>> George: So is 'semi' where K is less than unity, and 'super' where K is
>> unity?
>
>Rich, I can fax you a copy of the article.
Thanks, but no thanks, Tom. The SEMI or SUPER semantics thing is a
non-issue. The issue is why did Collins connect a 220pF cap. from each
grid to ground. When and if a 30L-1 owner takes a dipmeter and compares
the grid resonance with a directly-grounded 811A grid versus grounding
through the factory stock 220pF capacitor, the truth will out.
Why use such a capacitor?: The 811A has a moderate amount of internal L
between the grid cage and the base. Naturally, this tends to compromise
the ability of the grid to shield the cathode from the anode, and that
compromises VHF stability. Some of the 811A grid's internal L can be
cancelled with a 220pF capacitor. I believe that the 33 ohm R de-Qs the
grid resonance and provides a resonance-free path for DC grid current.
>I'm sorry Rich, we all overlook things from time to time. That's why
>I like to use peer review in designs.
"The Nearly Perfect Amplifier" was that. However, when I disclosed that
unnamed manufacturers were applying 48A of inrush current, or 5.95V to
3-500Z filaments, et cetera, I was accused of slander. It seems to me,
Tom, that your statement in QST about VHF current not flowing in 'coils'
(Ls) because inductive reactance increases with frequency--could have
used some peer review before it went to the QST printer. Perhaps it's
time for a retraction, Tom?
Try measuring the "directly grounded" screen resoance on an SK-300 with
a dipmeter and you will see that nothing is "directly grounded". At a
certain frequency, 1 inch of 3 inch width of "grounded" silver-plated
strap is a high Z RFC.
..snip...
>Do you think non-linear RF feedback, providing maximum gain
>compression when peak levels are reached, is a good idea?
No, but this is non-issue because the amount of negative feedback is
miniscule. I believe that the Collins engineers added the C for raising
the grid resonance and increasing VHF stability.
Rich---
R. L. Measures, 805-386-3734, AG6K
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