NEMA 1-15 type receptacles were quite common on the rear of imported Japanese amplifiers and receivers sold in the U.K. during the 1970s.
On units with multiple voltage settings, it would have been possible to also utilize the xfmr primary as an auto-transformer and keep a constant 100 or 110V on them, but I've never seen one wired that way.
They always just supply whayever voltage is fed into the unit. Some designs had one unswitched receptacle and one or two switched outlets.
