National NC 303 User manual

Ske NATIONAL
NC
303
COMMUNICATIONS RECEIVER

STANDARD
FORM
WARRANTY
ADOPTED
BY
THE
RADIO
MANUFACTURERS
ASSOCIATION,
INC.
This
equipment
is
warranted
to
be
free
from
defective
material
and
workmanship
and
repair
or
replacement
will
be made
of any
part
which
under
normal
installation,
use
und
service
discloses
defect,
provided
the
unit
is delivered
by the
owner
to the
manufacturer
or through
the
author-
ized
radio
dealer
or wholesaler
from
whom
purchased,
intact,
for examination,
with
all transportation
charges
prepaid
to
the
factory,
within
ninety
days
from
the
date
of sale
to
original
purchaser,
and
provided
that
such
examination,
discloses
in the
manufacturer's
judgment
that
it is thus
defective.
This warranty does not extend to any radio products
which have been subjected to misuse, neglect, accident,
incorrect wiring, improper installation, or to use in violation
of instructions furnished by the manufacturer, nor extend
to units which have been repaired or altered outside of the
factory, nor to cases where the serial number thereof has
been removed, defaced or changed, nor to accessories used
therewith of other manufacture.
Any part of a unit approved for remedy or exchange
hereunder will be remedied or exchanged by the authorized
radio dealer or wholesaler without charge to the owner.
This warranty is in lieu of all other warranties ex-
pressed or implied and no representative or person is
authorized to assume for the manufacturer any other
liability in connection with the sale of their radio products.
National
Company,
Inc.
reserves
the
right
to
make
any
change
in
design
or
to
make
addition
to,
or
improvements
in,
its
proucts
without
imposing
any
obligations
upon
itself
to
install
them
in
its
products
previously
manufactured.

INSTRUCTION MANUAL
for the
NATIONAL
NC303
COMMUNICATIONS
RECEIVER
SECTION 1 DESCRIPTION
1.1 GENERAL
Your National Model NC-303 is an amateur-band
receiver incerporating all the design features necessary
to provide optimum performance consistent with present
day operating requirements. Elimination of general
frequency coverage and all circuits not pertinent to
amateur operation has enabled National to produce a
compact, efficient receiver with the built-in rugged
dependability
characteristic
of
National
Company
prod-
ucts, Contributing to the utility of the receiver are a
Q multiplier rejection notch, an S-meter, variable IF
selectivity plus selectable SSB with a fast-attack — slow-
release AGC circuit, a muting circuit, a heterodyne
detector,
and
separate
noise
limiters
for
AM
and
for
SSB and CW reception. These operational features as
well
as
basic
design
improvements
result
in
a
receiver
with
exceptional
oscillator
stability,
high
sensitivity,
and
extreme
versatility.
Your
NC-303
features
a
double-conversion
super-
heterodyne
ciccuit
employing
15
tubes
including
the
rec-
tifier,
voltage
regulator
and
current
stabilizer.
Through
careful
selection
of
intermediate
frequencies,
excellent
selectivity
and
image
rejection
have
been
achieved.
Fre-
quency
coverage
includes
the
160,
80,
40,
20,
15,
11
and
LO meter
bands
plus
the
"X"
band,
The
“X"
band
functions
as
a tunable
IF
in
the
30-
to
35-megacycle
range
for
use
with
broad-band
crystal
converters
avail-
able
from
the
National
Company.
Individual
scales
provide
direct
reading
calibration
for
6,
2 and
14
meters.
Each
amateur
band
has
an
individual
calibrated
dial
scale.
Tuning
is facilitated
by
the
fact
that
only
the
calibrated
dial
scale
that
is in use
is visible.
Band-
scanning
is accomplished
with
ease
as a result
of
the
use
of
a heavily-weighted
tuning
knob
coupled
to
a
free-moving
gear
train,
The
tuning
knob
has
a rim-
drive
vernier
to aid
in fine
tuning.
Careful
attention
to
mechanical
design
has
resulted
in
tuning
action
without
any
trace
of
backlash.
The
outward
appearance
of
the
receiver
is
com-
pletely
modern
and
functional.
Cabinet
and
panel
con-
struction
permits
the
receiver
to
be
removed
from
the
cabinet
and
rack
mounted
without
the
addition
of
any
parts
other
than
mounting
hardware.
Adequate
ventila-
lion
is
provided
by
the
use
of
convection
cooling
through
holes
in
the
chassis
and
perforated
cabinet
lid

1.2 FREQUENCY COVERAGE
Your NC-303 tunes all the amateur bands from 160
through 10 meters plus a 30- to 35-mc band designated
as the "X” band foc use with external converters for
the 6-, 2- and 114-meter bands. Each dial scale is cali-
brated
for
only
one band,
Each
scale
has
band-limit
markings plus underscoring to indicate the phone por-
tion of the band. The dial drum rotates with the band
switch so that only the dial scale associated with the
band
being
tuned
is
visible.
The
following
table
gives
the frequency of each band tuned by your NC-303.
BAND
FREQUENCY
RANGE
160
1.8-
2.0
mc
80
3.5-
4.0 me
40
7.0-
7.3
me
20
14.0-
14.4
mc
15
21.0-
21.5
mc
11
26.5-
27.5
me
10
28.0-
29.7
mc
6
49,5
~-
34.5
me
(with
converter)
2
143.5
-
148.5
me
(with
converter)
IY
220.0
- 225.0
me (with
converter)
wwvyv
10.6
me (with
calibrator)
1.3. CONTROLS
The following controls appear on the front panel of
your NC-303:
Tuning Knob and Vernier
AFG — Audio frequency gaia control
REG — RF gain control
TONE
(HI-N-LO-PK)
~~
Audio
response
switch
ANL — Automatic AM and manual CW-SSB Noise
Limiters
MODE
(ACC-AM-CW-SSB)
—
Operating
mode
SELECT
(S-SB1-SB2-M-B)
— IF selectivity
BAND
— Tuning
range
selector
CWO — Heterodyne detector oscillator tuning
NOTCH - Q multiplier notch tuning
DEPTH — Q multiplier notch depth control
ANT — Antenna trimmer
CAL-SET — Pointer position control
OFF-CAL-WWYV — Crystal calibrator function
switch
XMT-REC — Standby-Operate switch
14 1F SELECTIVITY
The IF passband may be set at S(400 eps), SBI(2 ke),
$B2(2 ke), M(3.5 kc), or B(B kc), at the operator's
discretion. The S, M and B positions are centered on
80 kc, with the SBi and SB2 positions centered at 81.5
and 78.5 ke respectively. Figure 1 shows the IF selec-
tivity characteristics. With the ever incrcasing amount
of activity on the amateur bands, variable selectivity is
a must on any modern communications receiver. For
copying CW signals in the midst of heavy QRM, the
400-cycle bandwidth is invaluable. The SBI and SB2
positions are special features of your NC-303 which
allow instantancous one-knob selection of the correct
sideband
for
SSB
reception.
These
positions
provide
optimum bandwidths of 2 kc centered on the received
sideband.
Either
sideband
of
a
DSB
signal
may
be
selected
for
optimum
reception.
The
M_
position
is
provided to improve the readability of phone operation
when interference is heavy, and the B posit
possible to copy net stations or round tbl
with a minimum of retuning, Attention to the 8-ke
bandwidth
is
also
important
when
the
converters
in
the
VHE ranges are being used.
1.5 Q MULTIPLIER
An adjustable rejection notch is invaluable in re-
ducing interference caused by heterodynes in the recep-
tion of phone signals, The Q multiplier in your NC-303
provides a very sharp rejection notch that may be posi-
tioned anywhere in the IF passband to reject interfering
carriers. Use of the rejection notch does not affect the
intelligibility
of
the
desired
signal.
Figure
1
illustrates
the Q multiplier rejection notch.
1.6 NOISE LIMITERS
Noise suppression in your NC-303 is accomplished by
two separate noise limiters, one for AM reception and
the
other
for
CW
and
SSB
reception.
The
clipping
level
of
the
AM
noise
limiter
is
set
at
an
optimum
value
of
40%
to
50%
modulation
and
automatically
maintains
the best signal-to-noise ratio regardless of signal strength
One of the outstanding features of your NC-303 is a
double-ended
noise
limiter
separate
from
the
AM
noise
limiter with a manually adjustable clipping level for
CW
and
SSB.
This
limiter
clips
both
positive
and
negative noise peaks.
1.7.
MUTING
CIRCUIT
A
built-in
muting
circuit
silences
your
NC-303,
when
desired,
without
resorting
to
the
use
of
relays.
Any
point
in
the
transmitter,
which
sapplics
approximately
minus
22
volts
with
the
transmitter
on,
may
be
connected

