Paul Keinanen wrote:


Apart from aviation, the last time the last time I heard someone using
400 Hz for powering computers was in the early 1960's with a 50/400 Hz
motor/generator in the basement, feeding the anode supply of some tube
computers :-), in order to reduce the transformer and filter capacity
size.

MG Sets (400 Hz) powered many mainframe and midrange systems well through
the late 1970s; CDC's small graphics system called 'GRID' used a mini
(2500KVA) 400 Hz MG set and it was built with TTL and DTL, and the entire
1604, 3000, 6000, 7000 and most Cybers used large MG sets. The 160/160A/
8090 series could be equipped with 400 Hz (MG driven) supplies or 60 Hz
switchers (circa 1959-1966).

Regards,

Michael