Antique radio
An antique radio is a radio receiving set that is collectible because of its age and rarity. Types of antique radio. Morse receivers. The first radio receivers used a coherer and sounding board, and were only able to receive CW continuous wave (CW) transmissions, encoded with Morse code (wireless telegraphy). Later wireless telephony|transmission and reception of speech became possible, although Morse code transmission continued in use until the 1990s. All the following sections concern speech-capable radio, or wireless telephony. Early home-made sets. The idea of radio as entertainment took off in 1920, with the opening of  the first stations established specifically for broadcast to the public such as KDKA in Pittsburgh and WWJ in Detroit. More stations opened in cities across North America in the following years and radio ownership steadily gained in popularity. Radio sets from before 1920 are rarities, and are probably military artifacts. Sets made prior to approximately 1924 were usually made on wooden breadboards, in small cupboard style cabinets, or sometimes on an open sheet metal chassis. Homemade sets remained a strong sector of radio production until the early 1930s. Until then there were more homemade sets in use than commercial sets . Early sets used any of the following technologies: Crystal sets. These basic radios used no battery, had no amplification and could operate only high-impedance headphones. They would receive only very strong signals from a local station. They were popular among the less wealthy due to their low build cost and zero run cost. Crystal sets had minimal ability to separate stations, and where more than one high power station was present, inability to receive one without the other was a common problem. Some crystal set users added a carbon amplifier or a mechanical turntable amplifier to give enough output  to operate a speaker. Some even used a flame amplifier. Tuned radio frequency sets. Tuned radio frequency sets (TRF sets) were the most popular class of early radio, primarily because the Radio Corporation of America (RCA) had a monopoly on the superheterodyne circuit patents and it was more profitable for companies to jump into radio manufacturing TRF sets. These used several valves (tubes) to provide RF amplification, detection, and audio amplification. Early TRF sets only operated headphones, but by the mid-1920s it was more common to use additional amplification to power a loudspeaker, despite the expense. The sound quality produced  from "moving-iron" speakers used on such sets is sometimes described as torturous, although by the late 1920s the Kellogg-Rice dynamic (moving-coil) speaker had begun to find favor due to its superior sound-reproduction ability. Speakers widely used on TRF sets included: TRF sets used no regeneration, and were merely several stages (typically three) of tuned RF amplifiers in series feeding a detector tube which extracted the audio intelligence from the RF signal. TRF sets, depending on the number of stages they employed, could have poor-to-superb sensitivity (ability of the set to pick up faint signals ) and corresponding selectivity (ability to parse adjacent stations from one another). Audio reproduction quality of TRF sets was limited by the available loudspeakers. "High Fidelity" was not to become a radio marketing concept until the mid-1930s and was not realized until the advent of FM broadcasting. Reaction sets, also known as regenerative receivers, rely on positive feedback to achieve adequate gain. This approach provided high performance with a minimum number of expensive vacuum tubes, but these receivers tended to radiate RF interference in their immediate vicinity. Consequently, there was a significant amount of hostility by neighbors of "regen" set users  over maladjusted radios transmitting squealing noises and blocking reception on nearby properties. Early TRF sets had typically two or three tuning knobs and tube filament voltage-control rheostats, all of which had to be set correctly to receive a station. Later (late 1920s) TRF sets had ganged tuning (one knob was used to control all stage tuning capacitors simultaneously), AC house current operation, and eliminated the filament voltage adjustments. All of these changes greatly simplified operation and made radio a household appliance that even a small child could operate, instead of the highly skilled hobbyists of the brief preceding generation . Reaction sets also had the filament adjustment rheostats for each valve, and again settings had to be right to achieve reception. Superheterodyne receivers. In the era of early radio, only RCA and a select number of competing "prestige" radio manufacturers could afford to build a superheterodyne receiver (superhet). RCA had exclusive rights to the superheterodyne circuit patents and extracted high licensing fees from other companies who sought to build superhet sets. RCA also vigorously prosecuted patent infringers. This situation helped propel RCA to the forefront of radio manufacturers in the 1920s due to the higher efficiency of the superhet circuit-  a situation which lasted until the patents expired in the early 1930s, at which time a flood of low-cost superheterodyne receivers hit the market. Early (RCA-patent-era) superhets were often used with the relatively expensive moving coil speakers, which offer a quality of sound unavailable from moving iron speakers. Most post-1932 commercial radios were superhets, and this technology is still in widespread use in radio receivers today, implemented with transistors or integrated circuits. The advantages of superhets are: The disadvantages before about 1932 were: In general the technical and manufacturing advantages of the superhet ensured that the TRF  set became quickly obsolete once the patent restrictions on superhets were eliminated. Farm radios. Prior to the Rural Electrification Act of 1936, the vast majority of rural farms in America did not have electricity. Many rural areas of the Midwest and South did not receive commercial power until the 1960s. Until that point, special radios were made to run on DC power. The earliest so-called "farm radios" used the "A", "B", and "C" batteries typical of 1920s radio