KO GFF RESONANCE
cy
jacocvoLes
Figure 1. IF and Q Multiplier Selectivity Characteristics
to the muting terminals at the rear of the receiver,
When the transmitter is energized, the audio amplifier
in the receiver is cut off to prevent feedback or key
clicks,
1.8 SINGLE-SIDEBAND DETECTION
Incorporated in your NC-303 are unique features
which provide stable, distortion-free SSB reception with-
out noise bursts and/or ignition interference. The IF
selectivities of SELECT control positions SB1 and SB2
provide optimum bandwidths for SSB reception. (See
IF Selectivity Characteristic curves, Figure 1.) The
operator may select either sideband with one control
and may switch sideband without retuning the receiver
or CWO control. Frequency stability is assured in your
NC-303 by using a first conversion oscillator with regu-
lated plate voltage, heater current stabilization and a
carefully temperature compensated high-C circuit. The
use of a crystal controlled second conversion oscillator
eliminates any possibility of frequency drift from this
source, The heterodyne detector oscillator (CWO)
utilizes another high-C tuned circuit to provide stable,
distortion-free audio from the incoming SSB signal.
A special fast-attack — slow-release AGC circuit pro-
vides essentially constant-level output at all times. A
separate noise limiter has been included to improve SSB
and CW reception.
Your NC-303 has provision for a slow tuning rate by
means
of
a
push-to-engage,
pull-to-release
vernier
sim
drive
for
the
main
tuning
knob.
This
vernier
reduces
the
tuning
rate
to
one-seventh
of
that
provided
by
the
main
knob,
The SSB
signal
may
be
rapidly
tuned
in
by
the
main
knob,
then
the
vernier
may
be
engaged
to
easily
tune
for
maximum
intelligibility,
The
vernier
may
be
disengaged
at
any
time
without
changing
the
receiver tuning by pulling the vernier knob outward,
1.9
AUDIO
RESPONSE
A
tone
switch
has
been
provided
to
allow
selection
of
the
best
audio
response
for
the
existing
signal
con-
ditions.
Provision
is.
made
to
attenuate
the
low
and
high
frequency
portions
of
the
audio
spectrum,
either
individually
or
together.
1.10 VOLTAGE AND CURRENT REGULATION
The filament current of the first conversion oscillator
in
your
NC-303
is
regulated
throngh
current
stabilizer
tube V-13(4H4-C). The result of this regulation is less
than a 30-cycle shift in oscillator frequency on the 10-
meter band for a 10% change in line voltage. Plates
and screens of the Ist and 2nd conversion oscillators
ate
voltage
regulated
by
the
voltage
regulator
tube
V-11(OB2).

1.4L
CONVERTERS
AND
CABINET
The
National
NC-300C1,
NC-300C2
and
NC-300C6A
broad-band,
¢rystal-controlled
converters
tune
the
4.
2-,
and
G-meter
bands
respectively.
The
slide
rule
dial
of
your
NC-303
incorporates
three
separate
dial
scales
to
provide
direct-reading
frequency
calibration
when
the
converters
are
used
with
the
receiver.
Al]
operating
voltages
required
by
the
converters
are
available
at
the
accessory
socket
of your
NC-303.
The National NC-303 converter cabinet is designed
to
provide
a
convenient
and
attractive
means
of
mount-
ing
the
converters.
From
one
to
three
converters
may
be
mounted
in
the
cabinet
which
matches
the
receiver
cabinet
and
is
identical
in
size
to
the
NC-303
speaker
cabinet,
A
four-position
switch
is
mounted
on
the
front
panel
to
permit
operation
of
the
receiver
or
any
one
of
the
three
converters
without
changing
connections
to
the receiver or antenna.
1.42 S-METER
The
S-meter
gives
the
operator
a
truc
indication
of
relative
strength
of
incoming
signals.
‘The
meter
is
calibrated
in
S
units
from
0
to
9
and
in
decibels
from
$-9
to
40
db
over
S-9.
A
potentiometer
is
provided
on
the
chassis
to
zero-set
the
meter.
1.13. TUBE FUNCTIONS
The
following
table
lists
the
types
and
functions
of
all
tubes
used
in your
NC-303:
TUBE TYPE FUNCTION
6BZ6 RE Amplifier
6AHG6 HE Oscillator
6BA7
First.
Mixer
6BEG
Second
Converter
SECTION 2
241 GENERAL
All installation procedures are described in this sec-
tion. Figure 2 locates connection points oa the receiver
and depicts typical installations. Before proceeding with
installation, raise the hinged cover of your receiver and
make sure that all tubes are seated firmly in their sockets.
2.2) LOUDSPEAKER
A National type NTS-2 speaker or any permanent
12AX7 (2. Multiplicr
BJO First IF Amplifier
6B]6 Second IF Ampliticr
GALS AM Detector, Noise Limiter, AGC
6ALS SSB-CW Noise Limicer
6BEG Product Detector
12AT7 S-meter Amplifier and AF Amplifier
6AQ5 Audio Output Amplifier
SY3GT
High
Voltage
Rectifier
OB2 Voltage Regulator
4H4-C Current Stabilizer
1N1692 AGC Clamp Diode
1.14 POWER REQUIREMENTS
Your NC-303 requires a 105-130 volt, 30/60 cycle
AC source of supply. Power consumption is approxi-
mately 70 watts.
1,15 CALIBRATOR SOCKET
A socket is provided on the chassis to permit insertion
of the National XCU-303 or XCU-300 crystal calibrator
unit. When the O AL-W WY switch on your NC-
303 is in the CAL position 100 ke markers are generated
for
checking
dial
calibration.
When
it
is
in
the
WWV
position, the calibrator can be checked against the 10 mc
WWY signal. Calibration of the crystal calibrator
frequency against WWYV is available only with the
XCU-303 calibrator.
1.16
ACCESSORY
SOCKET
The
accessory
socket
provided
at
the
left
rear
corner
of
the
chassis
is
designed
lo
accept
suitable
external
accessories
within
the
power
limitations
of
1.5
amperes
at 6.3
volts
AC
and
25
milliamperes
at 150
volts
DC,
See
the
schematic
diagram
for
pin
connections.
Refer
to
Scction
3
for
instructions
on
the
use
of
external
accessories.
INSTALLATION
magnet
dynamic
speaker
with
a
3.2-ohm
voice
coil
inay
be
connected
to
the
speaker
terminals.
No
polarity
need
be
observed.
2.3. CHANGEOVER RELAY
A
terminal
marked
RELAY
is
mounted
at
the
rear
of
your
receiver.
When
the
XM1-REC
switch
is
set
at
XMT,
the
two
RELAY
terminals
are
shorted.
Thus,
they
may
be
used
to
complete
any
external
relay
circuit
whether
it
be
AC
or
DC
so
long
as
the
circuit
require-

wuree
ee ee
Z ANELIFIER
1
i
{
to
13 TRAKSMITTER
CONTROL CIRCUSTS
RELAY METHOD
GRID BLOCK METHOD
RECOMMENDED MUTING INSTALLATIONS:
DIPOLE
NORMALLY CLOSED
EXTERNAL
10K
CONTACTS
ON
ANY
RF
GAIN
CONVENIENT
RELAY
CONTROL IN THE TRANSMITTER
CONTROL SYSTEM
Sa
4 ws
TO
l TRANSMITTER
METHOD OF WIRING EXTERNAL RF GAIN CONTROL
RECOMMENDED ANTENNA CHANGEOVER AND SHORTING
RELAY INSTALLATION
CONNECT EXTERNAL
RF GAIN
CONTROL,
CONNECT TO GOOD EXTERNAL GROUND
PLUG IN
IF RECEPTACLE IS NOT USED
XCU+303 OR XCU-300
CRYSTAL CALIBRATOR
CONNECT RF OUTPUT
FROM (4,2 OR 6 METER
CRYSTAL CONVERTER
NATIONAL NTS - 2
\
SPEAKER
PROVISION FOR
MOUNTING COAX
RECEPTACLE
REMOVE LINK AND CON-
NECT TERMINALS TO
TRANSMITTER MUTING
VOLTAGE {~22v0C)
CONNECT IN SERIES WITH RELAY
ACTUATING VOLTAGE TO CONTROL
ON-OFF OF TRANSMIT"ER BY MEANS
OF NC-303 XMT-RES SWITCH
CONNECT
TC
NORMALLY
OPEN
CONTACTS
OF
T-8
RELAY
TO
DISABLE
RECEIVER
!N
TRANSMIT
CONNECT SINGLE WIRE
ANTENNA IF RECEPTACLE
IS NOT USED
Figure 2. Typical Installation Plan

ments do not exceed 5 amps at ¢25 volts AC. A typicul
citcuil might consist of a L10-valt AC antenna change-
over relay in parallel with the transmitter plate supply
selay, with one side of the AC line broken by the NC-
303 RELAY connector strip. When connected in this
manner the XMT-REC switch on the reectver front
panel performs all the required change-over operations
for the entire station
2.4 MUTING
A MUTE-GND-STDBY terminal strip is mounted at
the rear of the receiver, ‘Vhese three terminals provide
for two cotirely different methods of receiver muting
during transmitting periods. With no external connec-
tions made to the strip, the receiver will be muted
whenever the XMT-REC switch is placed in XKMT posi-
tion. If muting is not desired (for transmitter monitor-
ing etc.) a jumper wire may be connected between
STDBY and GND. ‘The receiver now operates regard-
fess of the XMT-REC switch position, For remote
switching of the receiver, connect leads from the re-
mote switch to the STDBY and GND terminals leaving
the NC-303 switch in the XMT position. 1f CW break-
in operation is desired, the MUTE and GND terminals
may be used to mute the receiver. To accomplish this
it is necessary to find a point in the transmitter circuits
that will provide a source of negative 22 to 50 volts
when the transmitter is on. (A 100,000 ohm resistor
connected to the grid of a keyed stage which develops
at least minus 22 volts with the key down will suffice.)
Since grid blocking is employed in your receiver, no
current will be drawn from the transmitter. Connect
the minus 22-volt lead to the terminal marked MUTE
and the transmitter chassis to the terminal marked GND.
Leave the XM'P-REC switch on the REC position, When
the transmitter is Lurned on or keyed, your NC-303 will
automatically mute. Since the muting circuit is well
filtered, no key clicks should be heard.
2.5 ANTENNA
A two-terminal strip is provided for connection of
antennas fed by unbalanced transmission line systems.
Usually the most efficient antenna is the onc which has
been tuned and adjusted for optimum transmitting re-
sults. For the 40-, 80- and 160-meter bands, a single
wire antenna of between 15 and 40 feet should provide
ample signal pickup. This antenna should be connected
to terminal A, and a good electrical ground should be
connected to terminal B. Switching the antenna from
the transmitter to the receiver is most easily accom.
plished by means of a relay actuated by the RELAY
terminals af your NC-303.
Any of the popular dipoles, heams cte.. whieh are fed
with 50- to FO ohm coaxial cable will be tdeal, fn in
stullations where it is desired to usc an already cxisting
antenns with @ 300-ohm balanced feedline, ur antenna
coupler
such
as
a
balun
can
be
used
te
match
this
an
tenna
to the
70-ohm
unbalanced
input
of your
NC-303.
Vhe
balun
may
be
cither
a quarter-wave
section
of coax
oc
a
pair
of
balun
coils
NOTE
If the receiver is used in close proximity to the
transmitting equipment some provision oust be made
to short the antenna terminals to ground during trans-
mitting periods to prevent damage to the antenna
coils, This is most casily accomplished by means of a
relay connected to the antenna terminals and ground.
‘The relay should be located within six inchcs of the
antenna terminal strip to prevent excessive pick-up.
A chassis hole is located close to the A-G terminal
strip to permit attachment of a flange-mounted coax
receptacle. Removal of the lead from terminal A and
reconnection to the center terminal of the receptacle
will then cnable the uscr to utilize an antenna coax
plug. Connect the coax to a coaxial plug which mates
with the fitting selected for your NC-303. An alternate
method is to connect the shield braid of the coax to
terminal G and the inner conductor to terminal A. A
good clectrical ground should be used. This may be a
convenicat cold water pipe scraped clean of paint and
oxidation or a suitable ground-rod driven into the carth
as close as. possible to your receiver location. The out-
standing sensitivity and signal-to-noise characteristics
of your NC-303 cannot be fully realized unless every
effort is made to provide proper antenna and ground
facilities.
2.6 CALIBRATOR SOCKET
The calibrator socket toward the rear of your receiver
chassis is factory wired so that it is only necessary to
plug in the National XCU-303 or XCU-300 crystal
calibrator unit, The OFF-CAL-WWYV switch on your
front panei will then energize the calibrator when de-
sired.
2.7 ACCESSORY SOCKET
This socket permits a variety of accessorics to be used
with your NC-303, Audio devices such as a crystal
phono pickup may be connected to pins 3 and 6. Heater,
Bi, AVC and ground connections asc available for
external converters, etc. The receiver I’ output is con-
nected to pin 4 for use with SSB devices and the RF
gain bus is brought to pin 1 for external conirol of
RF gain.

SECTION 3 OPERATION
The purpose of this section is to provide you with a
clear and concise understanding of the operating tech-
niques of your NC-303 to assist you in securing maxi-
mum
satisfaction
from
the
receiver.
The
design
of
the receiver circuits provides every feature necessary
for outstanding performance but a thorough knowledge
of correct operation is required to utilize these features
to full advantage. For complete appreciation of your
NC-303 READ THESE INSTRUCTIONS CARE-
FULLY.
3.1
CONTROLS
Complete utilization of the operating instructions is
not possible without a thorough understanding of all
front-panel devices. See Figure 3 for the location of all
controls, The control designations used correspond to
the markings on the receiver.
ce
ML ANT
S METER CONTROL
S METER
ZERO SET
$2 SI
OFF-CALWWV AFG
SWITCH CONTROL
CAL SET
CONTROL
si
BAN!
Bis
ANL (Automatic Noise Limiter) — The ANL control
is
used
for
CW
and
SSB
as
well
as
AM
reception.
This
control
incorporates
a
switch
which
turns
the
limiter
off when the control is rotated to its maximum counter-
clockwise
position.
With
the
receiver
set
for
AM
operation
turning
the
control
clockwise
just
enough
to
throw
the
switch
places
the
AM
limiter
in
operation.
the
ANL
control
in
this
position
the
AM
noise
limiter is in full operation, and automatically maintains
the
best
signal-to-noise
ratio
regardless
of
signal
strength.
This
AM
noise
limiter
is
preset
at
the
factory
to
clip
at
an
optimum
value
of
40%
to
50%
modula-
tion. Further rotation of the ANL control has no effect
on
AM
reception.
With your receiver set up for CW or SSB operation,
the clipping level of the CW-SSB limiter is manually
set by the ANL control. Optimum noise clipping of
TUNING TUNING MODE
CONTROL, DIAL INDICATOR
¢20
NOTCH
CONTROL
Re2
DEPTH
CONTROL
se}
XMT-REC
SWITCH
R37
VERNIER REG
CONTROL
Figure 3. Front Panel Control Locations

