This circuit is from a 1969 General Electric manual. The SCR may be the TIC106. Similar circuits from other sources are found on this website.
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....