On Nov 19, 2004, at 12:15 PM, jsb@digistar.com wrote:
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?
Correct, Jason
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.
This means it's emitting the most electrons -- which is hardly a bad
thing. However, a tube that has only 2000v of BD is almost certain to
eventually grid-filament short.
-- 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.
I have a copy somewhere. There is nothing extraordinary on it.
cheerz,
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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