tubes age 10
About the least trouble that I've had is the 6 or 7 dozen or so tubes in the old
Tektronix scope and the CA plugin that's usually in it. Over the last twelve years
or so, I've changed a set of 5 of the 5642 HV rectifiers, the 0G3 regulator and a
pair of 6CW5's that come to mind. Very well engineered piece of equipment. As
long as the tubes aren't noisy or shorted, they'll usually work fine in it even
when their test values are well below the normal "worn out" numbers that the
tester manuals list. I've had MORE transistors fail in the 547 than I have tubes
fail. Finding matched pairs of those old early 1960's transistors can be a real
pain, too. No BA collection is complete without a hundred plus pound tube type
Tektronix scope setting on the bench sucking up a thousand watts or so.
They're magnicifant pieces of gear that are first class examples what what
American industry was capable of producing at one time. Quality engineering,
craftsmanship, and best quality materials available, but mainly, when people
took pride in their work.
Tubes, as a whole, are a hell of a lot more reliable than a lot of people believe.
There were some really suck designed tubes/applications in the 1970's, such
as those damn compactrons used in televisions and used in applications like
RF amplifiers that they really weren't really up to. Ditto to the tubes in the power
supply for the IP-173 series panoramic adapters. I've not real impressed with
the life of the 6AK6's used in the R390A's either. They don't seem to last as
long as they should. For what it's worth, the RCA's seem to last longer then the
other brands. The 6DC6's on the RF deck are another one that should be
replaced every 6 months of 24/7 in the R390A's if you're interested
in peak performance.
On a side note, try to never install a new 5749 in the PTO module of an R390A.
Always use a good strong used one. The alignment will hold longer.
Just for kicks, measure the sensitivity of your receiver, remove and label the
tubes on the RF deck and replace them with new tubes. Then retest the
sensitivity. I'd almost bet money that you'll leave the new ones in there. :-)
Oh, about the only piece of gear that I have that gives a time frame for tube
replacement is my AN/PRM-10 Grid Dip Osc. The 955 acorn tube in the head is
supposed to be replaced every 300 hours. I was curious about this a while
back, so I tested the tube then let it run for a couple of weeks and sure enough,
the tube was flatter than hell. ;-) Which reminds me, I need to pickup a few
more spares, I only have a couple of them left. ;-( Thinking of the GDO, 6X4
rectifier tubes don't impress me much either either. I've went thru a lot of them
in the GDO, the RC and RCL bridgers, the old CV-116 when I used it (it has five
of them in it), and the pair of them in the TV-2 tube tester. The 6X4 is one of my
least favorite tubes.
One factor on "tube life" that's over looked is the application that the tube is
used in. As an example, lets look at the 6AK6 used in the R390A as an
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