>I think this thing has gone far afield of helping anyone build a
>clean PA. It seems Ian, Peter and I agree on the causes of IMD, and
>some good ideas to prevent IMD (regulating the screen and grid with
>low shunt impedance regulators).
If regulating the grid supply to prevent IMD is a good idea, then why
don't Eimac, Svetlana, Amperex, Philips and RCA say so in their
literature? OTOH, these manufacturers say to regulate the screen
supply. Does it seem likely that they all failed to reach the "EXACTLY
correct" conclusion?
Svetlana says the grid supply can have a Rout of 1000 ohms. Eimac
tyically says 100k ohms. I use 5k ohm to 15k ohm wirewound
potentiometers to adjust the output of an unregulated C-filtered bias
supply. If there is zero current out should the Rout be a big deal?
>Either system would require a warning device for grid current.
For a warning device, a current meter will suffice. In AB1, set the grid
V for zero grid current with the grid current meter. IF you switch to a
different radio, reset the grid V for zero grid current with max.. RF
out. That's all, folks!
>So why not use a stiff shunt regulated grid supply (to prevent
>splatter)
well of course, of course...................but does the splatter chatter
wash?.
>with a warning device that disables the PA if excessive
>grid current occurs? ...
Why not initially set the grid bias V so that zero grid current flows
when the exciter is producing max. RF out? Ummm. Because they haven't
been there?
Rich---
R. L. Measures, 805-386-3734, AG6K
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