Section VI
Paragraphs 6-34 to 6-39
unit which has been operating satisfactorily suddenly
drops off in performance, it is very unlikely that mis-
alignment is the cause.
Ball bearings should be lubricated as soon as
possible after cleaning, inspection, and test-
When misalignment is suspected as a cause of
ing. Never spin a ball bearing which is not
trouble check all other logical causes Of trou-
lubricated. Do not handle ball bearings with
ble before undertaking realignment.
fingers. Doing so may cause corrosion. Use
tweezers or gloves.
r-f chassis of the signal generator is accomplished by
Wipe the bearing with a soft, clean, lint-free cloth.
following the procedure outlined below.
Place the bearings in a clean, corrosion-resistant
wire basket, and suspend the basket in a container
a. Connect Power Cable Assembly CX-1095/U or
bf filtered benzene, U. S. Army Specifications No.
CX-1506/U to the 21VDC-29VDC connector on the sig-
4-1016B. Agitate the basket to aid in flushing out the
nal generator and to the source of power.
sludge. If necessary use a short bristled brush to
remove the dirt. Place the bearings in a clean cov-
b. Turn the METER switch to the LINE position and
ered container until ready to use.
turn the SET LINE TO 2 IV control until the meter
reads 21 0.5 volts.
6-35. INSPECTION OF DYNAMOTOR BALL BEAR-
INGS. Test each ball bearing by slowly rotating it.
c. Turn METER switch to B+ position and read B+
Beartngs showing pronounced bumps or stickiness
should be discarded and replaced. Inspect the bear-
voltage on meter. Reading should be 230 volts. Allow
10 minutes warm up.
ings for cracks, rough or pitted surfaces, and dam-
aged balls. The bearings should be a push fit on the
armature shaft and hand tight in the housing.
d. With METER switch to CAR position, and CAR-
RIER SET control fully counterclockwise adjust ME-
TER ZERO control until the meter reads zero.
INGS. Lubricate the bearings with AN-G-25 grease.
e. Set MICROVOLTS dial to read 1K or lower.
f. Turn MEGACYCLES control to 135.5 mc and set
Do not jam the bearings full of grease. Only
the meter to the red line with the CARRIER SET con-
enough grease to fill one side of the ball race
trol if possible.
is necessary. Packing the bearings with grease
g. Connect a d-c vacuum tube voltmeter to E1508
will tend to cause the grease to run through
the bearing seals and create excessive heat due
to churning during operation.
h. Insert the iron end of the tuning wand into L1503,
6-37. ALIGNMENT.
L1504, L1510, L1511, L1505 and L1506 (figure 6-11)
and note any increase in d-c voltage at E1508. In-
6-36. INTRODUCTION. Signal Generator SG-13/ARN
sert the iron end of the tuning wand into L1508 (fig-
is carefully aligned and tested before it is shipped
ure 6-11) and note any increase in output on the CAR
from the factory. The slugs and tuning capacitors are
meter. Insert the brass end of the tuning wand into
carefully adjusted at the factory and should never re-
the same coils and note any increase in E1508 voltage
quire more than a very slight adjustment.
or CAR meter reading. If a circuit is properly tuned
inserting either end of the tuning wand will cause the
output to drop. Note the results but do not make any
adjustments. It will be noted that the tuning of the
Do not change slug positions or adjust variable
last two coils toward the front of the r-f chassis is
capacitors except when making fine adjust-
much more critical than the tuning of the preceding
ments during actual alignment. Indiscriminate
stages.
tuning will inevitably result in a completely
misaligned instrument which will be difficult
i. Repeat step hat 108.5 megacycles.
to repair.
j. Measure the d-c voltage at E1508 as the MEGA-
If alignment is needed it is usually due to a change in
CYCLES control is rotated over the entire range. If
capacitance which can be corrected by adjusting the
the alignment is good the voltage will be at least -1.0
tuning capacitor only. The tuning slugs will seldom
volt for any frequency. This is an overall check of all
need resetting and when they do the change necessary
tuned circuits except the final circuit, Z1502.
will be very small. The need for alignment will be
indicated when it is not possible to adjust the needle
k. If the above steps indicate the need for alignment,
on the meter to the red line when the METER switch
continue with step 1, below. The final tank circuit,
is in the CAR position. This condition, however, can
21502, is the one most likely to require alignment.
be caused by faults other than misalignment such as
In most cases a slight adjustment of C1529 (figure
bad tubes or a faulty meter or metering circuit. If a
