The Progressive Crystal Set
This set is called a "progressive" set since you start with the basic unit and can get progressively more sophisticated by adding a trap and antenna matching network.
The prototype version uses a homemade vernier made from a CD and rubber grommet. The tapped transformer will match many different headset or speaker impedances. of plexiglass and poly-coated wood.
The tuning knob shaft is in a panel mount piece made for a 1/4" shaft. The threaded part of a an old potentiometer could be used, along with its 1/4 inch shaft.
Here is a rear view of the set. Notice the Bogen model T725 transformer.
Schematic of set.
Click for large view.
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