Bausophon - Medical instrument - Metal

An ancient German electric hearing aid from the brand “Bausophon” – presumably from the 1920s/1930s (carbon microphone/battery era, before transistor hearing devices). The set is unusually complete: the black cardboard box (original packaging), the dual earpiece with the two speaker membranes, the battery/amplifier unit with plug contacts, as well as the original printed “Gebrauchsanweisung für Bausophon-Hörapparate” with illustrations of the three model variants (Nos. 1–3). See photos, as part of the description.