National company Nc300 User manual

FOR

COMPLETE

APPRECIATION

OF

YOUR

NC-300,

READ

THE

800:

IMPORTAN

tuned

lo

tomorrow...

INSTRUCTION

BOOK

FOR

THE

NATIONAL

MODEL

NC-300

RADIO

RECEIVER

SECTION

1,

DESCRIPTION

lel,

GENEHAL

the

calibeared

Dandeocnonlo,

MELROSE,

MASS.

ducing

any

trace

of

backlash.

The

outward

appearance

of

the

receiver

is

com-

pletely

modern

and

functional.

Cabinet

and

panel

construction

permits

the

receiver

to

be

removed

from

the

cabinee

and

rack

mounted

without

modification

or

the

addition

of

any

parts

other

than

mounting

hardware.

Adequate

ventilation

is

provided

by

the

use

of

convection

cooling through

holes

in

the

chas-

sis

and

a

perforated

cabinet

lid,

1-2.

FREQUENCY

COVERAGE

‘The

NC-300

tunes

all

the

amateur

bands

from

160

through

10

meters

plus

a

30-35

mc.

band

designated

as

the

‘'X"

band

for

use

with

external

converters

for

the

6,

2

and

1

1/4

meter

bands.

Each

dial

scale

is

calibeated

for

only

one

band.

Each

scale

has

band

limit

marking

plus

underscoring

to

indicate

the

phone

portion

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

the

NC-300,

BAND

FREQUENCY

RANGE

160

18—-

2.0

mc

80

3.5—

4.0

me.

40

7.0-

7.3

me.

20

14.0-

14.4

me,

15

21.0

-

21.5

me.

1

26.5

—

27.5

me.

10

28.0

—

29.7

me.

6

49.5

—

54,5

mc.

(with

converter)

2

143.5

—

148.5

me.

(with

converter)

11/4

220

-—

225

me.

(with

converter)

1-3.

CONTROLS

The

following

controls

appear

on

the

front

panel

of

the

NC-300:

Tuning

Phasing

ALF,

Gain

Antenna

R.F,

Gaia

Cal-Set

Tone

LF,

(1-2-3)

ANL

C.W.0,

Mode

(ACC-AM-CW-SSB)

Xmr-Rec

Selectivity

(Off-1-2-3)

Off-Cal

Band

1-4,

IF

SELECTIVITY

The

IF

pass

band

may

be

set

at

$00

cycles,

3-5

ke

or

8

ke

at

the

operatot's

discretion.

Figure

1

shows

the

IF

selectivity

characteristics.

With

the

ever-

inckeasing

amount

of

activity

on

the

amateur

bands,

-2-

yariable

selectivity

is

a

must

on

any

modern

com-

munications

receiver.

For

copying

CW

signals

in

the

midst

of

heavy

QRM,

the

500

cycle

bandwidth

is

invaluable.

The

3.5-kc

position

is

provided

to

im-

prove

the

readability

for

phone

operation

when

inter-

ference

is

heavy,

and

the

widest

range,

8

kc,

makes

ic

possible

to

copy

net

stations

or

roundtables

with

a

minimum

of

retuning.

The

&kc

bandwidth

is

also

important

when

using

the

converters

in

the

VHF

ranges.

The

operator

will find

many

varied

combina-

tions

of

crystal

and

IF

selectivity

adjustments

that

will

best

suit

his

particular

receiving

requirements.

1-5.

CRYSTAL

FILTER

Exhaustive

tests

have

proved

that

the

crystal

filter

is

a

necessary

adjunct

to

communications

re-

ceivers.

Three

degrees

of

crystal

selectivity

are

provided,

The

Phasing

control

inserts

the

notch

in

the

selectivity

curve

so

necessary

to

interference-

free

reception.

The

filter

used

in

the

NC-300

has

been

specifically

designed

co

work

with

the

receiver

IF

circuitry.

There

is

but

one

limitation.

During

CW

operation,

the

crystal

filter

cannot

be

used

with

the

IF

switch

at

the

sharp

position

(3).

1-6,

TWO-WAY

RF

GAIN

CONTROL:

A

special

switch

is

made

an

integral

part

of

the

audio-frequency

gain

(AFG)

control

so

that

the

switch

may

be

operated

at

either

extreme

of

control

rotation,

By

means

of

this

switch,

the

RF

gain

control

may

be

removed

from

the

RF

amplifier

stage

permitting

the

stage

to

operate

at

maximum

gain

regardless

of

the

setting

of

the

RF

gain

control.

Thus,

when

maximum

front-end

gain

is

desirable

with

reduced

overall

gain,

the

action

of

the

control

can

be

restricted

to

the

IF

stages

only.

In

the

presence

of

strong

local

signals,

the

control

should

be

switched

into

the

RF

amplifier

cathode

circuit

to

prevent

overloading

by

retarding

the

RF

gain

control

as

necessary.

1-7.

MUTING

CIRCUIT

A

built-in

muting

circuit

silences

the

NC-300,

when

desired,

without

resorting

to

the

use

of

relays.

Any

point

in

the

transmitter,

which

supplies

approximately

minus

22

volts

with

the

cansmitter

on,

may

be

con-

nected

to

the

muting

terminals

at

the

rear

of

the

receiver.

When

the

transmitter

is

energized,

the

audio

amplifier

in

the

receiver

is

cutoff

to

prevent

feedback,

key

clicks

etc.

1~8,

SINGLE

SIDEBAND

DETECTION

To

receive

single

sideband

signals

satisfactorily,

the

CW

frequency

oscillator

(CWO)

must

supply

stable

output

of

sufficient

amplitude

to

maintain

adequate

carrier

re-insertion

voltage.

The

single-sideband

detector

used

in

the

NC-300

utilizes

the

heterodyne

detection

principle.

1-9,

CONVERTERS

AND

CABINET

The

National

types

NC-300C1i,

NC-300C2

and

NC-

300C6

are

broad-band,

crystal-controlled

converters

to

tune

the

11/4,

2

and

G-meter

Amateur

bands

respectively.

The

slide

cule

dial

of

the

NC-300

incorporates

three

separate

dial

scales

to

provide

direct-reading

frequency

calibration

when

che

con-

verters

are

used

with

the

receiver.

All

opcrating

voltages

required

by

the

converters

are

available

at

the

accessory

socket

of

the

NC-300.

The

National

NC-300

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

and

appearance

to

the

NC-300

speaker

cabinet.

A

four-position

switch

is

mounted

on

the

front

panel

to

permit

operation

of

the

ceceiver

or

any

one

of

the

three

converters

without

changing

connections

to

the

receiver

or

antenna,

1-10.

S-METER

The

S-Meter

gives

the

operator

a

true

indication

of

relative

strength

of

incoming

signals.

The

meter

is

calibrated

in

S

units

from

0

to

9

and

in

decibels

{com

S-9

to

40

db

over

S-9,

A

potentiometer

is

pro-

vided

on

the

chassis

co

zero-set

the

meter.

1-Ll.

TUBE

FUNCTIONS

‘The

following

table

lists

the

types

and

functions

of

all

tubes

used

in

che

NC-300:

TUBE

TYPE

FUNCTION

6BZ6

R.E.

Amplifier

6ANIG

HLF,

Oscillator

6BA?

First

Mixer

6BEG

Second

Converter

6BJ6

First

LE.

Amplifier

6BJ6

Second

I.f.

Amplifier

GALS

Detector

and

Noise

Limiter

6BEG

C.W,

Oscillator-feterodyne

Detector

12AT7

—-

SMeter

Amplifier

and

A.F.

Amplifier

6AQS

Audio

Outpue

Amplifier

SY3GT

High

Voltage

Rectifier

oB2

Voltage

Regulator

4Ha-€

Current

Stabilizer

wo

6

0

8

0

Ke

OFF

RESONANCE

XF

SELECTIVITY

CHARACTERISTIC,

SELECT

Swrttn

aT

OFF

FA

CP

Ke

OFF

RESONANCE

CRYSTAL

FILTER

SELECTIVITY,

TF

switcw

AT

3,8xC

(2)

Figure

1.

1.F.

and

Crystal

Filter

Selectivity

Characteristics

=~

1~12,

POWER

REQUIREMENTS

The

NC-300

requires

a

105—130

vole,

50/60

cycle

AC

source

of

supply.

Power

consumption

is

approx-

imately

60

watts.

1-13.

CALIBRATOR

SOCKET

A

socket

is

provided

on

the

chassis

to

permit

in-

sertion

of

the

National

type

XCU-300

crystal

cali-

brator

unit,

The

OFF-CAL

switch

on

the

front

panel

of

the

NC-300

provides

the

means

for

turning

the

SECTION

2.

2—-L.

GENERAL

All

installation

procedures

are

described

in

this

section.

