This circuit was published in a recent magazine as a past project. It is a crystal radio from October 1986 Radio Electronics magazine. The article detailed the assembly.
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....