In this circuit we have 100% negative feedback, and its act very similarity to voltage follower (non-inverting amplifier) Buffer amplifier - Wikipedia, the free encyclopedia
Voltage on output will be equal VB1 * Au = VB1 * 1 = VB1
So collector current of a T4 will be equal
Ic_T4 ≈ (VB1 - Vbe_T7) / (R10 + R11)