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

["James" <mustang3@xxxxxxx>]

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Phillip Slawinski
Sent: Saturday, June 20, 2009 10:05 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Tube choice for a VTTC 350khz?

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

Some snippers:
Hi Phil, I feel that you are tuned at a harmonic. I have tried tuning to
a harmonic several times for experiments; the overall performance is
less when tuned to a harmonic rather than the fundamental. I have found
that the position of the tickler coil has little effect. After all,
mutual induction is doing the work. I place my tickler coil low to
prevent flashover. I have fried several toobs when flashover hit the
tickler. I have measured the Fo on my VTTC's secondary, it's around
100KHz. The primary is tuned slightly lower. When run at very low power,
the frequency is at the primary's frequency. As the power is increased,
the frequency shifts to the Fo. The sound is a snap as the frequency
shifts. I feel that the high Q of the secondary determines the final
frequency. The primary has to be tuned off the fundamental (lower in my
case) for the frequency splitting. Now, most of you younger fellows have
never worked on radios or tvs that used IF transformers. 455Khz was the
frequency the IF strip used (sometimes 10.7MHz). The IF xmfrs had a
tuned primary and a tuned secondary. The frequency splitting was very
noticeable during tuning. I wish I would have had a triggered sweep
o'scope during those days. lol A vid of my VTTC running at 20KW input is
on utube as "big vttc". The toob is rated for 6KV, at 9KV the tube
flashes over on the outside. When the toob flashes over, it sounds like
a cherry bomb. Ask Sundog about that! I usually turn it up right under
the flashover point. My VTTC makes a flame off the secondary terminal,
no sword like sparks. A piece of #10 wire melts in seconds, the arc is
at least 1" in diameter at the discharge terminal. I am using a
full-wave bridge rectifier. This means the VTTC is running at a 120Hz
rate. This results in twice the applied power. I also like the 120Hz
note the coil makes. My horizontal VTTC uses two 5868 tubes and has a
1/2 wave doubler with 2 paralleled mot's. This make that 60Hz buzz.
VTTC's are my favorites, keep it up! James
 

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