Heathkit Heathkit SG-8 Istruzioni per l'installazione

Altri manuali per Heathkit SG-8

2

Indice

Altri manuali Heathkit Generatore portatile

Heathkit

Heathkit Heathkit SG-8 Istruzioni per l'installazione

Manuali Generatore portatile popolari di altre marche

Kohler

Kohler 20EORZ Manuale di istruzioni

Powerhorse

Powerhorse 83171 Manuale utente

HURST

HURST ML-630-SI Manuale utente

ETQ

ETQ TG4000 Manuale utente

Briggs & Stratton

Briggs & Stratton 40265 Guida all'installazione

ConMed

ConMed 7550 Manuale utente

Owon

Owon Waveform Generator Manuale utente

evertz

evertz 7700 Series Manuale utente

Power Stroke

Power Stroke PS906025 Manuale utente

Firefly

Firefly Cygnus CYG2400/460/24 Manuale utente

Draper

Draper PG950S Aggiornamento firmware

PowerBoss

PowerBoss PowerBoss Manuale utente

SDMO

SDMO SH 4000 Manuale utente

EINHELL

EINHELL STE 5500 Manuale utente

Wanco

Wanco WI3000P Manuale utente

Full Boar

Full Boar FBT-3300 Manuale utente

Dwyer Instruments

Dwyer Instruments ASG Manuale utente

Westinghouse

Westinghouse WH1000i Series Manuale utente

ASSEMBLY

AND

OPERATION

OF

THE

HEATHKIT

SIGNAL

GENERATOR

MODEL

SG-8

-•

5

c

•

•

>.*V

«c

L*

\

j

A-er-

/

qur

*

r

M&fill

I

*

.

'

•%

.

•

*.

I

*

.

>t

y:?

V*

1

5

%.

,

p

f

?

'4SiNV

•

»V

‘

■

\r

.

;?

■

I

I

t

•

V

,1,1

SPECIFICATIONS

Frequency

Range

Band

A.

Band

B.

Band

C.

Band

D.1

Band

E.

Calibrated

Harmonics..

Radio

Frequency

Output

Modulation

Frequency.

.

Audio

Output.

Audio

Frequency

Input.

.

Tubes

12AU7.RF

Oscillator-Buffer

6C4.Audio

Oscillator

or

Audio

Amplifier

Power

Requirements.105-125

v,

50/60

cycles

Cabinet

Size.5

1/2

wic

e

x

6

1/2

high

x

5

deep

Shipping

Weight.7

lbs.

160

kc

to

500

kc

500

kc

to

1650

kc

1.65

me

to

6.5

me

6.5

me

to

25

me

25

me

to

110

me

1:

0

me

to

220

me

In

excess

of

100,000

microvolts

Approximately

400

cycles

2

to

3

vo

ts

Approximately

5

v

across

1

megohm

MODEL

SG-8

TT

W

RF

“

0UT

INTRODUCTION

The-Heathkit

model

SG-8

Signal

Generator

has

been

designed

for

simplicity

of

construction

and

stability

of

operation.

A

little

care

taken

during

the

process

of

construction

will

reward

the

kit

builder

with

a

signal

generator

which

will

give

excellent

performance

and

will

be

both

pleasant

and

easy

to

use.

This

generator

has

been

engineered

so

that

it

will

be

valuable

to

the

radio

re¬

pairman,

ham

and

experimenter

over

a

wide

range

of

uses,

in

addition

to

being

a

rugged

and

highly

dependable

piece

of

test

equipment.

It

is

made

with

high

quality

parts,

conservatively

rated,

and

will

give

long

and

efficient

service.

The

model

SG-8

Signal

Generator

utilizes

factory

adjusted

coils,

thereby

eliminating

the

necessity

of

having

costly

equipment

available

to

cali¬

brate

the

finished

kit.

CIRCUIT

DESCRIPTION

The

RF

portion

of

the

SG-8

Signal

Generator

consists

of

a

12AU7

twin

triode

tube.

One

triode

section

of

this

tube

is

used

as

a

Colpitts

oscillator.

The

other

triode

section

is

used

in

a

cathode

follower

type

circuit

and

acts

as

a

buffer

between

the

oscillator

and

the

output

of

the

signal

gen¬

erator.

Four

inductances

wound

on

forms

comprise

the

coils

for

bands

A,

B,

C

and

D.

They

are

switched

into

the

circuit

by

means

of

the

band

switch.

TheE

band

coil

is

unique

in

its

construc¬

tion

insofar

that

the

heavy

buswire

of

which

it

is

composed

actually

forms

the

connections

be¬

tween

the

band

switch

and

the

tuning

condenser

for

all

of

the

lower

frequency

coils.

When

the

band

switch

is

placed

in

E

band

position,

a

short

is

placed

across

the

leads

of

the

E

band

coils,

thereby

making

it

a

closed

circuit

inductance

which

is

capable

of

tuning

from

25

to

100

mega¬

cycles.

