1. The problem statement, all variables and given/known data Hello, guys! I just wanted to make sure I do this right. 2. Relevant equations Forget about the rest of the circuit and focus only on Q2 and Q4. How to calculate R3? 3. The attempt at a solution The way I do it: R3 is basicaly the emitter resistance which purpose is to regulate Hfe. So in most cases the emitter is held at 1V at current of 1mA. We find R3 from the formula R3=1V/1mA = 1000ohms. When Q4 is connected to the emitter of Q2, the emitter will fall to 0,6V and the current through R3 will reduce, leaving room for the base current of Q4 I3=0,6/1000= 0,0006A=0,6A. I3 reduced from 0,001A to 0,0006A. Now we can find what the base current of Q 4 will be from IB=IE-I3=1mA-0,6mA=0,4mA.