[Prev][Next][Index][Thread]
Re: Pulsed Tube Coils
> Date: Mon, 6 Jan 1997 22:43:07 -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 Mon Jan 6 22:35:09 1997
> Date: Tue, 7 Jan 1997 00:03:16 -0500
> From: FutureT-at-aol-dot-com
> To: tesla-at-pupman-dot-com
> Subject: Re: Pulsed Tube Coils
>
> In a message dated 97-01-06 00:55:41 EST, you write:
>
> <<
> >>snip
> >> >> I was thinking of building a tube coil using a pair of
> > >572-B's (basically heavy duty 811's) with a filtered DC
> > >> >plate supply of about 2500 volts, the power supply would
> > >have a output filter capacitance of about 15 UFD and the
> > > >>circuit would be the typical link coupled feedback setup.
> > >> But I was going to use a square or triangle wave signal
> > > >to drive a power mosfet (IRF-511) switch in the filament
> > >center tap (cathode return) to gate the tubes conduction
> > > >> much the same as what a variable rate/dwell rotary gap
> > >would do in a disruptive coil, or even use a audio
> > > >source to modulate a fixed bias reference in the cathode
> > >>return. Any thoughts on this approach?
> >
> > > >> Mark Graalman
> > >>
> >>>snip
>
> >> pulsed tube coil using this system will still require a tetrode and
> >>AC (or
> >> >other up-ramping voltage) on the screen grid for long spark
> >>production. I
> >> definitely recommend pursuing this cathode-type control technique.
> >If you
> >> >try this technique Mark, I'd definitely be interested in your
> >>results.
> >
> >> John Freau
> >
> >>Mark, All, (update)
> >
> > >snip
> >got a nice 18" staccato spark most of the time, but since I was still
> > >using
> >the non-sync, pulsed AC system, sparks sometimes "broke into multiple
> >>spikes"
> >and lost spark length, due to incorrect pulse timing.
> >
> > Next, I hooked up the DC power supply, and ran the system. I only
> >>turned up
> >the power part way so far (I don't like seeing my components burn
> >up!), but
> >>the sparks seemed to be maybe a little better than using by grid
> >controlled
> >DC staccato (neither case here using the "AC on the screen-grid"
> >voltage
> >>technique). What I mean by "better" is the sparks seemed less
> >"plasma-like".
> > > But it's hard to judge at low power.
>
> >>>>snip
>
> > >John Freau
> >
> >
> > Hi John,
>
> > How do you think it may work out if the screen is
> > supplied by a 500 -600 volt DC source rather than AC? Or
> > tying the cathode to ground through a 2 or 3 volt zener
> for a slight amount of bias and switching the screen volt
> > age on and off with the transistor switch? Of course I'm
> still talking about using DC on the plate circuit, I guess my ordinal
> > thoughts on this were to have a "silent"
> output discharge then work on different modulation
> > techniques. It will be some time before I can do much in
> the way of any experiments, my shop is loaded up, torn up, with
> > construction stuff from working on the house etc.
> > But the ideas still flow.......................
>
> > Mark Graalman (WB8JKR) TCBA#1399
>
> > BTW, what type of waveform are you using to control the
> > switching transistor?
>
> >>
> Mark,
>
> I knew I forgot something in my my posts---I used a squarewave for all
> tests--it's all my generator can provide. And Yes, I suppose that if the
> proper waveform is fed to the "cathode lifting" control transistor, this may
> make it unnecessary to use the AC on the screen grid. Then DC on screen grid
> would be OK, or use a triode. But if duty cycle is high, a lot of power will
> be drawn.
>
> BTW, I did try connecting my negative control pulse to the screen, instead of
> the control grid in one of my earlier experiments--and the technique worked
> well, and in fact eliminated the potential problem of interaction between the
> neg. control voltage and the grid-leak network.
>
> I also like your idea of using cathode bias to eliminate the need for a
> negative control voltage or screen voltage to cut off the tube. I'm not sure
> what zener voltage rating would be needed here, may need to be more than a
> few volts--if this is what you generally had in mind--and I suppose you'll
> lose power due to cathode degeneration. There are certainly plenty of
> possiblilites here.
>
> In general, when pulsed, a DC coil and an AC coil will sound about the same,
> this is because if only one half cycle is passed, the ear will hear this as a
> "pop" rather than a tone. depending on the pulse rate, the sound can be like
> a chain saw revving up, or like a rat-tat-tat, or staccato sound. If you
> use voice or music modulation, that's another story, and I can see why you
> would want the DC for a quiet coil starting point. I think the DC with audio
> modulation should work very well, but sparks will probably be short, and the
> coil will probably draw a lot of power, you should hear the audio coming out
> of the spark. I never tried this but it should be pretty cool. Perhaps
> someone else has tried this? The coil could be voice actuated, so the tube
> can cool between words, music will probably draw a lot of power, you may have
> to keep the power low, or use a giant tube to keep it cool, etc.
>
> It sounds like your onto something here with these ideas, I'll be interested
> to hear what you come up with once you get your lab back on line. I don't
> know just how much I'll be able to do along these lines, always glad to hear
> of any new ideas that you'd like to share.
>
> Happy (modulated) coiling,
>
> John Freau
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). BTW, if you do this with a TC you
_WILL_ have an AM whatever band transmitter!, Thankfully the radiation
efficiency from this TC will be low as it is a miniscule physical
size compared to its wavelength of operation, and there is no antenna
attached. However, should Fred Bach up in Vancouver, Canada stumble
across your experiment while DX'ing, please send him a Reception
Report card quickly if requested! : )
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.
Once I get my big Coronatron fully on line making serious corona spray (I do
not yet have a secondary coil wound) I may 'dink' with an audio modulation
concept.
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.
If 'Man or Astroman' can receive these waves I'd like to hear from
you guys. I might be able to build a TC for you that will not only
allow you to communicate with your home planet, but do a neat stage
show here on earth as well!
If anyone ever picks up one of my modulated TC experiments and can
prove it I promise to QSL!
rwstephens