Rhenium in Tubes

Fellow tube collectors,

I came across an ebay auction that mentioned the use Rhenium in a receiving pentode.

I asked my friend Doug Coulter and he sent  back this instructive response.

Regards,

-Joe

 

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Joe,

I have the excellent book by Kohl on this, "handbook of materials and
techniques for vacuum devices". American vacuum society classics, pub
by AIP, expensive and very-very worth it anyway -- it's the good stuff
from a guy who designed tubes and manuf processes, all the arcane guild
things that were trade secrets not found in any other books.

It mentions the uses of Rhenium in vac tubes, and it's good stuff,
depending on if you can afford it.

It does a couple of things for you, particularly in direct heated
things. It increases the R of the W a lot in alloys, and also controls
embrittlement via grain growth control -- way cool. In addition, it
doesn't do the water dance like tungsten does, so they last a lot
longer. Tungsten will take water apart, oxidize, the W oxide then
evaporates, hits the H from the water on the tube walls, gives the
oxygen back to water, and the cycle repeats, which is one of the several
reasons W didn't get popular in light bulbs for a long time -- this
reaction just continues until all the tungsten is on the tube walls, the
water recycles forever, and is by far the hardest thing to eliminate
from the tube in the first place. The Re stops that cold in some
concentration. As it's more rare than W and also harder even to work
with, the stuff is expensive. I have W-Re thermocouple wire, and it's
doggone expensive stuff -- 10+ bucks a foot in thin sizes. I had this
app in the back of my mind when I bought it, as who knows when I may
need to have an electron emitter in a not so great vacuum. Due to the R
increase, the wire can be fatter too, which has mechanical advantages in
some cases. It was also used in alloys called "non sag" so filaments
could have tighter tolerances, like in those russkie peanut tubes for
example, betcha they use it about 5% Re in them for just those reasons.

Lots more on that if you need it, but that's the basics I know of.

Doug

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Hallo Joe

Long time ago I found on the WWW this photo indicating radioactive material in this tube 5751.

It is Rhenium-187 and the activity is denominated in µC.

Kind regards

 

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