We found this battery eliminator in a Radio Electronics magazine from August 1974. The transistor must be equipped with a heatsink and other voltages can be achieved by replacing the zener.
This circuit of a 1978 American publication monitors a telephone line by triggering a relay. The...
Found in 1965 General Electric technical documentation, this half-wave circuit controls shunt type...
The power supply shown in the figure provides voltages between 0 and approximately 15 volts, with...