Some of my earlier articles have shown crystal radios from the early days of radio. For example, I have an article with the history of the “foxhole radio” popularized by soldiers in World War 2. I also have a link to a 1922 newspaper article with details for building one. I also have links to this and this radio, both from 1914.
I received an e-mail from someone who wanted to build a crystal set with his grandson, who requested construction details and parts lists. There are many sites with such information, the best of which is The Xtal Set Society. You’ll also find some simple plans at this link. The first radio I made as a youth was basically identical to the fourth one shown on the bottom of the page. It requires only a board, a toilet paper tube, some enameled wire, a piece of metal to use as the slider, a diode, and the earphone.
It’s an interesting project, and as long as you have at least one fairly strong AM radio station nearby, almost any design you put together will work. If you have an antenna, ground, detector, and headphones, you’ll hear one or more stations as soon as you connect them together, in almost any configuration. Therefore, I can’t add much as far as construction details. Any of the sets you find on the internet should work just fine. It’s best to start with a simple set of plans and work your way up.
If you can’t find all of the parts locally, here are some tips on finding them.
The Detector
The heart of the crystal set is the detector. This is what changes the radio signals into an audio signal that you can hear. You have two options. First, you can simply buy a semiconductor diode. The most commonly used diode for a crystal set is the “1N34” or “1N34A”. You can buy it on Amazon at any of the following links. As you can see, they are quite inexpensive, and you can afford to stock up in order to make multiple sets.
The other “old style” detector is the “cat’s whisker” and crystal, from which the radio gets its name. The crystal is a piece of the mineral galena, which you can find at many hobby shops. At most science museums, you’ll find for sale samples of various minerals, and you’ll be able to find your piece of galena for a low price. (If you can’t find it locally, you can buy a chunk on Amazon.) To use it as the detector, you attach one wire to it firmly, perhaps with an alligator clip
or by firmly clamping it down. The other connection is a thin wire which makes contact only at one point. This other wire is called the “cat’s whisker”. You’ll need to rig up some kind of spring to keep the wire in contact with the crystal, and you’ll also need some method to move the wire around to look for a “sweet spot” on the crystal.
And for the mad scientist who wants a very unusual type of detector, you can make a detector using an open flame.
The headphones or earphone
The headphones or earphone will be the most difficult part to find. Unfortunately, most modern headphones will not work. The crystal set requires a “high impedance” headphone. Most modern headphones are “low impedance” and simply won’t work, unless perhaps the station you are listening to is extremely strong. Typically, a “high impedance” earphone or headphone will have an impedance of about 2000 ohms. Modern “low impedance” headphones, such as for a stereo or computer, are generally about 8 ohms. I’ve found that headphones with an impedance of 600 ohms generally work OK. So if you can find some of that approximate value, they will work. Old “language laboratory” headphones generally are about this value.
The most commonly used is an earphone like this one, which is available on Amazon:
As you can see, this one comes with a 3.5 mm plug. Since you’ll need to wire the earphone directly into your circuit, you have two choices. First, you can simply cut off the wire, or perhaps make the attachment with
alligator clips
.
If you want to keep the plug intact, you can purchase the matching jack:
This jack requires soldering, but it should work adequately by simply twisting the wires firmly around the lugs. If you want to invest in a soldering iron, they’re much cheaper than you probably expected. This one, for example, comes complete with the solder, as well as some other tools that might come in handy:
Another option is to use the low-impedance headphones but with a suitable transformer, such as this one:
One side will be marked “600 ohm” and the other side will be marked “8 ohm” (or similar terminology). Ignore the center pin on either side. Hook the other two terminals of the “600 ohm” side to the radio’s output, and hook the two outer terminals of the “8 ohm” side to the headphones. This will allow the headphones (which you can get at the dollar store) to work.
Wire
The best wire for winding the coil is enameled wire of about 24 gauge. This is also sometimes called “magnet wire”:
The enamel coating is insulation, so that the turns don’t short out. However, if you’re building a set with a slider, you’ll want to sand off the enamel at the top so that the slider can make contact with the wire.
For making connections between components, and for making the antenna, you’ll want flexible stranded wire such as this:
Capacitor
Some of the circuits will call for a capacitor, and some will show you how to make your own. (In older literature, the term “condenser” is used.) The simplest circuits don’t have one, and the exact value is not critical, and for most circuits a capacitor of 0.1 uF will be about right:
Another good source for ordering parts such as resistors and capacitors is Jameco Electronics. You can order online at.
Connectors and Hardware
Many of the early circuits will show “Fahnestock clips” for making connections. These certainly aren’t required, since you can simply twist the wires together. But if you want to give your crystal set a vintage look, they’re a nice touch. They’re also available at Amazon:
Most of the circuits you see are put together with wood screws, which you surely have lying around the house. If you don’t, you can go ahead and order an assortment such as this one:
If you need a piece of pine board to mount the whole thing, you can get that on Amazon as well:
Kits
If you want to bypass the whole procurement process and make a radio that works, but without the “retro” look, any of the following kits will fill the bill. They include everything you need along with directions:
