Plain dial only
The first electric Big Ben alarm clocks were introduced ca. August 1931. The three models introduced at this time were models 820, 830 and 840. Models 820 and 830 have a black composition (Bakelite) case, and model 840 is a mahogany case. They use the Sangamo self-starting synchronous motor. The motor runs the clock as well as winds the alarm mainspring. There is a key on the back for manually winding the alarm mainspring.