Trigger tube.
secondary clutch, which permits intermittent
slippage. During a part of each revolution, the
drum is driven by the secondary clutch, the drive
The talk-back circuit, only on Facsimile Trans-
being active only when the dog latch is engaged
ceivers TT-1A/TXC-1 through TT-1F/TXC-1, is
in the secondary clutch ring. During the rest
controlled by the STANDBY-MON-TALK switch
of each revolution, a cam operating on the dog
S5) on the front panel. The circuit is operative
latch disengages the dog latch from the secondary
only when the selector switch (S1) is in the
clutch ring, permitting the slippage (fig. 19).
When the STANDBY-
STANDBY position.
When a phasing pulse from the transmitting sta-
MON-TALK switch is in the TALK position, the
tion energizes the phasing magnet, the phasing
loudspeaker plugged into SPEAKER JACK J7
magnet armature is drawn to the magnet, the
becomes a magnetic microphone and transforms
travel of the stop arm is no longer impeded, and
speech sound waves into electrical currents, which
the primary clutch resumes rotation. The first
are transferred to the line through the speaker
phasing pulse may serve to phase the stop arm
transformer, amplifier stages V10, V11, and V12,
to the transmitting drum correctly, although
and output transformer T2 (figs. 51, 53, and 54).
several are allowed. Once the correct phasing is
For reception of voice signals with the switch in
established, additional phasing pulses pull the
either the STANDBY or MON position, the sig-
phasing magnet armature out of the way just as
nal from the line is fed through input transformer
the stop arm approaches it on each revolution.
T7, the GAIN control, amplifier stages V10, V11,
The PHASE switch then can be released. How-
and V12, and through the speaker transformer to
ever, the entire phasing operation is not complete
t h e speaker. The STANDBY-MON-TALK
until the stop arm actually engages the dog trip
switch makes the following circuit connections:
arm (fig. 20). Only then is the receiving drum,
a. Standby.
as well as the stop arm, phased to the transmitting
(1) The LINE binding posts are connected
drum. For this reason, the operator must allow
to the primary of input transformer T7
a few extra revolutions for the stop arm to catch
through S1, section 1, and S5.
up with the dog trip arm and transfer the drum
(2) The LINE JACK is connected to the
drive from the secondary clutch to the primary
secondary of input transformer T7
through S1, section 3, and S5.
clutch before assuming that phasing is complete.
