In article ,
"Antonio Vernucci" wrote:

According to the ARRL Handbook (1968 edition), the screen resistor must be
connected to the "hot" end of the modulation transformer secondary. This
seems
quite logical to me.

On the contrary, the EIMAC "Care and feed of power grid tubes" booklet states
that the screen resistor must be connected to the "cold" end of the
secondary.
Their argument is that, when plate voltage increases (due to modulation), the
screen current decreases and so does the voltage across the screen resistor,
thus resulting in a higher screen voltage.

Tony-

What if you connected a capacitor across the screen resistor connected
to the hot end of the transformer? This might tend to keep the DC
voltage drop constant, while coupling more audio to the screen grid.

Fred
K4DII

Tony-

What if you connected a capacitor across the screen resistor connected
to the hot end of the transformer? This might tend to keep the DC
voltage drop constant, while coupling more audio to the screen grid.

Fred
K4DII

Frad,

I am afraid I am unabke to follow your reasoning.

I cannot see how adding a capacitor, even a BIG one, can help keeping constant
the voltage drop across the screen resistor.

When you switch back from TX to RX, the screen current will go to nearly zero
and the voltage drop across the resistor will then tend to do the same. A
capacitor in parallel with the resistor would not succeed to keep the voltage
drop constant, as it would get discharged in a very short time.

73

Tony, I0JX