Ericsson's metal encased desk telephones 1893-1929

The first desk telephones were either completely open, naked metal devices, such as the American candlestick telephones and Ericsson's skeleton phones, with the components mounted in or on a wooden box. When the telephones became more reliable, the advantages of enclosing them as much as possible became clear. The components were protected from dust and dirt, the risks to people and the device were reduced, and suddenly there were flat surfaces for decorations or applying emblems or logos. A living material such as wood what was not well suited in terms of standardizing measurements, so in 1893 Ericsson was able to unveil a device with a metal casing. However, the lathed, black lacquered top piece and base were still made of wood. The device was cylindrical and was named No. 380/AC210, otherwise known as the Coffee Grinder (also Tea Caddy, Biscuit Barrel or Cookie jar). The nickname was given because it resembled a coffee grinder from Peugeot that was popular at the time.

With the cylindrical metal telephone from 1893, Ericsson took the first step in converting the desk telephone from a simple device to an attractive product with hidden technology. The device was still based on the principles of the skeleton phone, but in order to make room for the ringing inductor under the metal casing, the magnetized stand was replaced with two serial-linked magnets with the same horseshoe design as in the company's smaller wall-mounted telephones. With the removable metal casing that could be split in two, Ericsson paved the way for efficiently mounting components on a bottom plate.  The metal casing in turn was decorated with a sophisticated, classical design with soft, muted colors, fluted columns bound together with fanciful architraves and robust keystones framing magnificent flower arrangements that alternated with an abstract version of the same pattern.

However, the coffee grinder model was short-lived, due in large part to the fact that the compact ringing inductor limited the telephone's range. Metal encased telephones continued to be developed with the help of architects. Here Kungliga Telegrafverket (Swedish Royal Telegraph Company) took the lead with its pioneering 1894 device, which was designed by professor and Telegrafverket's architect Isak Gustav Clason. The result was a rectangular, house-shaped creation with a tall, profiled base with walls of black-painted sheet metal under a flat, somewhat cantilevered top piece.  Ericsson later refined this type of telephone in a series of different models, from one version with loose side plates held together by profiled corner moldings in 1901 to the last metal model with a molded cover, the art deco inspired WZ model. Ericsson's architectural consultant Torben Grut played an important role in this work, and in 1904 he was assigned the task of designing the first device in the new generation of desk telephones using a central battery. By placing the batteries in the central station and emitting a low voltage in the lines for the microphone and the signal, you could avoid both putting a battery in the microphone and enclosing the heavy and bulky ringing inductor in the device casing. The result was a considerably smaller and lighter desk model, which in 1909, could also be equipped with a surrounding cover of drawn steel plating instead of the previous threadable hood of bent and soldered sheet metal. 

The transition from a box hood to a case created the conditions for rational mass production of the telephones, and the casing's simple, scaled-down design heralded the functional design ideals of the 1900s. However, one weakness in manufacturing metal enclosed telephones was the time-consuming surface treatment that involved priming, filling, polishing, dusting, four coats of lacquer, affixing the label and decorations and varnishing. This phase of production, which could require a week, disappeared in one stroke with the transition to Bakelite.

Author: Lasse Brunnström

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