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Pictures dated 1921
MAIN AND SECONDARY TELEPHONE FOR MANUAL NETWORKS
CENTRAL BATTERY
CONVERTIBLE INTO TELEPHONES OF THE SAME TYPE FOR NETWORKS OF THE INTEGRAL
AUTOMATIC SYSTEM
In certain installations, it is sometimes necessary
to connect to the main unit, connected to the central unit, an additional
unit which, for its communications with the central unit, would use the same
line as the first. We have therefore designed for this
purpose a series of new model units. By means of these designs, it will be
possible to achieve the various desired combinations.
The main unit connected directly to the central unit is an ordinary
telephone set with folding equipment. It is supplemented by:
1) an
auxiliary box containing a generator with 3 magnets and a polarized ring,
2) a signal light,
3) a switch with three positions (the normal position
and two other positions numbered 1 and 2).
The secondary station is
identical in every respect to the main station except that it does not have
a signal light or an additional ringer.
These additional devices
serve either to transfer the line from the main station to the secondary
station, or to allow conversation between these two devices without going
through the central station, and finally to control these various
operations. The role of the key is defined by the following operating mode:
a) NORMAL POSITION
In this position, the ringer of the main station
is connected to the central line. From this position, all calls to the
central station are received by the main station. It will be possible to
call the secondary station back using its auxiliary generator.
b)
POSITION NO. 1
This position connects the secondary station to the
central station. During the conversation, the indicator light on the main
station is activated, thus connecting the line to the control panel. When
the receiver is hung up on the secondary station, the line is released and
the indicator light on the main station returns to its normal position,
indicating that the conversation has ended. At the same time, attention is
drawn to the main station and the key can be returned to its normal
position.
c) POSITION No. 2
The main and secondary stations are
connected in series with a local battery, allowing them to communicate
without intervention from the control panel. When the key is in this
position, the secondary station's additional ringer is connected to the
control panel line, so that the key can receive calls from that key.
GENERAL NOTE
When a call intended for the secondary station is received
by the main station, the latter will ring the secondary station, which, upon
answering, will turn its generator's crank. The main station will then set
the dial to position No. 1. The operation of the
signal at the main station will indicate to it that the conversation is in
progress. The operation of the key will not, even momentarily, break the
connection with the main station, as its contact springs are arranged in
such a way that the connection from the main station to the main station is
only broken after the secondary station is connected to the line.
This precaution is necessary for the possible reuse of these stations within
the networks of the integrated automatic system.
It is indeed
important in this system to use a key that avoids any untimely break in the
circuit, which would trigger the automatic devices at the central office and
cut off communication. The line to the central office
is freed, regardless of the key's position at the main station, as soon as
the receiver at the secondary station is returned to its hook.
The operators are equipped with two additional terminals that are normally
connected to the line terminals of each of them. If
these connections are removed and these additional terminals of the two
stations are joined by two new lines, the signaling currents between the
stations will pass through these latter lines, and the untimely sending of
the inrush current by one of the stations, on the external line regardless
of the key's position at the main station, will be completely prevented.
Table Telephones Main
Telephones 22666
Steel
cased telephone, for manual areas, with a handset, magneto generator, key and indicator.
72666
Steel cased
telephone, for automatic areas, with a dial, handset, generator, key and indicator.
Taken from the BTMC Catalogue - 1924
Click here for wall type extension telephones
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BELL
TELEPHONE MANUFACTURING Co.