Subscriber’s amplifying set

DP 100

This set is composed of a two-way amplifier and a telephone instrument, both fitted in one cover. The exterior of the set is similar to our standard telephones of Bakelite, e. g., DE 702. It is designed for use by persons with bad hearing and also for use with lines having poor transmission properties. For this latter reason amplification of outgoing speech has also been provided for. The maximum amplification of incoming speech is about 2.3 nepers (20 db) and this amplification can be regulated by means of a potentiometer, the knob of which is placed in the bottom right hand corner of the set. The input level should, however, not exceed about 1.3 neper (11.5 db), to avoid distortion. For outgoing speech the amplification is usually adjusted so that zero level is obtained at the near end of the line. For lines giving poor transmission the output can be adjusted to a certain positive level by altering the tappings of a transformer. In this manner the amplification can be regulated 0.8 neper (7 db) in steps of 0.2 neper (1.75 db). The highest possible output level will consequently be + 0.8 neper (7 db).

The set requires 1 battery of 1.5 V and 1 of 60V; these two batteries are cong tamed in a battery case which on request is supplied with the set. The valves are of the Marconi type L 11. The set has a large wall fitting, provided with a bell when it is to be connected to manual or automatic CB systems. When used for LB systems a smaller terminal block is supplied, the bell being then replaced by an ordinary magneto telephone which also provides the generator necessary for the signalling. The magneto telephone can of course be used when amplification is not required. The amplifier is switched on and off when the micro-telephone is lifted and replaced in its rest.

Height 140 mm, width 233 mm, depth 175 mm, weight inc. wall fitting 3.6 kg.


Taken from the L. M. Ericsson Telephones and Signalling Material Catalogue No. 188 (1934)

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Last revised: October 13, 2019