History of Radio and Home Electricity in the Early 20th Century

This Instructable is about the history of radio and electrical wiring technology in our homes during the Early 20th Century (1900-1949). Today's kids of the wireless age take their technology for granted because they have no reminders of the past. To fill that gap, this Instructable describes constructing two demonstration boards that show the progress of household radio and electric wiring technology in the Early 20th Century.

The first demonstration board covers three generations of radio advancement in this period: a crystal set, a vacuum tube radio, and a transistor radio. While more than twenty years passed before the advent of stereo, digital recording, and internet streaming, these boards show the early advancements that enabled these later technologies.

The second demonstration board covers three important generations of advancements in home electrical wiring: knob and tube, Romex, and LED. Most people never see this technology because it exists behind our walls. While electrical wiring is usually viewed as mundane, none of today's electrical devices could operate without it. This board shows the technical advancements in the Early 20th Century that facilitate today's advanced wiring and lighting technology.

These boards demonstrate technical progress, but they are not meant to be functional. Vintage radios required antennas that were inconveniently long, and electrical wiring needs potentially hazardous electrical power. Therefore, this Instructable is aimed more at teachers in need of demonstrations to facilitate classroom discussions, rather than at hobbyist Makers. The one exception is the crystal radio construction. It is described in detail and can be constructed using currently available components, allowing anyone to build it.

Crystal Radio

1. An empty Oatmeal "tube" container (can also be larger/smaller cardboard or PVC tube)
2. 50 feet of 24-26 AWG enameled coated copper wire
3. Cat Whisker detector with a galena crystal (if unavailable, use a 1N34 or 1N48 diode)
4. 365 uf variable tuning condenser
5. 100K resistor
6. Fahnestock spring clips to attach antenna, ground wires, and earphone connections (can be screws)
7. High impedance crystal earphone
8. A (long) outside antenna wire (~50')

Tube Radio

1. Vintage vacuum tube: #30, or equivalent
2. 200pf ceramic capacitor
3. .001uf ceramic capacitor
4. 365uf variable tuning condenser
5. 2 meg 1/4-1/2 watt resistor
6. 5 mH RF choke
7. 60-turn coil of #26 AWG enameled coated copper wire on a 3-inch form (can be PVC pipe)
8. 30-turn coil of #26 AWG enameled coated copper wire on a smaller form (toilet paper tube) placed inside the above coil
9. Antenna wire

Transistor Radio

1. Iron ferrate loopstick antenna coil
2. Variable tuning condenser
3. 1N34 germanium crystal detector (also IN60): germanium diodes vs. silicon diodes are more sensitive
4. PNP transistor (a modern version is a 2N2222)
5. 1.5-volt battery (AAA or AA)
6. .01 and .001uf disc condensers
7. Earphone

Electrical Wiring

1. Vintage ceramic knob and tube insulators, knife switch, ceramic plug & sockets, vintage light bulb
2. Romex electric wire, toggle switch, 3-prong grounded socket, and incandescent light bulb
3. Touch sensor, battery, and LED.

Two mounting boards of thin plywood or foam core, about 12" square to mount the two demonstration boards. When complete they can be hung on the wall, like picture frames, for convenient viewing.

Basic electronic assembly tools, including a soldering iron, diagonal pliers, etc.

Suggestions for suppliers of vintage components beyond Amazon and eBay are given in the last section

Marconi demonstrated the first experimental transmission of radio waves before the 20th Century, in 1897. Early transmitters used crude spark gaps and could only send basic on-off Morse code signals over short distances. Refinements in the Early 20th Century soon led to the first over-the-horizon transmission across the Atlantic Ocean in 1902 to a receiving station he built in Wellfleet, Massachusetts. Although experimental stations transmitting voice signals existed around 1910, the first commercial radio station with voice, KDKA, did not start broadcasting until 1920 in Pittsburgh, Pennsylvania.

Radio receivers capture invisible electromagnetic waves in an antenna wire and then detect the information contained in these signals. Significant advancements were made in radio technology in the early 20th century. Three early stages are illustrated on the board above: crystal radios, tube radios, and, for comparison, later transistor radios.