Figure

2

locates

connection

points

on

the

receiver

and

depicts

typical

installations,

Before

proceeding

with

installation,

raise

the

hinged

cover

of

the

receiver

and

make

sure

that

all

cubes

are

seated

firmly

in

their

sockets.

2-2,

LOUDSPEAKER

A

National

cype

NC-300TS

speaker

or

any

permanent-

magnet

dynamic

speaker

with

an

8-ohm

voice

coil

may

be

connected

to

the

speaker

terminals,

No

polar-

ity

need

be

observed.

2-3,

CHANGEOVER

RELAY

A

terminal

marked

Relay

is

mounted

at

the

crear

of

the

receiver.

When

the

Xmt-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

requirements

do

not

exceed

5

amps

at

125

volts

AC.

A

typical

circuit

might

consist

of

a110-volt

AC

antenna

change-

over

relay

in

parallel

with

the

transmitter

plate

supply

relay

with

one

side

of

the

AC

line

broken

by

the

NC-300

Relay

connector

strip.

When

connected

in

this

manner

the

Xmt-Rec

switch

on

the

receiver

front

panel

performs

all

the

required

change

over

operations

for

the

entire

station,

2-4,

MUTING

A

Stdby-Mute

terminal

strip

is

mounted

at

the

rear

of

the

receiver.

These

three

terminals

provide

for

two

entirely

different

methods

of

receiver

muting

during

transmitting

periods.

With

no

external

con-

nections

made

to

the

strip,

the

receiver

will

be

muted

whenever

the

Xmt-Rec

switch

is

placed

in

the

‘Xt

position.

If

muting

is

not

desired,

(for

tans-

calibrator

On

or

Off.

1-14.

ACCESSORY

SOCKET

The

accessory

socket

provided

at

the

left

rear

corner

of

the

chassis

is

designed

to

accept

suitable

external

accessories

within

the

power

limitations

of

1.5

amperes

at

6.3

volts

A.C.

and

25

milliamperes

at

150

volts

D.C.

See

the

schematic

diagram

for

connections

etc.

Refer

to

Section

3

for

instructions

on

the

use

of

external

accessories.

INSTALLATION

miter

monitoring

etc.)

a

jumper

wire

may

be

con-

nected

between

STBY

and

GND.

operates

regardless

of

the

Xmt-Rec

switch

position.

For

remote

switching

of

the

receiver,

connect

leads

to

Stdby

and

Gnd,

leaving

the

switch

in

the

Xmt

position,

If

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

circuitry

that will

provide

a

source

of

negative

22

to

50

voles

when

the

trans-

mitter

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

the

receiver,

no

current

will

be

drawn

from

the

transmitter.

Connect

the

minus

22-vole

lead

to

the

terminal

marked

MUTE

and

the

transmitter

chassis

to

the

terminal

marked

GND.

Leave

the

Xmt-Rec

switch

in

the

Receive

position,

When

the

transmitter

is

turned

on

or

keyed,

the

NC-300

will

automatically

mute.

Since

the

muting

circuit

is

well

filtered,

no

key

clicks

should

be

heard,

The

receiver

now

2-5.

ANTENNA

A

two-terminal

strip

i$

provided

for

connection

of

antennas

fed

by

unbalanced

transmission

line

sys-

tems.

Usually

the

most

efficient

antenna

is

the

one

which

has

been

tuned

and

adjusted

for

optimum

transmitting

results.

For

the

40,

80

and

160

meter

bands,

a

single

wire

antenna

of

between

15

and

40

feet

is

recommended,

This

should

provide

ample

signal

pickup

and

reduce

the

likelihood

of

inter-

ference

from

strong

undesired

signals

outside

the

IF

passband.

Switching

the

antenna

from

the

transmitter

to

the

receiver

is

most

easily

accomplished

by

means

of

a

relay

actuated

by

the

RELAY

terminals

of

the

NC-300.

Any

of

the

popular

dipoles,

beams

etc.,

which

are

fed

with

50

to

70-ohm

coaxial

cable

will

be

ideal.

In

installations

where

it

is

desired

to

use

an

already

pRWE

>——

100K

XMTER

FINAL,

GRID

BLOCK

METHOD

AMPLIFIER

To

ile

TRANSMITTER

CONTROL

CIRCUITS

RELAY

METHOD

RECOMMENDEO

MUTING

INSTALLATIONS:

OrPOLe

[

=

os

RECOMMENDED

ANTENNA

CHANGEOVER

RELAY

INSTALLATION

To

XMTR

TRANSMITTER

CONTROL

CincUITS

AND

SHORTING

CONNECT

RF

OUTPUT

PLUG

IN

FROM

1/,,2

OR

6

METER

xCU=300

CRYSTAL

CONVERTER

CRYSTAL

CALIBRATOR

CT

NORMALLY

CLOSED

EXTERNAL

(0K

CONTACTS

ON

ANY

RF

GAIN

CONVENIENT

RELAY

CONTROL,

IN

THE

TRANSMITTER

CONTROL

SYSTEM

MUTE_gNo_StOe

®

METHOD

OF

WIRING

EXTERNAL

RF

GAIN

CONTROL

CONNECT

EXTERNAL,

RF

GAIN

CONTROL,

MUTE

GND

FUSE

SPEAKER

2AMP

NATIONAL

NC-300TS

CONNECT

SINGLE

WIRE

ANTENNA

OR

CENTER

CONDUCTOR

OF

COAX

CONNECT

TO_GOOO

EXTERNAL

GROUND

SHIELD

BRAID

OF

COAX

REMOVE.

LINK

AND

CON-

NECT

TERMINALS

TO

TRANSMITTER

MUTING

VOLTAGE

{-22VDC)

CONNECT

IN

SERIES

WITH

RELAY

ACTUATING

VOLTAGE

TO

CONTROL

ON-OFF

OF

TRANSMITTER

BY

MEANS

OF

NC-300

XMT-REC

SWITCH

CONNECT

TO

NORMALLY

OPEN

CONTACTS

OF

T-R

RELAY

TO

DISABLE

RECEIVER

(N

TRANSMIT

Figure

2,

Typical

Installation

Plan

5-

existing

antenna

with

a

300-ohm

balanced

feedline,

an

antenna

coupler

such

as

a

balun

can

be

used

to

match

this

antenna

to

the

70-ohm

unbalanced

input

of

the

NC-300,

The

balun

may

be

either

a

quarter-wave

section

of

coax

or

a

pair

of

balun

coils.

NOTE

If

the

receiver

is

used

in

close

proximity

to

the

transmitting

equipment,

some

provision

mus¢

be

made

to

short

the

antenna

terminals

to

ground

during

transmitting

periods

to

pre-

vent

damage

to

the

antenna

coils.

This

is

most

easily

accomplished

by

means

of

a

relay

con-

nected

to

the

antenna

terminals

and

ground,

The

relay

should

be

located

within

six

inches

of

the

antenna

terminal

strip

to

prevent

exces-

sive

pick-up.

Connect

the

shield

braid

of

the

coax

to

terminal

G

and

the

inner

conductor

to

the

A

terminal.

A

good

electrical

ground

should

be

used,

This

may

be

a

convenient

cold

water

pipe

scraped

clean

of

paint

and

oxidation

or

a

suitable

ground-rod

driven

into

the

earth

as

close

as

possible

to

the

receiver

location.

The

outstanding

and

characteristics

of

the

NC-300

cannot

be

fully

appreci-

ated

unless

every

effort

is

made

to

provide

proper

sensitivity

signal-to-noise

antenna

and

ground

facilities.

2-6.

CALIBRATOR

SOCKET

The

Calibrator

socket

at

the

rear

of

the

receiver

chassis

is

factory

wired

so

that

it

is

only

necessary

to

plug

in

the

National

type

XCU-300

Crystal

Cali-

brator

unit,

The

OF

F-CAL

switch

on

the

front

panel

will

then

energize

the

calibrator

when

desired.

2-7,

ACCESSORY

SOCKET

This

socket

permits

a

variety

of

accessories

to

be

used

with

the

NC-300,

Audio

devices

such

as

a

crystal

phono

pickup

may

be

connected

to

pins

5

and

6.

Heater,

B+,

AVC

and

ground

connections

are

available

for

external

converters

etc.

1F

output

is

connected

to

4

for

use

with

SSB

devices

and

the

RF

Gain

bus

is

brought

to

1

for

external

control

of

RF

Gain

(see

paragraph

3-3).

The

receiver

SECTION

3.

OPERATION

The

purpose

of

this

section

is

to

provide

the

opera~

tor

with

a

clear

and

concise

understanding

of

the

operating

techniques

of

the

NC-300

to

assist

him

in

securing

maximum

satisfaction

from

the

receiver.

