20W 40-500kHz power amplifier 01

 The 20W power amplifier circuit is shown in Figure 8-3. It consists of three parts: preamplifier stage, pusher stage and power stage. In order to reduce
the phase shift in the large loop feedback, PNP silicon tubes are used in both the preamplifier and pusher stages.
    The preamplifier stage consists of VT1 to form a single-stage common-emitter amplifier, and R6 introduces series negative feedback, which not only ensures the stability of the working point of this stage, but also
improves the input impedance. In this way, when adjusting the gain, the input impedance of this circuit can remain stable.
    The push stage is a direct coupling amplifier circuit composed of VT2 and VT3. The local negative feedback of each tube emitter and
the parallel voltage negative feedback composed of R11 and R13 ensure that The output signal of this stage
is coupled to the power amplifier stage by the transformer Tl with a constant p of the operating point and gain of this stage .