[Amps] 3-500z Silly question

[Fuqua, Bill L]

  Yes and no.
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


________________________________________
From: amps-bounces at contesting.com [amps-bounces at contesting.com] On Behalf Of Bill, W6WRT [dezrat1242 at yahoo.com]
Sent: Thursday, September 03, 2009 9:50 PM
To: amps at contesting.com
Subject: Re: [Amps] 3-500z Silly question

ORIGINAL MESSAGE:


>> Is the filament of the 3-500z 5V-DC or 5V-AC??
>> The last two .PDF iv read its not stated as wich ....

REPLY:

This may be an old wive's tale, but I read years ago that DC should not be used
on a filament of a high power tube. The reason was that it creates a bias
condition where one end of the filament (in your example) would have a -5 volt
bias with respect to the other end. As a result the emission would be greater
from the negative end compared to the positive end, and the tube would age
unevenly.

This of course does not apply to indirectly-heated cathodes.

I have never seen any documentation of experiments done to prove the theory, but
it makes sense and has stuck in a back corner of my head for years.

73, Bill W6WRT
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