Found in a 1968 American documentation, this circuit uses an operational amplifier that is uncommon today. The feed must be symmetrical. The gain is 40 dB.
This circuit is from an American publication from the 60's. The power is on the order of 600 mW....
Other operational amplifiers series, such as the MC34072, MC34074, MC35071, MC35072, MC35074 d...
Found in a European magazine from the 90s, this circuit emits beeps that are several seconds apart to...