tubes age 239
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Date: Thu, 03 Mar 2011 16:37:59 -0500
Subject: Re: [R-390] Gettering old tubes
>He plugs in 10 at a time and he "cooks" them ..........
No, if by "improve" you mean react accumulated gas with the remaining getter
flashing. It does give one an opportunity to spot gross failures that occur
shortly after commissioning, or obvious parameter outliers. I built a system
something like this that also monitored noise when a client was building high-
performance tube equipment in the '80s. For most tube types, they ended up
discarding from 40 to 85% of the tubes they received from suppliers during
initial QC checks. We tried ALL of the suppliers, and bought up lots of NOS
tubes. It was such a problem that I even visited a number of the manufacturers
to see if we could persuade or help them make better products, and drafted a
business plan to build a tube factory (we concluded that it would not be
profitable to produce a quality product). Ultimately, they dropped the tube
equipment lines because it was so hard to find good tubes. As far as I can tell
from the tubes I encounter today, tube suppliers' claims have gotten wilder and
many old brand names are once again in use (no connection with the original
manufacturers, though -- in fact, most of the names are owned by distributors,
not manufacturers), but the tubes themselves have not improved since the
'80s. No commercial tube tester I have ever seen can determine anything
useful about the gas in a tube except for gross failures that can usually be
spotted visually by fogging of the envelope. You can get some idea by doing a
noise analysis, particularly if you simultaneously sweep the tube operating
point.
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Date: Sat, 05 Mar 2011 18:25:54 -0700
Subject: Re: [R-390] Gettering old tubes
I have this gut feeling that this is not something that you would likely do more
than once! <wink> The high current surges that would be produced would tend
to melt the screens / grids of the tubes unless the tube had a metal envelope. If
the envelope was glass then the spot of getter on the inside of the tube would
tend to get very hot and create thermal stresses in the glass envelope that
could cause cracking.
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Date: Wed, 9 Nov 2011 20:01:50 -0600
Subject: [R-390] 4PR65A
I HAVE HAD THIS TUBE FOR A LONG TIME. Oops. What is it use in? I have
(14 pages)
(10 pages)
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