Found in an old Popular Electronics this circuit is still current. The SCR can be of the 106 series and the relay according to the voltage used in the supply. The voltage can be 12 V.
Analog Devives EVAL AD5941 Electrochemical Evaluation Board This board provided by Mouser...
This circuit uses an optocoupler with a phototriac or optotriac to drive an external triac. The...
Found in a Hands-On Electronics from the 90s, this circuit produces the dial tones of an old...