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In many parts of Europe, a telephone set having the transmitter and receiver mounted on the opposite ends of a handle to form a unit, called a "microtelephone", has long been in general use. Since the use of such sets have chiefly been confined to the Old World, this style of instrument has become known in America as the European type telephone. The micro-telephone has many advantages not inherent in American telephone sets. For example, in using the conventional desk stand. which is the one commonly employed in the United States, the use of both hands is necessary - one to remove the receiver and the other to bring the transmitter into the proper position for conversation. If the user is forced to stand while conversing, it is necessary to continually hold the heavy desk stand: also transmission is apt to be poor at times when the user turns his head while talking, or otherwise does not speak directly into the mouthpiece. In using the European microtelephone, these conditions are not encountered, as the use of only one hand is necessary, and the transmitter is naturally held in the correct position for conversation, regardless of whether the head is turned.
While the American public were cognizant of these advantages and favoured the European
type instrument in preference to the types in vogue, American telephone companies
retrained from adopting it because of the transmission qualities of the micro-telephone,
which were unquestionably deficient, and therefore would not meet American standards.
Its adoption would therefore have already greatly increased maintenance costs. Efforts on the part of American telephone engineers to overcome these obstacles were unsuccessful until the advent of a Bakelite hand unit of the style illustrated. It was not until then that domestic telephone companies felt assured of a practical micro-telephone type instrument comparable in performance with the conventional desk sets.
These instruments fulfil along-felt want and have won public approval, in fact, the new telephones are rapidly supplanting the conventional telephone sets.
The type of receiver used, depends upon the circuit of the Monophone set and may be either one of the two watch case patterns described under "Design of Apparatus". The transmitter is of the Monophone type previously described.
Plunger Spring Assembly
The manner in which the interior of the cradle houses the plunger switch assembly is shown. A top and a cross-sectional view of the assembly also shown, which shows the details of the switching mechanism. When the hand unit is placed in the cradle, the plunger is depressed. Its motion is in turn imparted to roller bushes which force the springs apart: when the hand unit is removed from the cradle the reverse action takes place.
The spring assembly is covered by a name plate held in place by a spanner nut. The springs
are readily accessible for inspection and adjustment.
Types of Monophone Sets
These various types are illustrated above. The hand unit and plunger spring assembly in all types are of the same design and construction.
The bases of both types of Monophone desk sets are of moulded Bakelite. Metal inserts incorporated in the Bakelite serve for terminals. This construction provides a substantial base of lasting durability. The desk set with the round base requires a separate bell box. This bell box in appearance is the same as the bell box previously described, except that it contains a three-winding induction coil. The desk set embodying the ringer movement is provided with a separate Bakelite connecting block for making the connection between the desk stand cord and the line wires.
A bell box with a dial mounted on its face is used for the base of the wall type Monophone set. The cradle is mounted on the top of the box.
The extension wall Monophone set illustrated is often referred to as a bed-side set because of its adaptability for hospital service, does not employ a cradle to hold the Monophone.
The receiver end of the unit hangs on a metal fork similar to a receiver hook. The fork, however, does not move. Instead, the hand unit rests against a plunger which projects front the front of the cover. The plunger operates the switching device. Since this set is used for answering service only, in automatic telephone systems, it is not equipped with a dial. The base, which has a Bakelite cover, contains sufficient space for mounting the switching mechanism, an induction coil, a condenser and the necessary terminals.
As explained under "Automatic Telephone Circuits" two fundamental circuits are standard for Monophone sets. They are both of the anti side tone booster- battery type. In one circuit, the anti-sidetone booster principle as incorporated in a three-winding induction coil operating in conjunction with a permanent-magnet receiver. In the other circuit, this principle is incorporated in the induction-coil receiver.
Since the three-winding induction coil located in the bell box if the round-base Monophone desk set it is not possible to use the round base desk stand in conjunction with a bell box incorporating an ordinary two-winding induction coil when the permanent magnet receiver circuit is employed. If it is desired to replace an existing desk stand with the round-base Monophone desk stand and retain the old bell box, the induction coil receiver circuit Monophone desk stand must be used, as it only requires that the bell box contain a ringer and a condenser. If the existing bell box contains an induction coil it must be omitted from the circuit: i.e. the bell box should be rewired to conform with the circuit diagram for the telephone involved.
Last revised: October 04, 2012