My single 833A vttc -- first light!

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Brett Miller <brmtesla2@xxxxxxxxx>

All,

My single 833A vttc had first light tonight..at least,
first light with full power (due to the voltage
doubler being installed).

Performance was amazing, it easily started eating its
own breakout point, which was a heavy (one of the
larger ones) paperclip, straightened out and wrapped
around a bolt which sits atop my John Freau toroid.
You can see it happening in this picture:

http://hot-streamer.com/brett/vttc/single_833_noshunts_with_doubler.jpg

In that picture the coil is generating about 8"
swordlike streamers into free air, however, I have
video which shows some reach out to 14-15".  I could
possibly achieve an even greater distance once I set
up a grounded target for the discharge.  I may need to
mount a tungsten breakout point atop that toroid as
well.  Something interesting I noticed, was that after
the paperclip point melting into a sphere of molten
metal the swordlike streamers began to appear in
opposition and extend in various directions, with the
curvature of the small metal sphere as the radiant.

I have spent a lot of time tuning in the raw ac mode,
and I arrived at a combination of primary tap, grid
leak resistance, and feedback coil height, that seems
to provide optimum output at least current demand from
the mains.  However, as John F. and others warned me,
tuning a vttc is quite a challenge.....John, you sure
said a mouthful there.

Specs as of tonight:
-----------------------------------

Single used 833A...label rubbed off (possibly RCA?)

Plate transformer:  Large MOT with shunts removed

Voltage Doubler:  3 oven caps and one oven diode

Filament supply:  MOT with secondary cut off and
rewound with AWG12....provides 10.7v at around 9.8+A
at the filament pins

Secondary:  19" winding length on 3.5" PVC former

Primary:  28 turns AWG12 THHN, currently tapped at
turn 21

Feedback:  25 turns AWG23 magnet wire on slidable
form.
(coil did not oscillate at first...swapping these
wires *did* promote oscillation in my coil)  Currently
the plate seems happier with the feedback coil about 2
inches above the top of the primary.

Grid leak system:  2 in series 3K Ohm 50W Ohmite power
resistors in parallel with a single Yish 1.1nf 50kv
doorknob cap

Tank Cap:  2 Yish 1.1nf 50kv doorknob caps in parallel

Topload:  1 John Freau 1.75" x 6" spun aluminum toroid



Well, those are the specs I can think of...all grounds
tied to a common point and connected to the same rf
ground that gave great results in my 45" spark 12/60
disruptive coil.

I think I may have stated (at least to a few people)
that I wasn't interested in getting competitive spark
lengths here...but I think with some fine tuning (and
staccato of course) I will be up in the 20"+ range.
That would be extremely favorable.

Cheers,

-Brett




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