Re: First light with 833 tube coil, then silence

["Tesla list" <tesla@xxxxxxxxxx>]

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

David
VTTC are very sensitive to tuning.
Drawing 20 amps and producing 8" corona indicates a tuning problem
typically associated with the tank cap (C1) or primary inductance.

I would run (perhaps at lower power) without the staccato controller
when you set up the tuning. After you get it tuned add the staccato.
You don't need additional components to de-bug and tune.

If the plate transformer (MOT?) is still putting out voltage and the
doubler diode and caps are ok, you likely destroyed the tank cap C1.
If a tube coil worked once and then goes dead I would look at the
tank cap, a likely failure point. 833A's are very robust and can fail
under extreme over voltage
or total plate melt down. I have run them with holes melted in the
plate.

Tank caps in VTTC must be rated for RF and high current. I have
exploded 12,000 volt mica transmitting caps(nasty mess).
Just using a cap meter to test it won't give you a test as the
failure often is at high frequency.
What are you using for a tank cap? You need RF rated ceramics at
40kv, an MMC, or high current, high voltage micas.

I am assuming that you have the general specifications for your coil
that Steve has on his site. If so the grid leak components and values
are a reasonable place to start (you got 8" corona). If you have
everything connected properly (likely) my best guess is tank cap
failure.
Good luck
John

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

On Sep 23, 2006, at 7:31 AM, Tesla list wrote:

> Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>
>
> Hi all,
>
> Finally got the VTTC all wired together and tried out
> first light tonight. Was having trouble with the stacato
> driver as I couldn't get too much of anything out with
> the stacatto driver energized. I did start getting about
> 8" continous "swords " with the variac turned up to
> about 120 volts and drawing 20 amps (w/out stacatto).
> Didn't seem too efficient but this is my first time with
> a VTTC, ever. It's basically patterned after Steve Ward's
> 22" 833A VTTC: <http://www.stevehv.4hv.org/VTTCfaq.htm>http:// 
> www.stevehv.4hv.org/VTTCfaq.htm
> the third picture down. At least it did work some until
> I started trying to vary the resistance in the grid leak
> bypass resistor (R1). Now all of the sudden it won't
> put out anything, nada, zilch! I tested that resistor,
> the capacitor C2, and even tried swapping out 833A
> tubes, all to no avail. Every component checked out
> good and changing out the tube with spares didn't
> solve the problem either. Can any of you vauum tube
> gurus help me out here? :^))
>
> Thanks,
> David