Mellotron, the Optigan was an organ that used pre-recorded instrumental sounds to provide automated melody or back-up lines to the player -- the novelty was its use of optically-recorded discs, which borrowed the technology developed decades earlier for optical soundtracks on film. Although sold by a subsidiary of toy company Mattel, it was definitely not a toy; it was relatively expensive, and heavy too. I know this because one was left in the basement of my house; the tubes and other electronics were housed in the pedal assembly, which must have weighed at least thirty pounds. I'm embarrassed to admit that, not knowing what it was at the time, I left it on the curb -- hopefully some electronics enthusiast recognized what a treasure it was; all I know is, it was gone the next morning. Months later, I found one of the optical discs in the basement next to where the organ had been -- you can hear what this and other discs sounded like at the Optigan website.