[R-390] 6802 - standby

[Rodney Bunt]

Harry,

I knew that you shouldn't do it, but never really knew why.
This is the best explanation of the phenomenon I have ever heard.
Fills in a gap in my knowledge that I have had since 1968.

Rodney
VK2KTZ

--- Harry Joel <organic@cyberlane.net> wrote:
> 1/7/02 7:16:06 PM, Rodney Bunt <rodney_bunt@yahoo.com> wrote:
> 
> >My understanding of "not using standby"
> is the "poisoning" of the cathode, with filament current and no HT to "pull away" the electrons.
> >
> >
 For what its worth, here is what I was told when doing yeomans/apprentice work
 at TeKaWe (Telephon-Kabel und Draht Werke) in postware Nuremberg, way-way back in 1948.
 I was  working in the vacuum tube department. Getters (the silvery-shiny deposit on the inside
 of
 the tube, is used to absorb or trap any heavy molcules that might otherwise bombard
 the coating on the cathode. Electrons themselves cannot damage the function of the
 cathode coating. With no B+, they just form a cloud, loitering so to speak, around the
 cathode. The impurities caused by outgassing or sputtering of metallic molecules is what
 is deadly for the cathode. Anything emitted from a hot metal surface like the anode will,
 due to its positive charge be hurled toward the cathode and gradually "poison' it. 
 Golly, how I remember these exciting days. Having a dozen new, one-of the kind miniature
 tubes mounted up on the vaccum manifold. Learning the delicate touch of glass blowing.
 After evacuation, I had to slip a 5 turn 1/2-inch copper coil hooked to a 1000W LF transmitter
 (I got zapped more than once by absentmindedly touching the coil) ... over each tube in turn
 to get it red-hot to drive out any impurities, then finally getting the getter pill to evaporate
 and leave the silver halo. At that point, any clumsy move or jerking would break the small glass
 stem and air would rush in. I a millisecond a weeks work of the lab guyes in the white coats
would
 be trashed.
 They were not amused when this happened.
 
 Hope you dont mind a little reminiscing


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