When an alternator is used to supply constant current, it needs an adjustment that must be made as shown in the figure. The potentiometers are of low wire value with high dissipation.
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...