[R-390] fixin' gassy tubes

[blw]

Thought this tip from Nolan would be of use to someone, somewhere, some
time.......found it while searching for something else.


Barry




I had a few more than a half dozen inquiries wanting more info
about my mentioning "fixing" gassy tubes, so here's an explanation
of the method I use. I've been doing this for ages and have had a
pretty good rate of success. Sometimes a tube will break while
doing this. Your mileage may vary...

It's a very simple procedure involving the use of a glove, a Zippo
cigarette lighter, and a tube tester. I suppose that eye protection
would be a good idea. Also a fire extinguisher if your're a little
clumsy. <grin> I wouldn't advise doing this to any tube containing
radioactive isotopes. You wouldn't want have one break and possibly
contaminate you or the shack.

I make it a point to test all applicable "amplifier" tubes for gas
anytime I plug a tube into the tube tester. I've had some odd ball
problems with gear in the past that ended up being caused by gassy
tubes.

At any rate, lets say that I just pulled one of the 5814A's out of
the R390A and it tested as gassy. The first step is to leave it in
the tester for about ten minutes at it's normal filament voltage to
get the envelope good and hot. Think of it as preheating. Next, while
wearing a suitable glove, I pull the tube out of the tester and using
the Zippo, play a flame over and around the getter of the tube,
evenly for a few moments. I've never measured the amount of time that
it takes, it's just something that you'll develop a feel for after
you've done it a number of times.

The Zippo coats the tube with a layer of soot while doing this. This
is good. It helps prevent hot spots and helps to decrease the odds of
stress cracking the tube. I have had a lot more tubes break heating
them with a butane lighter than with a Zippo. A candle would probably
work OK too.

If you think you heated it enough, wipe it off and plug it back into
the tube tester and test it for gas again. Maybe it's fixed, maybe
it ain't and needs another treatment, and maybe the treatments
just flat out ain't going to work on that particular tube.

If you did heat it enough originally, you can often see a change
in the appearance of the getter. But not always. Don't you just love
something that's cut and dry? <grin>

If it doesn't test gassy anymore, leave it in the tester for about
a half hour and test it again to make sure. Usually gassy tubes show
up a lot easier after they've run for a while.

When doing octal tubes, sometimes the getter is in the bottom of
the tube below the edge of the tube base. This is one reason that
I don't like RCA 6K6GT's and prefer Sylvania or GE 6K6GT's. :-)
The Zippo method isn't practical for tubes built like this. ;-(

If you put your eye out, don't come crawling to me whining that I
owe you an eye or something...

my disclaimer below applies,
nolan


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