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1930's -- 1940's

These instructions are taken from the sheet included with a pair of telephones from the 1930's and refer to sets made from 1930 - 1948.


The Duplex Telephones are designed for service between two neighboring points and require only two wires connected from the "L" and "BL" terminals of one telephone to the "L" and "BL" terminals of the other.

Two dry cell batteries at each phone are connected in series and attached to the "B" and "BL" terminals. (See diagram, Fig. No. 1). It is important that the "B" terminal connect to the positive side of battery at one telephone and to the negative side of battery at the other telephone.

Phones should be mounted about 56 inches from floor to the center of mouthpiece, with mounting screws furnished.

Wires should be run through recessed opening at top and bottom of telephone case and firmly stapled to eliminate strain at terminals.

Fig. No.1 Back View of Telephones Connected Together.

The Duplex Telephone is designed to operate on a line up to 1000 feet long and will give satisfactory service if the proper size copper wire and the correct number of batteries is used at each phone, as per table, Fig. No.2.

On installations where the distance is over 200 feet between is required phones, the larger size wire recommended to reduce drop in line voltage.

If it is desired to have batteries located at a central point or at one end, run three wires as shown on diagram (Fig. No.3) and connect both sets of batteries in series as shown.

Fig. No.2


The size of wire required is determined by the distance between telephones and whether used inside or run outside between buildings. For inside use we recommend double cotton-covered copper wire in accordance with table, Fig. No.2---for outside, use twisted pair copper wire, rubber-covered, braided, in accordance with table, Fig. No.2. When ever possible, wires should be long enough to run direct from phone to phone. If it is necessary to add an additional length, scrape both ends of wire bright and twist together, solder joint making good solid connection and cover exposed section with friction tape.

Fig. No. 3


'Use standard dry cell batteries of 1 volts each. Be sure they test full voltage when connected. With ordinary use, they should last at least six months. These phones will not operate from a bell-ringing transformer as this device supplies only alternating current and will transmit the AC. hum over the line.

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