Colin says:
> Grid current alone would not cause distortion. Distortion would arise only
>when the grid current causes the plate current to saturate
Or if the regulation of the RF drive voltage was poor, or if the grid bias
shifted when grid current was drawn.
>how does the plate know it is cathode driven and therefore ok, yet distort
if
> the grid current comes while the cathode is grounded.
I think the answer to that is that distortion is reduced in gg because of
negative feedback. However, I haven't done the sums on how much feedback
there is.
It is interesting to read in Eimac's 'care and feeding', as well as
Pappenfus, that some grid current actually reduces distortion. It is also a
fact that spectrum analyser testing showed that my 4-250As produced better
IMD in AB2 than in AB1 - BUT they do have a shunt regulated bias supply, a
grid swamping resistor of 200ohms and a regulated screen supply. (And some
RF NFB, too - but that was there in AB1)
I will buy that grid current is bad if the circuit isn't designed for it.
73
Peter G3RZP
--
FAQ on WWW: http://www.contesting.com/ampsfaq.html
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|