DIORA AGA RSZ-50 ca.1947 from
An antique radio
is a radio
receiving set that is collectible because of its age and
uniqueness. Although collectors may differ on the cutoff dates,
most would use 50 years old, or the pre-World War II
Era, for vacuum tube
sets and the first five years of
Types of antique radio
Morse only sets
The first radio receivers used a coherer and sounding board, and
were only able to receive Morse code
thump it out on the board. This type of transmission is called CW
) or wireless telegraphy
. When wireless telephony
(ie transmission &
reception of speech) became possible, speech radio greatly improved
the usability of radio communication. Despite this, the antiquated
technology of morse code
continued to play an essential role in radio comms
until the 1990s.
All other sections of this article concern speech capable radio, or
Early home made sets
Homemade two tube radio from
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 breadboards
, 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:
These basic radios used no battery
, had no amplification and
could only operate headphones
. 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
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 sets
users added a
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
(TRF sets) were the most popular class of early radio
. These used one or more valve
(tubes) to provide amplification
. Early TRF sets only operated
, but by the 1930s it was more
common to use additional amplification to power a loudspeaker
, 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
The above are not altogether clear distinct categories, with
significant overlap, nor a complete list, but represent the
technologies in popular use.
The earliest TRF sets used no regeneration
, and had very poor RF
sensitivity and low 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
, also known as regenerative receivers. These rely on
. 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 radios transmitting
squealing noises and blocking reception
on nearby properties.
TRF sets had typically two tuning knobs and a reaction
adjustment, all of which had
to be set correctly to receive a station. Earlier reaction sets
also had filament
for each valve
, and again settings had to be right to
In the era of early radio, only the wealthy could afford to build a
(superhet). Such sets required many valves
and numerous components, and building one
was a sizeable project.
Pre-war superhets were often used with the relatively expensive
moving coil speakers
, which offer a
quality of sound unavailable from moving iron speakers
Most post-war commercial radios were superhets, and this technology
is still in widespread use in consumer radios
today, albeit implemented with transistors
and integrated circuits
The advantages of superhets are:
- Excellent sensitivity, enabling reception of foreign
- Complete stability
- Well controlled bandwidth
- Well shaped rf passband avoids the
uncontrolled tone variations of TRF sets, and gives good selectivity
The downsides for pre-war superhets were:
- Very high build cost
- High run cost due to many valves and
the need for large high power batteries
- Construction was a sizeable project
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
The console radio was the center piece of every house back in the
era of radio, they were big and expensive running up to $700 back
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
, General Electric, Montgomery Ward
(under the Airline brand name), Sears (under the Silvertone brand
radio-bar and many more. Brands such as Zenith
, 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
- "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.
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
, and is still
used in some products today.
In the 1930s some radios were manufactured using Catalin
, a colourable version of bakelite, but
nearly all historic bakelite radios are the standard black-brown
The affordability of more modern light coloured thermoplastics
in the 1950s made brighter
designs practical. Some of these thermoplastics are slightly
Early transistor radios
The invention of the transistor
possible to produce small portable radios that did not need a
warm-up time, and ran on much smaller batteries
. They were convenient and
chic, though the prices were high and the sound quality not so
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
containing a large number of transistors has surpassed
the use of singly packed transistors for the majority of radio
Transistor radios appeared on the market in 1949, 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
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
have not fallen in real terms.
- Early American sets - Regency, Motorola
- Sony TR series like the TR-55
Pre-war car radios were experimental only. They required a large
, 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
All early car radios used a vibrator power supply
to step up the
low voltage to high voltage for the valves
. Vibrator supplies are known for
reliability issues, and produce radio interference and some
Later car radios used valves
that ran on
twelve volts, eliminating the need for a vibrator.
The third generation of car radios were valve sets with a single
, and makers were very
keen to promote these as transistor sets. Some historic corn radios
badged as transistorised are in reality these hybrid valve
All-transistor sets eventually took over from valves as prices
sets needed many 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 sets for several
- Indirect emitters used in more or less all mains valve radios
from the late 1930s onward were slow to reach emission temperature, with
wait times routinely exceeding 10 seconds.
- The last generation of valves was nuvistors. These tiny devices reached emission
temperature fairly quickly.
In terms of financial valuation:
- Catalin 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 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.
Use of historic radios
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. You should
check or get the set checked before use. However it should be borne
in mind that meeting the regulations and safety standards of a new
radio is not required for home use, and PAT
inspectors can sometimes be overzealous on
this point. Someone with vintage radio knowledge is a preferable
choice. If in doubt, talk to people who know the subject.
'Universal 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. These sets
should be kept away from locations where water could be
accidentally spilt on them. In the United Kingdom one should be careful to connect the chassis to the
neutral side of the supply.
A minority of old radios are of
this type, generally the budget models.
'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 the internal "dropper resistor." Do not attempt
to shorten it. A fault in the radio has been known to cause the
mains leads to overheat with nasty consequences, hence their
popular name. If used, such sets are best run from a suitably
adjusted current limited power supply to prevent this possibility.
Curtain burner sets are usually miniatures.
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
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
- A long wire antenna will need to
- Fitting a local ground (earth) is frequently necessary, and
- A high impedance speaker (or transformer) 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 failure.
- The user should realise that permitting historic reaction sets
to oscillate causes them to transmit interference, which is
- Negative supply DC mains sets should
have their ground capacitor bypassed to convert them from live chassis to earthed chassis.
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.
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
versus push pull
, which affect
the types of distortion
these issues seem to be secondary in practice to the ones discussed
in this article, and are already well covered in other
Moving iron speaker
Home made 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 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
- 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
- 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
They were far from faithful in their reproduction of audio, and
their technical specifications were poorly controlled. An example
of this is their electrical
, 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
Inductor dynamic speaker
These enjoyed brief success but were quickly eclipsed by moving coil speakers
. The Inductor Dynamic
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 charactistic dull
Moving coil speaker
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
equipped set can be pleasant, and
mistakable for a modern portable radio.
Partial loss of bass and high frequency treble were normal, as with
today's small portable radios. A small amount of non-linearity
was also present.
Some sets were prone to suffering crossover distortion
as the battery
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
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
This modulation is created by a few factors working together:
- Low value smoothing capacitors cause significant 100/120 Hz
ripple on the HT line.
- Significant 50/60Hz internal wiring, ac heaters and high
impedance circuitry cause injection of 50/60Hz into all stages of
- Valve non-linearity in all