I did something similar, while back, with 807 , 1970's but used a back to front output transformer , with small 4 ohm transistor amp to the speaker windings . old primary 6k ohm was in series with the screen supply.

I used a potential divider for the screen voltage, lower resistor open ctt , tune for max RF out . then , flick the switch , screen to half voltage and modulated with the audio drive , gave good upward modulation , there was a cap to ground from the centre tap of the divider to couple audio to ground .

Graham
G0NBD



On Monday, 2 October 2017 15:44:20 UTC+1, Scott Dorsey wrote:
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.

Like I said it was very common in the old days

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

Weird! I've never seen that before! What tubes were common for that?
Can't be anything too delicate...
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."