This circuit, of my own design, is my current winner for sensitivity
and selectivity. Performance is truly astonshing. When used as a
receiver connected to a fine sound system it outperforms several
commercial AM radios that I have tested for sound quality.
Pay especial attention to the polarity of the coils when building
this set. They are wound clockwise from top to bottom looking down on
the coil. All the wire is 24 AWG.
It is also important to use 500pF variables to tune the entire
broadcast band. The more common 365pF units will work but will not tune
the entire band. Note that the rotor sides of the caps go to ground
(green clip in prototype). The stators are the ones with lugs attached
(white, red, and yellow alligator clips in prototype picture).
I added a level control to audio output because the output was
too loud on most stations using the low level mag input on a receiver,
causing distortion. The pot can adjust the level for best fidelity and
pulls in almost any local station. An alternative is to use a high
level input on the receiver. In that case, omit the pot and P2.
Here is the
prototype. The coil was wound with my coil winder, of course.
Now some photos: