75 years ago, the 1939 Allied Radio catalog carried these two kits. The “One Tube Flashlight Set” sold for $4.45, and included everything (tube, batteries, and coils) with the exception of the headphones, which started in the same catalog for 66 cents. The “Hurricane Receiver” sold for $3.85, but in addition to the headphones, also required a 6J7 and a 6F6 tube, which sold for 77 cents each.

Both sets ran on 6 volts. The one-tube “flashlight” set tuned shortwave, 18 to 200 meters, with four plug-in coils.

Both of these sets are regenerative receivers, and originated as construction articles in Popular Mechanics. The “Flashlight” set originated in the April 1938 issue, where it was billed as a “one-tube DX short-wave set” that ran on flashlight batteries, hence the name.

The “hurricane set” was featured in the February 1937 issue, which stated:

The primary idea behind the design is to provide a simple, rugged portable receiver that will work from a 6-volt storage battery, or a few dry cells, when other sources of power fail. When floods, hurricanes or other natural catastrophes occur and all ordinary means of communication go out, it is satisfying, and sometimes vitally important, to be able to learn from outside radio stations just what is going on. As a portable knockabout set, it also has other useful applications in the home, boat or camp.

The article promises that with six volts, the hurricane set with a 25-foot antenna should be sufficient for satisfactory reception of medium or high-power stations within a range of about 500 miles.

Parts List for “Flashlight Set”

If you are interested in building a one-tube radio, the “flashlight set” would be a good starter, and you can use the Popular Mechanics article for all of the construction details. Some of the parts might be difficult to find. But all of them are available online. Some of the links below are rather expensive, so it’s best to find most of the parts locally. But if you’re missing one or two items, you can find them at the links below.

Some of the values shown here are not identical to those shown in the article, but all of them are close enough. The only effect of substituting parts is that the tuning range of the radio will vary, depending on the exact dimensions of the coil, and the value of the tuning capacitor. Therefore, you’ll have to experiment a bit to figure out the exact tuning range of the radio once it’s done.

• Plug-in coil form
  • Plug-in Coil Forms at National RF
  • Plug-in coil forms at eBay
  • How to make plug-in coil forms
• Coil socket
  • 4-pin sockets at Antique Electronic Supply
• 30 ga. enameled wire
  • 30 ga. enamel wire at Amazon
  • 32-ga wire at Antique Electronic Supply
• 26 ga. enameled wire
  • 26 ga enamel wire at Amazon
  • 24-ga wire at Antique Electronic Supply
• 0-30 pF trimmer capacitor
  • 6pF – 80pF Trimmer Capacitor at Amazon
  • 34 pF trimmer capacitor at Jameco
    
  • 100 pF capacitor at Antique Electronic Supply
• .00014 uF (140 pF) variable capacitor
  • 365 pF capacitor at Antique Electronic Supply
  • 365 pF variable capacitor at Amazon
• 2 megohm resistor
  • 2 megohm resistor at Amazon
  • 1 Megohm Resistor at Jameco (use two in series)
    
    
• .0001 uF (10 pF) capacitor
  • 10 pF capacitor at Amazon
  • 10 pF capacitor at Jameco
    
    
• .0005 uF (50 pF) capacitor
  • 47 pF capacitor at Amazon
  • 47 pF capacitor at Jameco
    
    
• 200 kilohm variable resistor with switch
  • 500 kilohm variable resistor with switch at Jameco
    
  • 200K variable resistor at Amazon (without switch)
• RF Choke
  • RF choke at Amazon
  • RF choke at Jameco
    
    
• Type 49 tube
  • Type 49 Tube at Antique Electronic Supply
  • Type 49 Tube at eBay
• Tube socket
  • 5- pin Tube socket at Antique Electronic Supply
• Battery holder for one AA-cell battery
  • AA battery holder at Amazon
  • 1 AA cell holder at Jameco
    
    
• Battery holder for four AA-cell batteries
  • 4 AA battery holder at Amazon
  • 4 AA cell holder at Jameco
    
    
• Knobs
  • Knobs at Amazon
  • Knob at Jameco
    
    

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:

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A hundred years ago, the New York Sun for June 14, 1914 reported on the beginnings of the ARRL.

The article announces that “H.P. Maxim, who invented a silencer, hopes he has invented a communicator.” It outlines Maxim’s plan, which is generally what the ARRL accomplished soon thereafter. “The scheme is to get all the amateur wireless operators of the country, and they exist by the hundreds of thousands, interested in transmitting messages from coast to coast.” Maxim is quoted that the proposal is to “select those stations which are able to transmit from fifty to 100 miles and which are kept in perfect running order. And then all stations in the league which we are forming, to be known as the American Radio Relay League, will at a predetermined hour ‘listen in.’ That hour will probably be 7:30 each evening.”

Maxim points out that the intention is “to make this thing strictly amateur. The messages are to be relayed by courtesy. There will be no fees for receiving, delivering or relaying the messages. No money transaction of any kind is to be considered in connection with the league.”

He also notes that the Government is likely to be cooperative, since the relay proposal ensures that it “will make it unnecessary for an amateur to have a high powered set,” thus reducing interference.

The War slowed things down a bit, but the first “Transcon” test was successfully carried out in January, 1921, with a successful transcontinental message and reply in “two hours flat.”