We found this circuit in the April 1982 Radio Electronics magazine. It contains a good power stage whose transistor must be mounted on a good heat sink.
This radio version with a transistor for a crystal phone was found in a Japanese magazine from...
In this circuit of Texas Instruments an incandescent lamp is used as a light source, and lenses are...
This source whose voltage depends only on the zener diode used, can supply currents up to about 3 A....