Optasound 116R synchronous self-resolving cassette recorder

Year: 1976

According to "kjellpell" on filmshooting.com the Optasound 116R came in 3 different versions, version 1: No. 20075, version 2: No. 20175 and version 3: No. 20275:

Version 1: No. 20075 worked on the usual Digital 1/F, which means a 1000Hz tone burst was recorded on one track of the tape for every picture that run through the camera.
Version 2: No. 20175 used a 60 or 50Hz pilot-tone sync generator, which was standard for 16mm sync productions.
Version 3: No 20275 both the 60/50Hz pilot-tone AND crystal sync.