On Sep 3, 2004, at 1:40 AM, Steve Thompson wrote:
3) The screen material and coatings is different in the 4CX- designs,
and causes more secondaries when struck by primaries from the main
beam.
As a gross generalisation, I reckon that well used 4CX250s have higher
reverse
screen current and more flashover problems. I can imagine that tiny
amounts
of cathode material might disperse over time and contribute to the
effect -
does the same happen with the filament coating on directly heated
tubes?
Steve -- 'Tis unlikely since the carbon atoms that leave the tungsten
di-carbide emissive layer on a tungsten-thorium filament would be
unlikely to bond to the molybdenum grid. However, the barium that
evaporates from an indirectly heated cathode is notorious for sticking
to the grid and emitting primary electrons in the reverse direction.
Steve
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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