Modulated VTTC (plasma tweeter) question (fwd)

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Original poster: Tesla List Moderator <mod1-at-poodle.pupman-dot-com>



---------- Forwarded message ----------
Date: Sat, 24 Mar 2001 00:54:26 -0500
From: cwillis-at-guilford.edu
To: Tesla list <tesla-at-pupman-dot-com>
Subject: Modulated VTTC (plasma tweeter) question


Hi Folks,
I know quite a few people have done some experimenting with audio
modulation of Tesla coils, and you might be able to offer some advice on my
problem.

I just built a "plasma tweeter," which is a resonant coil base-driven by an
modulated RF oscillator.  The arc discharge from the coil then makes sound
according to the modulation. My system has a 6146-B tube operating at 10
MHz, which is screen grid modulated by a 6CL6 tube as a clamp modulator.
There is a 12AU7 AF amp preceding the 6CL6 to boost the very low AF input.

Anyway, here's the problem.  I have quite a bit of distortion in the output
at high volume, and I suspect it results from improper resistance values in
the clamp-tube and screen grid coupling.  I can find no information about
how to use this type of modulation, especially for this application.  So if
there's any help to be found, I figure one of y'all might have a comment.

About the "tesla coil" itself:  I am a newcomer to the idea of "plasma
tweeters", but the apparently standard RF circuit is very simple and
effective and gives similar performance to the more complicated circuit
that Dr. Reszotarsky has posted on pupman-dot-com.  The coil is base driven
right off the tube plate, and constitutes the only tuned circuit.  There is
an RF choke to block RF on the B+ lead, and a capacitor to block the B+ at
the base of the coil.  Feedback is capacitive, via a small electrode near
the hot end of the Tesla coil.  Bias the tube for class C and you have a
working, sparking "tesla coil" that can be built in literally a few
minutes. (Modulating it as a speaker and making it sound good takes a while
longer!)

-Carl