This circuit was obtained in an American documentation from the 80's. The transistors can be equivalent to those indicated and the crystal can reach a few tens of megahertz.
Found in a 90s nHands On Electronics, this circuit triggers a relay that shuts off the load when...
Another of the many similar configurations we have in this section. This one is from a Radio...
This circuit for incandescent lamps was found in the January 1980 Radio Elecronics magazine. The...