>
>> 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.
? 3-500Zs do not have ion pumps.
> > 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.
>
? Reading Tom's Adventures with Gettering invites comparison with Harry
Potter adventures.
>It would be an excellent idea on tubes that have been in storage a
>while.
>
? many 3-500Zs have graphite anodes. Do you recommend heating them,
Tom.?
>Most of the well known gassing problems are now called
>"parasitics", thanks to misinformation.
>
? I have tested many metal anode-cooler 3-500Z tubes that g/fil. shorted
after a big-bang. The majority had under 3uA of grid/anode leakage at
8000v. The subsequent autopsies revealed no arc marks on the grid.
>
later, Tom.
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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