simple three-IC superheterodyne radio to receive stations in the 4.5- to 10-MHz range
http://www.edn.com/archives/1996/080196/16di6.htm
It is basically a diode detector followed by a high-gain audio amplifier. It picks up everything at once!
http://www.techlib.com/electronics/allband.htm
Uses 74HC4053 as a mixer and is virtually immune to AM SWBCI. Unique 74HC86 XOR gate based heterodyned VFO, crystal oscillator and mixer.
http://www.qsl.net/kd1jv/dcrx.HTM
http://www.zen22142.zen.co.uk/Circuits/rf/amrec.html
http://www.web-ee.com/Schematics/Superhet/superhet.htm
http://www.web-ee.com/Schematics/Simple%20Superhet/simple_het.htm
a three stage receiver project which overcomes some of the limitations of this type of receiver, principally the provision of an rf amplifier ahead of the detector.
http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm
very simple AM radio
http://www.aaroncake.net/circuits/radio.htm