DESCRIPTION OF S-LINE AND KWM-2 DIAL ASSEMBLIES
AND THEIR ALIGNMENT PROCEDURES
4-15-61
Tuning of the amateur equipment vfo is accomplished through the use of two
separate adjustable components. These are:
1. The calibrating fiducial with the red calibrating line.
2. The dial assembly which includes two dial discs mounted on the vfo
shaft.
The calibrating fiducial is driven by rotating the zero set knob located in the
upper right-hand corner of the black escutcheon. Driving torque is transmitted
to the fiducial through a set of two friction drive washers, one washer bearing
on either side of the fiducial near the top edge.
In the event that the fiducial becomes bound or its operation becomes
irregular, the following adjustment procedure should be performed:
1. Loosen the setscrew on the zero set knob using a No. 4 Bristol wrench.
2. When the knob is turning freely on the drift shaft, rotate no fewer
than five complete turns, at the same time pressing it lightly against
the escutcheon. This allows the friction drive washers to center
themselves with respect to the fiducial and, at the same time, keep
the end play at a minimum.
3. Tighten the setscrew in the knob, and check the operation of the
fiducial.
If the above procedure does not improve the operation of the fiducial,
replacement parts are probably needed, and further checks should be made by
factory personnel.
The two dial discs of the dial assembly are, in addition, two gears. The
number of teeth on each of these gears is not equal, and when they are brought
into mesh with a common idler, as is done in the S-Line and the KWM-2, relative
motion between the two dials is produced. This motion is used to mask out one
of the two sets of numbers printed on the rearmost dial, thus allowing two
revolutions of the assembly over a bandwidth of 200 kilocycles. This
arrangement makes it possible to double the space between two consecutive
kilocycle graduations and, therefore, permits more accurate tuning of the vfo.
Improper mesh of the idler pinion with the dial discs may cause the dial to
malfunction in one of the following ways:
1. Too great a mesh will prevent the dial from being driven by the tuning
knob or may cause it to hesitate as it is being driven across the
range.
2. Too little mesh may cause the proper relative position between the two
dials to be lost.
In the event one of the above symptoms is present, the following procedure
should be performed:
1. Dismount the light bracket by removing the two black oval-head screws
from the top of the escutcheon. In the KWM-2, an additional self-
tapping screw must be removed from the extreme left side of the light
bracket, as viewed from the front of the radio. This will expose the
idler for visual inspection.
2. Check the mesh between the idler and the dials while rotating the
dial. The proper degree of mesh is from 30 to 70 percent.
3. If necessary, adjust the position of the idler by first loosening the
Phillips-head mounting screw through the hub until the idler can be
removed freely, and then hold the idler in the desired position while
the screw is being tightened.
4. If the relative position between the two dial discs requires
correcting, the idler must first be taken out completely and then
replaced after the proper position of the dials has been obtained.
5. Before the light bracket is replaced, the calibration of the dial must
be checked with the calibration signal and corrected if necessary.
For adjusting the 75S-1 and the KWM-2, rotate the vfo shaft for zero
beat against the crystal calibrator signal. The 32S-1 transmitter
calibration may be set by placing the transmitter FREQ CONTROL in the
SYNC position and tuning for zero beat against the receiver indicated
frequency.
The dial assembly, which includes the two dial discs, the black nylatron drive
ring, and the aluminum hub, is assembled with six 0-80 screws whose heads are
visible on the back of the aluminum hub. If these screws are not properly
tightened, the dials may be free to turn relative to the oscillator shaft and,
hence, cause the dial to drift out of calibration. If these screws require
tightening, carefully make the following check.
On older units of the S-Line and KWM-2, an all-nylatron drive ring was
used. These units can be identified by the absence of split lock washers
under the 0-80 screw heads and the presence of blue liquid varnish (Blue
Glyptal) applied as a liquid stake.
On newer units of the S-Line and KWM-2, a drive ring with an aluminum
outer rim is used. These units can be identified by the presence of
split lock washers under the 0-80 screw heads.
On the older units, the screws must be lightly tightened - repeat - LIGHTLY -
and then liquid staked or cemented. It is recommended that each screw be
removed individually to place a drop of liquid staking on the threads and then
re-inserted.
On the newer units, a minimum of seven inch-ounces of torque must be applied
when tightening the screws. No liquid stake or cement is required.
Seven inch-ounces will tighten screws properly. Seven inch-ounces of torque is
approximately equal to maximum force which can be applied to these screws with
the small to medium sized flat blade screwdriver which would be used on them.
