This circuit was obtained from Motorola documentation from 1969. The setting applies to other operating systems, including lower supply voltages. The zener determines the output signal.
This amplifier from 100 to 150mW was found in a Japanese documentation from 1967. The circuit uses...
This circuit is from a manual of JFETs and can be implemented with the BF245 and for the bipolar...
This source of some amps for voltages up to 40 V was found in an Italian magazine Elettronica...