[AMPS] DC Filaments???
William Fuqua
Wlfuqu00@pop.uky.edu
Wed, 01 Nov 2000 09:07:49 -0500
The amount of current drawn form the cathode has nothing to do with the
emission life.
In fact the hot cathode produces a cloud of electrons around it and creates
a virtual cathode that is about
one third the distance between the physical one and grid ( going from
memory here) and the current is actually drawn from
this pool or cloud of electrons. The life time of the cathode has to do
with the migration of materials within the cathode, evaporation
of materials and contamination.
I believe the source of this AC vs DC filament life time myth may
have come from the early work with halogen lamps.
There was a difference but that was in an high pressure gas device with a
very hot filament. No cathode current there.
73
Bill wa4lav
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