If the dial operation continues to be erratic after the above adjustments have
been performed, no further corrective action should be attempted by the
operator. Special equipment and some experience are required to carry out any
further adjustment and/or repair.
This installation of new dial parts requires a complete understanding of the
dial mechanism and its operation. The tools that are required are a Phillips-
head screwdriver, No. 4 and No. 6 Bristol wrenches, a 3/16 spin tight
(nutdriver) or wrench (pliers), a long-nose pliers, and a thin bladed small
cabinet screwdriver. The new parts are lubricated before they leave the
factory, and no further lubricant should be applied.
The dial assembly used in the S-Line and the KWM-2 is driven by the drive
washers mounted on the tuning knob shaft. The principle of the drive can be
demonstrated by placing the raised inner diameter of the black nylatron drive
ring between the two sets of drive washers. By rotating the tuning knob shaft
between the fingers, it is possible to feel the transmitted torque in the dial
assembly with the other hand.
The procedure followed while installing the new parts will consist of three
distinct parts. These are:
1. Disassembly.
2. Installation of New Parts, Alignment, and Reassembly.
3. Calibration.
The disassembly operation will involve removing the light bracket and the
oscillator from behind the dial. When this is done, access to the dial itself
is possible. The final step in this operation will be the removal of the black
plastic escutcheon from the front panel of the receiver. At this point,
replacement of the old parts with the new will begin.
To read and interpret the newly assembled dial, it is necessary to calibrate it
using signals of a known frequency. This will be the final step of the
installation procedure.
Following is a step-by-step description for each of the procedures.
1. Disassembly.
1.1 Remove the chassis from the cabinet by removing the four rubber feet
and the single Phillips-head screw from the bottom of the cabinet and
the two Phillips-head screws which are under the lid at the front of
the chassis. Pull the chassis forward out of the cabinet.
1.2 With the chassis right-side up on the bench, remove the 6AU6 tube
from the top of the oscillator chassis and the other tubes mounted in
the immediate vicinity of the oscillator. This will eliminate the
possibility of breaking them and provide added working space.
1.3 Remove the two black oval-head screws from the top of the escutcheon
(the black dial face plate located in the center of the front panel).
In the KWM-2, an additional self-tapping screw must be removed from
the light bracket at the extreme left, viewing the radio from the
front.
1.4 Pull the light bracket straight back until it is free of the screws
and adjacent components, and place it to one side of the chassis. It
is not necessary to remove any electrical connections.
1.5 Loosen the two setscrews on the dial hub, using a No. 6 Bristol
wrench.
1.6 Remove the two self-tapping screws which hold the oscillator assembly
to the chassis.
1.7 Keeping the dial pressed toward the front of the unit with one hand,
carefully pull the oscillator assembly back out of the way. Remove
the dial, and set it to one side. It is not necessary to remove any
electrical connections.
1.8 Check to see if the knob is secured by a clip or grub screws.
If there is no evidence of grub screw holes, the knob is secured by a clip.
Remove the tuning knob by pulling it, firmly, straight away from the
front panel. If the knob is secured by grub scews loosen them and remove
the knob.
1.9 The fiducial is the clear plastic sheet with the red calibrating
line. This is held in position by an aluminum bracket at the rear of
the escutcheon. Remove this bracket by removing the two Phillips-
head mounting screws.
1.10 Remove the idler assembly by removing the Phillips-head mounting
screw which passes through the hub, and set it to one side.
1.11 Remove the zero set knob by first loosening the setscrew with a
No. 4 Bristol wrench.
1.12 Push the fiducial to one side, past its stop, and pull the zero set
knob shaft through from the rear of the front panel. Leave the shim
washers in place on the shaft.
1.13 Remove the flathead screw next to the tuning knob shaft, and remove
the escutcheon by pulling it straight from the front panel. DO NOT
LOOSEN THE LARGE NUT ON THE PANEL BUSHING.
1.14 Remove the snap ring from the tuning knob shaft at the front of the
escutcheon, and pull the drive washer assembly through the panel
bushing from behind the escutcheon.
1.15 Remove the shim washers and snap ring from the drive washer
assembly, and place on the new drive washer assembly in the same
order.
2. Installation of New Parts, Alignment, and Reassembly
2.1 Mount the new drive washer assembly in the escutcheon in the
reverse order of step 1.14.
2.2 Remount the escutcheon on the front panel in the reverse order of
step 1.13.
2.3 Remount the zero set knob and the fiducial in the reverse order of
steps 1.11 and 1.12, making sure that the fiducial passes between
the two sets of washers. Make sure that the fiducial operates
freely and with a minimum of end play before tightening the setscrew
on the zero set knob.
