Antique radio - AbsoluteAstronomy.com

An antique radio is a radio

Radio

Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

receiving set that is collectible because of its age and rarity. Although collectors may differ on the cutoff dates, most would use 50 years old, or the pre-World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

Era, for vacuum tube

Vacuum tube

In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

sets and the first five years of transistor

Transistor

A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...

sets.

Morse only sets

The first radio receivers used a coherer and sounding board, and were only able to receive Morse code

Morse code

Morse code is a method of transmitting textual information as a series of on-off tones, lights, or clicks that can be directly understood by a skilled listener or observer without special equipment...

, and thump it out on the board. This type of transmission is called CW (Continuous wave

Continuous wave

A continuous wave or continuous waveform is an electromagnetic wave of constant amplitude and frequency; and in mathematical analysis, of infinite duration. Continuous wave is also the name given to an early method of radio transmission, in which a carrier wave is switched on and off...

) or wireless telegraphy. When wireless telephony (i.e. transmission & reception of speech) became possible, speech radio greatly improved the usability of radio communication. Despite this, the antiquated technology of morse code transmission

Continuous wave

continued to play an essential role in radio comms until the 1990s.

All other sections of this article concern speech capable radio, or wireless telephony.

Early home made sets

The idea of radio as entertainment took off in 1920, and radio ownership steadily gained in popularity as the years passed. Radio sets from before 1920 are rarities.

Pre-war sets were usually made on wooden breadboard

Breadboard

A breadboard is a construction base for prototyping of electronics. The term is commonly used to refer to solderless breadboard ....

s, in small cupboard style cabinets, or sometimes on an open sheet metal chassis. Homemade sets remained a strong sector of radio production until after the war. Until then there were more homemade sets in use than commercial sets.

Early sets used any of the following technologies:

Crystal set
Crystal set with carbon or mechanical amplifier
Basic Tuned Radio Frequency (TRF) Sets
Tuned radio frequency receiver
A tuned radio frequency receiver is a radio receiver that is usually composed of several tuned radio frequency amplifiers followed by circuits to detect and amplify the audio signal. Prevalent in the early 20th century, it can be difficult to operate because each stage must be individually tuned...
TRF Reaction Sets
Regenerative circuit
The regenerative circuit or "autodyne" allows an electronic signal to be amplified many times by the same vacuum tube or other active component such as a field effect transistor. It consists of an amplifying vacuum tube or transistor with its output connected to its input through a feedback...
Super-Regenerative Receiver
Superheterodyne Receiver
Superheterodyne receiver
In electronics, a superheterodyne receiver uses frequency mixing or heterodyning to convert a received signal to a fixed intermediate frequency, which can be more conveniently processed than the original radio carrier frequency...

Crystal sets

These basic radios used no battery

Battery (electricity)

An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

, had no amplification and could only operate headphones

Headphones

Headphones are a pair of small loudspeakers, or less commonly a single speaker, held close to a user's ears and connected to a signal source such as an audio amplifier, radio, CD player or portable Media Player. They are also known as stereophones, headsets or, colloquially, cans. The in-ear...

. They would only receive 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

Electronic selectivity

Selectivity is a measure of the performance of a radio receiver to respond only to the radio signal it is tuned to and reject other signals nearby in frequency, such as another broadcast on an adjacent channel....

, 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

Tuned radio frequency receiver

A tuned radio frequency receiver is a radio receiver that is usually composed of several tuned radio frequency amplifiers followed by circuits to detect and amplify the audio signal. Prevalent in the early 20th century, it can be difficult to operate because each stage must be individually tuned...

(TRF sets) were the most popular class of early radio

Radio

. These used one or more valve

Vacuum tube

s (tubes) to provide amplification

Amplifier

Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...

. Early TRF sets only operated headphones

Headphones

, but by the 1930s it was more common to use additional amplification to power a loudspeaker

Loudspeaker

A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...

, despite the expense.

