This NEC commercial amplifier was manufactured in Japan in the 1960s. The circuit uses 4 transistors from the time and was powered by a 9 V battery voltage formed by large batteries.
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...