The circuit presented was suggested by Texas Instruments in an opto-electronics manual. The transistor can be the BC548 and the supply voltage depends on the application.
Found in a Popular Electronics from the 80's, this circuit triggers an SCR keeping an LED on when...
Found elsewhere in this section, this circuit is from the April 1971 Radio Electronics magazine. Note...
This circuit works with practically any tunnel diode, transmitting signals in the FM range with a...