Re: vacuum tube construction. (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Sun, 12 Aug 2007 21:02:51 -0700
From: Jim Lux <jimlux@xxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>, tesla@xxxxxxxxxx
Subject: Re: vacuum tube construction. (fwd)

At 08:17 PM 8/12/2007, Tesla list wrote:

>---------- Forwarded message ----------
>Date: Sun, 12 Aug 2007 17:32:10 -0700
>From: Ed Phillips <evp@xxxxxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: Re: vacuum tube construction. (fwd)
>
>Tesla list wrote:
>
> >---------- Forwarded message ----------
> >Date: Sun, 12 Aug 2007 17:02:40 -0400
> >From: Scott Bogard <teslas-intern@xxxxxxxxxxx>
> >To: tesla@xxxxxxxxxx
> >Subject: vacuum tube construction.
> >
> >Hey guys.
> >     We build all sorts of things for our coils, capacitors, hand wound
> >transformers, all kinds of ballasts, Has anybody tried to build a vacuum
> >tube for a tube coil?  It sounds slightly crazy, but several of us, with
> >varying degrees of success have built plasma globes, Geisler tubes, etc,
> >which require a vacuum (although they are generally backfilled some with
> >noble gases).  If you were building it yourself, you could make it rather
> >large, to drive a rather big VTTC.  Just curious.
> >Scott Bogard.
> >
>     The construction of a power tube is not a matter for the home unless
>one has an unusual lab.  First of all requires very high vacuum.  Beyond
>that it requires special "cross-fires" [burners}fed with oxygen,
>equipment to handle hard glass, a special glass lathe to join the
>electrode assembly to the main envelope, proper anode, grid and cathode
>materials, a bakeout oven to anneal the tube after assembly and to
>maintain it at temperature during continued pumpint while the electrodes
>are heated with an induction heater until the asembly is "out gassed",
>and finally a design for the tube and some means of shaping the
>electrodes.  I can't say that no one has built such a tube "at home" but
>doubt it very seriously.  A big job even for professionals and requires
>all sorts of skills.

There used to be some sort of kit sold that allowed one to make your 
own triodes.  The envelope was prefabricated, and you'd need a decent 
high vacuum pump, and I suspect that they used some sort of getter to 
pump out the last little bits.

Actually, the volume is small enough that a LN2 cooled sorption pump 
would probably do the trick for the high vacuum, after roughing with 
something else.

That would get you a functional triode, and I've seen pictures of 
people who have built things like AM radios with them.

A power tube, though, that could do tens or hundreds of watts is not 
a trivial matter.  There's a lot of "art" in the tube making business.

Check out "the BellJar" for more details.


Jim