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RE: vacuum tube construction. (fwd)



---------- Forwarded message ----------
Date: Mon, 13 Aug 2007 07:52:30 -0400
From: Jeff Fink <revtec@xxxxxxx>
To: 'Tesla list' <tesla@xxxxxxxxxx>
Subject: RE: vacuum tube construction. (fwd)

I am new to this list and ironically this is the first post I have read.  

Over the years I have been experimenting with massive cold cathode vacuum
tube diodes, looking at the phenomena of PAGD (pulsed abnormal glow
discharge).  I was wondering if the tube could be used as the spark gap on a
TC.  I understand there could be X-ray production, but would it be
dangerous?  Another question: Would the X-rays register on 60's vintage
Civil Defense radiation dosimeters?

My tube design is incredibly easy to build when you consider that there is
no grid or filament, though some machine shop work is required.  They can be
easily disassembled for cleaning and modification.  

My largest is 12" diameter, using a 12" by 3" long by 1/2" wall pyrex tube.

The anode and cathode are 3/4" aluminum plates.  The tube sets into a
circular groove on each plate and is sealed with a 3/16" O'rings coated with
vacuum grease.  A hole and fitting on the cathode plate provides connection
to a refrigeration vacuum pump sold by Grainger, which developes a very nice
vacuum.  The tube lights off on only 600 volts.

Jeff

-----Original Message-----
From: Tesla list [mailto:tesla@xxxxxxxxxx] 
Sent: Sunday, August 12, 2007 11:18 PM
To: tesla@xxxxxxxxxx
Subject: Re: vacuum tube construction. (fwd)


---------- 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.

    By contrast, soft discharge tubes are literally child's play.

Ed




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