OTL power amplifier circuit in transistor radio b

In the circuit shown, the voltage at point A should be half of the power supply voltage, that is, Eo/2, so it is called the midpoint voltage. When the input signal
is in the positive half cycle, it is equivalent to adding a positive bias to VT6. VT6 is on and VT7 is off. The power supply voltage
charges the output capacitor C23 through VT6 and load B (speaker ), and the charging direction is left positive and right negative. During this period, B obtains a positive half-cycle current that changes sinusoidally from top to bottom
. When the input signal is in the negative half cycle, it is equivalent to adding a positive bias to VT7, VT7 is turned on, VT6 is turned off, c23 is given
a positive bias through VT7, and cz3 is discharged through VT7 and B. During this period, the load is discharged from bottom to top. A negative half-cycle current that changes sinusoidally. As a result, since
VT6 and VT7 work in turn, a complete sinusoidal output signal is formed on load B.
    In order to solve the problem of difficulty in pairing high-power complementary tubes in complementary symmetrical circuits and the need for large input power for high-power output, composite complementary symmetrical circuits
are used in many circuits .