CW and SSB signals will be obtained with the ANL
control
set
between
the
6
o'clock
and
10
o'clock
posi-
tions
depending
upon
the
signal
strength
of
the
received
signal.
‘The
CW-SSB
limiter
is
double-ended
and
clips
both positive and negative noise peaks, Noise conditions
will vary with localities, so the limiting level is a malter
of personal choice.
CAL-SET (Dial Pointer Adjustment) — This control
provides calibration correction for each band when used
with an XCU-303 or XCU-300 crystal calibrator, With
the mode switch at CW and the crystal calibrator
switched on, tune your receiver to zero beat at any 100-kc
point of the band, any slight error in dial reading may
be corrected by turning the CAI.-SET control to move
the pointer to the desired 100-kc dial position, This is
a mechanical adjustment of the dial pointer and in no
way
affects
the
receiver's
oscillator
frequency.
ANT (Antenna Trimmer) — This control is included
to provide a means of matching the RF tuned circuits to
varying antenna impedances. After the desired signal
is selected, the antenna trimmer should be adjusted to
produce maximum S-metec readings. If desired, the
ANT can be peaked on noise without signal.
MODE —- The MODE switch selects the mode of
operation i.c., ACCESSORY, AM, CW, or SSB. The
mode selected appears in the smalf round opening at
the left of the switch knob. The AM position is used
for normal amplitude-modulated transmissions, In the
ACC position, the audio amplifier is connected to the
accessory socket to permit use of the receiver with ex-
ternal accessories or as an amplifier for a phone-pick-up
or similar audio device. In the CW position, the hetero-
dyne detector is energized and AGC and S-meter circuits
are disabled. In the SSB position, the heterodyne
detector is used for carrier reinsertion and the special
fast-attack- slow-release AGC and S-meter circuits
are active.
NOTCH — This control tunes the rejection notch
across the IF passband and is operative only when
the DEPTH control is advanced from the OFF position.
Turning the NOTCH control tunes the rejection notch
continuously across the entire IF passband. In AM
operation this type of rejection filter permits rejection
of cither the desired or the interfering signal. Rejection
of either signal removes the heterodyne due to the inter-
fering signal. The correct setting is the onc that leaves
the desired signal quality essentially unimpaired. If a
wrong position is selected, the desired AM signal will be
garbled or completely missing. For SSB ‘reception it is
impossible to reject the desired signal, Because of the
very sharp (400-cps) IF selectivity bandwidth the
NOTCH and DEPTH controls are not normally required
SELECT --IF amplifier selectivity is determined by
the
position
of
this
control,
Position
S
provides
the
extremely-shacp
selectivity
required
for
CW
reception
on crowded bands, In this position, a selectivity band-
width
of
400
cps
centered
at
80
ke
is
obtained.
Positions
SB1 and
SB2
allow
instantaneous
selection
of
sidebands
for
SSB
and
AM
operation
with
the
proper
bandwidth
necessary
for
high-quality
interfer-
ence-free
reception.
Positions
SB1
and
SB2
each
have
a
bandwidth
of
2000
cps
and
are
centered
on
approxi-
mately
81.5
and
78.5
kc
respectively.
Position
M
provides
the
optimem
bandwidth
for
good-quality
interference-free
AM
reception.
In
this
position,
a
bandwidth
of
3500
cps
centered
on
80
ke
is
obtained.
Position
B
allows
high-quality
reception
where
inter-
ference
is
not
a2
problem
and
provides
a
wide
bandwidth
for
net
or
VHF
operation,
The
bandwidth
in
this
position
is
8000
cps
centered
on
80
ke.
TONE
(HI-N-LO-PK)
—
Adjustment
of
the
charac.
teristics
of
the
audio
circuits
is
permitted
by
the
TONE
control.
This
control
is a switch
with
four
positions
of
audio
response.
The
HI
position
attenuates
low
fre-
quency
tones
in
the
audio
signal.
In
the
N
position
the
audio
is
almost
flat.
The
LO
position
attenuates
high
frequency
tones
in
the
audio
signal.
The
PK
position
attenuates
both
fow
and
high
frequency
tones
and
boosts
middle
frequency
tones.
‘I'he
HI
position
noticeably
increases
the
readability
of
AM
and
SSB
signals
in the
presence
of
heavy
noise
interference.
The
PK
position
adds
to
the
overall
selectivity
of
the
receiver
in
CW
reception,
CWO
—
This
control
varies
the
pitch
of
the
generated
audio
tone
to suit
the
operator
when
receiving
CW
sig-
nals.
During
single-sideband
operation,
the
control
is
set
with
the
pointer
straight
up
and
all
tuning
is done
with
the
SELECT
control
and
the
tuning
knob.
It is not
necessary
to
move
the
CWO
control
when
changing
the
IF
selectivity.
OFF-CAL-WWV (Calibrate Switch) —If the XCU-
303
or
XCU-300
crystal
calibrator
is
plugged
into
your
receiver, this switch is used to turn the calibrator OFF
or
ON
(CAL),
or
to
set
the
calibrator
to
receive
station
WWV if the XCU-303 calibrator is used, The calibrator
provides a crystal controlled test signal every 100 kilo-
eycles
so
that
dial
calibration
may
be
checked
and,
if
necessary,
corrected
by
means
of
the
CAL-SET
control.
To
receive
station
WWV
with
the
XCU-303
calibrator,
turn
calibrate
switch
to
WWV
position,
switch
BAND
control until 40-meter scale is visible on the slide-rule
dial
and
tune
to
7.07
me
(marked
in
eed
on
dial
scale).
With
the
XCU-300
calibrator
WW
signals
cannot
be

received,
although
the
XCU-300
calibrator
will
continue
to
furnish
the
100
ke
test
signal
with
the
calibrate
switch
in
the
WWV
position.
TUNING
—
The
tuning
knob
provides
2
40-to-1
ratio
for
ease
in selecting
the
desired
signal
as indicated
on
the
slide-rule
dial.
Frequency
increases
with
clockwise
rotation
of the
knob,
The
tuning
knob
has
a tim-drive
vernier
which
provides
an
additional
7
to
1
ratio
to
aid
in fine
tuning.
Inward
pressuce
against
the
vernier
en-
gages
it
with
the
tuning
knob,
pulling
outward
on
the
vernier
disengages
it.
The
tuning
knob
has
a
calibrated
scale
on
its outer
edge
for
logging
purposes.
CAUTION:
Do
not
force
the
dial
pointer
against
the
extreme
ends
of
the
dial
scale,
Rough
usage
may
upset
calibration.
XMT-REC — This is a two-position toggle switch
which
may
be
set
at
XMT
to
mute
the
receiver
during
standby
and/or
transmitting
periods,
In
addition,
it
will
turn the transmitter on and off if the RELAY terminals
at the rear of the receiver have been connected to pro-
vide
this
function.
Since
the
XMT-REC
switch
performs
its
function
in
the
audio
and
IF
stages,
normal
operating
voltages are maintained on the oscillators and all other
frequency-critical circuits to ensure that no frequency
drift
will
occur
during
standby
periods,
DEPTH — This control activates the Q multiplier
and
controls
the
depth
of
the
rejection
notch.
For
normal
operation
adjust
the
DEPTH
and
NOTCH
controls
for
maximum
rejection
at
the
center
of
the
IF
passband
and
then
use
the
NOTCH
control
only
for
removing
inter-
fering signals. If the unwanted signal is very strong,
set
the
NOTCH
control
for
rejection
of
uawanted
signal
and
then
adjust
DEPTH
control
for
still
greater
rejec-
tion.
Repeat
this
procedure
again
for
maximum
rejection.
AFG
(Audio
Frequency
Gain
Control)
—
The
func-
tion
of
this
control
is
the
adjustment
of
audio
output
level
to suit
the
listener.
Turning
the
control
clockwise
increases
the
volume;
turning
it
counter-clockwise
de-
creases
the
volume.
BAND
(Band
Change
Switch)
—
This
control
is
used
to
select
the
desired
frequency
band
to
be
tuned,
Gear
reduction
is
employed
in
your
NC-303
to
assure
a
smooth
working
control
and
positive
locking
switch
positions.
For
this
reason
the
BAND
control
makes
more
than
one
revolution
in
switching
through
ail
10
bands.
The
band
to
which
the
receiver
is
set
is
identified
by
the
scale
visible
on
the
slide-rule
dial
since
the
dial
and
the
BAND
switch
are
mechanically
coupled.
Positive
stops
are
pro-
vided
at both ends
of
the
BAND
control
travel.
PHONES (Phone Jack) — Headphones of the high-
impedance type may be plugged into the PHONE jack
by using a standard two-circuit phone plug. There is no
DC voltage associated with the headphone circuit, The
loudspeaker is automatically silenced when the phone
plug is inserted.
RFG (RF Gain Control) — The sensitivity of the re-
ceiver is adjusted by means of this control. It controls
the gain of the RF amplifier and second IF stages, The
AC switch which turns your NC-303 on and off is
mounted on the RFG control. When this control is
rotated to its maximum counter-clockwise position the
AC power is shut off. Rotating the control slightly in
the clockwise direction will actuate the switch, turning
the receiver on and further clockwise rotation will in-
crease the receiver sensitivity until maximum is reached
at the full clockwise position.
3.2
SINGLE-SIDEBAND
RECEPTION
The
instructions
in
steps
1
through
18
adjust
your
NC.303
receiver
for
normal
reception
of
SSB
phone
signals.
1.
Set
ANL
control
at
OFF.
2. Set MODE switch at SSB.
3.
Set
DEPTH
control
at
OFF.
4. Set TONE control at N.
5.
Set
OFF-CAL-WWY
switch
at
OFF.
6.
Set
XMT-REC
switch
at REC.
7. Set SELECT control at M.
8.
Set
CWO
control
exactly
at
the
front
panel
mark,
9.
Set
CAL-SET
control
at
the
front
panel
mark.
10.
Set
BAND
switch
to
the
desired
frequency
range
as
indicated
by
the
slide-rule
dial
scale,
11. Turn REG control slightly clockwise until switch
clicks
and
dial
lights
come
on.
minutes
for
the
tubes
to
reach
operating
temperature
before proceeding.
Allow at least two
12. Rotate the RFG contro] further clockwise until
background
noise
causes
the
S-meter
to
read
approxi-
mately 1 S-unit.
13, Set AFG control to produce the desired back-
ground noise level.
14. Turn ANT control to obtain maximum back-
ground noise and S-meter reading. Steps 12 and 13 may
be repeated if desired
15. Rotate TUNING control until the desired signal
is located. Engage the VERNIER drive and slowly tune

