General Electric suggests this circuit in a 1980s documentation. The operational of the time is FET-type input. Modern equivalents may be used.
This circuit uses two Raytheon RC4558 operational amplifiers that are similar to the 741. The...
This audio amplifier circuit is from Ibrape's technical documentation from the 70's. The BC177 can be...
This progressive circuit has a lock allowing coded activation. We found this configuration in...