See: http://www.thereminworld.com/Forums/T/28789/theremin-circuits-scratchpad?Page=0
Some quite interesting, perhaps even astounding "discoveries" may be in progress at TW on this thread:
http://www.thereminworld.com/Forums/T/28789/theremin-circuits-scratchpad?Page=0
Latest simulation circuit for FET "clone" of RCA Armstrong oscillator. Note C5 now couples D-G which is the same as what occurs on the RCA.. Inductor values are now based on calculation using winding and form data.. All detailed at TW.
Analysis of RCA oscillator
Fets do not seem to optimally model the triode function -
Here is an experimental circuit allowing adjustment for gain and biasing, allowing cathode-plate resistance to be better controlled.
Slow H11F1 speed limits operation to lower frequency - amplifiers need gain to compensate for this
This is part of the collection of simulations etc related to evaluation of the operation of the RCA theremin, and relates to discussion on simulation which appears here: http://www.thereminworld.com/Forums/T/28796/rca-theremin?page=3
Possible UX-120 replacement circuit (RCA volume modulator) ?
Updated (simpler / safer)
Audio filter based on a guitar stomp box.
Hi Rob,
Just split your image so it can be posted at TW .. Hop this is ok. Fred.
Thanks, Fred. That's just fine.
I'm suffering from the flu and my brain is elsewhere 
