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.
The base of this circuit is one of the four Norton amplifiers existing in an LM3900 integrated circuit....
This simple CMOS metronome circuit can be mounted in a small box, providing both sound and light...
This circuit of an old American publication uses RF transistors to obtain unit voltage gain, but...