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AD 250 (Originally numbered as the No. 335)
Made with a polished oak frame, the lower part of which is a battery cabinet (internal dimensions: height: 200mm, width: 185mm, depth: 105mm).

Hanging microphone RE 4050 with cord RS 6500.
Five-magnet inductor RH 5050.
Ringer with 1000 ohm resistance.
Push button which should be pressed when the signal is given.
Three-way switch.

The device is equipped with a metal clip for holding an annotation pad.

The intermediate station can talk to either of the three lines, depending on whether the switch is placed in its left, right or middle position.

When the switch is in the normal position (on the left), two of the lines (L1 and L2) can send a signal to the intermediate station device. If the third line (L3) is also to be able to emit such a signal, an extra clock RA 10/1000 should be connected between the telephone set's two clamping screws marked L3.

When the switch is in the middle position, the lines L1 and L2 can signal to and talk to each other and at the same time the line L3 and the intermediate station can be in communication with each other. If it is desired that line L3 should also be able to connect with lines L1 and L2, a connection switch AF 340 is added: in this case the extra bell becomes redundant. At the same time that the line L3 is talking to one line, the other line can call and talk to the intermediate station.

When two devices talk to each other, the third cannot listen.

Back piece height: 715mm.
Back piece width: 250mm
Weight 9.6 kg

Taken from the L. M. Ericsson Telephones and Signalling Material Catalogue No. 122 (1930) - Swedish Translation

Also found in the 1905, 1912 and 1923 Ericsson Telephone Catalogues

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Last revised: March 27, 2024