Starting from a discussion about an electronic controller on Facebook, I looked through the literature to see the first reference, and this seems to be it!
Gentlemen, the Posi-trol HC100 transistorized electric hand control from Stern Electronics of LA, CA., in the preview section of the September 1963 issue of Car Model.
Along with a photo in the first Car Model Handbook this was the only mention of the controller - very expensive for the time, obviously.
After this come the "Hot Slot" from Downey Enterprises (California), with an ad in the July-Aug issue of Model Car & Track, and the Slot Master from Sedco, an ad in the June 65 issue of Car Model. Both were listed as "transistorized". The Hot Slot was $15.95 to $17.95 and the Slot Master $9.95 or $11.95. The Thoric "solid-state" model was listed in January 68 (MCS).
Don