The world's largest telephone exchange

The old telephone tower in central Stockholm which 50 years earlier was used by the main telephone station of Stockholms Allmänna Telefon AB (SAT).

As a result of the rapid increase in telephones in Stockholm, the main exchange of Stockholms Allmänna Telefonaktiebolag (SAT) on Oxtorsgatan soon became too crowded. Based on its success, the company invested in a new, much larger exchange in the center of the city. With its 7,000 lines, it became the world's largest telephone exchange.

A "telephone palace" was constructed on the lot between Malmskillnadsgatan 40 and Norra Smedjegatan 28 that had been purchased in 1884. The basement contained a steam boiler that was used for heating, and machinery for electric lighting. The telephone hall, on the third floor, was 110 feet long, 29 feet wide, with a 21-foot ceiling. It occupied the entire width of the building between the two streets. In addition, there were offices for the board of directors and management, other offices and an engineering agency, a laboratory, and facilities of various types for the telephone operators.

But the most striking feature of the exchange was the gigantic Telephone Tower. In those days there was no efficient design for telephone cables. Instead, lines had to be drawn to the exchange over rooftops. In the beginning, the Company used two-millimeter galvanized iron wire that was connected to the Tower, which was approximately 50 meters tall. At the inauguration in 1887, 4,000 wires led away from the Tower in all directions.

Each of the switchboards that had been used in the old central exchange could only serve 50 subscribers. Calls that an operator wanted to switch to subscribers on other switchboards had to be transferred via special connection lines, a system that became increasingly complicated the larger the exchange became. It would have been practically impossible to maintain an acceptable standard of service in an exchange with 7,000 lines. Instead, the company introduced a so-called multiple switchboard that made it possible for the operator, without anyone else's help, to reach all subscribers from her position. The system had been invented in the United States and had been tested at SAT?s exchange in Stockholm's Old Town beginning in May 1884 after Ericsson had begun producing switchboards based on the multiple principle.

The new central exchange was inaugurated ceremoniously in the presence of King Oscar II of Sweden, Prince Devawongse of Siam and other notables on July 12, 1887. The king was saluted in the great telephone hall by the singing of the national anthem by the telephone operators, accompanied by a choir that had been placed on a platform. The building had been decorated with oak leaf garlands and a sea of flags billowed on the Tower. The elegantly furnished instrument hall contained switchboards with a capacity of 8,500 lines -- the largest facility of its type in the entire world. The lines in the telephone hall alone measured more than sixty kilometers in length.

The enterprising H T Cedergren had a feeling for publicity and public relations. At the inauguration there were intervals during which songs and instrumental music were transmitted by wire from performers who were stationed at various locations on the outskirts of the city. Later, when Stockholm was visited by government dignitaries from different parts of the world, Cedergren was generally successful in insisting that a visit to the world's largest telephone exchange should be on their program. On such occasions, a small concert in honor of the visitors was performed on the stage of the Stockholm Opera House and transmitted to a room at the exchange -- in stereo! There were a number of microphones on the stage and the sound was transmitted to "double" receivers, one for each ear.

The importance of the Telephone Tower as a central connection point for Stockholm's telephone lines decreased more and more as the Company began to place lines in underground cables. The Tower remained as a characteristic feature of the Stockholm landscape until it had to be demolished following a fire in the building in 1952.

Author: K V Tahvanainen

© Telefonaktiebolaget LM Ericsson and Centre for Business History

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