[sdiy] Tetrode VCA?

[Scott Evans, Gen Mgr]

Years ago, when studying electronics in college, we still learned vacuum 
tube theory (yeah, it has been a while). Unfortunately, I did not keep 
my textbooks on tube technology :(

I recall that the tetrode tube exhibited interesting non-linearity when 
used as an amplifier stage. A tetrode has four electrodes, a cathode, 
control grid, screen grid, and anode. It also had, as I recall, a gain 
curve that actually inverted to produce negative gain and then inverted 
again to normal gain sort of like a backwards "S" on it's side. This 
led, of course, to the pentode type tube to correct these non-linear 
gain problems.

I thought this could make an interesting VCA for producing distorted 
waveforms. Has anyone in the group tried building something of this 
sort? Are there even any of these devices still built? Just a thought.

Scott