Slap a couple of screens in there between the filament and the plate and put a bias voltage on one of them and alter the other and waaa laaaa.... you got control of those little electrons. Man I loved vacuum tube theory and playing with those circuits back in the day. I still have a box in my shop with a pair of transformers (Input and output) from a Marshall and a bunch of parts including the tubes.

You can find my music at:
www.herbhartley.com
Add nothing that adds nothing to the music.
You can make excuses or you can make progress but not both.

The magic you are looking for is in the work you are avoiding.