System: Piano, Standardbass (unisonoric, logical)
(Collection Oriwohl, Nr. B-79)
Manufacture: Co. Hohner (Trossingen) around 1935
The development of mechanismally coupled basses led over many stages, variants and patents to a standardised chord system and manual, which was later referred to as the standard bass.
Its external appearance with button keys can be seen here on an instrument from the Hohner company.
The curvature of the piano keyboard is not a kink in the optics, but an attempt to make the keyboard of the piano accordion more ergonomically favourable.
This model is called Soberano and was also offered with a straight manual.