Simple AM receiver schematic?
The diode really isn't necessary (transistor base-emitter junction is sufficient).
But there are a few flaws....


The antenna has no ground reference. So much of the detected voltage goes to the antenna, not to the piezo.
The piezo is an AC device, like a capacitor. It would be better to provide a DC path from emitter to ground.


The inductor may be hard-to-find. You might try substituting a large-value resistor (one Megohm or larger).







simulate this circuit &ndash; Schematic created using CircuitLab