The earliest experimental radio receivers were invented around 1897. They were called crystal set radios because they used a small piece of galena mineral as a detector for radio signals, but they were crude and unreliable. The first practical crystal sets were developed in 1902. They were actually very simple and made with a few inexpensive parts, including a wire coil, a tuning condenser, a crystal detector, a resistor, and an earphone.

Early plans were published in a free booklet available from the U.S. Bureau of Standards to build simple, homemade crystal sets for $5 to $15. The the goal was to encourage the spread of the new technology. As a result, it quickly became a popular hobby. My dad told me stories about how he followed these plans to make several crystal radios when he was a kid around 1920. That was truly the beginning of the DIY movement and later influenced my own career.

The construction shown below utilizes historically accurate components, but the design is highly flexible and can be easily adapted with components available today. If you don't build anything else in this Instructable, give this one a try! You'll be surprised when you first hear music in your earphones from this simple device. I still remember my first experience after making one when I was about 10 years old. A completed crystal radio, along with its corresponding schematic diagram, is shown above.

The classic coil was traditionally wound on an empty cardboard Oatmeal container, which was available in most homes at the time. But almost any cardboard or plastic tube, including a mailing or toilet paper tube with a similar diameter, can be used. A trick to help wind the coil is to punch two small holes about 1/4 inch apart, toward the end of the cardboard tube. Then, loop the end of the copper wire through the two holes to anchor one end, leaving about 6-12" of unwound wire for one end of the coil connection. Then slowly wind the coil, counting the turns as you go. Tension the wire as you go and keep the windings close together to make a neatly wound coil. When you have approximately 100 turns, anchor the wire temporarily with masking tape and cut off about another foot of unwound wire. Carefully poke two more nail holes at the end of the coil and repeat the same looping motion to hold the coil tight after removing the tape. An example is shown in the pictures above.

Mount the variable tuning condenser next to the coil, then mount the cat whisker detector to the right of the condenser. Next, place two Fahnestock clips approximately one inch apart on the left side of the coil to connect the antenna and ground, and two more clips on the far right side to connect the earphone. Fahnestock clips are clever little spring wire connectors used by hobbyists in that era and shown in the picture above. If unavailable, you can use a small wood screw and just wrap the wire around it for a substitute.

Then, follow the wiring diagram, which involves connecting a wire from the antenna clip to the coil and one side of the tuning condenser, then to one side of the detector, and finally to the top earphone clip. Another wire from the ground clip on the left, to the coil, and then the other side of the condenser, and over to the bottom earphone clip. Finally, connect the resistor between the two earphone clips and connect the earphone wires to the clips.

The popular vintage detector was a small galena crystal that was probed by a tiny wire in an ingenious adjustable mount, called a cat whisker. Slightly later, a more convenient innovation was a tiny crystal cast inside a small ceramic tube with connecting wires. The most common was called a 1N34 diode. Later versions, more available now, were made even smaller and contained in a small glass tube. All three versions can be used and are shown in the picture above. If you get a modern diode, look for a germanium versus silicon type, as they will be much more sensitive. The circuit drawing is simplified with using available fixed value components just as an illustration of the wire connections.

Finally, the annoying part of these early radios is that you need to run a wire outside that is approximately 25-50 feet long for the antenna. You will probably have to string it under a closed window to get it inside your house. It doesn't have to be high, but make sure it doesn't touch the ground, and also keep it away from any source of electricity. Then you need to run another wire for the ground connection to a water pipe or a metal stake pounded in the ground.

All this may seem a little magical compared to pushing a button on your TV remote or iPhone, but your crystal radio is going to "detect" electromagnetic radio wave signals sent out by radio stations that appear as a varying voltage between the antenna wire and the gound wire and you will hear it in your earphone.

Second-generation radios using vacuum tubes started appearing around 1915-1920. Tubes had the advantage of amplification and, in some designs, negative feedback, both of which made the radio more sensitive than the earlier crystal sets. This enabled the use of much smaller/shorter antennas. They also did not require the annoying adjustment of the cat whisker on the galena crystal, as the vacuum tube could also act as a diode detector. Tube radios have the disadvantage of requiring a power supply, making their construction today more difficult.

