Re: Pulsed Tube Coil Work (with updates)

Tesla List wrote:
> Original Poster: FutureT-at-aol-dot-com
> In a message dated 99-03-10 16:41:32 EST, you write:
> << Original Poster: Alan Sharp <AlanSharp-at-compuserve-dot-com>
> > John,
> > My  interest is in pulsed mosfet driven magnifiers, rather than
> > tubes, but I suspect that secondary doesn't care whether it's
> > being driven by a mosfet or a valve.
> > Naturally I want to produce long sparks. I have in the past managed
>  12" at 150 - 800watts but I think I could do better.
>  >Could you describe what your best performing primary / topload /
> >secondary arrangement and make a guess at the input impedence of
> > the secondary. If its not too far from the 100kHz to 250KHz that I can
>  >work with I'ld like to reproduce it and drive it with my new mosfet bridge,
>  >either via a primary coil, or more likely build a matching transformer
> > and bottom feed it.
> > Alan Sharp (UK)
>   >>
> Alan,
> I don't think it's all that critical at least in the tube coils I build.
> There
> seems to be a wide range of acceptable secondary sizes, wire
> thicknesses, frequencies, etc.  I basically use two sizes of secondaries
> for the tube coils.  ONe is 3" by 11.5" wound with #28awg, with a 1.5"
> by 6" toroid, with point on top of it.  Resonant freq. is about 500kHz,
> The other is a 6" by 23" secondary
> also wound with #28 wire.  Resonant freq is about $110 kHz.
> But I know that others have used radically
> different wire sizes, such as #20awg, and gotten the same results.
> I have no idea what the input impedances are.  But the specs for
> some of these coils are at David Trimmel's website (he mentioned
> the address yesterday or so).
> I've tried a toroid on the larger secondary and it worked the same,
> but the toroid did help the smaller secondary and increased the
> spark by 1".  I didn't do any comparisons with other secondary
> sizes.
> John Freau

        On the subject of pulsed tube coils, I wish someone would try building
a self-pulsed coil.  Blocking oscillator principal which was used in VHF
radar transmitters about the beginning of WW2.  Tubes like the
VT-127/VT-227/VT327 (triode similar to a 100TH) would put out about 50
kw peak when running at around 10 kv on the anode.  A rectified NST
would be a neat way to power such an oscillator.  (With a suitably large
filter capacitor, of course.)  The design is very simple, just using a
"grid leak" in the megohm range.


Who will try it himself when he "gets the time to do it".