Thanks Rich,
What Rich says below is correct and is what I was trying to remember. I
was about to get the two confused, but it's been 20+ years since I read
about it too! Ionization would have to be because of some sort of gas,
and I thought about that after I sent the last post. If the blue appears
to be showing at the glass, it is normal. The old regulator tubes (0A2,
etc.) contained gas and was the reason they glowed.
73's
Will Matney
R.Measures wrote:
On Nov 19, 2004, at 9:42 AM, jsb@digistar.com wrote:
Question:
I was given a homebrew single 3-400Z amplifier which works but I noticed
with ZSAC the top of the glass envelope has a very faint blue hue when
looking across the top of the tube envelope. When looking down at
the top
of the tube I don't see this color, only when looking across the top -
keying CW does not pulsate the color, the blue hue is the same
regardless
of output power. I have a couple other old junk clunker 3-400Zs that do
the same.
Is this normal or is it an indication of gas?
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.
I have some 8163 Amperex 3-400Z in a Drake L4 that do not exhibit this
coloration, ever.
Amperex 8163s have a solid, machined graphite anode-cooler that has no
gaps where the filament-glow can be seen from above. OTOH, Eimac 8163s
have a sheet-metal anode cooler with small gaps between the fins that
allows one to see the filament-glow. My guess is that these
sight-paths to the filament is where the glass is fluorescing.
The Eimac 3-400Z tubes do, even after having been used
to produce enough output RF to turn the anode reddish-orange for 10-15
seconds. Or does the getter not getter that quickly...
-- 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.
thanks
73 Jason N1SU
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Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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