The types of speakers in use at the time were crude by today's standards, and the sound quality produced from the speakers used on such sets is sometimes described as torturous. Speakers widely used on TRF

Tuned radio frequency receiver

sets included:

moving iron horn speakers
Moving iron speaker
The earliest loudspeakers for speech and music were moving iron speakers. These are still used today in some miniature speakers where small size and low cost count, and sound quality is unimportant. A moving iron speaker consists of a ferrous metal diaphragm or reed, and a permanent magnet. The...
moving iron cone speakers
Moving iron speaker
The earliest loudspeakers for speech and music were moving iron speakers. These are still used today in some miniature speakers where small size and low cost count, and sound quality is unimportant. A moving iron speaker consists of a ferrous metal diaphragm or reed, and a permanent magnet. The...
tin can, magnet & wire based speakers
in a few cases a moving coil speaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...

The earliest TRF sets used no regeneration

Regenerative circuit

The regenerative circuit or "autodyne" allows an electronic signal to be amplified many times by the same vacuum tube or other active component such as a field effect transistor. It consists of an amplifying vacuum tube or transistor with its output connected to its input through a feedback...

, and had very poor RF sensitivity and low selectivity

Electronic selectivity

. Thus only nearby stations and strong distant stations would be received, and separating different stations was not always possible.

Most TRF sets were reaction sets

Regenerative circuit

, also known as regenerative receivers. These rely on positive feedback

Positive feedback

Positive feedback is a process in which the effects of a small disturbance on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system that responds to a perturbation in a way that reduces its effect is...

to achieve adequate gain

Gain

In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...

. This approach worked well enough, but is inherently unstable, and was prone to various problems. Consequently there was a significant amount of hostility over maladjusted radio

Radio

s transmitting squealing noises and blocking reception on nearby properties.

TRF sets had typically two tuning knobs and a reaction

Regenerative circuit

adjustment, all of which had to be set correctly to receive a station. Earlier reaction sets

Regenerative circuit

also had filament adjustment rheostats for each valve

Vacuum tube

, and again settings had to be right to achieve reception.

Superheterodyne receivers

In the era of early radio, only the wealthy could afford to build a superheterodyne receiver

Superheterodyne receiver

In electronics, a superheterodyne receiver uses frequency mixing or heterodyning to convert a received signal to a fixed intermediate frequency, which can be more conveniently processed than the original radio carrier frequency...

(superhet). Such sets required many valves

Vacuum tube

and numerous components, and building one was a sizeable project.

Pre-war superhets were often used with the relatively expensive moving coil speakers

Loudspeaker

, which offer a quality of sound unavailable from moving iron speaker

Moving iron speaker

The earliest loudspeakers for speech and music were moving iron speakers. These are still used today in some miniature speakers where small size and low cost count, and sound quality is unimportant. A moving iron speaker consists of a ferrous metal diaphragm or reed, and a permanent magnet. The...

s.

Most post-war commercial radios were superhets, and this technology is still in widespread use in radio receivers today, implemented with transistors or integrated circuit

Integrated circuit

An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

s.

The advantages of superhets are:

Excellent sensitivity, enabling reception of foreign broadcasts
Complete stability
Well controlled bandwidth
Well shaped rf passband
Passband
A passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.A bandpass filtered signal , is known as a bandpass signal, as opposed to a baseband signal....

avoids the uncontrolled tone variations of TRF sets, and gives good selectivity
Electronic selectivity
Selectivity is a measure of the performance of a radio receiver to respond only to the radio signal it is tuned to and reject other signals nearby in frequency, such as another broadcast on an adjacent channel....

The downsides for pre-war superhets were:

Very high build cost
High run cost due to many valves
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

and the need for large high power batteries
Construction was a sizeable project

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 an illegally constructed set from whatever parts one could make, which were very few indeed. Such a set typically used lighting flex for an aerial, a razor blade for a detector, and a tin can, magnet and some wire for an earpiece. I.e. they were crude crystal sets.

Wooden consoles

The console radio was the center piece of household entertainment in the era of radio, they were big and expensive running up to $700 in the late 1930s. Mostly for the wealthy, these radios were placed in hallways and living rooms.Most console radios were waist high and not very wide, as the years went on they got shorter and wider. Most consumer console radios were made by RCA

RCA

RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...

, Philco

Philco

Philco, the Philadelphia Storage Battery Company , was a pioneer in early battery, radio, and television production as well as former employer of Philo Farnsworth, inventor of cathode ray tube television...

