC's. The breakthrough
I've had has been related to moving the grid coil way up on the primary
form. Most plans I've seen recommend about 1 inch between the primary and
the grid coil. My coil has closer to 6 inches and my output improved
drastically. I'm getting 30 inch sparks with around 17A current draw with a
120V input. The coil actually runs best with the variac at about 75-80%.

You can see the coil running here:


It's powered by two MOT's in series, not parallel. The secondary is #28
wound on a 3.5 inch O.D. PVC form. The winding is about 17 inches. The
primary is about 28 turns of 10 AWG wound on 6 inch thin wall PVC. This is
basically the design shown on Steve Ward's page with a longer primary form.
A close up of the coil is here:


I'm using 10K of grid resistance with a 2700pF cap and the main tank cap is
about 2400pF.

I plan to put up a page with full construction details once I finalize the
design, but I'll be glad to answer questions if I can help anyone.

Comments are welcome.