Adjustment of OTL circuit operating point

Figure 3 is a typical OTL circuit. There are two points to adjust its working point: first, the midpoint potential (point C potential) is EC/2. Second, BG2 and BG3 provide a certain forward bias voltage.
First, adjust the voltage VC at point C. R3, R4, and R5 in Figure 3 are the collector resistors of BG1, of which R3 and C2 form a bootstrap circuit, and R5 is used to provide bias voltage for BG2 and BG3. In order to avoid excessive collector current of BG2 and BG3 due to inappropriate R5 value when adjusting VC, R5 can be short-circuited. R1 and R2 are the bias resistors of BG1. Adjust R1 to make VC=EC/2.
Then adjust the working current of BG2 and BG3. It can be seen from Figure 3 that the emitter voltage of BG2 and BG3 is determined by the voltage across R5, that is, VA-B=VBE1+VBE2, so as long as the size of R5 is adjusted, the purpose of adjusting the working current of BG2 and BG3 can be achieved. In actual adjustment, since the value of R5 is very small, a 100 ohm potentiometer can be used instead. Connect the ammeter in series between the collector of BG2 and EC. Adjust the potentiometer while observing the indication of the ammeter to make the current indication 5-10 mA.
It should be noted that when adjusting the current of VC and BG2, BG3, they will affect each other. After VC is adjusted, when adjusting IC2, IC3, VC will change again. Therefore, R1 must be adjusted again to make VC return to the value of EC/2. When adjusting R1, IC2, IC3 will change again, so it is necessary to adjust it repeatedly several times.