the
receiver
across
the
desired
signal
until
the
audio
output
is
normal
and
clearly
understandable.
16.
Set
SELECT
control
to
SBI
or
SB2.
pasition
the
signal
level
will
increase
and
show
improved
In one
signal-to-noise
ratio.
In
the
other
pesition
the
signal
level
will
be
missing,
or
greatly
attenuaicd.
Select
the
position
which
produces
the
Joudest
signal
17. Set AFG control to produce the desired listening
level.
18. Set TONE control to the position giving the
desired audio response.
19.
trol
fully
counter-clockwise.
‘To
shut
down
the
receiver,
turn
the
RFG
con-
Power
is now
removed
from
your
entire
receiver,
The AFG control should be used in most cases to
adjust the audio output level. The RFG control setting
obtained
in
Step
12
will
permit
accurate
S-meter
read-
ings to be obtained on modulation peaks, and should
normally not be changed unless operation is shifted to
another band, where steps (2 through 17 should be
repeated. Position SB1 provides upper sideband recep-
tion on the 160-, 80- and 40-meter bands; position SB2
for lower sideband signals on these bands. The side-
bands are reversed on the 20-, 15-, 11- and 10-meter
bands.
Various types of interference which may be encoun-
tered due to adverse receiving conditions can be mini-
mized by adjusting the following controls in the manner
described.
Heterodyne Interference: Turn DEPTH control
clockwise to approximately 180°-200°. Turn
NOTCH control to minimize heterodyne inter-
ference. Readjust DEPTH and NOTCH controls
alternately until the heterodyne disappears. The
quality of the desired signal will be essentially
unimpaired,
Atmospheric and Impulse Type Noise: Turn
ANL control clockwise until the best compromise
between interference reduction and signal clipping
is reached. For extremely heavy noise conditions
it is often helpful to set the TONE control at HI.
3.3 AM PHONE RECEPTION
The instructions in steps 1 through 16 adjust the re-
ceiver for the normal reception of AM phone signals.
1. Set ANL control at OFF
2. Set MODE switch at AM.
3, Set DEPTH control at OF.
TONE control at N.
5,
Set
OFF-CAL-WWYV
switch
at
OFF.
4 Set
10
6.
Set
XMT-REC
switch
at
REC.
7.
Set
IF
SELECT
control
at
position
M,
8.
Set
BAND
switch
to
the
desired
frequency
range
as
indicated
by
the
slide-rute
dial
scale.
9.
Set
center
dot
on
CAL-SET
knob
at
the
frone
panel
mack.
10,
Turn
RFG
control
slightly
clockwise.
Power
is
now
applied
to
the
receiver.
Allow
at
least
two
minutes
for
the
tubes
to
reach
operating
temperature
before
proceeding.
11.
Rotate
the
REG
control
further
clockwise
until
background
noise
causcs
the
S-meter
to
read
approxi
mately 1 S-unit.
12. Turn AFG control to produce the desired back-
ground noise.
13.
Rotate
TUNING
control
until
the
desired
signal
is
located,
Adjust
the
TUNING
control
very
carefully
for
maximum
S-meter
reading,
14, Turn ANT control to obtain maximum S-meter
reading. This control may be set, in the absence of a
signal, by adjusting it to obtain peak output from the
background noise.
15. Set AFG control to produce the desired listening
level.
16. Turn TONE control to a position giving the
desired audio response.
The AFG control should be used in all cases to adjust
the audio output level, The RFG control setting may
require readjustment for true S-meter readings. Refer
to paragraph 3.5. Position B of the SELECT control will
minimize the amount of cetuning necessary during net
or roundtable reception.
Various types of interference which may be encoun-
tered due to adverse receiving conditions can be mini-
mized by adjusting the following controls in the manner
described.
Hetcrodyne Interference: Tura DEPTH control
clockwise to approximately 180°-200°. Turn
NOTCH control to minimize heterodyne inter-
ference. CAUTION: two points of minimum inter-
ference will usually be noted. One is the correct
minimum, where the interfering catrier is rejected.
The other minimum occurs when the desired carrier
is rejected, which results in unintelligible output.
Always select the minimum interference point that
leaves the quality of the desired signal essentially
unimpaired. Readjust NOTCH and DEPTH con-
trols alternately until the heterodyne disappears.

Atmospheric and Impulse Type Noise: Turn the
ANL control slightly clockwise until the switch
clicks. The automatic AM noise limiter is now in
operation and a definite reduction of noise inter-
ference will be noted. Further rotation of the ANL
control will have no effect on AM signals. For
extremely heavy noise conditions it is often helpful
to set the TONE control at HI.
3.4 CW RECEPTION
The instructions in steps 1 through 18 adjust the re-
ceiver for normal reception of CW signals.
Set ANL control at OFF.
Set MODE switch at CW.
Set DEPTH control at OFF.
Set TONE control at N.
Set OFF-CAL-WWYV switch at OFF,
Set XMT-REC switch at REC.
Set SELECT control at S.
8. Set AFG control fully clockwise.
NY Pp YON
.
Set
CWO
control
at
approximately
11
o'clock
or 1 o'clock.
10.
Set
CAL-SET
knob
at
the
front
panel
mark.
1k. Set BAND switch to the desired frequency range
as indicated by the slide-rule dial scale.
12,
Turn
RFG
control
slightly
clockwise
until
switch
clicks
and
dial
lights
come
on.
Allow
at
least
two
min-
utes
for
the
tubes
to
reach
operating
temperature
before
proceeding.
13. Rotate RFG control further clockwise until
background noise is audible.
14,
Turn
ANT
control
to
obtain
maximum
back-
ground
noise
level.
15.
Rotate
TUNING
control
until
the
desired
signal
is
located.
16,
Carefully
peak
the
desired
signal
for
maximum
audio
output.
It
is
important
to
remember
that
the
IF
passband
is
only
400
cycles
wide,
so
the
TUNING
con-
trol
must
be
adjusted
very
slowly
and
carefully.
The
VERNIER
drive
may
be
engaged
and
used
if
desired,
17.
Reset
CWO
control
for
desired
beat
note.
The
CWO
control
should
be
left
in
this
position
when
turn-
ing
in
other
CW
signals.
18.
Set
RFG
control
to
produce
the
desired
signal
level.
1
If CW operation with AGC and S-meter operation is
desired, turn the MODE switch to SSB, Then advance
the RFG control as indicated in 3.2 and use the AIG
control to set the output level, Note that the fast-
attack — slow-release AGC circuit automatically keeps
the RF gain of the receiver at the proper level at all
times.
Your NC-303 will exhibit pronounced single-signal
properties which may be demonstrated by tuning the
receiver to the other side of zero-beat so that the pitch
is the same as before, and observing the marked reduc-
tion in output. The Q multiplier is not needed for CW
reception because of the extreme sharpness of IF selec-
tivity with the SELECT control in the § position.
An important aid to CW operation of an amateur sta-
tion has been included in your NC-303. It is frequently
desicable for the operator to monitor his own trans-
mitted signal while sending CW. To accomplish this,
two gain controls adjusted for two different signal levels
are necessary. The additional control may be mounted
on the station control panel adjacent to the transmitter
controls or at any other convenient location, Connect
the control as shown in Figure 2.
Adjust the external control to receive the incoming
signal at the desired level and adjust the RFG control
of the NC-303 for comfortable monitoring level. When
using an external RF gain control the XMT-REC switch
must be left at the REC position at all times.
Various types of interference which may be encoun-
tered due to adverse receiving conditions can be mini-
mized by adjusting the following controls in the manner
described.
Heterodyne Interference: Due to the extremely
narrow IF bandpass in the $ position, heterodyne
interference is minimized. When such interference
is encountered it can be reduced in the following
manner: set the CWO control to produce the same
beat note on the other side of zero beat. Note the
new magnitude of heterodyne interference and
choose the CWO setting that minimizes it, Engage
the vernier and carefully tuning your receiver to
produce the greatest signal-to-heterodyne ratio.
It may be possible to zero beat the interfering
heterodyne. Setting the TONE control to the HI,
LO, or PK position wil! also prove helpful in
minimizing hcterodyne interference.
Atmospheric and Impulse Type Noise: Turn
ANL control clockwise until best compromise he-
tween interference reduction and signal clipping is
reached.

