This circuit for the power grid was found in the June 1969 Radio Electronics magazine. The SCR and diodes are rated according to the power of the controlled load.
This circuit is from 1977 documentation, but can be assembled with BC548 for Q1, Q2 and Q4, BC558...
Found in American documentation from the 90s, this circuit uses components that are still common...
This high impedance input amplifier is suitable for the use with piezoelectric sources such as...