Re: VTTC Tubes (homemade!)

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

Original poster: "rheidlebaugh by way of Terry Fritz <twftesla-at-qwest-dot-net>" <rheidlebaugh-at-zialink-dot-com>

Jim:  You can try a heating element fron an old toaster. It is all mounted
on a mica suport to make it easier. A large copper pipe cap will make a
plate.You can mount your grid on two long screws to space your wires. You
can make insulators of low fire ceramic clay hardened in your oven at
"broil" Clay can be drilled and threaded when dry with care. Have fun
    Robert  H

> From: "Tesla list" <tesla-at-pupman-dot-com>
> Date: Mon, 01 Apr 2002 07:08:29 -0700
> To: tesla-at-pupman-dot-com
> Subject: Re: VTTC Tubes (homemade!)
> Resent-From: tesla-at-pupman-dot-com
> Resent-Date: Mon, 1 Apr 2002 07:14:32 -0700
> 
> Original poster: "Marry Krutsch by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <u236-at-earthlink-dot-net>
> 
> Hi Jim.
> 
> Comments scattered about.
> 
> Tesla list wrote:
>> 
>> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <jimlux-at-earthlink-dot-net>
>> 
>>> 
>>> Hi Again.  Here is the "plan".
>>> 
>>> My idea was to use several thoriated tungsten 1/16" rods as the
>>> filament
>> 
>> You'd need a pretty high current supply to get those suckers red hot so
>> they'll emit.  I suggest getting some tungsten wire, or scavenging a
>> filament from something else (i.e. lightbulb).  Tungsten wire is fairly
>> available mail-order from places doing special effects supplies (they use it
>> to "invisibly" suspend things.. 1 mil wire is invisible at normal distances
>> and will hold up several pounds) under the trade name "suspendo".
>> Straightening out a coiled lamp filament is probably out of the question
>> (brittleness, etc.)
> 
> The reason I chose those is because A) I have them, and B) I have a
> 5VAC -at- 400 amp XFMR.  Also, construction of a filament using thin wire
> would be more complicated than one made from rods (support structure).
> The rods could even stand up on their own.  But, I will keep my eyes
> open for tungsten wire.
> 
> 
>>> 
>>> Evacuating the tube would be crude, but possible (no vacuum pump).  The
>>> getter, which in this case would be lithium (extracted from lithium
>>> batteries), is cut into strips, and dropped through the hole in the top
>>> of the tube into a pan mounted to the top of the filament/grid module.
>>> Now the fun part!  Oxygen is jetted in through the hole, displacing the
>>> air in the tube.  The plug is then screwed down tight, sealed (brazed),
>>> and the whole tube is placed in a hot oven for a few hours.  During this
>>> time, the lithium ignites, and consumes the O2 in the tube.  This system
>>> gets rid of the leftover noble gas problem.
>> 
>> I'd suggest using a adsorption pump instead of all the oxygen and lithium
>> stuff.  Extracting lithium metal from a battery is going to be expensive and
>> pretty darn tricky.  Lithium is really, really reactive, and if your battery
>> is a Lithium Thionyl Chloride chemistry, there are other bad news aspects to
>> it.  The Amateur Scientist (and "the Bell Jar") described how to make a
>> adsorption pump, which can easily pull down a small enclosure in a "one
>> shot" scenario very cheaply.  You'll need a small amount of liquid nitrogen,
>> but that is readily available.  You might need to do a double pumpdown to
>> get the pressure low enough, depending on how much "junk" there is in your
>> original tube.
> 
> Actaully, all the lithium I have is from batteries.  A single AA
> battery has quite a bit in it, in the form of a long piece of thick foil
> (convenient size).  I have the extraction procedure down pretty well,
> and it is really very simple.  I don't know about the type of chemistry
> the batteries use.  I use Energizer batteries.
> 
>> Threaded plugs in any form are going to cause troubles with virtual leaks.
>> Real tubes that are made "one off"  (I'm familiar with Traveling Wave Tubes,
>> in particular) use a piece of metal tubing for the vacuum port that is
>> crimped to seal it off (they use a thing that looks like a bolt cutter with
>> custom jaws.. Felco is one mfr).  I suggest that you figure out a way to
>> heat your tube (externally or internally) while pumping, to help with the
>> outgassing.  A couple hundred degrees C would work nicely.
> 
> The plugs would be brazed in place to make the final seal.  I don't
> think that a good joint would leak.  (I could be wrong, though.)
> 
>> The getter is usually something like barium, and a bit of research will tell
>> you how they do it..  External/internal heating  is a good way.  Neon sign
>> places will have stuff for gettering.
>> 
>>> 
>>> Some of the evacuation procedure is questionable, but I will test it.
>>> I have some experience with lithium, and believe that this MIGHT work.
>>> 
>>> The design is hard to follow, but it is a bit clearer in my mind.  It
>>> sure would be nice if we could find an alternative to expensive tubes.
>>> 
>>> Thanks for putting up with my stupid ideas. :-/
>>> Winston
>>> 
>>> PS- I'll try a diode first, to test the idea.
>> 
>> It might be cheaper, parts cost, than purchasing a tube, but you're going to
>> spend a LOT of time, which is worth something. Your tube might wind up
>> having the performance of a $10 vacuum tube, except built with $50 in parts
>> and $1000 in time.  On the other hand, it is a "cool project".
> 
> As you say, this is far from practical, most likely.  However, the
> "cool project" aspect may be too much for me to resist :-)).
> 
>> Don't expect long life and reliability.  That's what a tube mfrs expertise
>> gets you (and repeatability, etc.)
>> 
>> You should get, if you don't already have it, a copy of John Strong's book:
>> "Procedures in Experimental Physics".  It is at just this level... Also, get
>> a copy of the Kurt J. Lesker catalog (big vacuum supplier) because of the
>> useful information in it.
>>> 
>>> 
>>> 
> 
> 
>