[Amps] DC versus AC filament power

[John Lyles]

Bill is spot on with his explanation here. In bigger tubes it even 
becomes less of a problem, of having nonuniform electron
flow in a tube for a particularly biased filament. This is because the 
fraction of filament voltage is much smaller than
the operating grid to cathode voltage. Some very large tubes require 
that DC be used to avoid potentially destructive
acousto-mechanical resonances in the filament structure.


73
John
K5PRO


> The filament would emit more on the side that is most negative with respect to the grid than the side that is most positive respect to the grid.
> However, this would mostly be noticed at idle conditions using a high mu triode or triode connected tetrode or pentode.
> However, under drive conditions the grid swings quite a bit positive and the difference between between emission between the two sides or ends of the
> filament is less. You could have one side of the plate get a little brighter than the other but I doubt that you would notice that because the power dissipated by the plate goes as it's temperature raised to the 4th power. So for one side of the plate to get about 10% hotter would require about a 46% increase in power being dissipated by it.
>    As far as aging goes, that does not have any thing to do with the electrons emitted but the length of filament ON time and temperature of the filament. The electrons are replenished by the power supply.
> 
> 73
> Bill wa4lav