This circuit is from a 1980's documentation for telecommunications. The circuit is used in SSB and the diodes must be suitable types for the application. The audio input is low impedance.
This circuit was obtained in a 1995 Electronics Now. It switches off a relay after an interval that...
This circuit with a MOSFET is from an old American documentation. The capacitor should be leak...
We found this circuit in old documentation. Modern equivalent operational amplifiers can be used....