Re: First light with 833 tube coil, then silence

["Tesla list" <tesla@xxxxxxxxxx>]

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

Hi Cameron, John G,

I checked the output of both of mt MOTs and they were both good.
I even checked to make sure that the MOT filter caps were taking on
a good charge after powering up by shorting a srew driver blade across
their terminals immediately after shutting down the power before the in-
ternal bleeder resistors bled down the charge, possibly suspecting the
diode had failed short circuit. The caps wouldn't always be left with a
full charge immediately after shutting the power down since they won't
always be shut down at the sine wave peak and in my case, they would
be left with a full charge every time after shut down.  Like I said before,
the main G3 tank cap makes absolutely no spark from shorting its 2
terminal ends with the power applied. I did not try this before the
output went to zero, but it stands to reason that this should reveal
some visible discharge if the cap is putting out oscillations into the
primary coil. Also, the primary coil now stays cold when I do turn
it on, whereas it would get warm after running it a few minutes
when there was an output, so it seems that no oscillations are getting
to the primary coil

Also, I think that my primary coil was a little short with its 30 turns
coupled with my 2 nFd primary capacitance since the output kept
getting a little better each time the I added more turns all the way
up to the 30th and final turn, when it was working. May opt for
a little bit primary cap, like 3 nFd, to make my current primary coil
tune in better once I figure out what's wrong. I think the #30 AWG
secondary coil is making it resonante at a lower-than-expected
frequency compared to the one that Cameron built using #28 AWG
wire.

David


----- Original Message -----
From: "Cameron B. Prince" <cplists@xxxxxxxxxx>
To: "'Tesla list'" <tesla@xxxxxxxxxx>
Cc: "'David Rieben'" <DRIEBEN@xxxxxxxxxxxxxxx>
Sent: Saturday, September 23, 2006 8:28 PM
Subject: RE: First light with 833 tube coil, then silence


> Hi John,
>
> I'm am aware of and agree with your statements. However, this is a G3 mica
> transmitting cap rated 12A @ 300kHz. The diode David is using is only
rated
> at 750mA and would normally go long before the cap would. I guess stranger
> things have happened, but I would certainly rule out every other
possibility
> before buying a new cap.
>
> This is the cap David is using:
>
> http://www.teslauniverse.com/images/vttc/DSC02483.JPG
>
> Notice it's almost as big as the tube...
>
> David is, if I'm not mistaken, running dual MOT's with the secondaries in
> series. I think it would be prudent to verify that one of those
secondaries
> hasn't opened and would consider this much more likely than cap, diode or
> tube failure.
>
> David, let us know what you find.
>
> Thanks,
> Cameron
>
>
> > -----Original Message-----
> > From: Tesla list [mailto:tesla@xxxxxxxxxx]
> > Sent: Saturday, September 23, 2006 7:49 PM
> > To: tesla@xxxxxxxxxx
> > Subject: Re: First light with 833 tube coil, then silence
> >
> > Original poster: "Dr. John W. Gudenas" <comsciprof@xxxxxxxxxxxxx>
> >
> > Cameron
> > Be cautious with just voltage ratings on mica caps (or any caps for
> > that matter).
> > They need to handle high current too If the duty cycle is high, such
> > as operating in self rectification without a staccato controller.
> > The current in the tank circuit can get get up there.  With my dual
> > 833A VTTC which produces 24" corona without a staccato controller
> > I can run for 10 to 15 minutes before things get hot. This coil
> > destroyed at least three new 12,000 volt mica transmitting caps
> > (typical ones about 3" x 2" x 4" with the screw terminals on top).
> > One blew out the bottom and left a very unpleasant mess. I switched
> > to very high current composite micas in an MMC arrangement.
> > These are .0024 mfd. They are black cylinders about 3" in diameter
> > and 5" long with large brass connectors on each end with 1/4 -20 bolts.
> > The rating was 20kv too. I tried one and had very poor spark output,
> > I saw this before cap failure. I put two in series then and
> > paralleled this with another string of two in series.
> > The coil worked great with no tank cap heating. The coil operates
> > around 250 kHz.  Cap problems ended completely. Good RF ceramics do a
> > decent job too.
> >
> > Cap dielectrics tend to get quite lossy at high currents and voltages
> > operating in the RF ranges.  If they can't handle the current they
> > die a rapid death.
> > I have also destroyed MMC's with my DRSSTC that I didn't
> > sufficiently  design for long duty cycles. Not from over volting, but
> > from too much current.
> >
> > Professors tend to get on soap boxes and preach, so today I am just
> > saying consider voltage and current in capacitor choice (obviously
> > dielectric too).
> > David will solve his problem as intersecting all our responses, we
> > suggested every component could be bad as well as wiring errors. Good
> > luck David.
> > Cheers!
> > John
> >
> >
> > On Sep 23, 2006, at 3:08 PM, Tesla list wrote:
> >
> > >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
> > >
> >
> > Snip ---- Snip ---- Snip
>
>