Children made their kasa radio and enjoyed it.
The Kasa Radio (A Radio Made from Everday Items) Necessary Materials
Summary of Making the Kasa Radio
How to Use the Kasa Radio
Some Interesting Experiments
Replace the Germanium Diode with an LED
It is known that if you forward-bias an LED, it can be used as the rectifier in place of the germanium diode.
However, if you expose an ultra bright LED, such as OptoSupply OSHR3131P, to sunlight, it can be used as the rectifier without a battery.
The exposed LED generates an electric current by a photovoltaic effect.
LED is self-biased by the current and capacitance of a piezo-earphone.
Here is an improved circuit of sunlight exposed LED radio.
Heated silicon diode rectifier
Also, a heated Si diode (e.g. 1N4148, 1S2076A, etc.) can be used as the rectifier.
The V-I (voltage-current) curve for the diode is shifted to the left by an increase in temperature.
At a high temperature, the curves for the Si diodes are approximate to those of room temperature Ge diodes.