[AMPS] Re: New G2DAF amplifier information

[measures]

>
>Rich said:
>
>"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."
>
>Rich, you are wrong.  This point has been discussed numerous times, but you
>have ignored it.  

There has been nothing that succesfully explains why this is not a 
problem.

> You keep citing the results of your friend Norm, who stuck
>a 1 mf cap on the screen.

Norm tried some new ideas after the original DAF circuit produced 
unacceptable distortion.  The last idea Norm tried was regulating the 
screen potential and increasing the bias v until there was zero grid 
current with max drive applied.  This produced acceptable distortion 
>
>The screen must follow the grid voltage, more or less.  

How much C at the screen in the orig. DAF?

>  Note that the
>original design used a minimum capacitance - which removes the rf from the
>screen - but no more. 

Next stop, downtown Regerationville. 

> Screen voltage must follow the control grid.  The
>control grid will not follow the input perfectly, as there will always be
>some delay in signals arriving at the control grid.  

And? 

>Ideally, the screen
>voltage must follow the control grid voltage precisely.  

If this ever happens, the screen would henceforth not be able to shield 
the grid from the damped VHF ringing that takes place in the 
anode-resonant circuit.  Not operating the screen at RF ground potential 
is like opening Pandora's VHF surprise box. 

> But, there is no
>perfect amplifier.  None of your amplifiers are perfect.  The real question,
>for the G2DAF amplifier, or any derivative, is how linear is it in practice.

indeed. 

>More particularly, how much does it splatter?  The bastard amplifier built
>by Norm  does not count.  And, the fact that you have heard bad examples
>does not prove that good examples do not or cannot exist.

Norm's DAF had semi-ok distortion compared to W6CHR's.  When CHR had his 
fired up on 3908KHz, splatter could be heard 100 miles away from 3990KHz 
to 3805KHz.  Is this awesome or what?
>
>My testing of varying screen voltage and grid voltage on an rf amplifier at
>varying rates indicates that it may be sufficient for the screen voltage to
>be able to follow the grid voltage at an audio rate, rather than an rf rate.
>
alas

>Finally, you keep citing the 3/2 power law as proof that the G2DAF amplifier
>must distort badly.  A few months ago I cited the definition from Eimac.
>Under their definition, there is no violation of the 3/2 power law.  

word games

>But, I
>have never heard your definition.  Please define your version of the 3/2
>power law and what is violated by the G2DAF amplifier and how that causes
>distortion.
>
for a given input signal potential, peak anode current varies according 
to the 3/2 power of relative screen potential.  When screen potential 
does not vary, the sole determiner of peak anode current is input 
potential.  Thus, linearity results.  In a linear amplifier, the sole 
determiner of peak anode current must be input  potential.  In a DAF 
amplifier the screen is busy determining peak anode current at an audio 
rate while the grid is trying to determine peak anode current at an RF 
rate.   
>
later

-  Rich..., 805.386.3734, www.vcnet.com/measures.  
end


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