Engineering:Model 102 telephone

Short description: AT&T telephone type of the late 1920s and the 1930s

Western Electric B1 Hand Telephone made from 1928 to c. 1932, with E1 handset featuring a prominent spit-cup mouthpiece. It was accompanied by a bell box mounted closely on a wall or a desk side. When equipped with a sidetone electric circuit, it was designated with the type 102 and designated after 1930 as the 202 hand telephone with an anti-sidetone circuit.

The model 102 telephone was a version of Western Electric's first widely distributed telephone set that featured the transmitter and receiver in a common handset. Although this type designation was not used before ca. 1930, predecessor types were produced starting approximately in 1927 with the A handset mounting, and the B handset mounting in 1928. Earlier telephones by Western Electric had been of the candlestick type which featured a transmitter fixed to the base, and a receiver held by the user to the ear. The design of the A handset mounting was inherited from the candlestick desk stands, while the B-type was slightly reshaped. Although the B handset mounting was produced until 1932, Western Electric introduced a newly designed models, the D handset mounting in 1930, which had an oval foot print to improve physical stability during dialing.

The model 102 telephone was based on the B or D handset mountings with the traditional circuit, not yet incorporating anti-sidetone compensation. It consisted of the handset mounting typically placed on the desk top and a physically separate bell box, or subscriber set. This box was typically mounted on a wall near the telephone or on the side of a desk. The desk set contained only the dial, a handset cradle with hook switch, and the handset positioned in the cradle, while the subscriber set contained the ringer and the electrical components to interface the unit with the telephone network.

The 102 telephone was plagued by problems of excessive sidetone, resulting in a poor experience for users hearing their own voice very loudly, and in extreme cases in early versions also unstable feedback from the receiver into the transmitter. This sometimes caused users to lower their voice to the point where the other party found them difficult to hear. This problem was resolved with a new anti-sidetone circuit which became known as the 202 hand telephone.

History

Patent illustration by G. K. Thompson of AT&T's first desk set telephone, the Type A handset mounting (without handset)

As early as 1890, Western Electric had been experimenting with handset types that combined the microphone (transmitter) and the ear piece (receiver) in the same hand-held unit, but two technical problems prevented them from reaching production at that time. First, the transmitters of the day did not work well unless oriented in a vertical plane. If operated at other angles, as would be expected in a hand-held unit, carbon granules in the transmitter would shift and move in an unacceptable manner, resulting in poor voice quality.

Another hurdle to the acceptance of a common handset model was that audio from the receiver was picked up acoustically by the transmitter either via the air space to the receiver, or conducted through the handle. Multiple passes via these paths result in amplification, and producing howling tones. The problems were aggravated by the signal boosting circuitry used in the subscriber set which resulted in a strong signal (sidetone) at the receiver of the speech of the user. Sidetone is desirable only to some fraction of volume so that the user has the assurance that the telephone is working correctly. Strong sidetone may cause users to lower the voice to unacceptable levels, so that the recipient receives insufficient signal level.

In the 1920s, developments in anti-sidetone circuitry and non-positional transmitters, which worked in any orientation, permitted Western Electric to develop a handset model substantially free of these problems. The resulting E1A handset was ready for production by the beginning of 1927. This handset was paired with a desktop stand, designed in 1922 by George K. Thompson of the American Telephone and Telegraph Company (AT&T) in U.S. Patent 1,508,424, It was essentially a candlestick with a shortened neck of approximately two inches in height, topped with a new cradle to secure the handset when not in use. The cradle incorporated the hookswitch as a vertical plunger actuating the electrical switch contacts. This initial design was released in limited supply as Western Electric's first handset subscriber telephone, issued with the type designations A1, A2, and A3, for various types of service.

During the first year of issuance of this telephone type, William H. Scharringhausen of the Bell Telephone Laboratories streamlined the design and filed a patent application on November 29, 1927 for the B-type handset mounting. It integrated the vertical shaft into the contours of a new circular base design. The circular base proved unstable during dialing, however, and public criticism over the poor esthetic style of Western Electric's telephones mounted. After issuing a wall-mounted handset telephone, designated as the C-type hangup hand telephone, with the E1 handset hanging on the side of the unit in a cradle hook, Bell Laboratories developed in 1929 a new, wider, elliptical base for the desk telephone. This design was designated as the D-type handset mounting and initially used the same electric circuit as its predecessors.

The Western Electric D1 hand telephone, an oval-base handset mounting produced from 1930 to c. 1939, was designated as the 102 Hand Telephone when equipped with a sidetone electric circuit, and designated as the 202 Hand Telephone with an anti-sidetone circuit.

With the introduction of a new type of electric circuit for subscriber stations, the anti-sidetone circuit, Western Electric began assigning numerical assembly codes to telephones based on the electrical configuration. Until then, telephones were primarily referred to by the part numbers used to construct them. With the new circuit variants, this became insufficient, resulting in the distinction between 100-series hand telephones and 200-series hand telephones. Thus, the type 102 was the new designation for the B1 or D1 handset mounting when used on common battery lines with a sidetone circuit, while the 202 was the anti-sidetone version. The previous types, i.e. the A and B handset mounting were typically not officially designated with these manufacturing codes, although they were covered by the same specifications and maintenance procedures.

See also

• Model 302 telephone
• Model 500 telephone

External links

• Western Electric Telephone Models—A look at the evolution of the Western Electric's dial telephones