Made possible by the invention of the transistor in 1947, transistor radios started being developed in 1954 and became the most popular electronic communications device in history, Billions were manufactured during the 1960s and 1979s. Their pocket size sparked a change in popular music listening habits, allowing people to listen to music anywhere they went.
Before the transistor was invented, radios used vacuum tubes. Although portable vacuum tube radios were produced, they were both bulky and heavy. The need for a low voltage high current source to power the filaments of the tubes and high voltage for the anode typically required two batteries.
The typical portable tube radio of the fifties was about the size and weight of a lunchbox and contained several heavy, non-rechargeable batteries one or more so-called A batteries to heat the tube filaments and a large 45- to 90-volt B battery to power the signal circuits.
The use of transistors instead of vacuum tubes as the amplifier elements meant that the device was much smaller, required far less power to operate than a tube radio, and was more shock-resistant. Since the transistor base draws current, its input impedance is low in contrast to the high input impedance of the vacuum tubes. It also allowed instant-on operation, since there were no filaments to heat up.
By comparison, the transistor radio could fit in a pocket and weighed half a pound or less, and was powered by standard flashlight batteries or a single compact 9-volt battery. The now-familiar 9-volt battery was introduced for powering transistor radios.
While on a trip to the United States in 1952, Masaru Ibuka, founder of Tokyo Telecommunications Engineering Corporation, now Sony, discovered that AT&T was about to make licensing available for the transistor.
Ibuka and his partner, physicist Akio Morita, convinced the Japanese Ministry of International Trade and Industry (MITI) to finance the $25,000 licensing fee, equivalent to $235,871 today.
For several months Ibuka traveled around the United States borrowing ideas from the American transistor manufacturers.
Improving upon the ideas, TokyoTelecommunications Engineering Corporation made its first functional transistor radio in 1954. Within five years, Tokyo Telecommunications Engineering Corporation grew from seven employees to approximately five hundred. Other Japanese companies soon followed their entry into the American market and the grand total of electronic products exported from Japan in 1958 increased 2.5 times in comparison to 1957.
In August 1955, while still a small company, Tokyo Telecommunications Engineering Corporation introduced their TR-55 five-transistor radio under the new brand name Sony.
With this radio, Sony became the first company to manufacture the transistors and other components they used to construct the radio. The TR-55 was also the first transistor radio to utilize all miniature components. It is estimated that only 5,000 to 10,000 units were produced.
To create smaller radios, it was not enough to make only the transistors smaller. The speaker, condensers, transducers, and other parts also had to be reduced in size. Adopting what might in one sense be called an aggressive approach, Sony engineers achieved greater reductions in scale via a bold strategy that eliminated the speakers to create an earphone-only radio.
Less than a month later, Sony kicked off sales of the little-known TR-2K transistor radio kit as well. The TR-2K was Japan’s first transistor radio kit and, when assembled, represented Japan’s second pocketable ultra-compact transistor radio.
At 5,700 yen, (the equivalent of $315 today) the TR-2K was cheaper than the 19,900 yen ($1,100 today) TR-55 because, in addition to enabling customers who bought the product to assemble it themselves using only a soldering iron, amplification for the speaker was unnecessary and it was possible to use cheaper transistors. However, it turned out that although the catalog said users could assemble the unit in four hours, customer service personnel were kept extremely busy with inquiries from customers who, at the time, were not used to electrical circuitry.
These troubles passed quickly and two years later, Sony came up with the 13,800 yen “pocketable” TR-63 radio, which had a speaker and became a huge best-seller.
For those interested, Sony has a very extensive history on their website that discusses the challenges of developing their own transistors, engineering visits to the US and Western Electric, designing their early products, etc. https://www.sony.com/…/CorporateInfo/History/SonyHistory/