Engineering:Model 202 telephone

Western Electric D1 telephone, often identified as the model 202.

The model 202 telephone was a desktop telephone produced by Western Electric for the Bell System from 1930 to 1939, and by Northern Electric in Canada. Refurbished units were installed into the mid-1950s. It was an updated version of the 102-type telephone, containing the newly developed anti-sidetone circuitry to reduce electronic feedback from the transmitter (mouthpiece) to the receiver (earpiece).

Like the type 102 hand telephone, the 202 consisted of the desk-top telephone instrument with the telephone handset and a physically separate subscriber set (desk set box) which contained the ringer and the electrical components to interface the desk set with the telephone network. The differentiation between the type 102 and 202 hand telephone sets was the type of electric circuit installed, while both models could use either the older circular telephone base or, starting in 1930, an oval handset mounting.

History

The 102- and 202-type telephones were developed from previous hand telephone versions based on the A- and B-type handset mountings which featured a circular base.

Patent illustration by G. K. Thompson of AT&T first desk set telephone (without handset)

The A-type handset mounting, described by George K. Thompson of the American Telephone and Telegraph Company (AT&T) in U.S. Patent 1,508,424 of 1924, was the first version of a desktop hand telephone, a Bell System term for a telephone featuring a handset comprising a microphone (transmitter) and ear piece (receiver) attached to the same handle, with a cradle device to secure the handset when not in use, and an electric switching circuit that connected the handset to a wall-mounted subscriber set (or desk set box, ringer box) with the telephone network interface. Thompson designed the A handset mounting as a derivative of the candlestick telephone with a shortened vertical shaft of about two inch height that had a handset cradle mounted on the top instead of a sideways extending switch-hook. The telephone was issued not until 1927, after the type E1A handset had been finalized late in 1926.

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. A new, wider, elliptical base was developed and introduced in 1930. This design was referred to as the D handset mounting. This newly designed telephone initially used the same sidetone electric circuit as the predecessors, but soon it was also equipped with the new anti-sidetone circuit that provided much improved audio performance.

While some sidetone is desirable, reassuring the user that the set is operating properly, too much sidetone created an unpleasant experience when the users heard their own voice or ambient sound very loudly. This causing them to lower their own speech volume to low levels unacceptable for transmission. The anti-sidetone circuitry contained a modified transmission hybrid transformer (induction coil) that reduced sidetone to proper levels.

With the introduction of anti-sidetone circuits in subscriber telephones in 1930, Western Electric began assigning assembly codes to telephones based on the electrical configuration. Until then, telephones were primarily referred to by the part designations used to construct them. With the new circuit variants, this became insufficient, resulting in the distinction between 100-series hand telephone sets and 200-series hand telephones. Thus, the type 102 was the new designation for the B1 and D1 hand telephones when used on common battery lines with a sidetone circuit, and the 202 was the anti-sidetone version of either handset mounting. The previous types, i.e. the A and B handset mounting were typically not designated with these new codes in publications, as they were commercially obsolete.

Construction

The 202 telephone, like the 102, consisted of two distinct parts. The desk-top set, containing only the dial and a cradle that secured a handset, which combined the receiver and the transmitter elements in one unit, in the on-hook position. The cradle contained a plunger that operated the hookswitch located underneath the cradle, inside the housing. The second part was a physically separate subscriber set (desk set box), in form of a metal or Bakelite box, which contained the ringer and the electrical components to interface the desk set with the telephone network. The desk set was connected to the subscriber set with a four-conductor mounting cord. The subscriber set was typically mounted either on the wall in close proximity, or to the rear or underneath a desk.

Newly manufactured units used the E1 type handset, whose development period began in ca. 1921 and was completed by 1927. The handset was molded in Bakelite, but the receiver and transmitter assemblies had an aluminum metal core. Its transmitter assembly that was extended by a hollow mouthpiece, known colloquially as a spit cup, to focus sound more effectively into the transmitter. The barrier-button transmitter element exhibited a cone shape into the spit cup, known as a bullet transmitter among collectors. This feature was eliminated about halfway through the handset production run, when in 1934 the transmitter element was changed to a more efficient type (F1) with better voice reproduction. The F1 element had a flat disk shape and was protected by a simple plastic screen as moisture barrier and a cover grill. This element became the standard transmitter of a new handset type (F) in 1937, and was in use in the Bell System until the 1960s. When this new handset became available, 202-type telephones were often refurbished with the new handset.

thumb|A Western Electric 202 Imperial telephone as issued in 1955 with a gold lacquered base and ivory Tenite plastic F1 handset. The subscriber set was painted in harmonizing color to the desk set. The vast majority of the original production run of the 202-type telephones were produced in black finish. For an extra fee, telephones and subscriber sets could be ordered in several other colors, both flat colors or hues with metallic luster.

Evolving models

In the 1950s, large quantities of old telephones were retired in favor of the popular new model 500 telephone, creating a stock pile of still usable parts. In 1955, Western Electric reissued the 202 painted in several colors, in an effort to use up these existing parts stocks, and to satisfy the growing demand for color telephones. The new manufacturing processes to produce the new line of color sets based on the 500-type telephone were not completed yet, and those set were only issued in black until 1953. The Continental line was created from a D1 base with an F1 handset, and was available painted in primarily ivory, green, red, and black, but other colors were made available by special customer order. The Silver Continental was a D1 base, plated in silvery rhodium and coupled with an ivory painted or molded ivory plastic handset. The Imperial was sprayed with gold lacquer, and was also supplied with an ivory painted or molded ivory plastic handset.

See also

• Model 302 telephone

External links

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