This power step for relay activation was found in the 1964 RCA transistors manual. The circuit is of the NF type and the transistors admit equivalents. R4 depends on the drive voltage.
This simple circuit, which appears elsewhere on this site, was found in a transistor manual from...
This transistorized astable for LEDs was found in the January 1992 issue of Radio Electronics...
This circuit works like a solid-state contactor. We find it in General Electric documentation from...