Analog Telephones "Nos. 4, 600, and 601 Automatic Desktop Telephone Sets" that Contributed to the Rapid Spread of Telephones Have Been Registered in National Museum of Nature and Science "MIRAI Technology Heritage"

—Actual Phones are Open to the Public for Viewing at NTT History Center of Technologies—

NTT Corporation (Head Office: Chiyoda-ku, Tokyo; Akira Shimada, President & CEO; "NTT") announces that three models of analog telephone sets (No. 4 Automatic Desktop Telephone Set, No. 600 Automatic Desktop Telephone Set, and No. 601 Automatic Desktop Telephone Set) owned by NTT History Center of Technologies managed by NTT were registered in "Essential Historical Materials for Science and Technology (short form: MIRAI Technology Heritage)^*1" of the National Museum of Nature and Science on September 13, 2022.
　These analog telephone sets were the world's leading high-performance telephones (at that time) that drove and embodied Japan's independent technological development during the Ministry of Telecommunications and Nippon Telegraph and Telephone Public Corporation eras preceding NTT. Actual examples of these telephones are open to the public for viewing at NTT History Center of Technologies.

1. No. 4 Automatic Desktop Telephone Set

Supporting social activities in Japan's postwar reconstruction period, this telephone set made its appearance in 1950 through Japan's independent technological development. By thoroughly researching what had been inferior acoustic components up to then and making fundamental improvements, it achieved superior call quality that could be described as cutting-edge for its time. In addition to high call quality, it featured a streamline design representing a design improvement as well.

2. No. 600 Automatic Desktop Telephone Set

In addition to a variety of improvements in addition to high call performance, this telephone set responded to the great demand for telephones in Japan's high-growth period. It enhanced reliability and facilitated mass production through diverse research studies that extended to upgrades in telephone circuitry such as introduction of a printed circuit board for the first time and revisions to the telephone set itself including the dialer and housing.
　This telephone set provided high performance and satisfied a great demand for telephones by improving performance with a design that referenced acoustic characteristics deemed necessary for a telephone as revealed by basic research and a design that considered part placement and assembly method with a view to automated manufacturing.

3. No. 601 Automatic Desktop Telephone Set

This telephone set supported the oil-crisis period following the era of rapid growth by significantly lowering costs and achieving high maintainability. In addition to adopting a mounting structure that assumed manual assembly taking into account the need for resource saving and a future drop in demand, it was a telephone that kept the global market in view by satisfying international standards including those for voice clarity and communication volume.

Reference: What is NTT History Center of Technologies?

The NTT History Center of Technologies exhibits in timeline fashion a collection of historical assets of the NTT group, accumulated as the result of the group's development of telecommunications technologies with particular focus on the half-century since the foundation of the Nippon Telegraph and Telephone Public Corporation.
　It introduces more than 1,500 technical historical materials in two parts: "Tracing the History" and "Exploring the technologies".
　So far, the following technical historical materials have been registered with the "MIRAI Technology Heritage".
　The NTT History Center of Technologies is open to the public for free visits. For details, please check the NTT History Center of Technologies website (https://hct.lab.gvm-jp.groupis-ex.ntt/).

Glossary / Supplement

^*1Essential Historical Materials for Science and Technology (short form: MIRAI Technology Heritage):
Among historical materials for science and technology, these are essential historical materials that have been selected since 2008 by the National Museum of Nature and Science as materials "representing important achievements in the development of science and technology and having great significance that should be passed on to future generations" and "having a major impact on daily life, the economy, society, and culture in Japan" and that have therefore been registered in the "Registry of Essential Historical Materials for Science and Technology."