>From owner-amps@contesting.com Mon May 4 19:37:52 1998
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>Subject: Re: [AMPS] Emission from Thoria Filaments
To: <amps@contesting.com>
>Date: Mon, 4 May 98 19:36:10 -0800
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>From: Rich Measures <measures@vc.net>
>To: <amps@contesting.com>
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>>
>>On Thu, 30 Apr 98 00:15:50 -0800 Rich Measures <measures@vc.net>
writes:
>>
>>>As it was explained to me, when Econco Broadcast Services
>>>(916-662-4495)
>>>rebuilds a thoriated-tungsten filament tube, No thorium is used to
>>>restore emission -- no matter how many times the tube is rebuilt.
>>>Acetylene gas (C^2 H^2) is the sole agent. When
tungsten/1.5%-thorium
>>>
>>>alloy is heated to c.1800 deg K in the presence of acetylene, carbon
>>>atoms from the acetylene molecule bond with tungsten atoms to form a
>>>tungsten-carbide layer at the surface, leaving hydrogen gas
byproduct.
>>>
>>>During recarburization, a continual input of acetylene brings in a
new
>>>
>>>supply of carbon atoms and forces out hydrogen.
>>>- - How does one determine how much tungsten carbide has been
>>>formed?:
>>> . Tungsten is a better electrical conductor than tungsten-carbide,
>>>so
>>>one can tell how thick the tungsten-carbide layer is by measuring the
>>>decrease in filament current as the process takes place. When the
>>>layer's thickness is determined to be sufficient, acetylene flow is
>>>stopped, the tube is pumped to a high vacuum and resealed. With
>>>careful
>>>control of fil. potential, emissive life is typically c.20k hours
>>>between
>>>recarburizations.
>>
>>I had heard that the quality way to rebuild a tube included a new
>>filament
>
>What is the name of a rebuilder who replaces the filament every time a
>tube is rebuilt, and does not use acetylene?
>
>Filaments are not carburized when they are made. Even if the filament
>were replaced with a new filament, the new filament would need to be
>carburized with acetylene.
>
>>wereand grid structure and was about 50-75% the cost of a new tube.
>>The less than reputable rebuilders used the acetylene method...
>
>What is the source of this information, Carl?
>
>- thanks
>
>cheers
>Rich...
>
>R. L. Measures, 805-386-3734, AG6K
>
>
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