Bell System Practices 1A Instruction Manual

BELLSYSTEMPRACTICES
Station Operations Manual
Minor Station Systems
SECTION C70.201.01
Issue 1, November, 1959
AT&TCoStandard
1A AND 1A1 SPEAKERPHONESYSTEMS
INSTALLATION AND MAINTENANCE
1.00 INSTALLATION
Control Unit
1.01 Locate and install the control unit in
accordance with the following:
• Allow 20 feet maximum cable distance be-
tween the control unit and other com-
ponents of the speakerphone system.
• Mount control unit:
1. On an insulated surface.
2. Within 6 feet of a 105- to 125-volt 60-
cycle ac commercial power outlet fur-
nished and maintained by customer.
Power outlet shall not be under control
of a wall switch.
• Place transmitter:
1. Within convenient reach of customer.
2. Three feet minimum from loudspeaker.
Note: There should be no obstruction between
the customer and transmitter or loudspeaker.
Under no circumstances connect the
power cord of the control unit until all
work is completed.
• Fasten the power cord with a Tinnerman
clamp (5A or 6A) and an ES-528772
bracket. Attach a tag (form E-3013) to the
bracket. This is the same tag that is used
on ground wire clamps. In certain areas
where local ordinances prohibit this method
of securing the cord, place only the tag near
plug end of cord. Be guided by local
instructions.
Associated Components
1.02 Fig. 1 and 2 show typical installations.
Fig. 1-Speakerphone System Components with
5928 Telephone Set
Fig. 2 -Speakerphone System Components with
Key Telephone Set and 656A Transmitter
© American Telephone and Telegraph Company, 1959
Printed in U. S. A. Page 1

SECTION C70.201.01
1.03 For installation of 661A transmitter and
A13A cord, refer to C Section covering 600-
type telephone sets.
Self-switching Circuit
1.04 Self-switching is the automatic transfer
from receiving to transmitting condition.
This circuit is controlled by a signal transmitted
by voice, room noises, or loudspeaker. The level of
signal necessary to cause switching has been pre-
determined. .
1.05 For lAl speakerphone installation, place
the audible signals where there will be no
interference with the self-switching feature. It
may be necessary to lower the volume of the
audible signal.
2.00 ADJUSTMENTS AND TESTS FOR
1A1 SPEAKERPHONE
ftAmplifier potentiometers and the poten-
tiometer on the applique (part of con-
trol unit) have been set with a test set
and ahall not be changed.
2.01 Adjustments consist of connecting the SP2
loudspeaker lead to various terminals of the
KS-14964, List 3 control unit. Proper connections
compensate for the acoustic reverberant condi-
tion of the room by inserting several values of
resistances in series with the loudspeaker.
2.02 If self-switching occurs during a test call,
the SP2 loudspeaker lead should be con-
nected for a more reverberant room condition. It
is, however, desirable to keep the resistance in
series with the SP2 loudspeaker lead to a
minimum.
2.03 As a guide in connecting the SP2 loud-
speaker lead for room adjustments, rooms
are classified into four types:
• TYPE 1 - Low Reverberation
Page 2
A room with very little echo or reverbera-
tion will have a large amount of sound-
absorbing material such as acoustic ceiling
treatment together with carpeting or rugs,
window or wall draperies, and upholstered
furniture. For _this type of room, connect
the SP2 loudspeaker lead to terminal 14 of
TSI.
• TYPE 2 - Moderately Low Reverberation
A room with a moderate amount of rever-
beration will have either carpeting or
acoustic-treated ceiling, and perhaps drap-
eries or upholstered furniture. Connect the
SP2 loudspeaker lead to terminal A of the
applique unit.
• TYPE 3 - Moderately High Reverberation
A room with this level of reverberation will
have less acoustic treatment than TYPE 2.
For this condition, conn.ect the SP2 loud-
speaker lead to terminal B of the applique.
• TYPE 4 - High Reverberation
A room with high reverberation will have
practically no sound-absorbing qualities. In
this condition, the SP2 loudspeaker lead
should first be tried on terminal B of ap-
plique and, if self-switching occurs, be
moved to terminal C of the applique.
ftA void using terminal C unless false gain
switching is objectionable.
D
3.00 TESTCALL FOR 1A 1 SPEAKERPHONE
When all connections have been made:
• Place a call to test desk.
• Adjust the loudspeaker volume to a mod-
erately loud listening level.
• Have the test deskman repeat the sentence,
"In what suburb does Joe live," several
times.
• If installer detects choppiness in the sen-
tence, particularly in the first b in suburb
and the t in what, connect SP2 loudspeaker
lead to the next terminal that adds resist-
ance (eg, terminal 14 to A and so on).
• Repeat this test at a high-listening level by
turning the volume control clockwise.
• When there is no choppiness, the room ad-
justment is satisfactory.

4.00 MAINTENANCE
Always remove power cord from. the
power outlet when working on control
unit.
4.01 For maintenance on control units, proceed
as follows:
• Check that power cord is connected to com-
mercial power outlet.
• Press ON button. If pilot light fails to
light, test power supply outlet with a neon-
lamp voltage tester or equivalent.
• When commercial power is entering the
control unit, and amplification seems to be
deficient in either receiver or transmitter
circuit or both, replace the amplifier unit
with one known to be serviceable.
• If changing the amplifier clears the trouble,
interchange the tubes, one at a time, from
good amplifier to defective amplifier. Orient
them so that the red mark on the tube base
faces both the top of the card and the dot
near the top end of the socket. If this does
not clear the trouble, it can be assumed
that trouble is internal in the amplifier.
Leave serviceable amplifier in place and
return defective amplifier according to local
instructions.
Note: Do not change amplifier gain controls.
• If trouble still persists, replace complete
control unit.
SECTION C70.201.01
4.02 Fluorescent lights, transformers, motors,
or other similar apparatus may cause an
inductive noise in the loudspeaker. Grounding the
amplifier chassis may eliminate this noise. In cer-
tain areas, local ordinances may not permit
grounding. Be guided by local instructions.
• The ground wire should be run separately
from a mounting screw inside control unit
to a radiator or an electrical conduit
system.
• If this does not eliminate noise, it can be
assumed that the ground is poor, and the
ground wire should be run to a cold water
pipe instead.
Where the regular transmitter (U1-type
receiver) is troubled by inductive inter-
ference fr.om power 3ource, the trouble
may be remedied by 'ltSinga 658A trans-
mitter (
HC3 receiver with a cpld-rolled
steel shield). These tra,mmitters are
completely interchangeable but used
onJ,yon a maintenance basis.
4.03 After working on equipment, test the com-
plete system. For lAl speakerphone test
call, refer to 3.00.
5.00 RADIO INTERFERENCE
Where radio interference is experienced in
the telephone set, a suppressor may be installed.
See C Section entitled Radio Signal Suppression
in Telephone Sets.
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