In

a

Colpitts

oscillator

circuit,

feedback

necessary

to

maintain

oscillations

is

obtained

from

a

capacitive

reactance

divider

across

the

inductance

of

the

frequency

determining

circuit.

In

the

model

SG-8,

a

capacitive

divider

is

obtained

by

the

use

of

a

split-stator

condenser.

The

ad¬

vantage

of

this

will

be

made

apparent

from

the

following

explanation.

For

example,

take

a

ca¬

pacitive

divider

composed

of

fixed

capacities.

As

the

frequency

across

the

condensers

is

in¬

creased,

the

reactance

of

the

condensers

is

decreased.

Therefore,

using

a

fixed

capacitive

divider,

as

the

frequency

is

increased

reactance

would

become

lower

until

a

point

was

reached

where

oscillations

could

no

longer

be

maintained.

By

the

use,of

a

split-stator

condenser

for

both

tuning

and

as

the

divider

network

as

the

frequency

is

increased,

the

capacity

of

the

con¬

denser

dividing

network

is

decreased.

The

reactance

of

a

condenser

for

any

given

frequency

is

inversely

proportional

to

the

capacity.

This

tends

to

maintain

the

reactance

of

the

network

fair¬

ly

constant,

thereby

permitting

oscillation

over

a

wide

range

of

frequency.

The

use

of

the

cathode

follower

as

a

buffer

stage

has

the

following

advantage:

The

characteris¬

tics

of

a

"cathode

follower"

are

very

low

output

impedance

with

an

extremely

high

input

imped¬

ance.

The

extremely

high

input

impedance

produces

little

or

no

loading

on

the

oscillator

circuit.

The

very

low

output

impedance

provides

a

very

stable

output

from

the

signal

generator.

The

effect

is

such

that

a

varying

load

on

the

output

of

the

signal

generator

will

produce

little

or

no

frequency

instability

of

the

oscillator.

The

signal

generator

incorporates

a

step

attenuator

for

coarse

control

of

radio

frequency

output

aftd

a

continuously

variable

attenuation

circuit

for

fine

control

of

the

radio

frequency

output.

The

audio

oscillator

is

also

a

Colpitts

circuit.

By

the

use

of

the

large

inductance

of

an

iron-

core

choke

and

relatively

high

capacity

in

the

capacitive

divider,

it

is

made

to

oscillate

al

ap¬

proximately

400

cycles.

This

type

of

oscillator

was

again

chosen

for

its

stability

and

purity

of

waveform.

With

the

modulation

switch

in

the

INT.

position,

400

cycles

audio

voltage

is

ap¬

plied

through

a

resistance

network

to

the

grid

of

the

cathode

follower

stage.

This

audio

vo’tage

is

impressed

as

an

amplitude

modulated

signal

upon

the

RF

output

from

the

cathode

folio

ver

.

At

the

same

time

the

audio

voltage

is

also

applied

to

the

external

audio

cc

nnt

tor

marked

OUT,

and

may

be

used

as

an

audio

signal

source

for

testing

amplifiers,

etc.

Wuh

the

modul

ition

switch

in

the

EXT.

position,

any

external

audio

source

of

any

frequency

may

be

used

to

modu¬

late

the

RF

output

of

the

signal

generator.

The

6C4

audio

oscillator

tube

then

becomes

an

am¬

plifier

stage

for

the

external

signal.

Page

3

I

The

power

apply

consists

of

a

transformer

which

furnishes

filament

voltage

to

the

6C4

and

12AU7

tubet

and

effectively

isolates

the

instrument

from

the

AC

line.

A

selenium

rectifier

is

connected

t<

one

winding

of

the

transformer

producing

half-wave

rectification.

An

RC

filter

network

cha

iges

the

pulsed

output

from

the

rectifier

to

fairly

pure

DC.

The

110

volt

input

has

both

sides

bypassed

to

minimize

the

signal

feeding

back

through

the

power

lines.

A

unique

de

ugn

feature

is

the

convenient

AF

IN-OUT

control,

which

adjusts

audio

input

if

ex¬

ternal

moduation

is

employed

and

likewise

adjusts

theAF

output

level

when

using

the

generator

as

a

source

of

audio

output.

9

PRELIMINARY

INSTRUCTIONS

AND

NOTES

TheHeathki

model

dG-8

Signal

Generator

when

constructed

in

accordance

with

the

instructions

in

this

mam

al,

is

a

high-quality

piece

of

test

equipment,

capable

of

years

of

trouble-free

serv¬

ice.

We

therefore

urge

you

to

take

the

necessary

time

to

assemble

and

wire

the

kit

carefully.

You

will

be

rewarded

with

a

neat

appearing,

well-built

and

dependable

test

oscillator.

This

manual

is

supplied

to

assist

you

in

every

way

to

complete

the

signal

generator

with

the

least

possit

le

<

hance

for

error.

We

suggest

that

you

take

a

few

minutes

now

and

read

the

en¬

tire

manual

thr

)ugh

before

any

work

is

begun.

This

will

enable

you

to

proceed

with

the

work

much

faster

wl

en

c

instruction

is

started.

