This circuit was obtained in a Popular Electronics from the 90's. The gain depends on R4 and R3. Transistors are general purpose types.
This car alarm was found in an American '80s documentation. The circuit automatically activates...
This is a basic astable circuit using the 555 IC and driving two LEDs. The phase on a rate giving...
This is one of the many versions of amplifiers with LM386. This was achieved in an old publication (1981). The...