Wiring a BJT differential amplifier in a circuit
Look at the circuit from &quot;M lab&quot;
Following up on the circuit of M lab, let us add ONE TRANSISTOR, and you will have a very useful OUTPUT CURRENT referenced to VCC.
The circuit OUTPUT, as is, running at +5 volts VCC, will provide about 0.5mA pulling up, or 0.5mA pulling down.
Let use boost that.
Simply add a 2N3906 PNP, emitter to VCC, and base to OUTPUT.
The new PNP's collector is now your output current.
This new transistor can provide up to  BETA * 0.5mA = 50 milliamp.
If you want to switch amps, then use a large bipolar NPN, emitter grounded, base to this new PNP, 1K resistor in parallel across the NPN emitter_base, and probably a high_current clamp diode from collector to ground so you can drive a relay. Have the clamp diode oriented with cathode (the line on the diode) to collector.