The

design

of

the

receiver

circuitry

provides

every

feature

necessary

for

outstanding

performance

but

a

thorough

knowledge

of

correct

operation

is

required

to

utilize

these

features

to

full

advantage.

For

com-

plete

appreciation

of

your

NC-300

READ

THESE

INSTRUCTIONS

CAREFULLY.

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

conteols.

The

control

designations

used

cor-

respond

to

the

markings

on

the

receiver.

ANL

(Automatic

Noise

Limiter)

-

The

ANL

control

is

used

oaly

for

phone

reception,

This

control

incor-

porates

a

switch

which

turns

the

limiter

off

when

the

control

is

rotated

to

its

maximum

counterclockwise

position,

Turning

the

control

clockwise

just

enough

to

throw

the

switch

places

the

limiter

in

operation.

Further

rotation

of

the

control

increases

the

limiting

action.

Noise

clipping

is

obtained

at

the

expense!

of

audio

quality

so

a

position

should

be

chosen

to

provide

maximum

noise

clipping

consistent

with

intelligibility.

Noise

conditions

will

vary

with

localities,

so

the

limiting

level

is

a

macter

satisfactory

of

personal

choice.

To

provide

noise

limiting

for

CW

reception,

the

IF

amplifier

of

the

NC-300

is

designed

to

limit

on

pulse

interference.

The

time

constants

incorporated

in

the

grid

circuits

are

very

short

to

permit

following

fast

pulses.

To

achieve

limiting

action

the

RFG

control

should

be

advanced

until

overload

is

approached.

The

AFG

control

should

then

be

adjusted

for

best

listening

level,

Then

the

RFG

control

can

be

used

to

adjust

for

best

limiting

action.

Experience

with

the

receiver

will

dictate

the

proper

settings

df

the

RF

and

AF

gain

controls

to

achieve

the

desired

point

of

IF

limiting.

CAL-SET

(Dial

Pointer

Adjustment)

—

Used

in

conjunction

with

the

XCU-300

Crystal

Calibrator,

this

control

provides

calibration

correction

for

each

band.

With

the

CW

oscillator

and

the

crystal

cali-

brator

switched

on,

and

the

receiver

tuned

to

zero

S-METER

CAL

SET

CAL SET

TUNING

MODE

ZERO

SET

INDICATOR

CONTROL

OIAL

INDICATOR

c2

sé

ANT

MODE

CONTROL

SWITCH

Re?

84

ANL

SELECT

CONTROL

SWITCH

cse

cig

cwo

PHASING

CONTROL

R46

slo

TONE

XMT~REC

CONTROL

SWITCH

ss

IF

$2

R51

st

TUNING

R37

SELECTIVITY

OFF-CAL

AFG

BAND

CONTROL,

RFG

CONTROL

SWITCH

CONTROL

SWITCH

CONTROL

Figure

3,

Front

Ponel

Control

Locations

beat

at

any

100-ke

point

of

the

band,

any

slight

acteristics.

the

crystal

filter

cannot

be

used

in

error

in

dial

reading

may

be

corrected

by

turning

the

combination

with

the

sharpest

IF

selectivity

posi-

CAL-SET

control

to

position

the

pointer

on

signal.

tion,

This

is

a

mechanical

adjustment

of

the

dial

pointer

and

in

no

way

affects

the

receiver's

oscillator

fre-

quency.

ANT

(Antenna

Trimmer)

—

This

control

is

included

to

provide

a

means

of

matching

the

RF

tuned

circuits

to

varying

antenna

impedances,

After

the

desired

sig-

nal

is

selected,

the

antenna

trimmer

should

be

ad-

justed

to

produce

maximum

S-Meter

reading.

MODE

-

The

Mode

switch

selects

the

mode

of

operation

i.e,

ACC-AM-CW

or

SSB,

The

mode

selected

appears

in

the

small

cound

opening

at

the

left

of

the

switch

knob.

The

AM

position

is

used

for all

forms

of

amplitude-modulated

transmissions.

In

the

ACC

position,

the

audio

amplifier

is

connected

to

the

accessory

socket

to

permit

use

of

the

receiver

as

an

amplifier

for

a

phono-pick-up

or

similar

audio

device,

In

the

CW

position,

the

CW

oscillator

is

energized

and

the

AVC

and

S-Meter

circuits

are

disabled.

In

the

SSB

position,

the

heterodyne

detector

is

used

for

carrier

reinsertion

and

the

AVC

and

S-Meter

circuits

are

active,

SELECT

(Crystal

Filter

Selectivity)

—

Three

de-

grees

of

crystal

selectivity

plus

an

Off

position

are

provided

by

the

SELECT

knob,

When

used

in

con-

junction

with

position

2

of

the

IF

switch,

the

Select

contro!

affords

the

desired

range

of

selectivity

char-

=

a

TONE

—

The

adjustment

of

the

characteristics

of

the

audio

circuitry

is

permitted

by

the

Tone

control.

Rotated

in

a

clockwise

direction

it

increases

atten-

the

higher

At

counterclockwise

position

it

actuates

a

switch

which

uation

of

frequencies.

its

extreme

effectively

attenuates

frequencies

below

the

voice

This

characterisec

range.

feature

is

provided

to

equalize

the

roll-off

the

filter.

Figure

4

illustrates

che

audio

characteristics

of

the

receiver,

CWO

(CW

Oscillator

Pitch)

~

This

control

varies

the

pitch

of

the

generated

audio

tone

to

suit

the

introduced

by

crystal

operator

when

receiving

CW

signals.

During

single-

sideband

operation,

the

control

is

set

at

1to

receive

lower

sideband

signals

on

the

160,

80

and

40-meter

bands,

at

2

to

receive

the

upper

sideband

on

these

bands,

The

converse

settings

are

used

for

the

20,

15,

11

and

10-metec

bands.

OFF-CAL

(Calibrate

Switch)

—

If

the

XCU-300

Crystal

Calibrator

is

plugged

into

the

receiver,

the

CAL

switch

is

used

to

turn

the

calibrator

Off

and

On,

The

test

signal

every

100

kilocycles

so

that

dial

calibra-

calibrator

provides

a

crystal

controlled

tion

may

be

checked

and,

if

necessary,

corrected

by

means

of

the

CAL-SET

conmol.

TUNING

—

The

tuning

knob

provides

a

40

to

1

=

:

ee

ge

=

——

i

HEH

=

Ht

ae

a

i

:

+

Ht

bal

fH

:

&

H

=

_

Ath

Hf

c

Hitt

Hit

ee

te

:

|:

it

2

+

tt

i

rresaate

Ht

fe

i

cee

ere

Ree

ae

i

:

}

an

i

it

itt

i

=

poeeette

HHH

He

‘

i

tt

:

bi

A

a

ah

#

i

co}

sa

a

KILOCYCLES:

Figure

4.

Audio

Response

ratio

for

ease

in

selecting

the

desired

signal

as

indicated

on

the

slide-rule

dial.

Frequency

increases

with

clockwise

cotation

of

the

knob,

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

con-

nected

to

provide

this

function,

Since

the

XMT-

REC

switch

performs

its

muting

function

in

the

audio

and

IF

stages,

normal

operating

voltages

are

main-

tained

on

the

oscillators

and

all

other

frequency-

critical

circuits

to

ensure

that

no

frequency

drift

will

occur

during

standby

periods.

PHASING

(Crystal

Filter

Phasing

Control)

—

Maximum

selectivity

is

obtained

when

the

crystal

filter

circuits

are

balanced

at

the

crystal

frequency.

The

Phasing

control

is

used

to

accomplish

this

balance.

In

addi:

tion,

a

characteristic

of

crystal

filters

is

their

ability

to

provide

a

pronounced

null

at

any

particular

fre-

quency.

This

feature

is

extcemely

useful

in

‘‘tuning

out’?

an

unwanted

signal

very

close

to

the

desired

signal.

This

control

is

operative

only

when

the

SELECT

switch

is

at

position

1,

2

or

3.

When

the

SELECT

switch

is

at

off,

it

is

importane

that

the

PHASING

knob

be

set

at

mid-position

in

order

to

peak

the

preceding

IF

stage.

IF

(IF

Selectivity

Switch)

-

In

order

to

provide

the

wide

range

of

selectivity

characteristics

neces-

sary

to

cope

with

the

variety

of

amateur

operating

requirements,

the

IF

switch

permits

the

operator

Co

select

one

of

three

different

IF

bandwidths.

Position

number

1

is

8

kc

wide,

position

2

is

3.5

ke

and

position

3

is

500

cps.

In

normal

phone

operation

the

3.5

ke

position

would

usually

be

used;

position

3

affords

the

sharpest

selectivity

and

is

normally

desirable

for

CW

operation,

Position

1

places

the

IF

passband

at

its

broadest.

