Hey, John:
I was also taught, as you describe, that the amount of recarburization is
limited by the brittleness of the resultant element. In small, closely
spaced tubes, you can rezap them beyond the point where they will crumble
during routine handling; forget about shipping! The trade-off is
emission life vs. fragility. With some big-boy tubes they can apparently
really layer it up and get very long emission life. Maybe you've run
into those in your far-out world.
The method, amount, etc. for each tube and and each refurbisher is
determined empirically. Black magic. Interesting stuff...
Gary
===========================
W3AM - Gary Blau
w3am@juno.com
http://www.qsl.net/w3am/
===========================
On Thu, 30 Apr 1998 13:20:58 -0600 John Lyles <jtml@lanl.gov> writes:
>I witnessed the recarb process on a big tube recently. It was
>essentially
>as AG6K described it. The gas used and the exact technique are sort of
>proprietary for each company but it was certainly an artform, watching
>the
>controlled amount of gas while monitoring emission and stopping at the
>correct moment for a particular tube.
>
>By the way, I have been taught that the additional thoria makes the
>filament MORE brittle. Pure tungsten is ductile, and as it is
>thoriated, it
>gets brittle, especially towards the end of emission life. One company
>was
>juggling the levels due to their source of Thoriated tungsten alloy,
>and
>compared performance with 1, 1.5, and 2 % TT levels. The latter one
>was a
>great emitter, but more fragile.
>
>John
>K5PRO
>
>
>
>--
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>
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