(8) The current adjust potentiometer.
(9) The east selector magnet (which produces receive copy).
c. The lighter area in figure 85 is not a part of the signal path when you are sending from west to east. However,
the parts in this lighter area do have current flowing in them. For example, the line winding of the relay at the west dc
repeater has current flowing through it continuously to hold its armature at the mark (M) contact.
d. When you are transmitting a mark from west to east, three circuits work in conjunction with one another. The
circuits are as follows:
(1) The west loop circuit. In this circuit current flows from the negative side of the battery near the transmitting
contacts, through the transmitting contacts, the selector magnet, the current adjust potentiometer, the line winding of the
send relay, the mark contact of the receive relay, to ground at the receive relay, and up from ground to the battery.
(2) The line circuit. In this circuit current flows from the negative side of the battery near the mark contact, of the
west send relay, through the mark contact, the current adjust potentiometer, the line, the winding of the east receive relay,
to ground, and up from ground to the battery near the mark contact of the west send relay. The current in this circuit is
normally adjusted to 30 ma, although in some equipment, it may be 20 ma.
(3) The east loop circuit. In this circuit the current flow path is the same as that in the west loop circuit.
e. The bias circuit for each send relay has current flowing in it at all times. Current flows from the negative side
of the battery through the bias current adjust potentiometer to the bias winding (contacts 2 and 7), and returns to the
positive side of the battery. Using a milliammeter (not shown), you adjust the current so that it is one-half of the line
winding current when a mark is being transmitted.
f. When you are sending a space at the west station, there is no current in the west loop
circuit. The bias winding of the send relay causes the armature to snap back, breaking the mark (M)
circuit and making contact with the space (S) circuit.
Current then flows in the line circuit in the