Marquardt tactile type ca. 1982
There is an unidentified Marquardt low-profile tactile switch that shares the same form factor as 6180 and 6184: Unknown Marquardt switch? This single example is dated 1989.
These switches are covered by US patent 4447687 “Pushbutton switch” filed in 1982, and are either contemporary with Series 6180 or slightly pre-date that series.
The same switches also appear in a full-size Perkin Elmer keyboard, which also features the LED version.
The Marquardt advertisement in Electronic Engineers Master 1985–86 appears to depict this switch, without naming it.
- Marquardt advertisement, Electronic Engineers Master 1985–86 Volume B, scanned by Bitsavers