Help analysing a discrete voltage regulator circuit
Look at T3/T4 as a differential amplifier with a 2 diode drop on the feedback ratio with the Zener voltage as the reference.  

Then it will make sense, even though it is a Common Collector driving a Common Base,  the voltage error gain is the same and the emitters don't need extra loads as they are share current as a virtual low impedance (base-ESR/hFE) with high collector to emitter gain ratio.

For simplicity I used a PNP series pass, but LDO's use a current source like that. The outputs use a Darlington Emitter Follower with high gain in front, so ignore that.

I just want to show that the impedance and gain of this feedback arrangement is just like a differential amp with offset and fewer parts.







simulate this circuit &ndash; Schematic created using CircuitLab

For more precision



Except use a LM137HVQML and complement everything for PNP emitter follower drivers on a negative rail used in this IC.