While perusing the "RCA Service Notes for 1929-1930" which includes the service data for my RCA Radiola 44 I happened to notice this:
What!?!? An RCA Theremin? I've built the usual theremin circuit which uses a non-contact capacitive coupling to vary the oscillation frequency feeding an audio amplifier and always kinda wondered as to it's origins and just where the Theremin name came from but never imagined RCA having any relationship to it! Early 1900s was a time when Spiritualism was popular and people were interested in such things as Ouija Boards and Seances so the "Aethereal" sounds produced by a Theremin fit right in. What I did not know was it was (and still is) considered a true musical instrument. Bob Moog of Moog Sythesizer fame even makes them still today!

RCATheremin.com

 

Never heard of Pink Floyd, Led Zeppelin and so many others using it?

 

Moog Synthesizers yes, Theremin no... Apparently, there is a small group of collectors and active users. There is also a registry for the 1920s RCAs.

 

The Theremin device does indeed have an interesting and entertaining history, and prior to MOOG appears to have been the more recently created musical device in quite a while. What separates the copies from the original is usually the different frequency versus movement relationship being more like other musical instruments. A more consistent octave per distance ratio rather than linear frequency versus distance moved.

 

The huge design difference was the use of Huge coils and of course tubes.

 

It was also, supposedly, used in the Original Star Trek intro music.

 

Very interesting, especially the way the volume control was done!! It looks like it varied the plate voltage of that first audio amplifier tube. Rather a smart idea that I had not thought of. Probably the most linear volume control scheme for many years.