November 2, 2012

Project: Morton Salt Box Crystal Radio Repair (Part 1)

The October 2012 Frankenstorm Sandy brought rain, hail, snow, and high winds to Western Pennsylvania.  We decided to ride the storm out in the workshop to work on a father and son project - to return a crystal radio to use.

Frankenstorm Sandy October 29

We had built a crystal radio and revived an antique headset a few years ago as a school science fair project.  We built the crystal radio on a breadboard and included an air variable capacitor, a 1N34A germanium diode, and fahnestock clips.

Fahnestock Clip

The Fahnestock clip was invented in 1907 is a classic simple wire connector that is both perfectly functional and looks great in a crystal radio breadboard project.

The 1N34A germanium diode starts to conduct around 0.1 volts.  This makes it a very good choice for use as a detector in crystal radios.

Diode Schematic Symbol

The breadboard was repurposed from an old sports award.  We used a belt sander to remove the finish and engraving.  The process yielded a breadboard with an attractive two-tone appearance.  This is a great way to save money too.

The air variable capacitor has an adjustable capacitance from 0 to 365 Pf.  These are not easy to find.  This type of air variable capacitor is worth searching for since they work very well and dress up the appearance of the breadboard.  They can also be salvaged from vintage junk radios.  The more common miniature tuning capacitors will work fine, though they don't looks as nice in an open breadboard project.

Variable Capacitor Schematic Symbol
With the passage of time, our home-brew crystal radio had fallen into disrepair after being packed, stacked, and moved around.  A crystal radio on a bread board is somewhat delicate and so it was no surprise that it was in need of a little TLC.

A crystal radio is a relatively simple device which makes it easy to troubleshoot.  To repair it, KC2VSR reconnected a few broken connections with a soldering iron.  We attached the radio to an antenna and ground and we were able to tune in a couple of strong local stations.

Crystal Radio and Vintage Headphones

Crystal Radio

In part 2, we experiment with the radio.

Good DX and 73, NJ2X

© Michael W. Maher and NJ2X.COM, 2012. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Michael W. Maher and NJ2X.COM with appropriate and specific direction to the original content.