[AMPS] DC Filaments???

[William Fuqua]

	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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