>
>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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