PSR-50 came out in 1985...there were three models...the 50, 60 and the top of the line PSR-70.

Here...I found the Yamaha chronology list:
http://www.yamaha.co.jp/manual/english/chron.php

[This message has been edited by ianmcnll (edited 01-18-2008).]
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Yamaha Tyros4, Yamaha MS-60S Powered Monitors(2), Yamaha CS-01, Yamaha TQ-5, Yamaha PSR-S775.