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.
The 747 is an old operational amplifier. This configuration suggested in the component manual is...
Suggested by Siliconix in 1980s documentation, this circuit uses currently uncommon components. The...
In the figure we have a circuit to excite a piezoelectric capsule taking advantage of its resonant...