Severe
Fading:
The
ANL
control
can
also
be
used
on
CW
to
provide
an
almost
constant
signal
level
on
severely
fading
signals.
To
utilize
this
feature,
set
the
RFG
control
for
desiced
signal
level
Use
the
ANL
control
to
clip
the
CW
signal
slightly
above
the
desired
level.
The
clipped
signals
do
not
materially
affect
readability
of
the
CW
signal.
near
the
bottom
of
the
fade
3.5
MEASUREMENT
OF
SIGNAL
STRENGTH
Signal
strength
measurements
referenced
to
the
local
ambient
noise
level
are
made
by
following
the
instruc-
tions
given
below,
It
should
be
noted
that
the
S-meter
of
your
NC-303
follows
the
average
signal
level
very
closely
in
all
modes
of
operation
and
does
not
merely
indicate
the
AGC
characteristics
of
the
receiver.
Thus,
the
S-meter
pointer
may
indicate
zero
between
words
of
a
single
sideband
transmission
while
the
background
noise
remains
low due
to
the
Jong
release
time
of
the
AVC.
A. Set RFG control fully clockwise and the MODE
switch at AM.
2. Set SELECT switch to M.
3. Set DEPTH control to OFF,
4, Tune receiver to a band setting where no signal
is heard so that the S-meter is reading background noise.
5.
Set
RFG
control
so
thai
the
meter
reads
halfway
between
©
and
S-1.
6.
Tune
in
the
desired
signal.
The
S-meter
will
indicate
the
strength
of
the
reccived
signal
in
S-units
from
1
to
9
or
in
decibels
above
the
S-9
level
from
0
to
40
db.
These
readings
will
remain
accurate
until
the
REG
control
is
moved
or
the
receiver
is
switched
to
a
different
band.
The
S-meter
circuit
compensator
requires
adjustment
only
when
it
is
impossible
to
obtain
a
zero
reading
with
no
antenna
connected
and
the
RFG
control
turned
fully
counter-clockwise.
See
Section
4.4
for
adjustment
pro-
cedure.
Design
of
the
S-meter
actuating
circuit
is
such
that
a
signal
stronger
than
that
necessary
for
full-scale
deflec-
tion
cannot
cause
the
meter
pointer
to
come
into
violent
contact
with
its
stop
pin
thus
preventing
possible
bend-
ing
of
the
meter
pointer.
When
the
MODE
switch
is
in
the
SSB
position,
CW
signal
strength
can
be
measured
by
following
the
pro-
cedures
given
in
3.4.
Measurement
of
the
signal
stcength
of
CW
signals
cannot
be
made
with
the
MODE
switch
in the
CW
position.
With the AC switch on the RFG control set at OFF,
or
when
the
MODE
switch
is
on
CW,
the
S-meter
pointer will return to its mechanical zero located on
the right-hand end of the meter.
SECTION
4
MAINTENANCE
DATA
4.1 GENERAL
All
circuits
in
your
NC-303
receiver
are
carefully
aligned
before
shipment
usiog
high-precision
laboratory
equipment
to insure
high
accuracy.
The
quality
of com-
ponents
used,
together
with
careful
design,
makes
any
realignment
unnecessary
unless
your
receiver
is tampered
with,
or
certain
part
or
tube
replacements
have
been
made.
In
no
case
should
realignment
be
attempted
un-
less
conclusive
tests
indicate
that
such
realignment
is
required.
Even
then
it must
be
remembered
that
your
NC-303
is
a
highly
specialized
instcument
and
should
not
be serviced
or realigned
by
any
individual
who
does
not
have
a
complete
understanding
of
the
functioning
of
the
equipment
and
who
has
not
had
previous
experi-
12
ence
adjusting
receivers
of
this
type.
In
addition,
be-
cause
of
the
calibration
accuracy
and
extreme
bandspread
of
your
NC-303
it
is
mandatory
that
adequate
test
equip-
ment
be
used.
Complete aligament of the receiver can be divided
into three steps as follows
(a)
2nd
IF
amplifier,
Q
multipliec
and
Product
detector
alignment.
(b) Ist IF amplifier.
(c) RE amplifier.
All circuits must be tuned in the above order when
complete alignment is required.

42 2ND IF AMPLIFIER, Q MULTIPLIER AND
HETERODYNE
DETECTOR
ALIGNMENT
The
second
intermediate
frequency
of
your
NC-303
must
be
aligned
at
exactly
80
kc.
The
signal
generator
used
must
be
capable
of
being
set
at
this
frequency
with
great
accuracy.
The
IF
transformers
are
tuned
by means
of adjustable
ferrite
cores.
The
IF
alignment
procedure
is
as
follows
(Disregard
the
BAND
switch
setting):
{1)
Connect
the
output
lead
of
the
signal
generator
to
pin
7
of
V3,
the
6BEG
2nd
converter
tube,
and
con-
nect
the
ground
lead
to
chassis.
Use
a
generator
output
connection
which
allows
the
generator
output
to
be
attenuated,
(2)
Set
the
MODE
switch
at
AM.
(3)
Set
the
SELECT
switch
at
position
S,
(4)
Set
the
RFG
control
at
its
maximum
clockwise
position.
(5) Set the XMT-REC switch at REC.
(6) Set the DEPTH control at OFF. Turn the
modulation of the signal generator off and set the fre-
quency of the generator at EXACTLY 80 kc. Increase
or decrease the generator output until the S-meter of the
receiver indicates $-5.
(7) Adjust L13, L12, L10, L9, L7 and Ls in that
sequence
to
produce
maximum
S-meter
reading.
Each
time
a
maximum
is
obtained
for
any
one
adjustment
reduce
the
generator
output
to
regain
the
S-5
reading.
Failure
to
reduce
the
generator
output
may
result
in
an
overload
condition
and
possible
incorrect
alignment.
Carefully
repeat
the
above
procedure
at
least
once
to
insure proper aligament. When the above procedure
is
followed,
it
is
not
necessary
to
disable
the
second
oscillator or AGC.
(8)
To
set
the
heterodyne
detector
oscillator,
plug
in
headphones
ot
connect
a
loudspeaker,
set
the
MODE
switch
at
CW
and
CWO
knob
at
center
(two
marks
aligned),
Keep
the
signal
generator
set
for
exactly
80
ke.
Adjust
T8
for
zero
beat
in
headphones
or
loud-
speaker.
(9)
The
Q
multiplier
should
be
aligned
after
the
second
IF
amplifier
and
heterodyne
detector
are
aligned.
Leave
the
signal
generator
set
at
exactly
80
kc,
feed
a
signal
to
the
signal
grid
of
the
second
mixer
(6BE6)
and
set
the
CWO
control
for
a
convenient
beat
note.
Turn
the
DEPTH
control
on
and
set
NOTCH
control
to
mid
position.
Adjust
the
slug
in
the
Q
multiplier
for
maximum
rejection
of
80-kc
signal
as
shown
by
13
minimum output. It may also be necessary to adjust
the DEPTH controi to gct maximum rejection.
The
following
adjustment
is
necessary
when
the
tube
in
the
Q
multiplier
is
changed.
Set
the
receiver
for
CW
operation
with
no
signal
coming
through
the
set
and
turn
NOTCH
control
90°
counter-clockwise
from
mid
position
(lowest
frequency).
Advance
DEPTH
control
to
its
maximum
clockwise
position.
Lift
up
receiver
cover
and
turn
screwdriver
adjustment
on
top
of
Q
multiplier
can
clockwise
until
the
Q
multiplier
breaks
into
oscillation.
slowly
counter-clockwise
until
oscillation
just
ceases.
Then turn screwdriver adjustment
4.3 FIRST IF ALIGNMENT
Set
the
receiver
for
AM
reception
with
the
SELECT
switch
in
the
S
position
and
the
Q
multiplier
off.
Apply
an
unmodulated
signal
from
a
signal
generator
tuned
to
approximately
2215
kc
between
center-section
stator
plates
of
main
tuning
capacitor
and
ground,
Adjust
the
tuning
and
output
of
the
signal
generator
for
a maxi-
mum
output
reading
of
S-5
on
the
receiver
S-meter
Once
the
tuning
of
the
gencrator
is set,
the
generator
frequency
should
not
be changed.
Adjust
the
four
slugs
on
the
2215-ke
IF transformers
T2
and
T3
for
maximum
output
as indicated
on
the
S-meter.
Reduce
the
output
of
signal
generator
to maintain
a meter
reading
of
S-5
as
each
slug
is peaked.
Once
these
adjustments
have
been
made
the
2215-kc
IF
is
properly
aligned.
4.4 RF AMPLIFIER
One
of
the
outstanding
features
of
your
NC-303
is
its
accuracy
of
calibration.
To
maintain
this
precision,
the
signal
source
used
for
front-end
alignment
must
have
the
accuracy
of
precision
crystals,
National's
XCU-303
or
XCU-300
crystal
calibrators
are
recommended
al-
though
any
reliable
secondary
standard
(crystal
con-
trolled)
can
be
used.
These
calibrators
can
be
used
in
conjunction
with
a
standard
signal
generator
to
insure
calibration
accuracy.
It
is
not
necessary
to
move
the
signal
generator
from
point
to
point
because
of
the
re-
stricted
frequency
coverage
of
the
receiver
and
the
limits
of
the
various
alignment
adjustments,
Connect
the
signal
generator
to
the
antenna
terminals
using
a
4-watt
te-
sistor
of
approximately
70
ohms
between
the
hot
lead
and
the
antenna
terminal.
The
generator
may
remain
connected
to
this
point
for
the
remaining
alignment
adjustments.
Leave
the
modulation
of
the
generator
shut
off
and
proceed
as
follows:
(1)
Set
the
CAL-SET
so
that
the
dot
on
the
knob
is
directly
below
the
marking
on
the
panel.
(2)
Set the
BAND
switch
according
to
the
Align-
ment
Chart.

