This circuit can be used as a lockable shield. A pulse activates the relay that remains on even after the pulse disappears. The transistor is general purpose.
The circuit is from Motorola's Linear Databook from 1990, but the configuration is current because...
Found in a 90’s 73 magazine for radio amateurs, this circuit provides a few milliamps of output...
This is another one of the many versions of this circuit that we have in this section. We found it in...