This circuit was found in a Popular Electronics from the 90's. The frequencies depend on the components indicated in the table next to the diagram.
Despite being from a 1969 publication, the transistors used have current equivalents such as BC548 and...
Found in a 1990s American technical brochure, this circuit is intended for alarms that use as...
Found in an old Electronic Design, this circuit provides an output voltage that is the absolute...