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Re: tube coils
Tesla List wrote:
>
> >From rwstephens-at-ptbo.igs-dot-netSat Sep 7 15:20:38 1996
> Date: Fri, 6 Sep 1996 14:29:31 -0500
> From: "Robert W. Stephens" <rwstephens-at-ptbo.igs-dot-net>
> To: tesla-at-pupman-dot-com
> Subject: Re: tube coils
>
> >Date: Thu, 5 Sep 1996 22:25:35 -0600
> >From: Tesla List <tesla-at-poodle.pupman-dot-com>
> >To: Tesla-list-subscribers-at-poodle.pupman-dot-com
> >Subject: tube coils
> >Reply-to: tesla-at-pupman-dot-com
>
> >>From major-at-vicksburg-dot-comThu Sep 5 22:18:48 1996
> >Date: Thu, 05 Sep 1996 18:26:27 -0500
> >From: RODERICK MAXWELL <major-at-vicksburg-dot-com>
> >To: tesla-at-pupman-dot-com
> >Subject: tube coils
>
> >I have not even finished my first capacitor discharge tesla coil and already I,m
> >looking forward to building a tube driven coil! I've odered a couple of books from
> >I.T.S. __Vacuum Tubes In Wireless Communication__ by Elmer E. Bucher ,and __Vacuum Tube
> >Tesla Coils__by J.F. Corum and K.L. Corum. I have built several high voltage projects
> >using induction coils and a solid state Mosfet driver, but I have never built
> >__anything__ that uses tubes.
> > In __Vacuum Tubes In Wireless Comunication__ it describes the vacuum tube as a
> >rectifier. It also shows the direction of electron flow from the filament to the plate.
> >This part I comprehend and understand well. What I have a hard time visualizing is
> >current flow from the plate to the filament! If the flow fom the filament to the plate
> >is composed of electrons, what is current flow from the plate to the filament composed
> >of and what is the mechanism that allows this to happen? Is it simular to hole flow in
> >semiconductor material???? Could someone that has experience with tube electronics
> >please answer these questions for me so I can sleep nights?
>
> Roderick,
>
> Ideally there should be NO current flow backwards in the one way
> device known as a vacuum tube. However, perfect devices almost never exist in
> the physical world and man-made vacuum tubes are no exception. Although
> there is a pretty good vacuum inside the tube envelope, and efforts are
> gone through to make the vacuum as high as is practicable, there are
> small quantities of loose gas molecules floating around. When
> electrons which are being emitted from the filament and travel at
> relatively high speed to the positive plate happen to collide with
> these loose molecules they can knock an electron out of these gas
> molecules thus ionizing them. Since these ionized gas particles are
> positively charged, they will be repelled from the positive plate and
> be driven into the cathode. Here you have a mechanism of reverse
> current flow. The cathode can actually be damaged by being bombarded
> by these ions, especially in tubes operated at high voltages.
>
> Some tubes (especially rectifiers) have actually been manufactured slightly gassy
> to deliberately allow reverse ion flow, and this ion bombardment is employed to
> heat the cathode to incandescence so that it will emit electrons
> without using the traditional resistive heating element and
> associated fillament power supply.
>
> You may have hear the term used saying an old tube has gone gassy.
> During the lifetime, gas molecules trapped in the glass walls and
> metal structures within the tube which were not released in the bake
> out and pumpdown at the factory, will over years of use free
> themselves into the vacuum space in the tube. When this situation is
> extreme, the tube will be seen to glow blue, like the aurora borielis, simply
> from the light of released ionized rarefied gasses.
>
> Hope you sleep better now. :)
>
> Regards, rwstephens
Well you fellas have clarified things rather nicely I think I'm feeling kind of
sleepy already (grin)! It may be a while before I build my first tube circuit but at
least I won't be completely ignorant as to how and what is occuring in the circuit.
By the way tubes sure are prettier to look at in operation than transistors (smile)!