Crystal Radio Coils by WØHII has ready made very high “Q” Crystal Radio Coils. They have a large variety of Litz wound Diamond-weave High “Q” Crystal Radio Coils from simple to very complex designs. Also custom Litz Wire coils made to your specifications.
Mike Peeble’s site “dedicated to the preservation of vintage radio building.” Peebles Originals contains a great selection of crystal radio kits and supplies as well as information on crystal radios, transistor radios, parts and kits.
Radio & Electronics Homebrew Hub is a great resource for ideas and projects dedicated to radio and electronics.
Star City Antique Radios and Test Equipment is a treasure of information on antique radios, tubes and test equipment.