In article , philo
wrote:

On 10/01/2017 08:31 AM, Scott Dorsey wrote:
In article , philo wrote:
On 09/30/2017 10:47 AM, Scott Dorsey wrote:
So, if I adjust the voltage on the suppressor grid of a pentode I can
alter
the gain of the tube substantially, but in the process I now am moving
most
of the current from the plate to the screen grid.

Are there any tubes out there with a sufficiently heavy screen grid that
this could be done with? I can always reduce the total current to
prevent
screen grid damage but then linearity suffers.

Do any small signal pentodes out there exist with heavy ruggedized screen
grids?

Sure that was done plenty of times back in the old days.

I think some of the cheaper Heathkit transmitters use SGM

No, other way around, I want to modulate the suppressor and not the screen.
Screen grid modulation is... not really very linear at all but requires
little drive, which makes it a win for inexpensive communications grade
radios.
--scott




Like I said it was very common in the old days

http://www.vias.org/basicradio/basic_radio_17_06.html

How old is the "old days"? I do not doubt it can be done, but I never
came across it before. The tubes I knew were the 807/1625 and 6V6/6L6.
I think the 6L6 had a Suppressor Grid, but it was internally tied to the
Cathode.

Heathkit definitely tried Screen Modulation. They went as far as
increasing carrier power during modulation, called "Controlled Carrier
Modulation".

I suspect Suppressor Modulation may not be as bad as Scott thinks, or
else the example given was done at a low power stage.

Fred
K4DII