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Audio Frequency responce of a VTTC plasma discharge

Original poster: "David Trimmell by way of Terry Fritz <twftesla-at-uswest-dot-net>" <davidt-at-pond-dot-net>


I have completed a series of simple tests to determine the frequency 
response on the CW plasma discharge of a VTTC. First I obtained a old Bogen 
PA amp (yeah! no more fussing with that tube amp, at least for now!), 35 
watts RMS with 25V 4.5, 8, 16, 18 (?) ohm output also a couple 70V 140 ohm 
outs, all with many inputs, etc.

First: I ran the output from the Signal Generator (Thanks Terry!) into the 
Amp, with every thing in the operational setup, using the 16 ohm output of 
the Amp (no power to the tubes!), I placed the scope probes across the 
output of the audio coupling (voltage/signal boosting transformer). This 
was too test the distortion/clipping of the audio signal.
Results: <60 Hz signal caused the amp too distort/cutoff at 500V P/P; >100 
to 10K Hz it would distort at 1000 to 1100V.  Knowing the limitations of my 
setup is essential.

Second: I fired up the coil (scope probe removed), running with 1.5 to 2.5 
inch discharge, I fed the amp with Audio F signals from the Sig Gen 
(keeping output well below the above shown Voltage limitations). Using my 
ears and a scope with probe/antenna to detect results.
Results: below 100 Hz distortion is very evident and will easily cut off RF 
output (flat line...) low volume output (wish I had a DB meter!), no live 
Voltage measurement. 100 to 300 Hz was similar, but volume would triple 
before flat line. >1KHz I could do close to setup max before flat line. (I 
need many more data points here).

There is a Equalizer on the Amp that lets me adjust the output on the 80, 
300, 1K, 3K, and 10K Hz bands. This also shows best response with the 80 Hz 
all the way down, the 300 Hz halfway down(+10 to 0 to -10), -5, and other 
bands at 0. This was tested with Music (Rock and Classical). One other 
thing to note is that the larger the output of the coil, the better the low 
frequency response, but only slightly.

This is all done with the design shown on my web site, except the secondary 
is 4"x16" #28, and tuned to about 380 KHz. www.ChaoticUniverse-dot-com

Has anyone else tried Grid Audio modulation of a VTTC? Or Audio modulation 
of a SSTC? I am really interested in verifying my suspicions regarding 
Frequency response of the plasma/spark discharge. Possibly something else 
is happening? Plate modulation (don't have that mongo amp!), or SSTC 
testing would verify?



David Trimmell