On Fri, 19 Nov 2004, R. Measures wrote:
> Hello, Jason -- Blue on the glass is not gas. It is caused by
> high-speed electrons fluorescencing the fluxing agents in the glass
> recipe. If the blue light is in the region between the anode and the
> grounded grid, that's atmospheric oxygen and nitrogen getting through a
> bad seal. Normally, glass fluorescence occurs in areas where the
> electron stream from the hot filament misses the anode and hits the
> glass. In time, the struck area of the glass turns brownish.
Interesting - so is it safe to assume that the blue fluorescence does not
appear when idle because the tube has no bias to pull the electrons away
from the ionization cloud? The blue glow only appears when the amplifier
is keyed and its intensity does not change when producing RF output vs.
ZSAC.
I'm bludgeoning the explanation but hopefully you'll get the gist - hi
> Amperex 8163s have a solid, machined graphite anode-cooler that has no
> gaps where the filament-glow can be seen from above.
I would love to see that machining process...
> OTOH, Eimac 8163s have a sheet-metal anode cooler with small gaps
> between the fins that allows one to see the filament-glow.
Nothing to be seen in any of these tubes inside the anode "compartment"
between the interior of the anode and exterior of the grid cage. The blue
glow is most noticeable, obviously, when the room lights are off but only
along the interior of the top dome of the glass envelope, and only when
keyed.
> My guess is that these sight-paths to the filament is where the glass is
> fluorescing.
That's it exactly. There also are "spots" along the base of the grid
flashing (or whatever it is called) that coincide with the openings along
the base of the anode flashing. Brownish smudges inside the glass as
well. The 3-400Z you hi-pot tested at 2000V, "rode hard, put away wet",
is the one that's the worst.
> -- I have not seen any gettering take place in any gassy 8163/3-400Z or
> 3-500Z. Neither Amperex or Eimac mentions such on their tech. spec
> sheets.
I wish I could find specs on the Amperex 8163 - I have searched high and
low on the net but no results. I guess i'm looking in the wrong place.
Thanks much...
73 Jason N1SU
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