[AMPS] Re: Norm's Circuit

[measures]

>Rich said:
>
>? The equipment used at the transmitting station was never a
>consideration.  Measurement of transmitted distortion was the whole
>ballgame.
>
>The question is what sort of amplifier was being measured.  Rich probably
>did measure distortion but the question is of what.

I measured the adjacent channel splatter that occurred when I heard 
Norm's voice 
>
>Norm's amplifier was published on page 157 of the New Sideband Handbook,
>published by Cowan Publishing Corp. in 1966 (6th printing) and written by
>W6TNS.  The circuit was designed by Norm Roller, W6EDD.  

Norm had several configurations of the screen circuit. My measurements of 
his amplifier took place around 1979.  

> It uses excitation
>to provide screen voltage through a clamp tube.  Screen voltage on this
>amplifier is  controlled by excitation.  One unique feature of this
>particular amplifier is that there is a 2 mfd capacitor between the screen
>grid and ground.
>
>A 2 mfd capacitor will prevent the screen voltage from following excitation
>variations and necessarily cause the circuit to fail.  

What value of screen bypass capacitor would have caused the circuit to 
not fail, Colin? 

>It will splatter.  It
>is not a G2DAF amplifier and it is contrary to his design.  This particular
>amplifier is in fact a cathode driven design.  

€  The measurements I performed were on a grid-driven circuit, according 
to Norm.  4CX250Bs are not suitable for cathode driven service due to 2w 
max.  grid. 

> The design is so poor that I
>question Norm's ability to design any linear amplifier.  

Norm eventually came up with a Class AB1 amplifier that had respectable 
distortion.  

>Interestingly
>enough, that particular design might pass a 2 tone test because the
>resulting screen voltage would be allowed to be constant in that case.
>
With any DAF config., 2-tone testing assuredly produces constant screen 
potential. 

cheers,  Colin

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


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