, General Electric, Montgomery Ward (under the Airline brand name), Sears (under the Silvertone brand name), Westinghouse, radio-bar and many more. Brands such as Zenith

Zenith Electronics

Zenith Electronics Corporation is a brand of the South Korean company LG Electronics. The company was previously an American manufacturer of televisions and other consumer electronics, and was headquartered in Lincolnshire, Illinois. LG Electronics acquired a controlling share of Zenith in 1995...

, Scott, Atwater-Kent, were mainly for the rich as their prices ran into the $500–$800 range in the 1930s and 1940s.

Table top wood radios

Table top radios came in many forms:

"Cathedral style", an upright rectangular box with a rounded top
"Tombstone style" were rectangular boxes that were tall and narrow like a tombstone
"Table top" were rectangular, with width being the larger dimension. Table top radios were usually placed in the kitchen, sitting room or bedroom, and sometimes used out on the porch.

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 brittle plastic, and dropping a radio could easily break the case. Bakelite is a brown-black mouldable thermosetting plastic

Thermosetting plastic

A thermosetting plastic, also known as a thermoset, is polymer material that irreversibly cures. The cure may be done through heat , through a chemical reaction , or irradiation such as electron beam processing.Thermoset materials are usually liquid or malleable prior to curing and designed to be...

, and is still used in some products today.

In the 1930s some radios were manufactured using Catalin

Catalin

Catalin is a brand name for a thermosetting polymer popular in the 1930s. Developed when the American Catalin Corporation took over the patents for Bakelite in 1927, Catalin is a cast phenolic, which can be worked with files, grinders and cutters and polishes to a fine sheen. Chemically, it is a...

, a colourable version of bakelite, but nearly all historic bakelite radios are the standard black-brown bakelite colour.

Plastic era

The affordability of more modern light coloured thermoplastic

Thermoplastic

Thermoplastic, also known as a thermosoftening plastic, is a polymer that turns to a liquid when heated and freezes to a very glassy state when cooled sufficiently...

s in the 1950s made brighter designs practical. Some of these thermoplastics are slightly translucent.

Early transistor radios

The invention of the transistor

Transistor

made it possible to produce small portable radios that did not need a warm-up time, and ran on much smaller batteries

Battery (electricity)

. They were convenient and chic, though the prices were high and the sound quality not so good.

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

Integrated circuit

containing a large number of transistors has surpassed the use of singly packed transistors for the majority of radio circuitry.

Transistor radio

Transistor radio

A transistor radio is a small portable radio receiver using transistor-based circuitry. Following their development in 1954 they became the most popular electronic communication device in history, with billions manufactured during the 1960s and 1970s...

s appeared on the market in 1954, but at a high price. By the 1960s, reduced prices and the 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 uneconomic to repair because mass production and technological improvements in numerous areas have made them so cheap to buy, while the cost of human labour and workshop overheads

Production, costs, and pricing

The following outline is provided as an overview of and topical guide to industrial organization:Industrial organization – describes the behavior of firms in the marketplace with regard to production, pricing, employment and other decisions...

have not fallen in real terms.

Early American sets - Regency, Motorola
Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....

TR series like the TR-55
TR-55
The TR-55, released in 1955, was Sony's first transistor radio, and the first to be made in Japan. The use of transistors rather than vacuum tubes allowed the device to be much smaller than earlier radios, and allowed them to be the first truly portable radio from Japan.-Technical...

Car radios

Pre-war car radios were experimental only. They required a large aerial

Antenna (radio)

An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

, reception was inconsistent, they required adjustment in use, which was not very practical. And they were of course not the most useful place to put an expensive radio.

All early car radios used a vibrator power supply

Vibrator (electronic)

In early electronics vibrators were used in inverter circuits to provide an alternating current electric power supply from a direct current source....

to step up the low voltage to high voltage for the valves

Vacuum tube

. Vibrator supplies are known for reliability problems, and produce radio interference and some mechanical noise.

Later car radios used valves

Vacuum tube

that ran on twelve volts, eliminating the need for a vibrator.

The third generation of car radios were valve sets with a single output transistor

Transistor

, and makers were very keen to promote these as transistor sets. Some historic corn radios badged as transistorised are in reality these hybrid valve sets.

