The circuit shown is for testing both signal diodes (low current) and rectifiers (high current). The circuit is from a 2000 Poptronics, and the transformer has a secondary winding of 100 to 300 mA.
This version of a mixer with a transistor appears elsewhere in this section and on this website. The...
This circuit, from a 1995 publication, powers incandescent lamps according to the power grid. The...
This circuit is intended for underwater communications. Of course, the critical point is the...