>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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