The SX-939 was introduced in 1974 - 1975. Rated at 70 watts RMS per channel into 8 ohms. Features, two bass and two treble controls, tone off/on, two tape in/outputs, tape duplicator switch, Dolby NR adaptor on/off, two head phone outputs, low and high filters, right and left mic inputs. FM muting and other features.
More pictures and specifications after the break.