He made his own amplifier that is awful with no negative feedback. ALL audio amplifiers have negative feedback, but not the simple one he designed.
A simple regenerative circuit makes an extremely poor radio that produces a lot of noise. I think yours begins to oscillate when you turn up the volume control. Increase the value of R14 and decrease the value of R1, then it will have less positive feedback.
A real AM radio is a super heterodyne that has its input tuned, an RF amplifier with automatic gain control, an oscillator, a tuned mixer, an IF amplifier with 3 or 4 tuned transformer stages then a diode detector. It can feed an LM386 power amplifier.