Since vintage vacuum tubes can be expensive, the construction shown here is primarily for illustrative purposes. But if you can obtain a tube and tube socket, the construction is a straightforward extension of the crystal set basics. There are two coils: one is connected to the antenna and ground, and the other is connected to the tuning capacitor, just like in a crystal set. A second, smaller coil is connected to the output of the tube and fed back by to the tube. The smaller coil is placed inside the larger one, as shown in the diagram. The construction shown here utilizes a vintage double coil, allowing the inner coil to be adjusted to change sensitivity. Similar coils are available from the sources listed, but you can also create your own two-coil version using a smaller tube, such as a toilet paper tube, to form the smaller coil. This can be inserted inside the larger Oatmeal box coil you made for the crystal set.

There is also a small coil, called an RF choke, that only allows audio to go to the earphone. Although these components are much less common than for the basic crystal set, they are easily available from sources listed at the end of this Instructable. If unavailable, you can substitute a .01 ufd ceramic capacitor.

Later advancements added more vacuum tubes to amplify the sound, allowing it to drive a loudspeaker and eliminating the need for earphones. Two later advancements were the superheterodyne and FM receiver designs, which added complexity but improved sensitivity and sound quality. For those interested in learning more about regenerative receivers, references are provided at the end.

The first transistor radios appeared on the market in 1954. Their major advantage was portability, sensitivity, and not needing bulky power supplies. Even the first versions were small enough to fit in the palm of your hand, could run on small, lightweight batteries, and did not require an external antenna or ground connection. The reconstruction example shown here is the simplest design, featuring only one hybrid transistor device and a crystal diode. However, this time, it can utilize the later generation of diodes with two wires, instead of the awkward cat whisker detector. The large wire coil is replaced by a much smaller coil that uses an iron "ferrite" bar to increase performance, and a miniaturized variable tuning condenser replaces the bulky metal plate condenser. They are connected in parallel to form a tuned circuit, just as in the previous designs.

These are all significant technical improvements that enabled more compact components. A simple one-transistor amplifier replaces the simple one-tube amplifier stage. Although not used here, the same approach of using a second coil to add regenerative amplification could also be employed in more advanced designs. The transistor used here only requires a small 1.4-volt AA battery for power.

Just like its tube ancestor, the basic one-transistor design can be significantly enhanced by adding transistor stages to increase sensitivity, amplification for a speaker, and later FM and stereo. However, an important point is that the improvement of this basic one-transistor design was only possible because it relied on reusing the technology from the earlier tube radio design theory.

Radio circuits may seem a bit magical compared to simply pushing a button on your TV remote or iPhone. However, technically, the antenna receives numerous transmitted electromagnetic radio wave signals sent out by radio stations, which appear as a varying voltage between the antenna wire and the ground wire. The desired station's signal is then sorted out, and the audible signal is detected and translated into sound for listening. Examining the three generations of radios reveals that this process is done by the same common elements.

1. A coil that is connected in parallel to a variable condenser at the front end. This combination is called a resonant circuit. It enables the radio to selectively tune in to the frequency of specific stations.
2. A detector that filters out the audio signal from the radio signal transmitted from the radio station.
3. An audio output that translates the audio signal into an audible sound that the listener can hear.
4. This can be an earphone the user an put to his ear to listen
5. An amplifier stage enhances the audio signal level to drive a loudspeaker for listening.

Thomas Edison demonstrated the first American home powered by experimental electrical power in 1882. However, there were unsettled technical debates between Edison and Tesla regarding the most efficient way to distribute power across an entire city. As a result, it took years before city-wide distribution was perfected and installed. Many American homes continued to rely on older candles and gas lamps for illumination for many years. By 1925, only half of American homes had access to electric power. By 1945, 85 percent of American homes were powered by electricity, with virtually all homes, including those in rural areas, finally having electricity by 1960.

Even after home electricity was available, it still took years to refine the best way to run wires through our homes to provide power for lighting and appliances. The demonstration board below illustrates the evolution over three distinct periods in the Early 20th Century. First, was early knob and tube wiring, between about 1880 to 1930. Although that wasn't replaced all at once, a second major type of wiring, known as Romex, became common around 1930. Romex had significant advantages in terms of installation convenience and safety. The third innovation is still ongoing, related to the availability of lower-voltage LED lighting. As with knob and tube, this is not an instant transition, but rather a gradual shift into new lighting innovations today.

