This circuit is from an American 1967 documentation and can be implemented with modern equivalent transistors. The circuit serves as a Q multiplier.
This control for motors up to 1 A was found in a Siliconix documentation using its own component....
This filter rejects the hum of 60 Hz from power grid, being placed between the signal source and...
In the figure we have an interface using an optical coupler and the comparator LM339 or any...