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TM 11-5830-255-14
audio power amplifier and the output is applied
through L-pad volume control AT1 to speaker
that have been selected by depressed pushbut-
LS1, thus channel A is monitored. MOD A push-
tons S1 through S20 on a selected basis. The
button is not illuminated. pushbutton selector
R (ring) lines provided for each channel from
switches S4A-B are mechanically interlocked so
1 through 20 are used to connect the negative
that operation of any one button releases the
dc from the associated ring button (either local
previous selection. Channel A audio input is con-
or remote) through section C of pushbutton
nected through terminals S4C-1 and S4C-2, ter-
switches S1 through S20. current limiting re-
minds TB1-1 and TB1-2 to amplifier 1. The
sistor R1 is used to limit the current flow
output of amplifier AMPL-1 is applied to the
through DS1. Channel lamps DS1 through DS20
VOLUME control AT1 and loudspeaker LS1 to
are illuminated on an incoming call by the ap-
produce the audio output from channel A. At
plication of -48V on the R leads from the
the same time, S4C-4 connects the negative lead
remote stations. They will also illuminate on
to lamp DS2, and, since DS2 is also permanently
calls originated from the central unit through
connected to the positive power terminal, chan-
the D contacts of pushbutton selector switches
nel A (OPER A) lamp is illuminated.
S1 through S20. Release button (marked REL)
operates and closes contact D operating release
(2) Channel B is monitored similarly
relay K2, which actuates the mechanical release
through selector switch S4D- and S4D-2. Chan-
mechanism of the selector switch. An unused and
nel B is operated through the OPER B button
unmarked spare button is provided.
controlling selector switches S4E-1 and S4E-2,
and channel B lamp DS3 (OPER B) is illuminated
d. Power Circuit. The 48-volt dc supply is
through S4E-4.
protected by indicating type fuse F1 rated at 2
amperes, and controlled by ON-OFF toggle
(3) Indicator lines L5 and L9 on terminal
switch S23, placed in the negative lead from
board TB3 are connected to -48V dc whenever
terminal 2 of TB3. Termimal 1 of TB3 is strapped
OPER channels A or B, respectively, are oper-
to terminal 3 to provide a positive common re-
ated to power the channel indicator at the re-
turn from the selector switch lamps DS1 through
mote stations.
DS20, talk relay K1, and to alarm DS21 through
(4) Whenever channel A or channel B is
protective and voltage dropping resistor R1.
operated, selector switch S4C-3 or S4E-3 con-
Thus, operation of all active components is com-
nect -48V dc to diode CR1, or CR2, respec-
pleted by controlling the negative lead. All am-
tively. This forward biases the diodes, connect-
plifiers are permanently connected to the power
ing aural alarm DS1 through push-to-call
supply through pin terminals 8 (-) and 9 (+)
(RING) switch S2, when the RING button is
on the modules, TB1-13 and 14, respectively.
pressed, causing the illuminated channel to ring
Terminals 4 through 8 of TB3 are strapped
at both local and called locations.
together to supply 8 negative voltage through
b. Talk Circuit. W h e n t h e L I S T E N - T A L K
contacts D of S1 through S20 to provide a local
switch is set to the TALK position, S1 connects
and remote lamp indication when a channel se-
relay K1 to negative 48V dc through contacts
lector pushbutton is operated, thereby indicat-
1 and 2 and switches loudspeaker LS1 to the
ing the channel in use.
input of microphone preamplifier TLC-503, and
the output of amplifier AMPL-2 to the selector
4-4. Remote Intercom Unit Circuit Analysis
switches through relay contacts 3 and 4. Thus,
(fig. F0-3)
the talk output is connected to the VF lines
through either channel A or channel B OPER
a. Listen Circuit.
pushbutton, the output is adjusted for 8 nomi-
(1) In the LISTEN position, LISTEN-
nal -6 dBm.
TALK switch S1 and relay K1 remain inopera-
tive, and output power amplifier TLC-409 is
c. Power Circuit. The 43V dc supply from the
ready for operation with 48V dc applied to mod-
station source is controlled through fuse F1, an
ule power terminals 8 and 9. When MON A
indicating type fuse rated at 1-ampere, and tog-
switch is depressed, selector switch S4B-1 and
gle switch S3 is placed in series with the nega-
S4B-2 connect terminals TB3-3 and TB3-4 to
tive lead from terminal 2 on terminal board
the audio (VF) line of channel A to AMPL-1.
TB3. The positive lead of the power supply from
The incoming VF is applied to the TLC-409
TB3-1 is permanently connected to the selector

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