Door buzzer or alarm (CB20492E)

This solar powered circuit was found in a 1991 documentation. The transistor is a general purpose NPN.

Telephone Monitor (CB12655E)
This circuit of a 1978 American publication monitors a telephone line by triggering a relay. The...
Shunt motor control (CB7939E)
Found in 1965 General Electric technical documentation, this half-wave circuit controls shunt type...
Variable Power Supply for the Experimenter (CB16079E)
The power supply shown in the figure provides voltages between 0 and approximately 15 volts, with...