Hello everyone, my name is Gordon McCall, and this is my crystal radio contest entry.
The appearance of this radio was inspired by all the 1920's crystal radios that I have seen in books and on various auction sites on the web. I have always liked the look of those old homebrews with the classic Atwater Kent knobs, home made tap selector switches, crystal detectors, and variocouplers. Way too cool!
Although none of the parts on this radio are vintage, many of them were fabricated from commonly available materials. The tap lugs are 12-24 brass screws with the heads turned down on a lathe. The switch arm is a piece of brass band, cut, drilled, and polished. The crystal detector stand is a piece of oak with polished brass hardware. The brass block the iron pyrite crystal is mounted on was made from the square end of a 1/2" pipe plug. The variocoupler was the most fun. The stator is 4" and the rotor is 3", both cores were dried in the oven and sealed with shellac. The 1/4" dowel shaft is center drilled for the rotor wires to exit out the back. Wooden spacers on the shaft are plugs cut with a 3/4" hole saw. The coil parameters are noted on the schematic. The 365pf variable capacitor was purchased from The Xtal Set Society. The front panel is a 6" by 11.5" piece of bakelite. The knobs and fahnstock clips were purchased from Antique Electronic Supply.
This radio performs quite well, better than I had expected anyway. So far I have logged 16 stations, including 9 DX stations and 3 low power locals (1-5kwatts). I use a single sound powered element, 150' antenna 30' up, and ground to a cold water pipe. Not bad for a simple circuit, the variocoupler really works well when adjusting sensitivity/selectivity and the ability to tune the antenna coil helps too. Special thanks go to John Davidson for coaching me through the coil design of variocouplers and variometers. This radio was a great learning experience for me. I hope you like looking at it as much as I enjoyed building it!
Gordon McCall (gm69camaro)