Re: First light with 833 tube coil, then silence

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "David Rieben" <drieben@xxxxxxxxxxxxxxx>

Hi John,

I'm really starting to believe the main cap is toast, too ;^(
It's a 12 kV, .002 uF (2 nFd) mica transmitter cap. The
system still draws current but not much until I start reach-
ing about 120 volts input (that's when cheap MOTs start
to saturate).  The primary coil isn't getting warm either since
the output went dead. Also, I can stick a conductive rod
across the terminals of the tank cap while it's energized
since the output went dead and there's absolutely no spark,
no matter what the variac is set at. The mica cap did NOT
"blow up" and still checks out at 2 nFd with my capacitance
meter but it sure is looking dead to me, though. I will try
reversing the grid coil polarity the brian suggested first and
if that dosen't fix it, it's off to get a new cap.

David

----- Original Message -----
From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Saturday, September 23, 2006 1:31 PM
Subject: Re: First light with 833 tube coil, then silence


> 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
> >
>
>
>
>
>
>