Re: [TCML] Tube choice for a VTTC 350khz?

[Phillip Slawinski <pslawinski@xxxxxxxxx>]

Hi All,

I've been doing VTTC research of my own lately and I've observed some
some interesting results.  I started by measuring the fundamental
frequency of the primary and secondary with a TC Tuner.  I put wire on
the secondary to simulate the spark loading of a 33" streamer.  This
put F1 at about 260kHz, the primary was in this range too.  The fun
begins when I turn the coil on.  The coil does not operate anywhere
near 260kHz, but rather between 450kHz and 470kHz depending on grid
placement.  What is even stranger is that the operating frequency is
rock steady.  Tt doesn't matter if the coil is pushing out 1/2" fuzz,
or throwing 33" sparks, it stays locked to one frequency.  The only
way I have been able to vary the frequency at which it operates is by
moving the grid coil up or down on the form.  My VTTC is like that of
Cameron Prince, with the tickler coil high above the primary.

Here's a recent scope capture I obtained while running the coil.
These are measurements of the e-field taken near the secondary /
primary.

http://www.flickr.com/photos/pslawinski/3634828940/

The cursor is located on the secondary / primary F1.  To the right is
the coil's Fo (454kHz in this case).

-Phillip Slawinski

On Sat, Jun 20, 2009 at 02:54, Frosty<frosty90@xxxxxxxxx> wrote:
> Regarding the sword like sparks, I've found with my solid state coils, the
> spark appearance dosen't seem to depend on the actual resonant frequency,
> (my small coil runs at about 350khz and my larger one below 200khz, and both
> can give sword like sparks). From what I've found, simply through
> experimentation, the spark appearance seems to depend mostly on how you
> modulate the rf. (since tube coils and solid state coild both operate
> similarly in terms of wave forms, I think what applies to SSTCs will apply
> essentially to VTTCs as well). I've found that half wave rectified supply,
> or any other smooth low frequency envelope produces the straight sparks,
> regardless of the resonant frequency. Rapidly changing envelopes seem to
> give jagged sparks, and the shorter the pulses, the louder and more jagged
> they seem to get. Higher audio freqency (above about 200hz ) modulation
> seems to give bushy sprarks.
>
> The sound of the sparks changes suprisingly with modulation as well. A
> single pulse of half wave rectified pulse make a singe long sword spark, and
> a very plesant dull thud/ popping sound, but not loud, yet a spark of the
> same physical size, but a short square pulse of modulation, is VERY loud.
>
> An interesting thing to try would be to power a small tube or solid state
> coil from the output of a big audio amp (I have tried this on a small low
> power SSTC once), and observe the different spark formations with different
> signals in.
>
>
> Cheers,
> Jesse
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