On Tuesday 26 October 2004 21:30, R. Measures wrote:
> On Oct 26, 2004, at 7:26 AM, Bill Fuqua wrote:
> > At 03:41 AM 10/26/2004 -0700, R.Measures wrote:
> >> Thus, when a higher-mileage grid becomes warm from the flow of normal
> >> grid current, the barium coating on it begins emitting electrons in
> >> the Wrong stinkin' direction - and the anode-current starts
> >> decreasing. The barium that sticks to a gold-plated grid of an 8877
> >> can apparently be partly dislodged by vertically and firmly tapping
> >> the top of the tube with a 4oz hammer -- which is the same procedure
> >> that is used to dislodge gold meltballs from the cathode and from the
> >> anode insulator.
My thought was that the cathode material is more likely to be very fine films,
maybe even closer to atomic level deposits, formed from low level long term
evaporation rather than significant particles. In what you describe, I reckon
the cathode material will have been evaporated by whatever caused the metal
to melt, and it will have condensed into the metal balls as they formed.
> >
> > I am confused, how does the barium emit current in the wrong direction?
>
> The side of the grid closest to the cathode receives most of the barium
> oxide (BaO). When heated, BaO emits electrons toward the cathode.
Is this likely to overcome the force of any applied voltage?
Steve
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