Hohner Atlantic III piano accordion. Three voice (low reed, and two medium reeds) with 9 couplers (4 are repeats), mute switch, 3 couplers on the 5 voice bass side.
This is a lovely instrument – the 1960s Atlantics were fitted with composite pads (a sandwich of leather and foam attached to the keys and which form an air seal until you operate a key e.g. sound a note), and over time the foam in the pad disintegrates. All the pads on the bass and treble were replaced. The internal condition is good with no valve noise, and the instrument is in tune and sounds great. See the video below.