The circuit is from a June 1995 Electronics Now. The relay is power-dependent and both R1 and R2 should have close resistances in operation.
This one is from an 80's EDN. Transistors can be general purpose types. The frequency is...
This power supply is not protected from shorts in the output. Output voltage is given by the...
This static switch or electronic contactor was found in a 1968 Motorola publication. The triac...