This circuit is from a 60's documentation. The capacitance C1 can be between 20 pF and 0.01 uF depending on the generated frequency. Equivalent transistors may be employed.
This is the conventional application of the UCN4202 to control a 12 V stepper motor with current...
This circuit has very high input impedance and a differential input. The gain is 1,000 and the...
This circuit was found in a 1980s documentation. Modern general purpose transistors can be used....