Found elsewhere in this section, but from other sources, this circuit is from a 1964 Electronic Design. The transistor is from the era and the power voltage depends on this component.
This amplifier for hearing aid was found in a 1968 documentation using an integrated of the time....
We obtained this circuit from a 1993 documentation. The circuit has 9 current ranges that are...
In the figure we have the transmitter of a data transmission system with optical fiber suggested by...