The series features the mouthpiece (transmitter) and the earpiece (receiver) combined into a hand-held unit, originally named a hand telephone, or handset.
Although early patents by C. E. McEvoy and G. E. Pritchett did not yield commercial devices in 1877,[2] R. G. Brown of New York succeeded the following year in devising a combined transmitter and receiver handset, that he used in a local telephone exchange system in the district of the New York Gold and Stock Exchange.
[3] Having little success in promoting the device elsewhere in the U.S., Brown left for France to become Electrical Engineer of La Société Générale des Telephones in Paris.
While already popular in other countries, Western Electric produced handsets for export into the European market,[5] but the Bell System had more stringent requirements than any other administration, due to the long distances of communication involved.
[6] Two major technical problems prevented the handset from reaching production stage for use by subscribers in the Bell System.
If operated at other angles, carbon granules in the transmitter would shift and move in an unacceptable manner, resulting in poor voice quality.
[7] The second hurdle to the acceptance of a common handset model was that audio from the receiver was picked up acoustically by the transmitter and amplified.
[5] This resulted in howling tones, due to the hollow handles providing an acoustic channel between receiver and transmitter.
After the end of World War I, new efforts concentrated on the resolution of these deficiencies, as new research yielded insight into electric circuit theory for anti-sidetone compensation, and new hope of progress.
The construction of the handset was changed from using hollow metal handles to solid Bakelite, a molded plastic material that was gaining acceptance in the telephone industry.
With the solid construction the engineers were able to suppress acoustic feedback from receiver to transmitter to acceptable levels, by elevating the mechanical resonance frequencies of the handset sufficiently to avoid interference with the speech range.
It was essentially a candlestick base with a shortened shaft of approximately one and one half inch in height, topped with a new cradle for the handset.
The release of the new hand telephone set uncovered mechanical flaws, so that a new base was designed to replace the shortened candlestick.
This was improved with the anti-sidetone speech circuitry which was finally introduced the following year (1931) in new sections for equipment in the Bell System Practices.
However, with the onset of the worst years of the Great Depression, distribution of telephone sets with this new circuit was largely delayed.
New and existing telephone service installations in the U.S. were in decline and staffing at Western Electric was reduced by eighty percent.
Thus, the type 102 was the new designation for a handset mounting when used on common battery lines with a side-tone circuit,[18] and the 202 was the anti-sidetone version.
[21][22] The first version of the new hand telephone sets was marked by AT&T as D-76869, a specification type for small quantities of new equipment.
The A2 handset mounting was made for special measured two-party line service and the A3 was for private telephone and residence systems.
However, type B handset mountings continued to be produced until c. 1932, and installation of 202-type telephones with the anti-sidetone circuit were delayed due to the economic conditions of the Great Depression.
In 1930, consultants to the Bell Laboratories suggested changes and additional colors to the previous palette: ivory, gray-green, old rose, Pekin red, and dark blue were now in fashion, in addition to the metallic hues called old brass, dark gold, statuary bronze, and oxidized silver.
The new subscriber set was about half the size, was lighter, cheaper to manufacture, and had a cover molded from Bakelite, a material that was becoming fashionable in the era of Art Deco design.
The D1 handset mounting was substituted for this assembly code shortly after, when it was released to the operating companies, and documented in the Bell System Practices.
For field work, where the assembly code was not important,[33] the procedures for the 102 specification were extended to the prior A and B handset mountings.
The Continental line was created from a D1 base with an F1 handset, and was available painted in primarily ivory, green, red, and black,[35] but other colors were made available by special customer order.
It comprised a molded dial-in-handset,[36] that was a complete telephone except for the ringer and switch hook functions, which were provided in a plastic base unit that served to cradle the handset when not in use.