Simply Symmetry
Crystal Radio for Casual Listening

    Having been inspired by a building contest, I built this radio in January and February 2001 for use in my workroom.  This is a crystal radio, using no outside power or batteries.  It derives its power from an outside antenna strung across the roof of my house.  It is quite sensitive, and it's efficient enough to drive a speaker directly from the earphone jack (that's right, no amplifier), which never fails to astound me.  With Walkman-style headphones, the fidelity is awesome, rivaling FM.  Who would think AM could sound so good!

    The radio is not the only thing that must be sensitive.  I must be, too.  Because my workroom is visible from the kitchen and living room, it's imperative that I include the SAF (Spousal Acceptance Factor) into my design specifications.  I chose to use all new parts in this project.  The wood is poplar, browned in the sun, covered in two coats of laquer, sanded and finished with paste wax.  You can glimpse a hint of its beauty in the images.
 
     Crystal Radio enthusiasts will note the striking absence of wiring.  Crystal radios are so simple, they are often built with exposed wiring.  I've seen enough of those I decided to try something that looked truly wireless.  It also helped me get close to my design goal of perfect symmetry. 
    The tube is a 12 inch section of 2" PVC pipe.  It was wound as one long coil, then cut in the middle.  (Sorry, I don't recall how many turns, but don't worry, it's not critical.)

     The wires to the slider bars run down internally through the wood supports.  All other wiring is on the underside of the wood base.  Wire emerges through small holes on the back sides of the variable capacitors and transformer.

     This view shows the antenna and ground binding posts at the back edge.  These are made of brass 10-32 screws and big knurled nuts.  The knurled nut bears down on a brass washer with its underside soldered to a 10-32 hex nut.  The wood is countersunk just enough to receive this hex nut so that when the screw is tighened from the bottom, it draws the nut/washer assembly tightly together.
    This view shows the slider assembly.  It uses square brass tubing with a strip of sheet brass soldered to it.  Note that the insulation has been removed from the 16 guage wire along the paths of the four sliders.  Note the red and black ink on the square tubing, marking the best slider positions.

    Barely visible at the bottom left and center are blue wires emerging from holes in the wood where they are soldered to the variable capacitor and the transformer.  Visible toward the top left is the brass knurled knob for the antenna connection.

Schematic

Update: 11-29-03

     I don't sell plans or instructions for this radio.  I built it a while back, and just about everything I know about it is featured on this web page.   If you want to build a radio like this, please read the text carefully.  If you have a hard time figuring out how to build yours from what is provided here, a crystal radio kit (available elsewhere) is probably a better choice for you.  Although this page is not intended to be used as a set of plans, it will have to suffice for do-it-yourselfers.  As an alternative, you might try building another type where I do provide instructions.

     One more thing: For this radio to work you MUST have a good antenna and ground connection.  Those are not covered here.  There are serious safety considerations involved.  You can find such infomation on the web.

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