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.