ALIGNMENT
CHART
ADJUST
ADJUST
ns
sTEP
|
BAND
SIGNAL
aberreR
to,
|
TO
RECEIVE
ADJUST
FOR
SOURCE
TO:
:
:
|
TEST
SIGNAL
MAXIMUM
OUTPUT
C68A
Repeat
steps
1,
3
and
4
if
necessary
C6sB
Repeat
steps
1,
3
and
4
if
necessary
C68C
Repeat
steps
1,
3
and
4
if
necessary
Co6sD
Repeat
steps
1,
3
and
4
if
necessary
CO9A
Repeat
steps
1,
3
and
4
if,
necessary
C6OB
Repeat
steps
1,
3
and
4
if
necessary
C69C
Repeat
steps
1,
3
and
4
if
necessary
Co9D
T30
cn
Repeat
steps
1,
3
and
ie
4
if
necessary
14

TO #3- oO
40.2 o
TO+O6 v6
AC LINE VOLTAGE - 1/5 VOLTS. 6ALS 0.5 TO
HIGH IMPEDANCE VACUUM TUBE mie
VOLTMETER USED. 6AC- oO
CONTROL SETTINGS:
BAND — 1.8-2MC.
MODE—AM EXCEPT WHEN MEAS- abe Len
URING V8 WHEN IT IS AT CW. |ro-/5° ym,
RFG —MAXIMUM CLOCKWISE
POSITION. 6BU6 REL.
DEPTH—MAXIMUM
CLOCKWISE
G6AC-
oO
POSITION.
SELECT —POSITICN M.
TONE — POSITION N. a4 ntG0,
ANL — OFF. -O.5 +160
oy TO-15
CAL - OFF. aac)
ALL VOLTAGES MEASURED FROM 6BUG a
SOCKET PIN TO CHASSIS
ALL VOLTAGES DC EXCEPT AS
NOTED.
TOLERANCE = +10%
Figure 4. Tube Socket Voltages
(3)
Set
the
MODE
switch
at
AM.
(4)
Set
the
DEPTH
at
OFF.
(5)
Set
the
SELECT
control
at
position
S.
(6)
Set the
REG
control
fully
clockwise.
The
S-meter
of
the
receiver
will
be
used
as
the
indi-
cating
instrument
for the
ensuing
procedures
and,
at
all
times,
the
output
of
the
signal
generator
must
be
ad-
justed
to
produce
an
S-meter
reading
of
approximately
S$-5.
When
the
XCU-303
or
XCU-300
is
used,
the
RFG
control
can
be
used
to
regulate
the
signal
strength.
Make
all
adjustments
in
the
order
set
forth
in
the
Alignment
Chart.
The
inductance
adjustments
are
made
by
moving
the
small
loop
of
wire
inside
the
oscillator
coil
forms,
using
an
insulated
alignment
tool
or
a
small
diameter
bakelite
rod.
Because
of
the
2215-kc
first
IF
BOTTOM VIEW
15
and the limited range of the trimmers, images will not
be readable on your NC-303 so no special precautions
need be taken in this regard.
44 §S-METER ADJUSTMENT
The S-meter balancing resistor R44 is used to obtain
a zero meter rcading in the absence of signal input to
the receiver. To make this adjustment set the controls
as follows: Set the RIG control at mid-range. Set the
MODE switch at AM. Set the AFG at any position.
Disconnect os short the antenna connections. Adjust
the S-meter balancing resistor R44 to produce a 0 read-
ing on the S-meter. This is a screwdriver adjustment
located on top of the chassis,
4.5 VOLTAGE DATA
The voltage measurements on Figure 4 wili facilitate
any servicing which might be required on your NC-303.

46 DIAL CORD STRINGING
In the event of breakage of the dial scale actuating
cord of the dial pointer cord, the instructions shown oa
Figure 5 shouid be studied with care before attempting
teplacement. Failure to carry out these instructions cor-
rectly will result in incorrect indications of band scttiag
and Frequency. The dial scale in view at the front panel
MUST
correspond
to
the
frequency
range
being
tuned.
4.7 TUBE REPLACEMENT
ser aano swivch AT 20 MEYER BAND. WITH CAL-SET HAIRLINE AT CENTER
‘Tubes which become weak or defective should be re-
placed. In the case of the 4H4-C current regulator, a
type 6V6 may be used as a temporary substitute. This
substitution will sacrifice some of the current regulating
qualities provided by the 4H4-C but will keep the re-
ceiver operative, Type 4H4-C regulators are not gencral-
ly available at most supply houses. A replacement can be
obtained
from
National
Co.
or
any
National
Co.
author-
ized service station. A type 4H4 will not provide the
requited regulating action,
(OF CUTOUT, TUNE (M KNOWN SIGNAL OF 14.2 Mc. NOTE POSITION OF CAPACITOR ROTOR
BY MARKING ROTOR WITH PENCIL ACROSS TOP OF STATOR PLATES.
@remove Pcastic OAL ScALE ORM BY WITHORAWING THE SIX PHILLIPS-HEAD
‘SCREWS
ON
THE
TOP AND
BOTTOM
OF
THE
PLASTIC
ORUM,
QD easten serine were.
™~
CRIMP FERRULE SLIGHTLY
To PREVENT SLIPPING.
PULL EMDS OF CORD, STRETCHING
SPRING UNTiL POINTER SHOWS
No LOST MOTION THROUGHOUT
Dis TRAVEL.
‘CRIMP FERRULE SECURELY
AND TRIM CORD ENOS,
PASS
CORD
THRU
POINTER
AS
SHOWN.
@reerace onum. reser caraciton ar
la.2lde MARK.
BET AT EXACTLY 14,2 @Y SLIDING
POINTER ALONG DIAL CORD.
LOOP CORD AROUND PULLEYS AS SHOWN,
WRAP CORD AS SHOWN. USE MASKING TAPE OR
SIMILAR ADHESIVE TO WOLD CORD IN GROVE GG) —
OF ORIVE DRUM. ROTATE THE ORIVE ORUM TO
THEEAD
GORD
BS
SHOWN.
DRAPE
LOOSE
GORD
OVER TOP OF DIAL ORUM BRACKET.
S)REWOVE ASKING TAPE FROM DRIVE ORUM.
KEEPSTENSION ON DIAL GORD TO PREVENT.
UNTHREAOING:
nore:
CORD SHOWN EXPOSED FOR CLARITY,
CORD LENGTH 4.250 FEET.
FOR FINE ADJUSTMENT,
LOOSEM SCREWS RETIGHTEN.
FOR COARSE 40JUSTMENT OF DIAL
SCALE,JUMP BEAD CHAIN ON
SPROCKET. TIGHTEN CHAIN GUIDE.
SET BAND SWITCH
AT EXTREME
COUNTERCLOCKWISE,
Posirion,
‘CHAIN GUIDE DETAIL
LOOSEN CHAIN GUIDE, SECURE
CHAIN-CORD ASSEMBLY 4S SHOWN.
POSITION DRUM SO THAT 160 METER BAND
SCALE 1S CENTERED IN DIAL WINDOW.
ASSEMBLE AS SHOWN,
CHAIN CENGTH= 6 '4*.
‘CORD LENGTHS=20" EACH.
Figure 5. Cord Stringing Guide
16

