[AMPS] heating tubes....

[Tom Rauch]

> 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.

That would work fine with ham tubes like 3-500Z's or other tubes 
with the gettering material coated on the anodes.

It would be an excellent idea on tubes that have been in storage a 
while.

Most of the well known gassing problems are now called 
"parasitics", thanks to misinformation.




73, Tom W8JI
w8ji@contesting.com

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