RE: First light with 833 tube coil, then silence

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Cameron B. Prince" <cplists@xxxxxxxxxx>

Hi David,

I seriously doubt that mica cap is bad... They are built to handle a lot
more than you are throwing at them with your VTTC. When I ran it on mine it
stayed ambient temperature.

Notice that 12kV rating is not peak or maximum, it's nominal and you are
only at 50% of that with the VTTC.

Cameron

> -----Original Message-----
> From: Tesla list [mailto:tesla@xxxxxxxxxx]
> Sent: Saturday, September 23, 2006 2:41 PM
> To: tesla@xxxxxxxxxx
> Subject: Re: First light with 833 tube coil, then silence
>
> 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
>  > >
>  >
>  >
>  >
>  >
>  >
>  >