All capacitors
+£10%,
500
vdew
unless otherwise
noted,
Air Variable:
3 sections
7440.3 mmf, part
of CL
of Cl
of Cl
Antenna
Trimmer
Ceramic; 100 mmf
Disc: 0.01 mfd,
500 vdew
Disc: 0.01 mfd,
500 vdew
Mica: 1000 mmf
Disc: 0.01 mfd,
500 vdew
Mica: 470 mmf
Disc: 0.01 mfd
—0% +100%,
500 vdew
Disc: 0.01 mfd
0% +100%,
500 vdew
Ceramic: 100 mmf
+5%,
300
vdew
Ceramic: 100 mmf
5%,
300
vdew
Ceramic: 100 mmf
5%,
300
vdew
Ceramic: 100 mmf
£5%,
300
vdew
Mica:
33
mmf
Paper: 0.01 mfd
20%,
400
vdew
Disc:
0.01
mmf
0% +100%,
500 vdew
DESCRIPTION NATCO TYPE
7.4-40.3,
mmf,
pact
14.4-80.7 mmf, part
NC-303 PARTS LIST
CAPACITORS
11779
A12502
D-825-C-304
2-C14-Z25V-103-GMV
2-C14-Z5V-103-GMV
NCS-19-102-K5
2-€14-25V-103-GMV
NCS-19-471-K5
2-C14-Z5 V-103-GMV
2-C14-Z5V-103-GMV
CM-15-C-i01-J
CM-15-C-101-J
CM-15-C-101-]
CM-15-C-101-]
NCS-15-330-K-5
NCP-4-103-M
2-C14-Z5V-103-GMV
17
=
DESCRIPTION
NATCO
TYPE
Paper: 0.022 mmf | NCP-2-223-K
+10%,
400
vdew
Disc: 0.01 mmf
—0% +100%,
500 vdew
Trimmer, Air:
100 mmf
Mica: 680 mmf
+5%,
500
vdew
Mica: 120 mfd
“29%,
300
vdew
Mica: 150 mfd
+2%,
300
vdew
Ceramic: 10 mmf
+1 mmf, 500 vdew
Mica:
470
mmf
Disc:
0.01
mfd
—0% +100%,
500 vdew
2-C14-Z5V-103-GMV
A12501
NCS-19-681-J-5
NCS-35-121-G-3
NCS-15-151-G-3
CCC-21-SL-100-F
NCS-19-471-K5
2-C14-Z5V-103-GMV
2-C14-Z5P-502-K
NCP-4-473-M
Disc: 0.005 mfd
Paper: .047 mfd
+:20%,
400
vdew
Mica:
270
mmf
5%,
300
vdew
Disc: 0.01 mfd
—0% +100%,
500 vdew
Disc:
0.01
mfd
0%
+100%,
500 vdew
Paper: .047 mfd
+20%,
400
vdew
Ceramic: 10 mmf
+1
mmf,
500
vdew
Mica: 150 mmf
+2%,
300
vdew
Mica: 150 mmf
+:2%,
300
vdew
Electrolytic: 8 mfd,
250 vdew
Not
Used
CM-15-C-271-J
2-C14-Z5V-103-GMV
2-C14-Z5V-103-GMV
NCP-4-473-M
CCC-20-SL-100-F
NCS-15-151-G-3
NCS-15-151-G-3
338-34

PARTS
LIST
(CONT'D)
CAPACITORS (CONT'D)
BOL DESCRIPTION
NATCO TYPE
C38 | Paper: 0.047 mfd
20%, 400 dewv
C39 | Paper: 0.047 mfd
20%, 400 dewv
C40 | Paper: 0.1 mfd
20%, 400 vdew
C41 | Disc: 0.01 mfd
0% +100%,
500 vdew
C42 Mica: 220 mmf
5%, 300 vdew
C43,
|
Mica:
150
mmf
+2%,
300
vdew
C44 | Mica: 150 mmf
2%, 300 vdew
C45} Not Used
C46 | Not Used
C47 Ceramic: 240 mmf
+2%, 300 vdew
C48 Ceramic: 12 mmf
+5%, 500 vdew
C49 | Ceramic: 15 mmf
C50 | Mica: 470 mmf
C51 Ceramic; 0.01 mfd
+100% —0%,
500 vdew
C52 Airc Variable:
12-100 mmf
C53 Mica: 470 mmf
C54 Ceramic: 100 mmf
C55
Mica:
33
mmf
C56 | Paper: 0.01 mfd
20%,
400
vdew
C57
Ceramic:
47
mmf
C58 Mica: 3600 mmf
+5%, 300 vdew
C59 | Mica: 470 mmf
+10%, 500 vdew
C60 | Paper: 0.01 mfd
20%, 400 vdew
C61 | Paper: 0.47 mfd
20%,
200
vdew
NCP-4-473-M
NCP-4-473-M
NCP-4-104-M.
2-C14-Z5 V-L03-GMV
RCM-15-B-221-J-3
NCS-15-151-G-3
NCS-15-151-G-3
Al4157
CC-20-UJ-4 20-5
Ds25D-467
J665-56
Ko46.2
Al250L
1665-56
D825C-304
NCS-19-330-K-5
NCP.-4-103-M
CCC-20-SL-470-K
NCS-19-362-J-3
NCS-19-471-K-5
NCP.4-103-M
NCP-2-474-M
DESCRIPTION
NATCO TYPE
Electrolytic
40-40-40-20
mfd,
250 vdew
Mica:
.001
mfd
+20%,
1000
vdew
Ceramic:
4
mmf
+0.2
mmf
Mica:
0.001
mfd
+20%,
1000
Mica:
0.001
mfd
+20%,
1000
vdew
Disc:
0.01
mfd,
500
vdew
Mica Variable: 4
sections, each
5-80 mmf
Part of C68
Part
of
C68
Part of C68
Part of C68
Mica Variable: 4
sections, each
5-80 mmf
Part
of
C69
Part
of
C69
Part of C69
Part
of
Coy
Air Variable:
2.8-19.7 mmf
Air Variable:
2.8-19.7 mmf
Air Variable:
2.8-19.7 mmf
Air Variable:
2.8-19.7 mmf
Air Variable:
2.8-19.7 mmf
Air Variable:
2.8-19.7 mmf
Air Variable:
2.8-19.7 mmf
Air Variable:
2.8-19.7 mmf
C19458.4
RCM-30-B-102-M-10
CCO-20-C1.-040-C
RCM-30-B-102-M-10
RCM-30-B-102-M-10
2-C14-Z5V-103-GMV
A12493
Al2493
Al2744
Al2744
Ai2744
A12744
Al2744
A12744
Al2744
Al2744
18