All-transistor sets eventually took over from valves as prices fell.

Warm-up time

Most valve

Vacuum tube

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.

Bright emitter valves universal in the early 1920s came on in a small fraction of a second, effectively instantly.
Direct dull emitters typical of the late '20s and 1930s came on in around a second. This type of valve continued to be popular in battery
Battery (electricity)
An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. Since the invention of the first battery in 1800 by Alessandro Volta and especially since the technically improved Daniell cell in 1836, batteries have become a common power...

sets for several decades more.
Indirect emitters used in more or less all mains valve radios from the late 1930s onward were slow to reach emission
Emission (radiocommunications)
Emission is the radiation or radio signal produced or emitted by a radio transmitting station....

temperature, with wait times routinely exceeding 10 seconds.
The last generation of valves was nuvistor
Nuvistor
The nuvistor is a type of vacuum tube announced by RCA in 1959. Most nuvistors are basically thimble-shaped, but somewhat smaller than a thimble. Triodes and tetrodes were made, although tetrode nuvistors are rare. The tube is made entirely of metal and ceramic. Making nuvistors requires special...

s. These tiny devices reached emission temperature fairly quickly.

Valuation

In terms of financial valuation:

Catalin
Catalin
Catalin is a brand name for a thermosetting polymer popular in the 1930s. Developed when the American Catalin Corporation took over the patents for Bakelite in 1927, Catalin is a cast phenolic, which can be worked with files, grinders and cutters and polishes to a fine sheen. Chemically, it is a...

plastic radios and high end console radios sell at the top of the market.
Cathedrals, tombstones and large table tops are midrange
wood/bakelite table tops are in the lower mass production bracket and often sell for less than $40 each, although collectible sets (Such as the DAC90, made by Bush Radio in Britain) often sell for much more.
The valuation of 1920s and 1930s sets depends primarily on condition and appearance. Well presented breadboard
Breadboard
A breadboard is a construction base for prototyping of electronics. The term is commonly used to refer to solderless breadboard ....

sets command a high price tag, but tatty or uninspiring samples don't. Although fairly rare, the difficulties in using such sets affect their sale value.

Post-War commercial sets

Post-war radios merely require plugging into the mains, once any faults are resolved.

Some sets have a safety issue that should be addressed, usually due to deterioration in the condition of the mains lead. Universal sets (sometimes called AC/DC sets) use a live chassis, and should be inspected carefully to ensure no screws, grub screws on knobs, or any other live metal part can be touched.

'Curtain burner' sets are an uncommon low cost type of universal set with a mains lead that warms up in use.The idea of this is to remove the need for an internal "dropper resistor." Shortening the lead or replacing it with a copper lead will damage the tube filaments by excess voltage. A fault in the radio has been known to cause the mains leads to overheat with nasty consequences, hence their popular name. Curtain burner sets are usually miniatures.

Pre-war

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-war 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:

Failed components are to be expected, and these must be fault-found then repaired
Repair of parts is practical, but not trivial
Some of these sets never worked very well and may benefit from some skilled debugging
3 power supplies are needed to replace the originally used A, B and C batteries(unless self biasing is used) (or DC mains).
A little detective work is needed to find out what PSU voltages are needed
A long wire antenna
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...

will need to be erected
Fitting a local ground (earth) is frequently necessary, and quite easy
A high impedance
Electrical impedance
Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...

speaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...

(or transformer
Transformer
A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

) is needed
Some means to keep fingers away from the exposed live connections on the rear is wise, and often legally obligatory.
With 1920s and earlier sets using bright emitter valves, the end user should understand the use of the filament rheostats to avoid rapid valve
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

failure.
The user should realise that permitting historic reaction sets to oscillate causes them to transmit interference, which is illegal.
Negative supply DC mains sets should have their ground capacitor bypassed to convert them from live chassis to earthed chassis.

