7
1/4
IN.
7
1/2 IN.
8
I/2 1N.
Fig. 1 1 -KS-1 6846, list 2 Loudspeaker
2. 1 6
The K 8 loudspeaker and the KS-16846, 12
loudspeaker are 45-ohm speakers. Do not
substitute other speakers for the K8 or KS-16846,
12 loudspeakers in the 7 A System.
KEY TELEPHONE UNITS
2. 1 7
The circuitry for the 7A Communication
System is provided by 400-series KTUs.
A. 400-Type KTU (CO or PBX Line Circuit)
2. 1 8
The 400-type KTU (Fig. 12) is a 4-inch unit
which provides a key telephone set with CO
or PBX line service. Additional information on
the 400-type KTU may be found in Section 518-215-400
and CD- and SD-69513-01.
Note:
The latest version of the line circuit
KTU is the 400G. All earlier line circuits are
rated MD but can be used when available.
B. 424A or B and 424C KTU (Dial Intercom, 1 9-Code
Selector Circuit)
2. 1 9
The 424A o r B KTU is a n 8-inch dial selective
intercom unit. Additional information may
be found in CD- and SD-69567-01.
The 424C
(Fig. 13) is the preferred KTU for replacements
ISS 3, SECTION 5 1 8-450- 1 00
and new installations.
In the 7 A System, the
424B/424C KTUs provide the following:
•
Rotary dial selection
•
Nineteen dial codes (nine single-digit and
ten 2-digit codes).
Note:
In the 7A System, the first digit of
the 2-digi t code is 1; therefore, 1 is not
available as a station code. Code 2 is dedicated
to paging which leaves codes 0 (attendant
station) and 3 through 19 available for station
codes.
Do not use
a 424A KTU
in the
7 A
System.
C. 440A (MD) KTU (TOUCH-TONE Adapter Circuit)
2.20
The 440A KTU (Fig. 14) is an 8-inch unit
that provides TOUCH-TONE dialing when
used in conj unction with the 424B/424C KTU.
Additional information on the 440A KTU may be
found in CD- and SD-69906-01.
Note:
The 440A KTU is superseded by an
improved TOUCH-TONE adapter, the 478B
KTU, which should be used for replacement
and for new installations (see 2.27).
D. 45 1 A or 451 B KTU (Music-On-Hold Circuit)
2.2 1
The 451-type KTU (Fig. 15) is a 4-inch unit
that is used with an exte!'nally mounted
33A voice coupler to connect a customer-provided
source of music to a maximum of seven CO/PBX
lines placed on hold.
Note:
The 451A KTU was formerly identified
as a 123A IU.
E.
452A KTU (Power Failure Transfer Circuit)
2.22
The 452A KTU (Fig. 16) is a 4-inch unit
that automatically "cuts through" up to
seven CO/PBX lines to external line ringers in the
event of power failure.
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