2.4 Remount the fiducial bracket in the reverse order of step 1.9. A
small amount of Artgum eraser or beeswax placed on the end of a
screwdriver will aid in holding the screws in place on the tip while
they are being replaced.
2.5 Mesh the raised inner diameter of the black nylatron drive ring with
the drive washers. This operation can be viewed through the
inspection hole in the hub. Use care and make sure the ring surface
seats in the space between the drive washers.
2.6 Holding the dial in position, insert the oscillator shaft through
the hub and into the nylon bushing in the front panel. Turn the
dial by rotating the tuning knob shaft to make sure that the dial is
being driven. Tighten the setscrews onto the oscillator shaft.
2.7 At this point, the oscillator must be aligned so that no side load
is applied to its shaft due to misalignment with the nylon bushing
in the panel.
Viewing the radio from above, visually align the front surface of
the oscillator chassis with the front panel, and replace the two
self-tapping screws which mount the oscillator to the chassis. As a
check, turn the radio over, and observe the alignment of the dial
assembly with the front panel. The front surface should be parallel
with the panel.
2.8 Loosen the two No. 6 nuts at the rear of the oscillator chassis
until the oscillator moves freely on the mounting bracket. Set the
radio with the panel facing up, and rotate the tuning knob until the
oscillator centers on the mounting bracket. The oscillator should
now be aligned horizontally (step 2.7) and vertically. Very
carefully tighten the two No. 6 nuts, and set the radio back in an
upright position.
2.9 Once again, loosen the two setscrews in the dial hub until the dial
assembly is free to turn on the oscillator shaft. Rotate the tuning
knob no fewer than eight complete revolutions to allow the dial
assembly to seat itself axially with respect to the drive washers.
Do not tighten the setscrews at this time.
2.10 Adjust the fiducial until the red line is vertical, and then align
one of the 10-kc marks behind the red line. Directly behind this,
align the center digit of a three-digit number.
2.11 Carefully mount the idler assembly, refer to step 1.10, making
certain that the dial alignment is not disturbed. Make sure that
the washer behind the idler gear lies between the fiducial and the
clear plastic dial.
2.12 Rotate the dial by turning the tuning knob shaft, and check for
interference between the idler and the dial. If there is
interference, loosen the idler mounting screw and pull the idler
away from the dial. Tighten the mounting screw and recheck. The
mesh should be from 30 percent to 70 percent during complete
revolution of the dial assembly.
2.13 Replace the tuning knob.
3. Calibration
3.1 Tighten one of the setscrews on the dial hub, and rotate the dial
counterclockwise until it comes against the stop.
3.2 Loosen the setscrew, and rotate the tuning knob counterclockwise
holding the oscillator shaft stationary, until the dial has passed
6- to 7-kc marks past the 0 mark. Tighten both setscrews.
(To align the numbers so they appear centered in the window my also
be accomplished by rotating the dial assembly in the proper direction
a few complete revolutions with the setscrews securing the hub to vfo
shaft loosened to allow free rotation. The numbers will
automatically center in the window.)
3.3 Rotate the dial clockwise until it comes against the stop. Check
whether the dial has come to a stop at approximately an equal number
of kilocycle marks past 200 as it had past 0. If not, readjust as
outlines in step 3.2 until the dial comes to a stop at equal points
past the 0 and 200-kc marks.
3.4 Final calibration of the dial is accomplished as follows:
a. Replace the 6AU6 and other tubes removed.
b. Make the external power connections.
c. Adjust the zero set until the red line of the fiducial is
vertical.
d. Turn on the receiver, and rotate for a zero beat against the
100-kc calibrator. For the 32S-1, place the FREQ CONTROL in the
SYNC position, and rotate for a zero beat against the receiver
indicated frequency. If the dial calibration is excessively to
the left or right, loosen the setscrews in the aluminum hub, and
rotate the vfo shaft slightly for a zero beat condition with the
hairline in a more nearly vertical position. Retighten both
setscrews in the aluminum hub. Check the calibration of the dial
mechanism; the frequency calibration accuracy should be within
1 kc after midband calibration at the 100-dial marking.
3.5 Remount the light bracket in the reverse order of steps 1.3 and 1.4.
3.6 Remount the chassis in the cabinet in the reverse order of step 1.1.
4. If the dial requires further alignment, refer to the service instructions
section of your operating manual under VFO End point adjustment, VFO
centering and VFO overtravel.
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