Calculation problem

[SneaKSz]

Hello i want to know what voltage is at the base of T1. I can't succeed in trying to find this voltage.

**broken link removed**
my calculations : Vb3 = 1.4V => Ve3=0.7V Ie = 0.7V/120 = 6mA = I1+I2.
I1 = 0.7V/390 = 1.8mA , I2 = 4.2mA.

Vb1 = 0.7 + 0.7 + Uce1 = ???

and VB1 ≠ VCC*R3/(R3+120+100k)

can someone clear this up for me?

ty

 

[Jony130]

This is good first assumption
VB1 = VCC*R3/(R3+120+100k)

And remember that I1 = IR9+Ib_T4
Ic_T4 ≈ (VB1 - Vbe_T7) / (R10 + R11)≈ (0.5Vcc-Vbe)/(R10+R11)

 

[SneaKSz]

This is good first assumption
VB1 = VCC*R3/(R3+120+100k)

And remember that I1 = IR9+Ib_T4
Ic_T4 ≈ (VB1 - Vbe_T7) / (R10 + R11)≈ (0.5Vcc-Vbe)/(R10+R11)

I dont get that last one :d

 

[Jony130]

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)