Another idea would be to use a second low power modulation transformer with a
separate amplifier feed off the same mike amp and with it's own level
adjustment to only modulate the screen. You'd need two level adjustments in
addition to the main mike gain control to set the proper levels for the high
power plate modulator and the low power screen modulator. The screen
modulator would only need to be a few watts, maybe single class A 6L6 or 6V6.
I realize this is getting more complicated than just the choke in the screen
circuit, but that's the beauty of home brew, trying things out just for the
heck of it.

I sometimes tend to be perfectionist, and I would then not like to start a
project pursuing a compromise solution from the very beginning. So, I would like
to have the screen modulated too, not just the plate.

With regard to the separate audio amplifier for the screen, it should work but I
am not sure whether some phase shift could occur between the two amplified audio
signals (apart from the 180-degree phase ambiguity that can be easily resolved
crossing the wires of one of the two modulation transformers).

I have come to the conclusion that using a filter choke on the screen probably
is the simplest way to go, and the safest for the final tube too.

73

Tony I0JX