Moog's whole entree into electronic music was via the Theremin. He wrote an article in Radio & TV News in the 50s describing how to "repurpose" some old radio parts into a Theremin, and later wrote an updated solid-state version of the circuit for Popular Electronics.
There was a Theremin project in Popular Electronics using tubes and stuff, probably in the mid to late 1950's. A friend and I made one and discovered that it doesn't matter what kind of musical instrument it is, if you want to be good playing it you probably have to have some talent and invest some practice time. (neither of which applied to us)
-- Frank B Strauss, DMD