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 circuit recognizes a tone determined by the tuned input circuit (R3 / R4 / C2). The circuit...
This CMNOS crystal-based circuit generates a 2 Hz signal. It was found in the October 1994 issue of...
This is one of the possible configurations using the LM139, 239 or 339 voltage comparators. The...