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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!


> 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