sets; these farm radios were identical to those used in cities. Somewhat later, farm radios were made to be run on  6 volts from a car or tractor battery, using an electromechanical vibrator to create a pulsating DC current that could be stepped up through a transformer to create the high voltage needed for the plates of the tubes- exactly as contemporary car radios did. Other farm radios were designed to run on 32 volts DC, from a bank of lead-acid storage batteries charged from a gas powered generator or a wind-charger. The 32-volt system could also power other specially made appliances as well as electric lights around the farm. Other farm radios, especially from the late 1930s  to the 1950s, reverted to using a large "A-B" dry cell that provided both 90 volts for the tube plates and 1.5 volts for the tube filaments, as did most tube-based portable radios of that era. Foxhole radios. World War 2 created widespread urgent need for radio communication, and foxhole sets were built by people without access to traditional radio parts. A foxhole radio is a simple crystal sets radio receiver cobbled together from whatever parts one could make (which were very few indeed) or scrounged from junked equipment. Such a set typically used salvaged domestic wiring for  an antenna, a double-edged safety-razor blade and pencil lead (or bent safety-pin) for a detector, and a tin can, magnet and some wire for an earpiece. Razor blades of the era were chemically coated ("blued") and this coating could function as a diode, in the same way that a galena-catwhisker detector operates. Wooden consoles. The console radio was the center piece of household entertainment in the era of radio. They were big and expensive, costing hundreds of dollars in the late 1930s and were often coupled with a phonograph. Tending to be a major acquisition for  a middle-class family, these large radios were usually placed in living rooms. Most early console radios were tall and narrow, but as the years went on they got shorter and wider in accordance with the Art Deco design precepts which had become popular Consumer console radios were made by RCA, Philco, General Electric, Montgomery Ward (under the Airline brand name), Sears (under the Silvertone brand name), Westinghouse, Motorola, Zenith and others. Brands such as Zenith made a few high priced models ("Stratosphere") mainly produced moderately priced radios Some premium makers such as E. H. Scott and Silver-Marshall started  around $500–$800 range in the 1930s and 1940s. Table-top wood-cased radios. Table top radios came in many forms: Bakelite. The availability of the first mass-produced plastic Bakelite allowed designers much more creativity in cabinet styling, and significantly reduced costs. However, Bakelite is a very brittle plastic, and dropping a radio could easily crack or break the case. Bakelite is a brown-black mouldable thermosetting plastic, and is still used in some products today. In the 1930s some radios were manufactured using Catalin, which is the phenolic resin component of bakelite, with no organic filler added, but  nearly all historic bakelite radios are the standard black-brown bakelite color. Bakelite as used for radio cabinets was traditionally brown, and this color came from the ground walnut shell flour added to the thermosetting phenolic resin as an extender and strengthening agent. Plastic era. The affordability of more modern light coloured thermoplastics in the 1950s made brighter designs practical. Some of these thermoplastics are slightly translucent. Early transistor radios. The invention of the transistor made it possible to produce very small portable radios that did not need a warm-up time, and ran on much smaller batteries. They were  convenient, though the prices were initially high and the sound quality of early models was not nearly as good as tube radios. Later models equalled or surpassed tube models in audio quality. Transistors also made it possible to manufacture portable FM radios, which was impractical using tubes. Transistor radios were available in many sizes from console to table-top to matchbox. Transistors are still used in today's radios, though the integrated circuit containing a large number of transistors has surpassed the use of singly packed transistors for the majority of radio circuitry. Transistor radios appeared on the market in  1954, but at a high price. By the 1960s, reduced prices and an increase in desire for portability made them very popular. There was something of a marketing war over the number of transistors sets contained, with many models named after this number. Some sets even had non-functional reject transistors soldered to the circuit board, doing absolutely nothing, so the sales pitch could advertise a higher number of transistors. Vacuum tube radios and early transistor radios were hand assembled. Today radios are designed with the assistance of computers and manufactured with much greater use of machinery. Today's radios  are usually uneconomical to repair because mass production and technological improvements in numerous areas have made them so inexpensive to buy, while the cost of human labor and workshop overheads have increased greatly in comparison. Car radios. The earliest car radios appeared not long after commercial radio broadcasts commenced, but were experimental only. They were expensive, required a large aerial, reception was inconsistent, and they required adjustment in use, which was not very practical. By the early 1930s most car radios, no longer experimental, were superheterodynes and used a vibrator power supply to step up the low voltage to high  voltage ("B+" voltage of anywhere from 90 to 250 volts) for the vacuum tubes. Vibrators are relatively unreliable as electromechanical components of limited life, buzz audibly, and produce radio interference. A few radios used a bulkier and more expensive motor-generator or motor-alternator set called a "dynamotor" that spun a high-voltage generator or alternator using a 6 or 12V DC motor. Filaments were powered using 6V and later 12V DC power from the vehicle's electrical system directly. With the introduction of transistors, the earlier ones suitable for audio frequencies only, car radios were valve sets with a  