This circuit was originally recommended to give the call signal on intercoms. However, it can be used with other applications. The circuit is from 1978 documentation. The transistor may be the BC548.
Found in a 90s Popular Electronics, this circuit keeps an LED on when a phone is in use. Can be...
This amplifier stage, obtained in a 1980 publication, has a low input impedance and a high output...
This circuit was found in an American magazine in 1976. It doubles the frequency of TTL signals in the...