Due to my job as Electone instructor, I was fortunate to have played a GX-1 at Yamaha headquarters...also played the EX-42, which was one of their first stage models, some of the perks of being an Electone instructor.

One of my favorite early Electones, besides the D-85 I owned, was the E-75, and both these organs featured Yamaha's PASS (Pulse Analog Synthesis System) in a console cabinet and were very close relatives to the monstrously heavy and monstrously sounding CS-80 synthesizer.

There is a good timeline regarding Yamaha products here: http://www.yamaha.co.jp/manual/english/chron.php

Ian