Re: Idea for big VTTC

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<cwillis-at-guilford.edu>
> 
> Hi Drew,
> 
> I would be very interested in a large-scale tube coil effort.  It's quite
> likely that some surprises and interesting effects are to be found in  >10 kW
> CW and pulsed tube coil systems, which to my knowledge have not ever been
> built.  If someone has a lot of spare dough to blow...this would be a most
> worthwhile project.  It's one of my goals in life to make a 100 kW Staccato
> tube coil :>)
> 
> About building your own tubes- I think the technical and economic demands
keep
> most of us from being able to make a good tube.  You need a plethora of
> refractory metals and ceramics, vacuum pumping equipment, etc.  But that
> shouldn't deter you from building your own tube, even if it cannot handle
power
> and has lousy performance.  I think it's a super idea that will give
anyone an
> opportunity to learn about not only tubes, but also high vacuum
technique, for
> example.  And with the bell jar and vacuum pump you suggested, I don't think
> you'd have too hard a time getting a triode that actually worked.  (Here's an
> interesting tidbit I found in looking through "Demonstration Experiments in
> Physics" (Sutton, 1938):  apparently you can build a "fresh air triode",
i. e.
> 1 atm.,  complete with oxide-coated filament, that allows you to make a
> "qualitative determination of several important characteristics of
> three-electrode tubes, such as dependence of plate current upon electrode
> separations, potentials, filament temperature"....etc.) I'm betting if
you make
> a simple triode in a medium-vacuum bell jar, even with an aluminum foil
plate,
> window-screen grid, and lightbulb filaments, you could make a small RF
> oscillator with it...  probably not a tesla coil though!
> 
> -Carl

	No where near that easy.  In order to get decent transconductance and
saturation plate the current the spacings must be quite small, requiring
accurate construction techmiques.  I've tried here on a small scale and
made tubes (continuously) that worked enough to measure the
characteristics, but in order to get a few milliamps of emission the
pure Tungsten filament had to be so hot that it tended to melt the
aluminum plate material I tried to use.

	Save your money and buy your tubes.  Playing around with vacuum systems
is indeed fun, but..............

	By the way, I'd never build a coil if I had only one power tube on
hand.  Things do happen and if you blew one up it would sure be nice to
have a spare so that all of your work wasn't in vain.

Ed