transistor output stage; makers promoted them as transistor sets. Some historic car radios badged as transistorised are in reality of this type. All-transistor sets eventually replaced sets with vacuum tube after transistor technology improved and prices fell significantly. Chrysler and Philco announced an all-transistor car radio in the April 28, 1955, edition of the Wall Street Journal. This Philco car radio model was the first tubeless auto set in history to be developed and produced. It was a $150 option for 1956 Chrysler and Imperial cars and hit the showroom floor on October 21, 1955. Warm-up  time. Most valve sets needed a few seconds for the valves to heat up, though there were exceptions. Warm-up times changed as valves went through several generations of design. Use of vintage radios. Line-operated commercial sets. Using vintage radios generally requires inspection and repair or refurbishment before they can be safely operated. In most cases, at least the power supply section of line-operated radios must be refurbished to prevent damage to other components, but it can be assumed that most of the vintage capacitors are electrically "leaky" and that the electrolytic capacitors in the power supply have  either lost capacity (leading to excess "hum") or shorted (potentially causing a damaging or fire-inducing short-circuit). In their original state, they complied only with the limited safety standards of the time, and almost none used fuses. AC-operated radios using power transformers require repair and refurbishment of the power supply section before operation, as any failures are likely to stress or damage the power transformer, necessitating a costly repair. AC/DC sets using a no power transformer may be either "curtain burners" using a resistance cord to drop the line voltage, or warm/hot chassis radios using a  series-string filament circuit where the voltages add up to the line voltage. They were named "AC/DC" because they operated on either AC or DC line voltage, which was not possible with a transformer-based set. Either type of AC/DC radio can present the "hot" line of the line voltage on the chassis of the radio ("hot chassis") or isolated from the chassis by a single capacitor ("warm chassis"). This presents a safety problem, as depending on the direction of the non-polarized plug, the hot side of the line voltage can be connected directly to all the  metal parts of the radio any time it is plugged in, regardless of whether it is powered on or not. Proper repair or refurbishment requires an isolation transformer to remove the live connection, and care should be taken to never touch any metal part of the radio (chassis mounting screws, bare control shafts, etc.) when the radio is plugged in. Many radios with a hot chassis use interlocks on the back to ensure that the line is disconnected before the rear can be accessed for tube replacement. Later transistor-based AC table radios typically used power transformers and operate safely , but with likely hum from failed electrolytic capacitors in the power supply, and likely low volume from other failed electrolytic coupling capacitors. There were a few early transistor table radios using "hot chassis" principles, but these are very rare. Early battery-operated sets. The minority of all-in-one commercial ac mains sets that appeared in the 1930s are plug & play. Such sets should be checked for the possible existence of live metalwork accessible to the user, and a general safety check is advisable. Many will need a repair of some sort. However other not all-in-one types of  pre-Depression-era radio are more demanding to put into service, being a long way from plug & play. Setting up such radios requires a bit of electronics skill. There are several issues with them: Sound quality. The sound quality of antique radios depends on the technologies used in the set. The type of speaker is the main differentiator, with mains or battery also making a significant difference. All valve sets produce 2nd harmonic distortion, which is fairly euphonic. Some also produce significant 3rd harmonic distortion, which is less pleasant to the ear. Discussion is often heard about the distortion of  triode versus pentode valves, and single ended versus push pull, which affect the types of distortion produced, but these issues seem to be secondary in practice to the ones discussed in this article, and are already well covered in other articles. Loudspeaker types. Moving iron speaker. Homemade pre-war sets usually used some form of moving iron speaker, usually horn or cone loaded, and occasionally disc loaded. The sound quality of such radios is generally unimportant, since almost any defect in the audio signal will be masked by the butchery visited upon it by the loudspeaker. The question of sound  quality is heavily dominated by the speaker in these cases. Moving iron speakers suffer the following defects: The sound of moving iron speakers has a strong unmistakable character. They were far from faithful in their reproduction of audio, and their technical specifications were poorly controlled. An example of this is their electrical impedance, which varied across the audio spectrum by a ratio of more than 100:1. It is not unusual for an electronics student, on hearing some of the specs of these devices, to conclude that they could not have been capable of reproducing speech. Yet they do, and with  a sound that can not be mistaken for anything else. Inductor dynamic speaker. These enjoyed brief success but were quickly eclipsed by moving coil speakers. The Inductor Dynamic Speaker solved the worst problems of earlier moving iron types, and provided a relatively pleasant listening experience. The main defect of ID speakers was poor treble response, giving them a characteristic dull drone. Moving coil speaker. These speakers were mostly of sufficient quality that the radio's characteristics become significant. Transformer coupled sets suffered loss of bass & reduced treble, grid leak sets where rf and af were amplified by the same valve  gave some nonlinearity, and output stages always provided a little more non-linearity. However the quality of a moving coil equipped set can be pleasant, and mistakable for a modern portable radio.