In Europe a lot of AM transmitters for medium wave have been switched off. When you want to listen to an old AM receiver a small AM modulator can help to fill the gap as your private radio station. Here is a first idea for such a small transmitter:
As RF source a 12 Mhz crystal and a CMOS IC HCF4060 is used. It provides a very stable square wave signal of 750 khz that is used as carrier signal.
The two transistors BC546 and BF245C are used to modulate the carrier with an incoming audio signal. Finally a small LC circuit provides some basic harmonics suppression. With 30cm wire as antenna it should be possible to receive the signal over a distance of about 1 meter.