Marquardt tactile type ca. 1982
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