520
Item nr.
Early solid state hearing aid.
Production | Germany, 1958. |
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Semi- conductors | 3x OC71. |
Cabinet | Steel. Size 7x6x2cm. Weight 140 gr. |
Power | Batt 1xAA. |
Removal of the front panel reveals the back of the PCB, with the cores of three audio transformers and the large microphone. Opening the back reveals the three OC71 transistors; bottom left of the picture shows adjustments to align the machinery to the user's needs.
The OC71 was introduced in 1954, and succeeded by various transistors introduced in 1957 (OC75) and 1960 (AC125). Because hearing aids often use the modernest techniques, I assume this unit to be built between 1957 and 1959, but I couldn't find any direct sources about the building year.
Audium had an agency in Amsterdam (Singel 160). Mick sent me this schema of the very similar Audium 800, a model of year 1956/7.
Obtained | 8/2020 from Barneveld Market; sn=47864. |
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Condition | 8; neat and works. |
Value (est.) | 6,8€. |
The earpiece is a magnetic piece with DC resistance about 300 Ohms and 1k impedance. The plug has one of the pins slightly thinner, so it fits only in one position. It is not interchangeable with the plugs of the Phonak hearing aid or the Tecla pocket radio (both tubed).