via this auction
"Very nice and ultra rare Johnson Intonation Trainer Synthesizer from 1966 with Tunable Keyboard.Made by the E.F. Johnson Co in 1966 Waseca, Minnesota U.S.A.
Speaker in case, it can also connect to external amp or mixer.
Note from users:
Voicing - choose from four voices, basic sine wave to reedy / edgy
Scale Selector - choose between reference (tempered tuning) or tunable
Tunable Scale Controls - correspond to notes on keyboard and adjust pitch in tunable mode
Originally used to test the relationship of pitch-matching and pitch-discrimination abilities
It's FULLY polyphonic with vibrato etc. Cool for Drones and Experimental music, original manual inlcuded.
Excellent cosmetic conditions with an unique design and in perfect working order."
You can find a few demos in previous posts here.
