>
>Rich says:
>
>> Since the typical grid terminating resistor is 450 ohms, instead of the
>>exciter seeing a 50-ohm load through the 1:9 transformer, it now sees a
>>191/9 -ohm load.
>
>Rich, the argument is this:
>
>You claimed that running grid current in a grounded cathode tetrode caused
>distortion. You at least implied that this was always and inevitably the
>case.
>
You picked the 8170 tetrode.
see http://www.vcnet.com/measures/8170.JPEG
- The characteristic curves show the region of best linearity is the
area of no grid current. This is why Eimac recommends zero grid current
for literally dozens of their garden variety tetrodes. .
>I claim that this is not necessarily so. The caveat is that the design takes
>care of grid current loading,
How would you go about convincing a modern transceiver that a 22-ohm load
(the 8170 with grid current) is ok?
>provides stable bias and screen supplies, and
>that the tube is suitable.
>
>Further, there is a large body of professional literature over the years
>showing how to achieve satisfactory Class AB2 operation of tetrodes.
I have seen many large bodies of late but this is ASSuredly not one of
them. For grid-driven service, I say that AB1 is cleaner than AB2.
Please name a particular tetrode where AB2 is cleaner than AB1.
>TheG2DAF does not to my mind, necessarily, with all tubes and arrangements,
>fall into that category.
Indeed. G2DAF's gnoring the 3/2 power law does not earn high engineering
marks.
> I am willing to concede that with some tubes and
>some time constants, it could be satisfactory
The way Part 97 is worded, ham radio splatter is satisfactory provided
it does not extend beyond the edge of the amateur radio service band.
As Mr. Rauch pointed out, a fly in the DAF ointment is the fact that the
grid v peak and the sceen v peak are seldom - if ever - in phase. The
bottom-line with with the DAF design, is that it is possible to have
virtually any screen potential at the grid v peak. . . The grid v
varies at an RF rate but the screen v does not - and none of the DAF
enthusiasts appear to have even given it a thought. .
> (There are more things in
>heaven and earth, Horatio, than are dreamt of in your philosophy)
>
>End of story.
>
not quite. . Verily, I say unto you that the universal 3/2 power law
changes not. . .
>
cheers, Peter
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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