>Rich wrote to Lars:
>
><However, during SSB
><voice modulation, the screen potential fluctuates widely and the IMD
><increases significantly. // Eimac recommends a constant screen
><potential for best linearity.
>
>-This is nothing new to me Rich, It could just be a "not invented here
>syndrom"
>from Eimac.
>What do you know your self ?
I know that to produce linear amplification from a tetrode or pentode,
the screen potential needs to be fairly constant.
> Quoting only one source is'nt always very convincing.
RCA, Amperex, and others say this too. So do engineering texts. This
is the way tetrodes and pentodes work.
>We have seen in the techno history other cases when the
>BIG company kills an idea' and the rest of the crowd is then
>quiet and accepts the BIG companys "standard"
>
Consider the case of "Cold Fusion". Pons and Zimmerman made an error in
their power calculation which led them to believe they were getting more
power out than they were putting in. However, was not true. Yes, folks,
P = I x E really is correct. However, some people still believe in the
Cold Fusion delusion.
>
>>......Lars wrote:
>>Myself, I have built all three amps using G2DAF design. A very clever and
>>clean design wich
>>I highly recommend! If you are interested I can mail you some drawings as
>>well as plots from IMD measurements.... ...
>
>
>Lars, we all like to see and read the results from this measurements.
>Especially when I do know you have access to a nice Lab.
>
>Lars also says:
>>Well, if noone can´t come up with something new,
>>I guess there is no point starting this discussion all over again,
>>as we covered the subject quite deeply about a year ago.
>
>Well,, last time the technobladder lead nowhere, I still do not
>know if G2DAF is garbage or not.
It led to disclosure of how the G2DAF circuit manages to produce
acceptable IMD measurements by use of the 2-tone test -- i.e., which
produces constant screen voltage during the IMD test. It led to
disclosure that screen voltage fluctuates widely during modulation with
the G2DAF circuit, which is why typical IMD is c. -22db with SSB voice
modulation.
>The only thing for sure is that more and more DAF's is popping
>up on the bands.,ie low bands, not to far away from here.
>
>Or prehaps the brain power on this list is not powered enough
>to sort out if Emac is indeed right or if Mr G2DAF was a
>genius or not.
>
A genius would probably have understood that the screen's following a 3/2
power law means Not Linear. For example, doubling screen V nearly
triples peak anode current. Linear this is not.
- The good news is that it's easy to build a regulated screen supply
using a 723 and a power FET so that linear SSB operation can be achieved.
Such a circuit is available on my Web site.
>Lets rumble,,,
>
To splatter or not to splatter, that is the question.
Rich. Measures. Web site: www.vcnet.com/measures
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