AFG

(Audio

Frequency

Gain

Control)

—

Two

func-

tions

are

performed

by

this

control,

The

first

is

the

customary

adjustment

of

audio

output

level

to

suit

the

listener.

Turning

the

control

clockwise

increases

the

volume;

the

volume,

turning

it

counterclockwise

decreases

The

second

function

is

the

switching

of

the

RE

gain

control

out

of

the

RF

amplifier

circuit

for

optimum

performance

during

CW

operation,

Turning

the

AFG

control

fully

clockwise

so

that

the

switch

is

actuated

removes

the

RF

gain

control

from

the

RF

stage

and

allows

the

RF

amplifier

co

run

at

full

gain.

This

affords

better

reception

of

weak

signals,

It

should

be

noted

that

regardless

of

the

switch

posi-

tion,

the

gain

of

the

second

IF

amplifier

is

always

adjustable

by

means

of

the

RFG

control.

The

AFG

control

may

then

be

returned

to

the

desired

position.

To

place

the

RFG

control

into

the

RF

amplifier

cir-

cuit,

rotate

the

AFG

contol

to

its

full

counterclock-

wise

position

so

that

the

switch

is

thrown,

then

the

AFG

contrql

may

be

reset.

This

setting

affords

an

improvement

in

reception

when

strong

interfering

signals

are

encountered,

BAND

CHANGE

SWITCH

—

This

control

is

used

to

select

the

desired

frequency

band

to

be

tuned.

Gear

reduction

is

employed

in

the

NC-300

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

all

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

mechan-

ically

coupled.

Positive

stops

are

provided

at

both

ends

of

the

BAND

control

travel.

PHONES

JACK

=

Headphones

of

the

high-impedance

type

may

be

plugged

into

the

PHONES

jack

using

a

standard

two-circuit

phones

plug.

There

is

no

DC

voltage

associated

with

the

headphone

circuit.

The

loudspeaker

is

automatically

silenced

when

the

phones

plug

is

inserted.

RFG

(RF

Gain

Control}

—

The

sensitivity

of

the

receiver

is

adjusted

by

means

of

this

control.

It

may

control

the

gain

of

the

RF

amplifier

and

second

IF

stages,

or

the

second

IF

stages

only,

depending

upon

the

position

of

the

RF

gain

switch

mounted

on

the

AF

gain

control.

This

two-way

feature

may

be

used

at

the

discretion

of

the

operator,

and

generally,

the

gain

control

will

be

restricted

to

the

IF

ampli-

fiers

when

maximum

CW

sensitivity

is

desired

to

provide

better

ceception

of

weak

signals,

If

very

stcong

local

signals

tend

to

cause

overloading,

the

RF

gain

control

should

be

switched

into

the

RF

amplifier

circuit

co

permit

reducing

the

RF

amplifier

gain,

The

AC

switch

which

turns

the

NC-300

ON

and

OFF

is

mounted

on

the

RF

gain

control,

When

this

control

is

rotated

to

its

maximum

counterclockwise

position

the

AC

power

is

shut

off.

Rotating

the

con-

trol

slightly

in

the

clockwise

position

will

actuate

the

switch

and

turn

the

receiver

on.

Further

rotation

increases

the

receiver

sensitivity

until

maximum

is

reached

at

the

full

clockwise

position,

3-2.

PHONE

RECEPTION

The

instructions

in

Steps

1

through

16

adjust

the

receiver

for

the

normal

reception

of

Phone

signals,

1.

Set the

ANL

control

at

OF

F,

Set

the

MODE

switch

at

AM.

Set

the

SELECT

control

at

OF

F.

Set

the

TONE

control

at

OFF,

Set

che

OF

F-CAL

switch

at

OFF.

Set

the

XMT-REC

switch

at

REC.

Set

the

IF

control

at

position

2.

Turn

the

AFG

contol

fully

counterclockwise

until

che

switch

clicks,

then

advance

it

approximately

to

mid-position.

9.

Set

the

BAND

switch

to

the

desired

frequency

range

as

indicated

by

the

slide-rule

dial

scale.

10.

By

means

of

the

CAL-SET

knob,

center

the

hairline

in

the

diamond-shaped

cutout

directly

above

-9-

the

knob.

11,

Turn

che

RFG

control

fully

clockwise.

Power

is

now

applied

to

the

receiver.

Allow

at

least

two

minutes

for

the

tubes

to

reach

operating

temperature

before

proceeding.

Set

the

AFG

contcol

to

provide

the

desired

audio

level.

12.

Rotate

the

TUNING

control

until

the

desired

signal

is

located.

Adjust

the

TUNING

control

very

carefully

for

maximum

S-Meter

reading.

13.

Turn

the

ANT

TRIM

and

PHASING

controls

to

obtain

maximum

S-Meter

reading.

These

controls

may

be

set,

in

the

absence

of

a

signal,

by

adjusting

them

to

obtain

a

peak

ia

the

background

noise.

14.

Set the

AFG

control

to

produce

the

desired

listening

level.

15.

the

desired

audio

response.

Turn

the

TONE

contro!

to

a

position

giving

16.

To

shut

down

the

receiver,

turn

the

RFG

control

fully

counterclockwise.

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.

Various

types

of

interference

which

may

be

encoun-

tered

due

to

adverse

receiving

conditions

can

be

minimized

by

adjusting

the

following

controls

in

the

manner

described,

NOISE

LIMITER

~

When

an

AM

signal

is

accom-

panied

by

static

peaks

or

noise

pulses

of

high

inten-

sity

and

short

duration,

the

best

signal-to-noise

ratio

will

be

obtained

by

turning

On

the

ANL

control,

In

general,

it

will

be

found

that

turning

this

control

just

far

enough

to

actuate

the

switch

will

effectively

minimize

interference

caused

by

external

noise

pulses.

In

cases

where

the

noise

pulses

are

ex-

tremely

pronounced,

a

higher

degree

of

noise

sup-

pression

will

be

realized

by

advancing

the

ANL

control.

Advancing

the

control

fully

clockwise

will

introduce

some

audio

clipping.

This

is

an

inherent

characteristic

of

all

noise

limiters

and

the

operator

must

choose

the

setting

which,

under

severe

con-

ditions,

will

produce

best

readability.

TONE

CONTROL

—

The

TONE

control

can

be

used

to

adjust

the

upper

and

lower

cut-off

frequencies

of

the

audio

amplifier,

IF

SELECTIVITY

—

The

NC-300

incorporates

two

separate

means

of

adjusting

its

selectivity

char-

acteristics

(IF

and

SELECT

controls).

This

para-

graph

deals

with

the

IF

control.

For

normal

phone

reception,

the

IF

switch

will

satisfy

narrow

band-

width

requirements

in

position

L

(8

kc)

or

position

2

(3.5

ke).

The

500-cycle

position

(3)

is

too

narrow

and

should

not

be

used

for

phone

signals.

CRYSTAL

FILTER

SELECTIVITY

AND

PHASING

—

The

increased

selectivity

afforded

by

the

crystal

filter

will

frequently

prove

useful

for

phone

reception,

2

1

of

the

SELECT

control

will

probably

Posi

prove

most

useful.

In

this

position,

the

PHASING

control

becomes

operative.

By

careful

adjustment

of

the

PHASING

control

the

unwanted

sigeal

can

usually

be

reduced

sufficieatly

co

permit

copying

the

desired

signal.

Experience

in

the

use

of

the

IF,

SELECT

and

PHASING

controls

will

ultimately

indicate

various

combinations

of

settings

that

best

suit

the

varying

operating

conditions

encountered.

3-3,

CW

RECEPTION

The

initial

adjustment

of

the

receiver

controls

for

CW

reception

is

the

same

as

given

in

Section

3-2

with

the

following

exceptions.

Set

the

MODE

switch

at

CW.

Set

the

CWO

control

at

its

mid-scale

position,

Rotate

the

AFG

control

clockwise

until

the

switch

is

actuated,

Then

rotate

clockwise

approximately

to

mid-position.

The

audio

level

of

the

receiver

should

be

adjusted

by

means

of

the

RFG

control.

Strong

CW

signals

cannot

block

the

IF

circuits

but

will

resule

in

an

unnecessarily

high

background

noise

level.

Always

keep

the

RFG

control

below

the

point

where

this

condition

occurs,

If

short-duration

pulse

interference

(ignition

etc.)

is

encountered,

the

noise

reduction

feature

of

the

IF

limiter

circuits

may

be

utilized

to

good

advantage.

Advance

the

RFG

control

and

retard

the

APG

control

until

limiting

occurs.

This

limiting

takes

place

in

the

last

IF

stage

and,

because

of

the

extcemely

fast

time

constants,

the

limiting

action

is

similar

to

that

encountered

in

FM

receivers.

For

CW

reception,

the

IF

control

may

also

be

used

in

its

sharpest

position

(3).

