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RE: Really big VTTCs
Original poster: "Cameron B. Prince" <cplists@xxxxxxxxxxxxxxxxx>
This was a very well worded and informative response. Thanks Dave!
Cameron
> Original poster: Sparktron01@xxxxxxxxxxx
>
> Hi Dave! Happy New Year!
>
> See my responses below...
>
> -------------- Original message ----------------------
> From: "Tesla list" <tesla@xxxxxxxxxx>
> > Original poster: David Speck <dave@xxxxxxxxxxxxxxxx>
> >
> > List,
> >
> > I asked this question a couple of years ago, but never really got a
> > definitive answer.
> > I've seen experimenters construct disruptive coils with secondaries
> > from a few inches long to 60 feet tall. Current SSTCs are
> > approaching or surpassing the performance specs of the disruptive
> > coils every day.
> >
> > By comparison, VTTCs seem to have topped out at a 4" x 20" secondary,
> > driven by one to four 833A tubes. The consensus seems to be that you
> > can get just about as good performance from one 833A as with 4 of
> > them, if you design the coil right. Perhaps 36" discharges seem to
> > be the limit for VTTCs on a good day.
> ---------------------------------------------
> You are comparing a relatively high Z vacuum tube (1 k ohm typical) to a
> IGBT that is generally << 0.1 ohm even for a "sucky" device. Switching
> efficiencies in VT powered equipment will struggle to exceed 60-75%
> (source to load), while IGBT's/FET's are often >95%.
>
> One way to gain a power advantage with VT's is to use high voltage
> power tubes (like hard switch radar modulators like 4PR**** and similar
> where you can operate input voltages of >10kV. But then you will deal
> with x-ray generation, and capacitor voltage/current rating limitations.
> Another design tack (which I have done on 3 separate occasions), is
> to use push pull, where you will effectively double the tank voltage swing
> and theoretically increase spark length by ~40% (sqrt of 2).
> ----------------------------------------------
> > Is there some physical or electronic limitation to the design and
> > construction of a really big VTTC? With the availability of big
> > surplus power tubes (10 kW or more) on eBay, and the possibility of
> > multiple parallel free MOTs for input power, is there a physical
> > reason why no one has built a 12 x 60 or 18 x 90 VTTC?
> ----------------------------------------------
> See below insert from earlier TCML posting dated Jan 17, 2003
> concerning known "large" (i.e high power) VTTC's that have been
> built.
>
> Robert Stephens from Ontario built a very large VTTC using
> DC power supply and 3 air cooled 5kW plate dissipation class
> tubes (BR1160) out of AM or MF short-wave transmitters, if up to full
> capability would be able to deliver nearly 50kW (short duty)
> to tank circuit. Check archives for "Coronatron". If Robert is
> out there, maybe he can pipe in with an update (or at least the
> present URL documenting work).
>
> Bill Wysock I believe posted a while back about tests performed
> in Hawaii using a LF communication system for testing insulators
> (<50kHz), notable in that power was very large VT transmitter in
> the 100-200kW input range feeding a helix / resonator
> through a matching line, length of arcs measured at 25kHz
> breakdown alludes me but was on the order of 4-7'.
>
> Several years ago, Ross Overstreet built a large VTTC using an
> induction heating VT(3CX2500H3), tube is capable of up to
> 4kW short duty anode overload (2.5kW continuous), and
> comfortably 10kW to tank, 20" of spark running arguably
> 1/10 of tubes capability.
>
> Induction Heating VT's are ideal for VTTC service.
> They are designed for severe overloads, ion back
> bombardment, and overvoltage/overcurrent sins that
> would detonate or melt down glass tubes.
>
> David Sloan in 1934 used two hand built triodes running
> push pull at 15kV AC to deliver 100-200kW into a resonator
> for development 1MV for generation of intense X-rays for
> early cancer treatment (predecessor to modern linac
> radiation sources). This work may be available on
> hotstreamer or on the Web somewhere
> (Review of Scientific Instruments).
>
> I've heard from several sources that an extremely large
> bipolar VTTC was built capable of several 100kW input,
> may be Internet / Folk / Technology Legend, never saw
> any pictures, experimental composition, creators or
> other technical details.
>
> Largest VTTC I've personally witnessed was
> John Freau's (HI!) triple and quadruple 833 coil, fed
> by a 7.2kV PDT, capable of measured sparks in
> the 38" range, input power was in the 5-7kVA
> range. Ed Wingate has a similar VTTC using
> graphite 833C's, capable of nearly 30" discharges
> at ~ 4 - 5kVA input.
>
> Realize, just having the tubes is not enough,
> you have to in no particular order:
> 1. Cool them.
> 2. Power them
> 3. Find _very_ high voltage - high power
> capacitors capable of continuous
> RMS tank currents in the 10's or
> hundreds of RF amps
> 4. Start worrying about primaries catching
> on fire from thermal rise from RF currents
> and skin effects on primaries (high rms
> currents).
> 5. Watch for fires caused by collateral
> induction heating effects around
> energized primaries and secondaries.
> 6. Prevent primary to secondary breakdowns
> due to HV used in tank
> 7. (NEW) If running above 10-12kV pk anode
> voltage, be concerned about soft X-ray
> generation and potential (no pun) exposure.
> 8. (NEW) Power, controls and support hardware
> for personnel protection and to protect the tube
> itself.
>
> Building a really large VTTC would be a much
> more challenging exercise IMO then building an
> equivalent power SG driven TC.
>
> Today's state of affairs are no different then when I
> originally penned this posting. Just be aware the
> "infrastructure" to build a really big VTTC is probably
> 10X greater then the cost / time required to locate
> the tubes. Tubes with 10kW plate dissipation may
> have filament powers in the kW range. Filament
> transformers (unless you hack a variac or MOT) will
> be as hard and expensive to procure as the tubes.
> Having access to high power MF transmitter/induction
> heater components would give you a "leg-up" on
> construction.
> ----------------------------------------------------------
>
> > Ten foot sword like discharges would be neat to watch!
>
> ---------------------------------------------------------
> I agree, just from a safe distance so you don't get
> RF burns from contacting random metal...;^D
>
> Regards
> Dave Sharpe, TCBOR/HEAS
> Chesterfield, VA. USA