I purchased a Crystal Radio Receiver Tonka Biplane on ebay. The pictures above are of Mine. The front round section in back of the propeller on the $15.00 kit has 8 wound coils on it with a diode in the rear. Your earphone's two wires connect on one coil and one of the other  7.  A coil is reserved for the antenna.

The conversion resembles a set of engines around the propeller and is cute but worth only about $30.00.

I saw the first one just before I went south for vacation but forgot to bid and it went for $27.00. When I returned I contacted the seller and he said he had another he kept for himself. I offered him $30.00. He put it on ebay and I ended up with the "Buy it Now" at $69.00. As a Crystal Receiver it was poor. I replaced the diode for a 1N34.

The seller has since sold one or two for $100.00. There is a difference on the coils in that he is using sewing spools to speed up the coil winding process. All in all the work  is not worth $100.00 and I recommend some other builders crystal sets that perform better.