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Re: Pulsed Tube Coils
> Date: Sat, 11 Jan 1997 11:25:25 -0700
> From: Tesla List <tesla-at-poodle.pupman-dot-com>
> To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> Subject: Re: Pulsed Tube Coils
> Reply-to: tesla-at-pupman-dot-com
> Subscriber: FutureT-at-aol-dot-com Sat Jan 11 10:52:03 1997
> Date: Fri, 10 Jan 1997 16:39:51 -0500 (EST)
> From: FutureT-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Re: Pulsed Tube Coils
>
> In a message dated 97-01-10 00:53:38 EST, you write:
>
> <<
> > Mark, John, All,
>
> > I have employed audio modulation of a CW vacuum toob TC on several
> > occasions. The straight forward feed back coil regenerative triode
> >oscillator with grid leak bias responds well if run from a well
> > filtered DC HV supply and powered through a transmitteer type plate
> >modulation transformer with a big audio amplifier sized to deliver
> > 50% of the average oscillator plate input power (just like some commercial
> AM
> >broadcast band transmitters).
> >snip
> >Most recently I introduced audio modulation into my 1 kW vacuum tube
> >TC while it was powered on full wave rectified, filtered DC by placing the
> high
> > impedance secondary winding of a step up transformer (like a single ended
> >class-A plate circuit to voice coil audio transformer) in series in the grid
> leak bias
> > circuit of the TC. What I got was negative modulation, i.e., maximum
> modulation
> > signal amplitude resulted in the smallest output spark. This technique is
> best
> >used with triodes and works not too bad. John is quite correct that the
> sound
> >comes from the expanding/contracting plasma interaction of the output
> >fuzz-ball. It is definitely a neato or way-cool effect!
>
> >Mark, using your idea and introducing the audio through a suitable
> >impedance transformer winding on the tube filament (cathode) circuit
> >to ground could work very well, but the audio horsepower required
> >will be even more than that required by plate modulation. Here's a
> >similar but quite novel new idea Mark and John. You might
> >try operating the toob TC oscillator on unfiltered AC and place an
> >SCR into the cathode circuit. Once turned on the SCR will stay
> > conducting until the 60 Hz power reversal shuts it off, but you could
> >gate the turn on time with an audio signal much like a lamp dimmer
> >application. If one of you or anyone else tries this, let me know
> >how it works out.
> > snip
> >I have had plans to attempt voice modulation of the output lightning
> > storm from a disruptive discharge TC for some time now and know
> > exactly how I'm going to attempt it once I finally 'get a round
> >tuit'. For now I'll only share that my proposed technique recognizes
> > Niquist's Theorem for audio sampling rate and will necessarily employ
> >a rapid rotary break to sample the audio spectrum where most energy
> >in human speech is concentrated. This should produce an amazing stage
> effect.
> >snip
>
> >rwstephens
> >>
>
> Robert,
>
> Thanks for the informative post, it's good to hear from someone who's done
> this type of work. I just happen to have some SCRs....hmmm.
>
> Your coronatron seems like a real powerhouse! I'm looking forward to your
> results.
>
> Safe and effective coiling,
>
> John Freau
John,
I forgot to point out that with the SCR in the cathode return
circuit you will not be able to generate a high fidelity audio sound
from the top discharge with an audio modulation input triggering the
SCR. With the 2X sampling frequency Niquist consideration, the
highest audio frequency you could get faithfully would be 30 Hz. If
you place full wave diodes on your plate supply transformer and rectify but
do not add any storage DC filter caps you will get a higher 60 Hz audio
throughput capability, still not high enough even for recognizable
speech through the beast, but only if you are able to successfully commutate
the SCR off at this shorter interval where the supply will not cross, but merely
drop to near zero. The whole point of the SCR idea was to generate
an _effect_ and be able to modify the characteristic of the discharge
with things like audio, but probably even better, a variable
frequency pulse generator! Have fun.
I'm looking forward to some interesting results from my Coronatron as
well. Hopefully soon. I still need to make a HV resonator. Thanks.
rwstephens