Complementary voltage switching class D power amplifier circuit

The complementary voltage switching class D power amplifier circuit is shown in the figure. Transistors VT1 and VT2 are both 3DA12.
    Among them, two same type (NPN) tubes are connected in series, and the VT of the body tube is 3DK41C.
A constant DC voltage VLr=12V is applied to the collector:
    the input circuit passes through the high-frequency transformer Tl, so that I...this tube V'I. 1 and VT2 obtain
the reverse square wave excitation voltage. Since the voltage applied to the input terminals of two series n¨ij journal (NPN) transistors
is large enough and opposite in phase, the two transistors are in a switching state and conduct alternately.
    The voltage across the loop is a square wave. The magnitude is equal to the DC power supply voltage V(Jc. k,
cJ form a high-Q series circuit to select the fundamental frequency. Therefore, this amplifier is called
a voltage switching class D amplifier.