Historical clue formulations

• Early synthesizers — 2025-01-03
• Pioneering synthesizers introduced in the 1960s — 2023-05-02
• Early synthesizers — 2010-10-04
• Musical equipment popularized in the 1960s — 2010-10-01
• Keyboard instruments — 2007-08-12
• Instruments with keys — 2006-12-31
• Early synthesizers — 1995-05-18
• Early synthesizers — 1994-09-18
• Electronic synthesizers — 1994-07-27