Obtained in an Electronic Design from 1968, this circuit has the voltages determined by the zener diodes. Transistors can be modern equivalents.
The circuit shown is from the Texas Instruments optoelectronics manual, applying to low power...
This circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...
This filter that rejects a frequency range determined by the double-T was found in the August 1993...