The circuit shown uses an operational amplifier that is uncommon nowadays. The circuit was obtained in a 1994 Linear Applications Handbook by National Semiconductor.
We found this frequency meter circuit in a 1974 documentation. The circuit is powered by 12 V and...
This high gain small signal amplifier circuit was found in an old publication on transistors....
This circuit can be used with input voltages up to 750 V, regulating the current between 200 uA...