This circuit found in an American documentation from 1964, alters the duration of a pulse and can operate at frequencies up to 10 MHz. The transistors are from that time.
This amplifier with very high input impedance was suggested by Texas Instruments in a manual of...
Using only a ULN5804 integrated circuit, stepper motors up to 500 mA can be controlled from TTL...
Constant current sources are used in applications such as battery chargers, electrolytic tanks, etc....