I use the old fashioned but accepted method to measure tube
temperatures, a range of Tempilaq paint or Omega's labeled versions of
the same, Omegalaq. It takes some practice to get a dot of paint without
making a glob. Try it on a piece of metal in your oven first. Place it
on locations of the tube that are air cooled, or not. Such as around the
filament connector rings, the screen ring, the ceramic seal under the
anode (use a very small dot here). It should work on glass tubes as
well, just keep the amount small. It is not a cheap method, though, as
you need a range of temperatures to get any resolution. I tend to use
100, 115, 125, 139, 150 deg C or something like that. Then run the tube
at full power, shut down and read the results. Rarely do I like to
exceed 150 deg C in commercial amplifier designs, as the thing may have
to work at higher elevations or with dirty air filters at some point.
73
John
K5PRO
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