[¢

is

important

to

remem-

ber,

however,

that

the

IF

passband

in

this

posi

is

only

500

cycles

wide

so

chat

the

receiver

tuning

and

CWO

tuning

must

be

adjusted

very

slowly

and

carefully.

The

crystal

filter

must

be

off

when

this

sharpest

setting

is

used.

For

the

reception

of

CW

signals

the

action

of

the

crystal

filter

is

similar

to

that

for

phone

reception

except

that

full

use

of

the

sharp

selectivity

position

may

be

used

without

the

loss

of

intelligibility

ex-

perienced

in

phone

reception.

When

maximum

selec-

tivity

is

used

(SELECT

switch

at

pos

must

be

used

in

tuning.

When

the

receiver

is

slowly

‘ion

3),

care

tuned

across

the

carrier

of

the

received

signal,

the

beat

note

produced

will

be

very

sharply

peaked

in

outpuc

at

a

particular

audio

pitch.

This

peak

in

response

indicates

the

correct

receiver

dial

setting.

The

setting

of

the

CWO

control

must

be

such

that

the

beat-note

peak

is

well

within

the

audible

range

so

that

the

receiver

peak

response

may

be

readily

observed.

After

the

receiver

has

been

correctly

tuned,

the

pitch

of

the

beat-note

peak

may

be

adjusted

by

means

of

the

CWO

control

to

provide

an

audio

tone

which

is

pleasing

to

copy

or

coincides

with

any

response

peaks

in

the

speaker

or

headphones.

Under

these

conditions

the

receiver

will

exhibit

pro-

nounced

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

observe

the

marked

reduction

in

ourput.

This

laeter

dial

setting

is

not

recommended

for

use

other

than

to

demonstrate

the

single-signal

properties

of

the

receiver,

With

the

receiver

tuned

to

crystal

peak

an

interfering

signal

may

be

attenuated

by

proper

setting

of

the

PHASING

control

since

this

control

has

little

effect

on

the

desired

signal.

As

in

phone

operation,

combinations

of

contol

settings

may

be

selected

to

suit

varying

requirements

except

that

it

must

be

remembered

that

the

crystal

filter

cannot

be

used

with

IF

switch

at

position

3,

It

is

possible,

by

means

of

judicious

manipulation

of

these

controls,

to

copy

signals

which

would

be

com-

pletely

unreadable

on

receivers

which

do

not

incor

porate

these

features.

An

important

aid

to

CW

operation

of

the

amateur

station

has

been

included

in

the

NC-300.

It

is

fre~

quently

desirable

for

the

operator

to

monitor

his

own

transmitted

signal

while

sending

CW.

To

accomplish

this,

two

gain

conrols

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

on

Figure

2.

Adjust

the

external

control

to

receive

the

incoming

signal

at

the

desired

level

and

adjust

the

RFG

control

of

the

NC-300

for

comfortable

monitoring

level.

When

using

an

external

RF

gain

contol

the

XMT-REC

switch

must

be

left

at

the

REC

position

at

all

times.

3~4,

SINGLE-SIDEBAND

OPERATION

Provision

has

been

made

in

the

NC-300

for

the

reception

of

single-sideband

transmissions.

The

low

IF

frequency

(80-kc)

involved,

and

the

oscillator

circuit

design

provide

an

extremely

stable

oscil-

lator

with

a

high

equivalent

level

of

injection.

Make

the

initial

adjustments

as

in

paragraph

3-3

of

this

section.

While

runing,

set

the

MODE

switch

at

AM

until

the

SSB

signal

is

located

then

switch

to

SSB.

Set

the

CWO

control

to

receive

the

SSB

signal.

Posi-

tion

Lis

used

for

lower

sideband

reception

on

the

160,

80

and

40-meter

bands,

position

2

for

upper

sideband

signals

on

these

bands.

The

sidebands

are

reversed

on

the

20,

15,

11

and

10-meter

bands,

Optimum

reception

is

obtained

by

careful

adjustment

of

the

CWO

control

about

this

The

selec-

tivity

controls

may

be

set

at

the

positions

which

provide

the

maximum

readability

under

a

particular

set

of

receiving

conditions,

reception,

the

widest

bandpass

offers

no

particular

For

single-sideband

advantage,

and

interference

elimination

will

probably

be

the

criterion

for

choice

of

bandwidth

settings.

Normally,

IF

switch

position

2

would

be

used.

Reduc-

tion

in

background

noise

is

best

effected

by

adjust-

ment

of

the

RFG

contol.

3-5.

MEASUREMENT

OF

SIGNAL

STRENGTH

The

strength

of

a

received

signal,

as

indicated

by

the

S-Meter,

will

be

correct

oaly

when

the

receiver

is

properly

adjusted.

Atmospheric

noise

levels

will

differ

in

different

localities.

An

S-Meter

does

not

have

the

ability

to

recognize

the

difference

between

this

noise

level

and

an

actual

signal,

By

adhering

to

the

following

instructions,

this

problem

is

overcome

and

accurate

S-Meter

readings

will

resule.

I.

Set

the

RFG

control

fully

clockwise

and

the

MODE

switch

at

AM.

2.

Set

the

SELECT

switch

at

OFF.

3.

Tune

the

receiver

to

a

band

setting

where

no

signal

is

heard

so

that

the

S-Meter

is

reading

back-

ground

noise.

4.

Set

the

RFG

control

so

that

the

meter

reads

half-

way

between

0

and

S-1.

5.

Tune

in

the

desired

signal.

The

S-Meter

will

indicate

the

strength

of

the

received

signal

in

S-Units

from

1

to

9

or

in

decibels

above

the

S-9

level

from

zero

to

40

db.

These

readings

will

remain

accurate

until

the

RFG

control

is

moved

or

the

receiver

is

switched

to

a

different

band,

The

S-Meter

circuit

compensator

requires

adjust-

ment

only

when

it

is

impossible

to

obtain

a

zero

read-

ing

with

no

antenna

connected

and

the

RFG

control

curned

fully

counterclockwise.

See

Section

4-5

for

adjustment

procedure.

Design

of

the

S-Meter

actuating

circuit

is

such

that

a

signal

stronger

than

60 db

above

$-9

cannot

cause

the

meter

pointer

t

come

into

violent

contact

with

its

stop

thus

preventing

possible

bending

of

the

meter

pointer,

Measurements

of

the

signal

strength

of

CW

signals

cannot

be

made

with

the

MODE

switch

in

the

CW

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

or

60-cb

end

of

the

meter.

SECTION

4.

MAINTENANCE

DATA

4-1.

GENERAL

All

circuits

in

the

NC-300

receiver

are

carefully

aligned

before

shipment

using

high-precision

lab-

oratory

equipment

to

insure

high

accuracy,

The

quality

of

components

used,

together

with

careful

design,

makes

any

realignment

unnecessary

unless

the

receiver

is

tampered

with,

or

certain

part

or

tube

replacements

have

been

made.

In

no

case

should

realignment

be

attempted

unless

conclusive

tests

indicate

that

such

realignment

is

required.

Even

then

it

must

be

remembered

that

the

NC-300

is

a

highly

specialized

instrument

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

adjusting

receivers

of

this

type.

In

addi-

tion,

because

of

the

calibration

accuracy

and

extreme

bandspread

of

the

NC-300

it

is

mandatory

that

ade-

quate

test

equipment

be

used.

Complete

alignment

of

the

receiver

can

be

divided

into

three

steps

as

follows:

(a)

IF

Amplifier

and

CWO

Alignment.

(b)

Second

Conversion

and

Crystal

Filter

Alignment.

(c)

RF

Amplifier.

All

citcuits

must

be

tuned

in

the

above

order

when

complete

alignment

is

required,

All

alignment

adjust-

ments

and

controls

are

shown

on

Figures

6

and

7.

4-2,

IF

AMPLIFIER

AND

CWO

ALIGNMENT

The

second

intermediate

frequency

of

the

NC-300

must

be

aligned

at

exactly

80

kc.

The

signal

genera-

tor

used

must

be

capable

of

being

set

at

this

fre-

quency

with

precise

accuracy.

The

IF

transformers

are

tuned

by

means

of

adjustable

Ferrite

cores,

These

adjustments

are

located

on

Figure

7,

The

IF

alignment procedure

is

as

follows:

(1)

Distegard

the

Band

switch

setting.

(2)

Connect

the

output

lead

of

the

signal

generator

to

7

of

V3,

the

6BE6

2nd

converter

tube

and

connect

the

ground

lead

to

chassis.

Use

a

generator

output

connection

which

may

be

attenuated,

(3)

Set

the

MODE

switch

at

AM.

(4)

Set

the

IF

switch

at

position

3.

