Dual Litz Honeycomb Coils Crystal Radio

Posted on Feb 5, 2014

I hope that this crystal set is well received by all of you. My #62 radio combines the features of some of my earlier radios. It combines the one piece approach of my #48 set and the dual detector of one of my recent sets. The coil arrangement is a dual honeycomb coil, both mounted in an clear acrylic tube. So the coupling between the coils can be

Dual Litz Honeycomb Coils Crystal Radio
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adjusted, one of them is on a pivot and can be turned with a knob. If better selectivity is desired, the antenna coil can be rotated perpendicular to the main coil. This reduces the coupling between the coils, making a sharper signal peak. The coils are made with 165 strand, 46 gauge litz wire. This circuit will also work with a spider or space wound coils. The litz can have 44 gauge or 46 gauge conductors, depending on your budget. The three variable capacitors are dual gang types with 270 pf capacitance per section. These were obtained on the surplus market. I made them work very well in this radio. For example, the antenna input capacitor is one section at 270 pf. But at the top of the broadcast band, the adjustment can be a little touchy. By adding the second antenna terminal connection, which places the two sections in series, the maximum capacitance is cut in half. The capacitor next to it is used in parallel with the antenna coil. Both sections are tied in parallel for a maximum of 540 pf. The main detector tuning capacitor has one section directly connected across the tank coil, while the other section has 270 pf in series going to the coil. This gives a maximum capacitance of 400 pf. I am able to tune the entire band using the full range of the capacitor. The capacitors also have a 2:1 gear arrangement. This makes the tuning a little nicer. The main detector tuning has a 6:1 vernier drive connected to the 2:1...

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