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Note the EX-1 is not the pre-cursor to the GX-1. That would be the "EX-42 (1970–1977, stage model, design origin of GX-1)" according to the
list of Yamaha products on Wikipedia.
"RARE YAMAHA EX-1 ELECTONE ORGAN / SYNTHESIZER W/AMPLIFIED SPEAKERS

2 main 61-note keyboards, a 37-note solo Synthesizer keyboard (with after touch and side-to-side key modulation capabilities), and full pedalboard, with coupling available between all keyboards and pedalboards. The solo keyboard can provide synth sounds similar to those used by Keith Emerson on 'Fanfare for the Common Man' and 'Peter Gunn'.

Built-in arpeggiator and (primitive) drum machine, effects, knee-lever control, great night-lighting system(!), auto-pitch bend, wah-wah pedal, reset Tones setting board, Sample & Hold with Synchro Auto-Rhythm and Auto Bass/Chord, headphone and Leslie speaker cabinet outputs, and much much more.
Includes the 2 large Yamaha TF-III self-amplified speaker cabinets and connecting cables. These will definitely shake the house!
A copy of the operation manual with full specifications, etc., Very rare and unusual piece, excellent condition - total weight with speakers is about 1000 pounds, so arrangements will have to be made BY BUYER for pick-up / crating / cartage by Keyboard Carriage or a similar moving company.
Yamaha EX-1 Electone Organ is in excellent condition, and is fully functional. This auction includes the Yamaha EX-1 Electone Organ, Bench, Pedalboard, two (2) TF-III Amplified Speakers, the operations manual and brochure"