How to calculate the collector and emitter resistors in a differential amplifier with transistors
Firstly, you probably need to set V4 to be 0 volts (midway between the power rails) if you are testing the front end differential amplifier. Currently it appears to be set to a value called &quot;V&quot; and I can't see what this is anywhere.
But, your circuit has a massive voltage gain so reduce the input voltage AC amplitude to produce a decent sinewave on the output. Remember that when you &quot;close the loop&quot; the circuit gain will become much lower due to negative feedback and the actual levels at the bases of the transistors will be around a milli volt or so. That is about the right sort of level you'll need to use when testing your differential front-end.