(5S)

Set

the

RFG

control

at

its

maximum

clockwise

position,

(6)

Set

the

XMT-REC

switch

at

REC.

(7)

Turn

the

modulation

of

the

signal

generator

off

and

set

the

frequency

of

the

generator

at

EXACTLY

80

ke.

Increase

or

decrease

the

generator

output

until

the

S-Meter

of

the

receiver

indicates

S-5.

(8)

Adjust

L13,

L12,

L10,

L9,

L7

and

LS

in

that

sequence

to

produce

maximum

S-Meter

reading.

Each

time

a

maximum

is

cbtained

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

subsequent

incorrect

alignment.

When

the

above

procedure

is

followed,

it

is

not

necessary

to

disable

the

second

oscillamr

or

AVC,

Spurious

signats

from

this

source

will

only

appear

if

the

input

from

the

generator

is

too

high.

(9)

To

set

the

CW

oscillator

plug

ia

headphones

or

connect

a

loudspeaker,

set

the

MODE

switch

at

CW

and

the

CWO

knob

3/4

of

a

division

(knob

marking)

clockwise

from

center.

(10)

Adjust

L16

for

zero

beat,

4-3,

SECOND

CONVERSION

AND

CRYSTAL

FILTER

ALIGNMENT

The

first

IF

frequency

of

rhe

NC-300

is

2215

ke

+3

ke,

The

exact

frequency

is

determined

by

the

tolerance

of

the

crystal

in

the

crystal

filter,

For

this

reason

the

exact

setting

of

the

signal

generator

will

be

determined

by

the

crystal

peak

frequency.

The

following

alignmenc

procedure

must

be

used.

(1)

Sec

the

BAND

switch

at

80

meters.

(2)

Move

the

output

lead

of

the

signal

generator

to

connect

to

the

stator

of

the

first

mixer

tuning

capacitor

(center

section

of

the

main

tuning

capaci-

tor),

The

ground

lead

may

be

connected

to

the

capacitor

frame.

(3)

Set

the

IF

congol

at

position

I.

(4)

See

the

SELECT

control

at

position

3.

(5)

Set

the

PHASING

control

at

its

center,

(6)

Tune

the

signal

generator

slowly

from

2212

to

2218

ke

observing

the

S-Meter

closely,

The

crystal

peak

will

be

evidenced

by

a

sharp

upward

swing

of

the

S-Meter

pointer.

Carefully

set

the

signal

generator

at

the

exact

peak

of

the

crystal

frequency

and

leave

it

at

chat

setting.

(7)

Set

the

SELECT

control

ac

OF

F

and

the

IF

con-

trol

at

position

2,

(8)

Align

the

2215

kc

IF

stage

and

crystal

filter

by

first

adjusting

L6,

This

is

the

second

conversion

oscillator

tuned

circuit

and

must

be

tuned

very

slowly

and

carefully.

The

oscillator

must

operate

80ke

above

the

first

incermediate

frequency.

If

two

peaks

are

noted,

use

the

peak

which

occurs

with

the

adjusting

screw

most

nearly

withdrawn,

The

peak

will

be

evidenced

by

a

pronounced

increase

in

the

S-Meter

reading.

(9)

Set

the

signal

generator

2

ke

either

side

of

the

crystal

frequency

noted

in

step

(6).

Set

the

SELECT

switch

at

position

1

and

adjust

14

for

maximum

output,

To

check

this

adjusonent

move

the

SELECT

switch

to

2

and

then

to

3,

the

bandpass

should

increase

in

sharpness

at

each

position

as

noted

by

listening

co

background

noise.

(10)

Return

the

signal

genetator

to

the

exact

crystal

frequency

and

set

the

SELECT

switch

at

OFF.

Adjust

C16

for

maximum

output.

(11)

Adjust

T4

and

L2A

for

maximum

S-Meter

deflec-

tion.

Keep

the

output

of

the

generator

low

enough

to

give

maximum

readings

of

approximately

S-5.

(12)

Set

the

signal

generator

exactly

160

ke

higher

than

the

setting

determined

in

step

6.

Increase

the

generator

output

to

obtain

an

S-Mecer

reading

of

SS.

Tune

12B

for

minimum

meter

reading.

Return

the

generator

frequency

and

output

to

their

Tune

L2A

for

maximum.

Repeat

adjustment

of

L2B

and

L2A

as

described

above

until

tue

maxi-

mum

and

minimum

are

achieved.

(13)

Disconnect

the

signal

generator

and

keep

SELECT

control

at

off.

Rotate

the

PHASING

control

to

obtain

maximum

background

noise.

The

control

should

now

be

at

its

exact

center

position

or

180

degrees

diametrically

opposite.

if

this

is

not

the

condition,

set

the

control

on

center

and

adjust

T4

for

maximum

background

noise.

(14)

The

following

two

checks

may

be

performed

to

prove

that

the

second

conversion

oscillator

is in

correct

atignment,

(15)

See the

MODE

switch

at

CW,

the

SELECT

switch

at

OFF,

the

PHASING

contro]

at

center

position,

and

the

IF

switch

at

position

3.

Rotate

the

CWO

knob

about

its

center

and

listen

to

the

back-

ground

noise.

Two

peaks

in

noise

with

a

null

between

will

be

heard.

The

ull

should

occur

with

the

CWO

knob

set3/4of

a

knob

division

clockwise

from

center.

If

this

is

not

the

case,

place

the

CWO

knob

at

this

setting

and

adjust

L1G

to

ebtain

the

null.

(16)Sec

the

IF

switch

at

position

2 and

the

SELECT

switch

at

3.

The

null

should

occur

with

che

CWO

knob

at

its

centec

setting.

Set the

SELECT

switch

at

OFF.

The

null

should

again

appear

at

the

CWO

knob

center

setting.

If

this

is

noc

the

case,

set

the

CWO

knob

at

center

and

adjust

L6

to

obtain

the

null,

4-4,

RF

AMPLIFIER

One

of

the

outstanding

features

of

the

NC-300

is

its

accuracy

of

calibration.

In

order

to

maintain,

this

precision,

the

signal

source

used

for

front-end

alignment

must

have

the

accuracy

of

precision

crys+

tals.

A

secondary

standard

(crystal

controlled)

will

suffice,

or

the

XCU-300

Crystal

Calibrator

may

be

used.

Either

of

these

last-mentioned

units

may

be

used

in

conjunction

with

a

standard

signal

generator

to

insure

calibration

accuracy.

Owing

to

the

restricted

frequency

coverage

of

the

receiver

and

the

limits

of

the

various

alignment

adjusoments

it

is

not

necessary

to

move

the

signal

generator

from

point

to

point.

Connect

the

signal

generator

to

the

antenna

terminals

using

a

1/2

watt

resistor

of

approximately

300

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

contro

to

position

the

hairline

ia

the

center

of

the

diamond-shaped

cutout.

(2)

Set

the

BAND

switch

according

to

the

Alignment

-12-

ALIGNMENT

CHART

SET

RECEIVER

TO:

ADJUST

TO

RECEIVE

TEST

SIGNAL

ADJUST

FOR

MAXIMUM

OUTPUT

C68A

Repeat

steps

1,

3

and

4

if

necessary

C68B

Repeat

steps

1,

3

and

4

if

necessary

14.4

mc

14.2

mc

14.0

me

14.4

mc

C68C

Repeat

steps

1,

3

and

4

if

necessary

CésD

Repeat

steps

1,

3

and

4

if

necessar,

C69A

Repeat

steps

1,

3

and

4

if

necessar:

C69B

Repeat

steps

1,

3

and

4

if

necessary

C69C

Repeat

steps

1,

3

and

4

if

necessary

-13-

cé9D

Repeat

steps

1,

3

and

4

if

necessary

Chart.

(3)

Set

che

MODE

switch

at

AM.

(4)

See

the

SELECT

switch

at

OFF.

(5)

Set

the

IF

control

at

position

3.

(6)

Set the

REG

control

fully

clockwise.

The

S-Meter

of

the

receiver

will

be

used

as

the

indicating

instrument

for

the

ensuing

procedures

and,

at

afl

times,

the

output

of

the

signal

generator

must

be

adjusted

to

produce

an

S-Meter

reading

of

approximately

5

S-Units.

When

the

XCU-300

is

used,

the

REG

control

can

be

used

to

regulate

the

signal

strength.

Make

all

adjustments

in

the

order

set

forth

in

the

following

Aligament

Chart.

The

trimmer

capacitors

and

inductance

trimmers

are

located

on

Figures

6

and

7.

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-ke

firse

IF

frequency

and

the

limited

range

of

the

crim-

mers,

images

will

not

be

readable

on

the

NC-300

so

no

special

precautions

need

be

taken

in

this

regard,

4-5,

SMETER

ADJUSTMENT

The

S-Meter

balancing

resistor

R44

is

used

to

obtain

a

zero

meter

reading

in

the

absence

of

signal

input

co

the

receiver,

To

make

this

adjustment

set

the

controls

as

follows:

Set

the

RFG

control

just

far

enough

in

the

clockwise

direction

to

trip

the

AC

switch.

