[Amps] tube flatulence - gettering

[Will Matney]

Jason,

In smaller receiving type tubes, and sweep tubes, that was seen in new 
tubes. The pale blue color was seen inside the anode or coming from the 
guts of the tube through holes in the anode. It's been so long now where 
I read about this, but it seems like it had something to do with 
ionization somehow from molecules of the anode or cathode, I forget 
which. I would imagine this could happen on larger glass tubes also. A 
gassy tube will arc and remind you of a flash bulb going off. The old 
receiving-sweep tubes which were gassy had a dead give away in that the 
silver coating formed by the getter(s) flashing would turn white when 
air entered the envelope. If B+ was applied, it would look like a small 
lightning storm inside with small flashes here and there. On large glass 
tubes, the arcing can be heard somewhat due to the power of the arc.

Now I'm not sure on the explanation above as I'm trying to quote from 
memory of about 20 years ago. As long as they're not arcing, and have 
proper output, run them. Old tubes should be cooked for 24 to 48 hours 
before applying B+ by just letting the heater to run. They can also be 
done a similar way by heating them up and slowly applying B+ in steps 
over time. Some call this "gettering" but the old term I always heard 
was "baking one in". Gettering was actually flashing the "getter" inside 
of a tube which consumed the last amounts of any air. If I recall, the 
getter had a magnesium coating which was flashed. It then created the 
silvery coating on the glass where the chemical reaction took place. 
Hope this helps for an explanation, if I'm incorrect on this, somebody 
please explain it.

Best & 73's

Will Matney


jsb at 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?
>
>I have some 8163 Amperex 3-400Z in a Drake L4 that do not exhibit this
>coloration, ever.  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...
>
>
>
>thanks
>
>73 Jason N1SU
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