This circuit was found in a 1967 Electronics World. Transistor Q1 can be a TIP321 and Q2 can be a BC558. The indicator lamp is optional.
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...