This circuit is from a 1969 EEE magazine. The transistors are from that time, but the circuit can be implemented with modern equivalents, such as 2N2646 for Q3.
Carbon microphones are no longer used in most projects. However, finding one in the scrap metal, it...
This circuit produces a strong tone of audio or ultrasound, depending on the values of components C1 and...
This alarm from an old 1978 publication uses PNP transistors and driver and output transformers that are...