Re: My VTTC: The Quest For Longer Sparks

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Original poster: "Dr. John W. Gudenas" <comsciprof@xxxxxxxxxxxxx>

Chris
VTTC coils are very sensitive to tuning which includes proper
impedance match with your tubes. This is only a guess,
but it certainly sounds like your VTTC system is not in tune. You
might try adjusting your tank capacitance in pico farads and
see what happens. I produce 24-26 inch discharge running in self
rectified mode and longer in a staccato mode. This is with
a dual 833A system. I used a vacuum variable capacitor to find the
best tune for the tank circuit. Considering that increasing
plate voltage doesn't translate into longer discharge for you, also
indicates something is mismatched. Quite frankly, it is much easier
to use triodes and get everything in tune, albeit I suspect you have
already heard this.
Not much advice, but it is the best I can offer.
Good Luck.
John

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

On Oct 29, 2005, at 6:22 PM, Tesla list wrote:

> Original poster: "Chris Fanjoy" <zappyman@xxxxxxxxxxx>
>
>   After much tweaking and other work, I have my dual 813 VTTC
> producing some nice thick sparks of about 9" or so in length. But
> from what I've read, I should be able to get considerably more from
> this coil. Here are the specs of what I'm using now:
>   -Power supply is a large MOT with voltage doubler
>   -Secondary: 4" x 23", 27AWG, fr=157KHz
>   -Primary: about 23 turns #12AWG, on 8" form
>   -Tank Cap: .0056uF /40KV (TDK UHV-6A x 2)
>   One theory I have is that the primary coil coupling isn't high
> enough - a narrower primary may be needed. Or perhaps it should be
> redesigned to use a larger tank cap.
>   I'm powering the coil with a Variac, and it's worth noting that
> the sparklength peaks when the Variac reaches about 70 volts, and
> cranking to 120 doesn't seem to make any difference.
>   Any ideas? I'd be happy with even some 12" sparks.....