Re: 833A problem resolved, and others to be solved

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Sundog by way of Terry Fritz <teslalist-at-qwest-dot-net>" <sundog-at-timeship-dot-net>

Hi Steve,

  It sounds like your tuning is drifting a bit.  On my quad 833A coil, I 
had a 3.5" PVC secondary (white pvc), and a 4.25" primary/grid form (green 
drain pvc), and had no trouble at full power, other than parts 
heating.  But, if I started moving around the coil, or changed the size of 
the topload, things got pretty nasty.  Kickback into the tubes, sparks and 
corona in bad places, etc.

   I tuned my VTTC with an O-scope and a signal generator, then used a 
dummy load at full power to watch the coil drift out of tune as the tank 
cap heated up.  The dummy load was 10 turns of 12ga THHN on a section of 3" 
PVC pipe, with a 60w household bulb across the ends as a resistance.  I 
ended up with about 40-50khz drift from cold (room temp, about 80 deg F) to 
hot (pretty hot to the touch, so the insides of the caps were scorching 
hot).  You may be seeing the same effect.  You may try putting a dummy load 
in place of the secondary, and use a wire antenna and an O scope to watch 
the primary frequency as the coil runs.  Keep tabs on the temperature of 
the components and tubes, (shut it off and discharge the tank cap first!), 
and note if there's any frequency drift.  If the frequency drifts upwards, 
you may try tuning the tank circuit a tad low to begin with, so that as it 
heats up at full power it'll come into better tune.  Won't take much 
adjustment to do it.

  Another thought is that the secondary is becoming more loaded by the 
streamers, and the extra top capacitance from the ion cloud (VTTC's have a 
pretty big field on top) is dragging Fres of the secondary down, so that 
it's lower than what you would measure with a signal generator and 
scope.  Try lowering the tank frequency a tad and see if that helps.


   One of the semi-solutions I came across while working on my own coil, 
was to use clear silicon to coat the primary and grid windings, and to run 
the grid leads through thin nylon tubing, then pumping silicon through the 
tubing (held the tubing in the nozzle of the caulk gun and squeezed away 
until the tube was full).  I usually get plenty of corona on the grid 
winding where it comes on and off of the primary form.  I also coated the 
bottom 1/4 of the secondary with silicon caulk (used my finger to spread it 
and my winding jig to turn the coil).  That helped some, but it only really 
helps the symptoms, not the problem.

Hope it helps!

Shad


At 02:58 PM 1/18/2003, you wrote:
>Original poster: "Dr.Resonance by way of Terry Fritz 
><teslalist-at-qwest-dot-net>" <resonance-at-jvlnet-dot-com>
>
>
>You need a better insulating material.  Rubber is not very good at high
>frequencies.  Try polystyrene instead --- very good at RF frequencies.
>
>Dr. Resonance
>
>
>
>
>----- Original Message -----
>From: "Tesla list" <tesla-at-pupman-dot-com>
>To: <tesla-at-pupman-dot-com>
>Sent: Friday, January 17, 2003 7:32 AM
>Subject: 833A problem resolved, and others to be solved
>
>
> > Original poster: "Steven Ward by way of Terry Fritz <teslalist-at-qwest-dot-net>"
><srward16-at-hotmail-dot-com>
> >
> > Ok,
> >
> > I had this problem with my dual 833A tube coil, where one tube got red,
>and
> > the other didnt.  So i made a tapped grid coil, this worked great.  Each
> > tube got a spread out redness on the plate at about the same power input
> > (very, very close).
> >
> > NEW PROBLEM!
> >
> > I now (now that i can crank her up) get a spark that jumps down from about
> > 4/5ths of the secondary coil, to the grid coil.  Thats not good!  I have a
> > thick rubber insulation sheet wraped around (loosely) the secondary to
> > insulate it from the primary and grid coils(or rather them from it).  But
> > it still managed to arc about 9" over a rubber surface!  Of course the
>coil
> > was making some serious 20-22" sparks.  John Freau has a similar dual 833A
> > coil.  He only has a 12" tall (i think) secondary (where as mine is 17"
> > tall of a thicker wire guage) and does not have insulation, and his coil
> > makes 24" sparks, with much tighter quarters between the secondary
> > potential, and the primary and grid coils. I realise the rubber is helping
> > the arc to creep, because it can arc farther over an insulator(rather than
> > air). Without my insulation there, it arced more easily (but than again,
>it
> > was a slightly different setup, i need to retest this).  So, i can only
> > propose that i raise the secondary up about 3", and loose some coupling.
> >
> > IF anyone has ant suggestions to this new problem, i would like to hear
> > them,  Thanks guys.
> >
> > Steve Ward.
> >
> >
> >
>