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

Vacuum tube

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

Triode

A triode is an electronic amplification device having three active electrodes. The term most commonly applies to a vacuum tube with three elements: the filament or cathode, the grid, and the plate or anode. The triode vacuum tube was the first electronic amplification device...

versus pentode

Pentode

A pentode is an electronic device having five active electrodes. The term most commonly applies to a three-grid vacuum tube , which was invented by the Dutchman Bernhard D.H. Tellegen in 1926...

valves

Vacuum tube

, and single ended

Amplifier

versus push pull

Amplifier

, which affect the types of distortion

Distortion

A distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice...

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.

Moving iron speaker

Home made pre-war sets usually used some form of moving iron speaker

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

Loudspeaker

. The question of sound quality is heavily dominated by the speaker in these cases. Moving iron speakers suffer the following defects:

Gross non-linearity
Heavy intermodulation distortion
Little bass response
Poor treble response
Strong undamped resonance in the middle of the audio spectrum
Noisy chattering when presented with a loud bass note
Tendency of the moving iron to stick to the pole piece, resulting in a 'whack' sound followed by very little sound output.
Gross impedance mismatch
Need for adjustment
Prone to demagnetisation
Horn speakers were strongly directional
Cone speakers were readily damaged

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

Electrical impedance

Electrical impedance, or simply impedance, is the measure of the opposition that an electrical circuit presents to the passage of a current when a voltage is applied. In quantitative terms, it is the complex ratio of the voltage to the current in an alternating current circuit...

, which varied across the audio spectrum by a ratio of more than 100:1.

It is not unusual for an electronics

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

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

Loudspeaker

. The Inductor Dynamic Speaker solved the worst problems of earlier moving iron types

Moving iron speaker

, and provided a relatively pleasant listening experience. The main defect of ID speakers was poor treble response, giving them a charactistic dull drone.

Moving coil speaker

These speakers

Loudspeaker

were mostly of sufficient quality that the radio's charactistics 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

Loudspeaker

equipped set can be pleasant, and mistakable for a modern portable radio.

Battery sets

Partial loss of bass and high frequency treble were normal, as with today's small portable radios. A small amount of non-linearity

Distortion

was also present.

Some sets were prone to suffering crossover distortion

Crossover distortion

Crossover distortion is a type of distortion which is caused by switching between devices driving a load, most often when the devices are matched...

as the battery

Battery (electricity)

voltage fell. This is a rough unpleasant type of distortion. In sets prone to this, significant care was taken to avoid it, or in some cases at least minimise it.

Mains sets

Most old valve radios are in this category. Mains sets suffer the same defects as battery sets, but have a redeeming feature that gives them a characteristic warm & pleasant sound. The audio output of nearly all post-war mains valve sets is modulated by 50 & 100 Hz or 60 & 120 Hz, creating an array of extra frequencies in the audio signal. This extra content gives an impression of warmth & depth, and is easily mistaken for good bass response.

This modulation is created by a few factors working together:

Low value smoothing capacitors cause significant 100/120 Hz ripple on the HT
HT (vacuum tube)
__FORCETOC__In vacuum tube technology, HT or high tension describes the main power supply to the circuit, which produces the current between anode and cathode...

line.
Significant 50/60 Hz internal wiring, ac heaters and high impedance circuitry cause injection of 50/60 Hz into all stages of the radio
Valve non-linearity
Distortion
A distortion is the alteration of the original shape of an object, image, sound, waveform or other form of information or representation. Distortion is usually unwanted, and often many methods are employed to minimize it in practice...

in all stages

External links

[news:rec.antiques.radio+phono]
The Antique Radio Shack- Source of high end and unusual antique radios 1920s to 1950s.
Classic Radio Gallery - Website containing a large viewing gallery of antique radios.
Phil's old Radios - Collection of radio ranging from the floor-standing models of the 1930s to the pocket transistor radios of the '60s.
Antique Radios: A Collector's Resource - Website containing forum, gallery and more.
The Philco Repair Bench - Website containing hints and information about Philco radios and more.
The New Jersey Antique Radio Club provides an environment within which new and experienced collectors can share information regarding radio history and restoration.
the Radio Attic - Over 1,000 antique radios for sale, with photos.
the Radio Attic's Archives - Photos of over 8,000 unique identified radios, plus audio, amateur, and test eauipment.
WhiteRadios.com - Antique Radio Gallery, History, and Appraisals - Website dedicated to collecting radios and perpetuating the love of the hobbie..

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.