Between 1880 and approximately 1930, the first type of home electrical wiring was known as knob-and-tube wiring. It consisted of a pair of single, twisted copper wires with thread-wrapped, natural rubber insulation. They were color-coded as a black "hot" wire and a white "neutral" wire. These ran in parallel, separated by a few inches within walls and ceilings. They were supported by porcelain knob insulators and protected by hollow porcelain tubes when they passed through walls. The entire system involved extensive drilling, nailing, and wire splicing, creating hidden safety hazards throughout the home. The early natural rubber insulation deteriorated after about 20 years, leaving any remaining knob and tube wiring extremely hazardous.

The knob and tube demonstration shown above features two vintage, cotton covered, 14-gauge twisted wires entering from the left through two white ceramic insulating tubes that pass through a simulated wall stud. One wire connects to a knife switch, a metal lever that rotates to open a connection to an output wire linking to one side of a ceramic two-prong light socket. The other input wire passes through the ceramic tube to a vintage fuse in a ceramic socket, and connects from the other side of the fuse to the second terminal on the two-prong socket. A vintage two-wire plug is inserted into the socket. These wires connect with a two-conductor lamp cord that links the plug to a light bulb socket with a vintage filament light bulb. At that stage, light bulbs used Edison's invention of a thin, carbonized thread filament. Because these early light bulbs were not as bright as later tungsten bulbs, the glass shell was left clear to let more light through.

In the 1930s, Romex cable, with stable synthetic rubber insulation replaced the early natural rubber-covered knob and tube wiring. The hot wire ran beside the neutral wire in a single cable, greatly reducing installation time and labor. In 1965, a bare copper ground wire was added as a third "ground" wire in the same cable for improved safety. This made Romex wiring inexpensive, easy to install, and safe over time.

The Romex demonstration board has a single Romex cable entering on the left side. After a couple of inches, the outer cover of the cable splits open to expose the three wires inside. The black hot wire connects to a common light switch, which is typically hidden behind a wall cover. The uninsullated copper ground wire also connects to the switch. A black hot wire then connects between the switch and a three prong wall plug. The white neutral wire connects directly directly to the plug. A plug with a light cord then connects to a light socket with a more modern tungsten filament, frosted light bulb.

LEDs were invented a long time ago, but the first commercially viable, inexpensive versions were not available until about 1962. This initiated a gradual transition to LEDs, accelerated by improvements in efficiency and the development of blue LEDs around 2010, which enabled brighter white LEDs.

The LED construction is a very simple circuit consisting of a 9-volt battery, a 330-ohm resistor, an LED, and a touch switch. A simple TinkerCad schematic is shown. The circular component shown is a touch-switch assembly, not a button battery.

Although LEDs became practical later in the 20th century, they are included on this Early 20th Century board to illustrate how the technology continued to evolve throughout the century.

Component Sources

Vintage parts are available with some searching. Start with the sources below, but also check on eBay and Amazon-

https://www.mikeselectronicparts.com/product-category/components/

https://unitednuclear.com/crystal-radios-parts-c-27_98/

https://www.mikeselectronicparts.com/product/1n60/

https://www.tubesandmore.com/products/diode-1n34a-germanium

http://www.xtalman.com/detectors.html

https://antiqueradiosandparts.com/index.php?route=product/product&product_id=1868

Circuit Examples

https://www.circuitbasics.com/what-are-am-radios/

https://techlib.com/electronics/reflex.htm

https://www.geojohn.org/Radios/MyRadios/FirstRadio/FirstRadio.html

Crystal Radios: https://techlib.com/electronics/crystal.html

Technical Articles

https://en.wikipedia.org/wiki/Crystal_radio

https://www.electronics-notes.com/articles/history/radio-receivers/cats-whisker-crystal-detector.php

https://www.computerhistory.org/siliconengine/semiconductor-rectifiers-patented-as-cats-whisker-detectors/