George,
Yup, I have heard some call this gettering too which really isn't the correct
term per say, but understand what they're trying to do. I always called it
"burning them in", but it's the same thing. What I was getting at, someone had
mentioned that a tube could getter itself by an internal arc or flash which is
happening inside a gassy tube. Once a vacuum is lost to where a tube wont
withstand it plate voltage rating, it's pretty much shot or the way I was
always told. Even on receiving tubes, I remember what a gassy tube would do to
a TV set, you'd have one heck of a picture going on. Of couse if gassy enough
they'd flash around inside looking like a bunch of little flash bulbs going
off. Those were the ones that the getter material on the glass had already
turned white. Most of the transmitting tubes dont even have an internal getter
though like the smaller tubes have. I guess they just evacuated the tube with a
higher vacuum pump then let them bake in.
Best,
Will
*********** REPLY SEPARATOR ***********
On 10/1/05 at 9:36 AM exray@bellsouth.net wrote:
>Wiil,
>
>For years it was and is common practice to outgas tubes by applying HV at
>low current i.e. one or two ma. till the tube arcs. Then reduce the HV a
>tad till the tube stops arcing. Leave the HV at this value for 30 minutes
>or so. Then raise the HV slightly.
>
>Also try to run the tube at reduced HV and a heavy load. Get it as hot as
>possible. Then reduce the current to 1 or 2 ma. and raise the HV. This is
>a long process. BE certain to use a current limited supply.
>
>When you can hold off 20 to 30% more than rated HV your finished!
>
>George
>W4IW
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