DC coupling circuit a that raises the base potential of VT2

.DC coupling circuit a that raises the base potential of VT2

In order to enable the two-stage DC coupling circuit to amplify normally, the base potential of the VT2 tube must be raised. The figure shows
a practical circuit for raising the base potential of the VT2 tube. Figure (a) shows that the emitter of VT2 is connected to a resistor RaZ. Although this method raises the base
potential so that both VT1 and vr2 can amplify normally, the second-stage voltage amplification factor is seriously reduced.
    In order to raise the base potential without reducing the amplification factor of VT2 too much, Re2 is replaced with a voltage regulator tube D; as
shown in Figure 1-41 (b). The function of the resistor R in the figure is a current-limiting resistor to ensure that the voltage regulator tube works in the voltage stabilization zone.