New for 2008! All 660 litz coils are now wound on forms cut using a CNC machine. The prices remain the same.

After years of crystal radio research and hobnobbing with some of the real experts, I can now offer a large, efficient and very high Q coils that you can add to your crystal set project. These coils are intended for the very serious crystal radio hobbyist. If you have the ceramic insulated stator variable capacitors and the high performance diodes, you are ready for Überlitz Coils!

Each coil uses litz wire with 660 strands of #46 wire, nylon served made by the Kerrigan-Lewis Wire Co. There is a generous lead length for the connections. My coils are untapped for best high impedance operation. The best in sensitivity and selectivity can only be obtained in this manner.

This quality litz has been carefully wound on a 1/8 inch (3 mm) thick white HDPE (high density polyethylene) forms. The dimensions are 7 inches wide by 7-3/4 inches tall (17,75x19,7 cm) for the 240 µH and 6 inches wide and 6-3/4 inches tall (15,25x17,15 cm) for the 150 µH coil. There are three mounting holes in the bottom that will accept #8 hardware.

There are now several versions of the regular winding- Überlitz coils. The coils that are 240 µH are for detector coils. This will tune the entire band with a good 365 pF or higher capacitors. The maximum / minimum capacitance range ratio should be 11:1.

The 150 µH coils are for use in antenna tuning units using a dual gang variable capacitor. To tune the entire band, a 365 pF or higher is recommended. Two variable capacitors in this circuit gives you better sensitivity and selectivity control. Single coil radios can be made with this coil.

The new item are my contra wound coils. My contra coils have two windings that are wired in series or parallel depending on the section of the band you want to listen to. On the high range, much better performance is obtained due to the parallel nature increasing the number of strands in the coil. My dual coils are closely matched in inductance. It takes me longer to make one of these coils but it is worth it. A low loss D.P.D.T. switch is required for series / parallel switching. Please read the special contra coil instructions at the bottom of this page.

Don't guess what your coils might end up being. Use my crystal radio building experience and my Bavarian German roots to get the best in large litz coils. BTW, these coils will work great with your one tube DX radio.

Please go to my main ordering page and put yours on order.

                                Coil Price List
     Inductance  Winding     Use    Wire Size  Width  Price US$  Order
        240      Regular   Detector  660/46  7    inches   $ 99    U240-660
        150      Regular   Antenna   660/46  6    inches   $ 85    U150-660
   
        Custom   Contra    Either    660/46  7    inches   $109    UCXXX-660
           
          
        Inductances are nominal. The actual value will vary a little but
        they are close. The regular wound coils can be trimmed to suit
        your exact conditions. Design subject to change at any time. 
		
        Contra coils are custom wound. Prices good up to 250 µh values. 
   
         
         

When you build your crystal set with an Überlitz detector coil, the coil should be custom wound for optimum performance. The custom winding depends on the variable capacitor you intend to use. Referring to the diagram above, besides the coil and main tuning capacitor, a trimmer capacitor (up to 75 pf) should be used. Also, the radio internal capacitance should be considered. This tends to be around 20 pf in the high performance radios I have measured. You may determine your own value if you like.

The idea is to have a coil that will tune to the bottom of the band with the coil wired in series, and reach to over 1000 khz at the series high end. The parallel low end should have a 30 to 50 khz overlap with the series high end. Also, the dial spread should be as large as possible. I like at least 240 degrees across the band in the two halves added.

All this design centers around the variable capacitor you are going to use. I built a radio with as little as a 15 - 280 pf spread but it was difficult. A capacitor with a maximum value of 330 pf to 500 pf capacitor is recommended. The minimum capacitance should be in the 15 to 20 pf range.

Want to wind your own coils? I now have available professionally made forms for sale. These are CNC machine made forms. The material is High Density PolyEthylene (HDPE). The forms are 7 and 6 inches (17,75 and 15,25 cm) wide. The cost is $29.50 for each form (either size) or a pair for $49.50.