When was the first arranger keyboard as we know them today launched and what was it?

NOTE: Don’t confuse an arranger keyboard with a single manual keyboard that included the easy play features of organs, (From which arranger keyboards developed) but a genuine arranger keyboard.

Curious

Bill
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English Riviera:
Live entertainment, Real Ale, Great Scenery, Great Beaches, why would anyone want to live anywhere else (I�m definitely staying put).