This is the circuit of the commercial Japanese megaphone of the 60s model DM-218. The circuit uses a compression speaker (horn) and is powered by 4 large batteries. The output power is 2 W.
This headphone amplifier was found in a 1966 documentation. The transistor is made of germanium and the...
The signal injector illustrated in the figure uses a single integrated circuit and generates...
The note sequence for this circuit is achieved through integrated circuits controlled by the 555....