Set

the

MODE

switch

at

AM.

Set

the

AFG

control

fully

counterclockwise

so

that

the

RF

gain

switch

is

actuated,

Ground

both

A

terminals

of

the

Antenna

terminal

strip

to

the

chassis.

Adjust

the

S-Meter

balancing

resistor

R44

to

produce

a

zero

read-

ing

on

the

S-Meter.

This

ts

a

screwdriver

adjustment

located

on

top

of

the

chassis.

4—6.

MEXER

IMAGE

TRAP

ADJUSTMENT

Che

mixer

image

tcap

should

ordinarily

not

require

readjustment.

If

readjustment

does

become

necessary

due

to

replacement

of

L18

or

C86,

or

inadvertent

maladjustment

of

these

components,

proceed

as

follows:

(1)

Set

the

Band

switch

at

the

20

meter

band

and

the

dial

at

14.1

mes.

(2)

Connect

a

signal

generator

as

outlined

in

par.

4-4,

Tune

the

generator

to

9670

ke+and

adjuse

the

output

to

produce

an

audible

audio

output.

(3)

Tune

C86

for

minimum

output,

4-7.

VOLTAGE

DATA

The

voltage

measurements

on

Figure

5

will

facili-

tate

any

servicing

which

might

be

required

on

the

NC-300.

4—8.

DIAL

CORD

STRINGING

In

the

event

of

breakage

of

the

dial

scale

actuating

cord

or

the

dial

pointer

cord,

the

instructions

shown

on

Figure

9

should

be

studied

with

care

before

attempting

replacement,

Failure

to

carry

out

these

instructions

correctly

will

result

in

incorrect

indica-

tions

of

band

setting

and

frequency.

The

dial

scale

in

view

at

the

front

panel

MUST

correspond

to

the

frequency

range

being

cuned.

4-9,

TUBE

REPLACEMENT

Tubes

which

become

weak

or

defective

should

be

replaced.

In

the

case

of

the

4H4C

current

regulator,

a

type

6V6

may

be

used

as

a

temporary

substitute.

This

substitution

will

sacrifice

the

current

regu-

lating

qualities

provided

by

the

4H4C

but

will

keep

the

receiver

operative.

Type

4H4C

regulators

are

not

generally

available

at

most

supply

houses,

A

replace

ment

can

be

obtained

from

National

Co.

or

any

National

Co,

authorized

service

station.

A

type

4H

will

not

provide

the

required

regulating

action.

-14—

xe

ACCESSORY

SOCKET

va

nes

ACCESSORY

ae

SOCKET

CALIBRATOR

ve

‘SOCKET

6BEG

6ac—

o

-0.32—

-—+18

vi

as

°

6

40.2

°

es

aC

CONDITIONS

a

wer

e

AC

LINE

VOLTAGE

-

115

voLTS.

6ALS

0.3

HIGH

IMPEDANCE

VACUUM

TUBE

VOLTMETER

USEO.

6ac

—o

CONTROL

SETTINGS

BAND

—

|.8-2MC

+26

436

MODE—AM

EXCEPT

WHEN

MeAs-|

72°

ae

URING

ve

WHEN

IT

1S

aT

cw.

|

~2°

3!

RFG

—MAXIMUM

CLOCKWISE

POSITION.

6BN6

+26

SELECT

—

OFF.

Ac.

e

AFG

—MAXIMUM

CLOCKWISE

POSITION.

16

POSITION

|.

+e

+150

TONE

—

OFF,

06

+50

ANL

—

OFF.

v4

CAL—

OFF

6aJ6

4

ALL

VOLTAGES

MEASURED

FROM

‘SOCKET

TO

CHASSIS.

ALL

VOLTAGES

DC

EXCEPT

AS

NOTED.

TOLERANCE

=

+10)

ANT.

FRONT

Figure

5.

Tube

Socket

Voltages

x

CALIBRATOR

SOCKET

vis

anac

Lz8

IST

MIXER

TUNING

cri

14

CRYSTAL

FILTER

TUNING

crs

RYSTAL

FILTER

TUNING

Rag

3

METER

‘AuusT

Main

TRIMMER

TUNING

%

00

NOT

DISTURB

THE

SETTING

OF

THE

SCREWS

AT

THE

TOP

OF

THESE

CANS.

Figure

6.

Component

Locations,

Top

View

of

Receiver

age:

clo

Figure

7.

Capacitor

and

Alignment

Adjustment

Locations,

Bottom

View

-16-

Figure

8.

Resistor

and

Miscellaneous

Component

Locations,

Bottom

View

-l7-

Q\ser

sano

switcH

AT

20

METER

BAND.

WITH

CAL-SET AIRLINE

AT

CENTER

OF

CUTOUT,

TUNE

IN

KNOWN

SIGNAL

OF

14.2

Me.

MAKE

SURE

CAPACITOR

Reuaina’

hr

THiS

SETFine

Domne

Sond

Seinen

its

eco

scion

@rewove

ovat

scALe

onde

ey

wiTHORAMING

SCREW

On

MIONT

SIDE

OF

TO

PREVENT

SLIPPING.

RECEIVER

AND

RETAMING

RING

FROM

LEFT

CxO

OF

BRUM

OTE

PONTOON

PL

ENDS

OF

conD

STRETCHIm

OF

sPmino

WASHER

AND

DAUM

IAL

CORD

TO

Pemule

Peach

Pert

eae

srnme

WNT

FOLNTER

sows

TO

PREVENT

Omuw

CORD

FROM

SLIPPING

OFF

PULLEYS,

aanwTion

we

oo

Teuton

on

Git

Sa

eek

Sata

fase

conD

Tau

POWTER

pl

perpen

@arercace

onuu.

ser

rownre

EXACTLY

14.2

BY

SLIOING

DIAL.

CORD

AROUND

PULLE}

LOOP

_conu

JAROUND

PULLEYS.

CORD

SHOWN

EXPOSED

FOR

CLARITY.

CORD

LENGTH

4.250

FEET.

FOR

FINE

ADJUSTMENT,

LOOSEN

SCREWS

RETIGHTEN.

6B

FOR

COARSE

ADJUSTMENT

OF

DIAL

SCALE,

JUMP

BEAD

CHAIN

ON

SPROCKET,

TIGHTEN

CHAIN

GUIDE.

_@

POSITION

ORUM

SO

THAT

160

METER

Bano

SCALE

1S

CENTERED

IN

DIAL

WINDOW.

SET

BANO

SWITCH

AT

EXTREME

COUNTERCLOCKWISE

(G)

POSITION,

CHAIN

LENGTH

=

6

4°.

CORD

LENGTHS=20"

EACH.

Figure

9.

Cord

Stringing

Guide

PARTS

LIST

CAPACITORS

(CONT'D)

cl

Air

Variable:

3

sections

C1179

C41

|

Ceramic:

0.01

mfd

+100%,

-0%

|

K946-2

CIA

|7.4-40.3

mmf,

part

of

CL

C42

|

Mica:

220

mmf

+20%

665-44

CIB

/7.4-40,3

mmf,

part

of

CL

C43

|

Mica:

150

mmf

45%

J665-37

CIC

|

14,4-80.7

mmf,

pact

of

C1

C44

|

Mica:

150

mmf

45%

J665-37

c2

Air

Variable:

3-50

mmf

A12502

C45.

|

Mica:

1,000

mmf

+2%,

1666-69

fon)

Ceramic:

100

mmf

D825C-304

300

vdew

c4

Ceramic:

0.01

mfd+100%

-0%|

K946-2

46

|

Mica:

2,700

mmf

£5%,

J666-28

cs

Ceramic:

0.01

mfd

+100%,

-0%

|

K946-2

500

vdew

C6

Ceramic:

100

mmf

DB25C-304

C47

|

Ceramic:

240

mmf

+2%,

A14157

c7

Ceramic:

0.01

mfd

+100%,

-0%

|

K946-2

300

vdew

cs

Mica:

470

mmf

J665-56

C48

|

Ceramic:

12

mmé

15%

CC20UJ

120)

C9

|

Ceeamic:

0.01

mld

+100%,

-0%|

K946-2

C49

|

Ceramic:

15

mmf

D825

D-467

C10

|

Ceramic:

0.01

mfd

+100%,

-0%|

K946-2

50.

|

Mica:

470

mmf

4665+56

C1

|

Ceramic:

39

mmf

D825D-455

C51-

|

Ceramic:

0.01

mfd

+100%,

-0%

|

K946-2

C12

|

Ceramic:

