The transformer in this power supply can have a secondary winding from 1 to 15 A of current. Voltage is given by the zener diode. Transistor 2N3055 must be mounted on a good heat radiator.
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...