IF amplification and detection circuit in AM radio

Shown is the IF amplification and detection circuit of an AM radio . The intermediate frequency signal output from the mixer of the mixing stage
is added to the base of the intermediate frequency transistor VT4 after passing through the intermediate frequency transformer Ti. The collector load of VT4 is the primary winding of the intermediate frequency transformer T2. The primary winding
is connected in parallel with the 200 p capacitor . The resonant circuit resonates at 465 kHz. The secondary of T2 is connected to the base of the intermediate frequency amplifier tube VT5. The intermediate frequency
signal amplified by VT5 is then sent to the detection circuit through the intermediate frequency transformer T3 . The detection diode VD4 modulates the audio signal on the intermediate frequency carrier. Take it out and send it to the audio power amplifier. At the same time, it forms an automatic gain control signal through the resistor 12kn and adds it to the base bias of VT4.