Peter Chadwick wrote:
>Rich said
>>Below the resonance freq. of the grid, it is difficult to make a g-
>g stage oscillate because the grid acts as a shield between the input
>and the output<
>
>If the grid resonance is high enough ( for example, a tube with a grid
>collett, and a grid 'cage' construction so the inductance is very low)
>then if the anode circuit is resonant below the grid resonant
>frequency, the thing should be unconditionally stable if Terman is right.
In straight-through VHF/UHF amplifiers that have the grid ring grounded
through a finger-stock collet, the 8877 is stable up to at least 432MHz.
With a tuned circuit at both input and output, those amplifiers have
every opportunity to oscillate... but they don't, unless the constructor
makes a mistake and creates some other feedback path.
>That suggests the only parasitic suppressor needed is a bit of
>inductance in the plate lead - which you probably get anyway.
Granted that inductance is impossible to avoid, but why would it be
"needed"?
>This suggests that it would be easy to get another of these run away
>stories that totally changes the content to rubbish........
This list has a history of grinding through the same "debates" again and
again and again... but six months later, the facts are forgotten and
back comes the same old nonsense.
It's as if somebody's technical memory is lacking a backup battery.
:-)
--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek
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