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.
This configuration appears elsewhere on this site. We obtained it from a 90s Radio Electronics, based...
This circuit is from a Fairchild digital clock module shown in the March 1977 issue of Radio...
This good power amplifier, a few tens of watts, is part of an article in the December 1972 Radio...