This circuit from a Radio Electronics from October 1965 shows how to obtain the action of an SCR when triggering a relay using two transistors. The relay is according to the circuit supply voltage.
This 1995 circuit uses an audio amplifier that is no longer common today. However, other...
Found in a Popular Electronics from the 90s, this circuit uses common components with several...
This circuit is from the 80's but uses common components today. The relay is voltage sensitive...