[Amps] neg screen I in tetrodes-- TSPA

[R.Measures]

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