At 11:48 PM -0400 9/5/00, W8JI wrote:
>The context of my post was "cooking" the tube anodes to de-gas
>the tubes by running the tubes at 300-400 watts dissipation for
>several hours.
Interesting, my comrades at Brookhaven Nat Lab in NY do this with new
Burle 7835 triodes. They detune the PA output, and run the tube off
resonance. They then drive them to get the dissipation at 100-200 kW,
and leaves them that way for a while, watching the ion pump current
increase and when it decreases, they back them off. By detuning, the
peak fundamental RF voltage is not as high across the tube, reducing
the risk of arcs inside. But it gets nice and toasty. Wonder if this
would work in a ham tube. Just watch the plate color?
DON'T TRY THIS AT HOME< WITHOUT HAVING ADEQUATE COOLING, USE TEMPILAQ
PAINT ALL AROUND THE SEALS FIRST!
We degass the same tubes, but don't cook them this way, instead we
run them a long time at increasingly higher power and duty factor, to
get the gas out of the envelope and into the internal ion pump. But
we have them tuned at resonance. These tubes now have built-in 2
liter/second ion pumps, which help keep them clean and high vacuum.
Even so, if they are off for months, they need some processing time
before slamming big RF out of them.
John
K5PRO
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