Model 102 telephone
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. Althought 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 the version of the D handset mounting with the traditional sidetone circuit. It consisted of the handset mounting typically placed on the desk top and a physically separate desk set box or subscriber set. This box was typically mounted on a wall near the phone 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 with 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 resulted in users lowering their voice to the point where the other party found them difficult to hear. This problem was resolved with a new anti-sidetone circuit for the D1 telephone which became known as the 202 hand telephone.
As early as 1890, Western Electric had been experimenting with handset types that combined the transmitter and the 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, referred to as carbon noise.
Another hurdle to the acceptance of a common handset model was that audio from the receiver was picked up acoustically by the transmitter and amplified, resulting in howling tones, called acoustic feedback, due to the hollow handles providing an acoustic channel between receiver and transmitter. 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 free of these problems. The resulting E1 handset was ready for production in 1927. This handset was paired with a base that was essentially a candlestick with a shortened neck of approximately one inch in height, topped with a new cradle for the handset. 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, the model A1.
Although the E1 handset was built to complement the anti-sidetone circuitry, such circuitry was still not ready by the time the A-type desk set was released. However, the solid Bakelite construction of the handset suppressed acoustic feedback to acceptable levels.
As work continued on the anti-sidetone circuitry, a new base was designed for the E1 handset to replace the shortened candlestick. The new design streamlined the design to include the neck into the contour of the base, resulting in the type B handset mounting. This type retained a circular foot print of the base. The B-type desk set was followed by a wall-mounted handset telephone, designated as the C-type hangup telephone, with the E1 handset hanging on one side of the unit in a cradle for the receiver end.
In use, the B-type telephone base proved unstable during dialing, and was replaced with the D-type handset mounting in 1930. A wider, oval base improved its stability. While the D1 mounting base was initially deployed electrically identical to the prior models, the anti-sidetone audio circuitry was introduced in short order the same year.
With the introduction of the anti-sidetone circuit, Western Electric began assigning 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 D1 handset mounting when used on common battery lines with a side-tone circuit, and the 202 was the anti-sidetone version with a D1 handset mounting. The previous types, i.e. the A and B handset mounting were not designated with these manufacturing codes, although they were covered by the same specifications and maintenance procedures.
- Mountjoy, Richard (1995). 100 Years of Bell Telephones. Schiffer Publishing. p. 138. ISBN 0-88740-872-9.
- Meyer, Ralph O. (2005). Old Time Telephones! Design, History, and Restoration. Schiffer Publishing. p. 63. ISBN 0-7643-2282-6.
- Meyer, Ralph O. (2005). Old Time Telephones! Design, History, and Restoration. Schiffer Publishing. p. 64. ISBN 0-7643-2282-6.
- AT&T, Bell System Practices, Section C32.102 Issue 2 (1 June 1931) Sidetone Hand Telephone Set
- AT&T, Bell System Practices, Section C32.103 Issue 1 (1 June 1931) Anti-Sidetone Hand Telephone Sets
- AT&T, Bell System Practices Section C32.101 Issue 1 (1 August 1930), Hand Telephone Sets—B Types—Description and Use
- Western Electric Telephone Models — A look at the evolution of the Western Electric's dial telephones