>>> Any change in current causes a resonant circuit to ring. Ringing
>>> amplitude depends on how fast the current changes and on Q. Faster
>>> and
>>> more Q =s more V. I have heard from more than a few TL-922 owners who
>>> report that a big-bang, flashover, and damage occurred when their 922
>>> was un-keyed.
>>
>> Sure, but how fast does the current change? By the time the decoupling
>> capacitors have charged to allow the tube to drift into cutoff, I doubt
>> the rise time alone is going to make the anode ciruit ring at vhf.
>
>
> During the Grate Parasitics Debate in 1996, a member of the audience
> hauled his SB-220 to work and loosely coupled the anodes to a HP
> spectrum analyzer. When the 220 was keyed, he observed damped-wave
> ringing at 112MHz at on And at off.
I wish I could reproduce that. I've tried repeatedly with spectrum
analyser and 'scopes and only ever find operating frequency ringing,
even with suppressors removed. I've tried with a couple of amplifiers,
and also with a tank circuit I put together where I can apply pretty
quick steps of up to 10A.
Can anyone help point me in the right direction?
Steve
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