There is an entire bunch of not very well known things going on with this circuit.
The K596 FET is from a capacitor microphone and has current of about 300 uA at gate voltage=0. If you use an ordinary FET you will need some negative bias, you can experiment with various LEDs between the source and ground.
Q3 acts as an upper cascode transistor, Q2 acts as a folded cascode transistor. An increase in current through the FET causes Q3 to conduct more, a decrease in the current through the FET causes Q2 to conduct more.
Q2 directs some of the FET signal to provide Armstrong oscillator type positive feedback.
Q3 directs some of the FET signal to a current mirror based AM detector.
The audio output may need some additional RF filtering before going to an audio amplifier and a supply rail decoupling capacitor would be good.
I'm just experimenting with this circuit in the AM band with good results, how it holds up at different frequencies I don't know. Anyway technically it seems good in terms of sustaining amplifier phase lag or lead, impedance matching etc. I don't have LTSpice at the moment to fully check. The built behavior seems fine.