[AMPS] Emission from Thoria Filaments
Mon, 04 May 1998 19:53:35 EDT
On Thu, 30 Apr 98 00:15:50 -0800 Rich Measures <email@example.com> writes:
>As it was explained to me, when Econco Broadcast Services
>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
> . Tungsten is a better electrical conductor than tungsten-carbide,
>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
>control of fil. potential, emissive life is typically c.20k hours
I had heard that the quality way to rebuild a tube included a new
filament and grid structure and was about 50-75% the cost of a new tube.
The less than reputable rebuilders used the acetylene method....and a few
charged the full rebuild price although others were honest and charged
Perhaps someone will explain the true story.
BTW, in case anyone did not see my last message I had to go away on a
family matter for a week.
Hope I didn't miss anything of value.
73 Carl KM1H
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