We found this circuit at Popular Electronics. The components are still current. Changes can be made to obtain higher voltages, as indicated in the second diagram.
We found this configuration of band rejector filter or band rejector with operational 741 in a...
This oscillator can use any CMOS inverter. The circuit is crystal controlled and was found in the...
This circuit was found in a 1967 US documentation. It shows how to build a gain control by digital...