Mystery Crystal Sets As School Projects
Eighteen Mystery crystal sets of this design were constructed by primary school students as a class project in the USA.
The secondary coil was wound on top of the primary to simplify coil winding for the children, and the variable condenser was made out of coke cans.
Michael Lee's Mystery Crystal Set
He is very pleased with the performance
Philip Miller Tate's Mystery Crystal Set From The UK
The first image shows the set 'in use'. The box is an old "Taylor's" presentation box for a bottle of vintage port (no, I never got to sample the port!) with a convenient sliding lid, rebuilt, stained, and varnished. The large tuning knob, incidentally, is one of the first 'collet' type knobs which grips the shaft concentrically rather than using a grub screw, manufactured by the British Electrical Resistance Company Ltd ('BERCO') prior to their patent on the design. It came to me in a collection of 'junk', in its original box.
The second view is of the interior with the lid slid back. The coil is wound on 66mm diameter down pipe. The variable capacitor is a 400pF + 300pF three-turn, with only the 300pF section in use. Diode and headphone capacitor (which, as other people have commented, seem superfluous) are mounted on the jack socket. The 'phones are Ericssons, probably 1930s or 1940s.
The final unit receives nine local and national stations by day, and DX by night (Germany, Holland, Sweden, Spain) with only a 20-foot aerial.
Mike Peebles' Mystery Crystal Set in Washington State, USA
I finished your set this evening (9th July 2000) and played with it a bit. I have two extremely powerful stations: 860 Khz and 1550 Khz. and they are very difficult to remove. At best attenuating them a little is about all I can do. The set seems to be very selective and I found better results with the ground removed.
It does work better with a "Catwhisker" type detector. I am not able to experiment with DXing due to the two overpowering stations, but I believe this set to be a great DXer. It has great volume and the selective mode is far the best as the broad mode is too broad for my conditions, here. Made the set so the fixed and catwhisker modes can be switched, and used all handmade brass parts. Made the detector handle in the drill press. Has an Alder base with a 1/8" plywood dial panel.
Had lots of fun building it and it works very well. Hope to see more projects from your side of the earth. Thanks for providing us so much fun!