62

mmf

D825D-472

C52

|

Air

Variable:

12-100

mmf

AL2501

C13

|

Ceramic:

1

mmf

£20%

D825D-470

C53

|

Mica:

470

mmf

4665-56

C14

|

Ceramic:

39

mmé

D825D-455

C54

|

Cecamic:

100

mmf

D825C-304

C15

|

Ceramic:

6.8

mmf

25%

D8250-475

C55

|

Ceramic:

5

mmf

D825D-401

C16

|

Mica

Variable:

5-20

mmf;

A12312

C56

|

Paper:

0.01

mfd

+20%,

Q693-19

part

of

CFI

400

vdew

cl7

Ceramic:

5

mmf

£20%

D825D-40

1

C57

|

Ceramic:

47

mmf

D8251-466

C18

|

Ceramic:

.01

mfd

+100%

-0%

|

K946-2

C58

|

Paper:

0.01

mfd

+20%,

Q693-19

C19

|

Differential,

Air:

25

mmf,

BI2510

400

vdew

part

of

CFL

C59

|

Paper:

0.001

mfd

£20%,

Q693-1

C20

|

Ceramic:

3

mmf

+0.25

mmf

D825D-499

400

vdew

C2L

Ceramic:

39

mmf

D825D-455

C60

|}

Paper:

0.01

mfd

420%,

Q693-19

C22}

Mica:

120

mmf

+5%

1665-34

400

vdew

C23

|

Mica:

150

mmf

£5%

665-37

C61

}

Paper:

0.47

mfd

120%,

Q693-89

C24

|

Ceramic:

5

mmf

+20%

D825D-401

150

vdew

C25

|

Ceramic:

3

mmf

+0.25

mmf

D825D-449

C62

|

Electrolytic:

40-40-20

mfd,

A13183

C26

|

Ceramic:

0.01

mfd

+100%,

-0%|

K946-2

250

vdew

C27

|

Ceramic:

100

mmf

+5%

DB25C-342

C63

|

Mica:

0.001

mfd,

1,000

vdew

|

J667-50

C28

|

Paper:

0.047

mfd

£20%

693-28

C64

|

Ceramic:

§

mmf

1D825D-401

C29

|

Mica:

9L0

mmf

12%,

300

vdew|

J666-67

C65

|

Mica:

0.001

mfd,

1,000

vdew

|

J667-50

C30

|

Mica:

3,600

mmf

+2%,

J666-66

C66

|

Mica:

0.001

mfd,

1,000

vdew

|

J667-50

300

vdew

C67

|

Ceramic:

0.01

mfd

+100%,

-0%

|

K946-2

C31

|

Ceramic:

0.01

mfd

+100%,

-094

K946-2

C68

|

Mica

Variable:

4

sections,

A12493

C32

|

Paper:

0.047

mfd

420%,

693-28

cach

5-80

mmf

400

vdew

C6BA

}

Part

of

C68

33.

|

Ceramic:

5

mmf

+20%

D825D-401

COBB

|

Part

of

C68

C34

|

Mica:

150

mmf

45%

J665-37

C68C

|

Pare

of

C6B

C35

Mica:

150

mmf

+5%

J665-37

C68D

|

Pare

of

C68

C36

|

Mica:

1,000

mmf

42%,

666-69

C69

|

Mica

Variable:

4

sections,

AL2493

300

vdew

each

2.2-40

mmf

37

|

Mica:

3,600

mmf

42%,

666-66

C69A

|

Pare

of

C69

300

vdew

CO9B

|

Part

of

C69

C38

|

Paper:

0.047

mfd

420%,

693-28

C69C

|

Pact

of

C69

400

vdew

69D

|

Pact

of

C69

39

|

Paper:

0.047

mfd

20%

693-28

C70

|

Air

Variable:

2.8-19.7

amt

A12744

400

vdew

C71

|

Air

Variable:

2.8-19.7

mmf

A12744

C40_|

Paper:

0.1

mfd,

400

vdew

2693-34

C72_|

Air

Variable:

2.8-19.7

mmf

A12744

PARTS

LIST

(CONT'D)

RESISTORS

(CONT'D)

Description

Nateo

Type

CAPACITORS

(CONT'D)

Air

Variable:

2.8-19.7

AL2744

Fixed:

|

megohm

5569-61

Air

Variable:

2.8-19.7

me

A12744

Fixed:

1

megohm

969-61

Air

Variable:

2.8-19.7

mmf

A12744

Fixed:

27,000

ohms

969-42

Aie

Variable:

2.8-19.7

cmt

AL2744

Fixed:

100,000

ohms

969-49

Air

Variable:

2.8-19.7

mmf

—

|

A12744

Fixed:

100

ohms

4569-13

Paper:

0,047

méd

+20%,

2693-28

Fixed:

10,000

ohms

969-37

400

vdew

Fixed:

10,000

ohms

869-37

Paper:

0.022

mfd,

400

vdew

|

(693-23

Fixed,

Wire-Wound:

1,800

1959-26

Paper:

0.022

mfd,

400

vdew

|

Q693-23

ohms

+5%,

5

wates

Paper:

0.022

mfd,

400

vdew

|

Q693-23

Fixed:

39,000

ohms,

2

watts

|

572-44

Ceramic:

100

mmf

+5%

DB25C.-342

Variable,

Wire-Wound:

A13598

10,000

ohms

Fixed:

68,000

ohms

369-47

Paper:

0,001

mfd

+20%,

400

vdew

Q693-1

Ceramic:

0.005

mfd+100%,-0%|

K946-1

Fixed:

100,000

ohms

4569-49

Ceramic:

15

mmf

8251-467

Fixed:

68,000

ohms

1569-47

Mica,

Variable:

35-35

mmf

|

Al2312

Fixed:

+500

otms

349%

1569-87

Fixed:

270,000

ohms

569-54

Fixed:

33,000

ohms

4560-43

Variable,

Wire-Wound:

L216

1,000

ohms

Fixed:

3,300

ohms

}569-3L

Variable:

500,000

ohmsiwith

|

13596

Paper:

.22

mf

400

vdew

693-40

+10%

tolerance,

500

volts

working

on

all

capacitors

unless

otherwise

noted.

*

RESISTORS

Fixed:

|

megohm

4569-61

SPST

switch

S7)

Fixed:

33

ohms

J569-7

Fixed:

|

megohm

J569-61

Fixed:

330

ohms

4569-19

Fixed:

270,000

ohms

J569-54

Fixed:

100

ohms

J

569-13

Fixed:

470,000

ohms

J569-57

Fixed:

47,000

ohms

$569-45

Fixed:

470,000

ohms

369-57

Fixed:

220,000

ohms

J

569-53

Variable:

1

megobm

(with

ALL697

Fixed:

470

ohms

4569-21

SPDT

switch

$3)

Fixed:

68,000

ohms

J569-47

Fixed:

220

ohms,

2

watts

JS72-17

Fixed:

100

ohms

3569-13

Fixed:

100

ohms

J569-03

Fixed:

100,000

ohms

J569-49

Fixed:

10,000

ohms

969-37

Fixed;

22,000

ohms

569-41

Fixed:

470,000

ohms

1569-57

Fixed:

2,200

ohms

J569-29

Fixed:

10,000

ohms

J569-37

Fixed:

220

ohms

+5%

J569-L08

Fixed:

4.3

ohms

5%,

|

watt

K098-48

Fixed:

1,500

ohms

15%

J

569-87

Fixed:

4.7

megohms

569-69

Fixed:

12,000

ohms

569-38

Fixed:

10,000

ohms

}

569-37

Fixed:

1

megohm

569-61

Fixed:

10

ohms

569-1

Fixed:

330-1200

ohms

+10%,

1/2

wate

(value

individually

chosen

co

meet

requirements

J569-

Resistors

10%

tolerance

1/2

watt

except

as

noted,

of

each

receiver)

C.12721

Fixed:

1

megohm

$569-61

Crystal

Filter

Assembly

Fixed:

1

megohm

569-61

Knob:

ANL

B11800

Fixed:

1,000

ohms

+5%

J569-139

Knob:

Tone

BEL801

Fixed:

330

ohms

+5%

969-140

Knob:

IF

B11802

Fixed:

560

ohms

J

569-22

Knob:

Zero

ALL969

Fixed:

2,200

ohms

J

569-29

Knob:

CWO

B11804

Fixed:

1

megohm

J569-61

Knob:

AFG

,

B11805

Fixed:

1,200

ohms

£5%

4369-79

Knob:

Aateana

Trimmer

1311803

Fixed:

56

ohms

+5%

J569-141

Knob:

OF

F-CAL

ALL969

Var:

100,000

ohms

incl

S6

A13597

Knob:

Band

Switch

ALI917

*

Resistors

see

Page

22

National Company NC300 User manual

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