We find this circuit in American documentation from the 1980s. It consists of a frequency folder using a varicap. The capacitors and coils depend on the frequency of operation.
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....