http://www.dogstar.dantimax.dk/theremin/bamtrat.htm
"What happens if you start to restore an old AM battery-operated tube table radio... and put it back together all wrong? The answer - BAMTRAT! (Battery AM Tube Radio Authentic Theremin).
While such a project might offend the sensibilities of collectors, I decided to go ahead with it because this poor old radio had been sitting in my "to do" corner for several years, and I could never quite get the motivation to restore it. After all, the reward for all that work would have been just another AM radio.
Instead, I decided to re-use all the major components to create a tube theremin with as authentic a sound as possible. A novel "differential tuning" approach makes for ease of tuning using the original tuning dial. The close-coupled antenna coil, used as the variable pitch oscillator, duplicates Lev Termen's trick of using hard coupling to provide that unique saw-like classic theremin sound.
Schematics:
http://www.dogstar.dantimax.dk/theremin/bamschem.htm
Tech. Details:
http://www.dogstar.dantimax.dk/theremin/bamttech.htm
Sound Samples:
http://www.dogstar.dantimax.dk/tubestuf/sounds.htm#bamtrat
"