The

large,

fold-in

pictorials

are

handy

to

attach

to

the

wall

above

your

work

space.

Their

use

will

greatly

simplify

the

construction

of

the

kit.

These

diagrams

are

repeated

in

smaller

form

within

the

manual.

We

suggest

that

you

retain

the

mamal

in

your

files

for

future

reference,

both

in

the

use

of

the

signal

generator

and

for

its

mainten

mce.

UNPACK

THE

KIT

CAREFULLY

AND

CHECK

EACH

PART

AGAINST

THE

PARTS

LIST.

In

so

doing,

ycu

will

become

acquainted

with

each

part.

Refer

to

the

charts

and

other

information

shown

on

tho

inside

covers

of

the

manual

to

help

you

identify

any

parts

about

which

there

maybe

a

question.

If

some

shortage

is

found

in

checking

the

parts,

please

notify

us

promptly

and

return

the

inspection

slip

with

your

letter

to

us.

Hardware

items

are

counted

by

weight,

and

if

a

few

are

missing,

please

obtain

them

locally

if

at

all

possible.

Read

tho

note

on

soldering

on

the

inside

of

the

back

cover.

Crimp

all

leads

tightly

to

the

termi¬

nal

before

soldering.

Be

sure

both

the

lead

and

the

terminal

are

free

of

wax,

corrosion,

or

other

foreign

substances.

Use

only

the

best

rosin

core

solder,

preferably

a

type

containing

the

new

activated

fluxes,

such

as

Kester

"Resin-Five,

"

Ersin

"Multicore,"

or

similar

types.

NOTE:

GUARANTEES

ARE

VOIDED

AND

V/E

WILL

NOT

REPAIR

1ENTS

USED.

DRE

SOLDER

OR

PASTE

FLUXES

HAVE

BEEN

SOLDER,

IT

IS

RECOMMENDED

THAT

A

NEW

IN

DOUBT

ABOUT

SOLDER,

IT

IS

REC

'

MARKED

"ROSIN

CORE

RADIO

SOLDER

Resistors

and

condensers

generally

have

a

tolerance

rating

of

±20%

unless

otherwise

stated

in

the

parts

list.

Therefore

a

100

KO

resistor

may

test

anywhere

from80Kft

tol20Kfi.

(Thelet¬

ter

K

is

commonly

used

to

designate

a

multiplier

of

1100.)

Tolerances

on

condensers

are

gen¬

erally

even

greater.

Limits

of

+100%

and

-50%

are

common

for

electrolytic

condensers.

The

parts

furnished

with

your

Heathkit

have

been

specified

so

they

may

not

adversely

affect

the

op¬

eration

of

the

finished

signal

generator.

In

order

to

expedite

delivery

to

you,

we

are

occasionally

forced

to

make

minor

substitutions

of

parts.

Such

substitutions

are

carefully

checked

before

they

are

approved,

and

the

parts

sup¬

plied

will

work

satisfactorily.

By

checking

the

parts

list

for

resistors,

for

example,

you

may

find

that

a

2.2

megohm

resistor

has

been

supplied

in

place

of

a

2

megohm

as

shown

in

the

parts

list.

These

changes

are

self-evident

and

are

mention'd

here

only

to

prevent

confusion

in

check¬

ing

the

contents

of

your

kit.

We

strongly

urge

that

you

follow

the

wiring

and

parts

layout

shown

in

the

manual.

The

position

’age

4

TEST

LEAD

ASSEMBLY

j\\\w;\v\\k

FfFFFFTR

i

i

■

HWHHi

Figure

11

The

test

lead

is

assembled

as

shown

in

Figure

11.

One

end

of

the

shieldedcable

is

connected

to

the

shielded

plug;

the

other

end

has

alligator

clips

mounted

on

it

for

connection

to

the

equipment

under

test.

First,

remove

the

spring

cable

guard

from

the

connector

plug

by

loosening

the

screw

in

the

side

of

the

plug.

Slide

this

spring

over

the

shielded

cable,

with

the

small

end

of

the

spring

toward

the

end

that

is

to

be

connected

to

the

plug.

The

outside

insulation

on

the

cable

is

then

cut

back

for

a

length

of

about

3/4",

then

flare

the

shield

braiding

at

the

end

of

the

cable

so

that

it

may

be

pushed

back

over

the

small

end

of

the

spring

cable

guard.

The

inner

connector

is

then

stripped

for

a

length

of

approximately

1/8".

The

assembly

at

this

point

is

slid

back

into

the

connector

so

that

the

inner

coaxial

wire

passes

through

the

rivet

in

the

insulated

end

of

the

connector,

the

cable

guard

with

the

shielded

braid

flared

over

the

end

is

pushed

back

into

the

connector

and

the

screw

tightened

to

hold

it

in

place.

Solder

the

inner

connector.

Slit

lengthwise

Circular

cut

METHOD

OF

PREPARING

SHIELDED

LEAD

Shielded

test

lead

ready

lor

connector.

Figure

12

On

the

other

end

of

the

shield

cable,

the

outer

insulation

is

cut

back

about

4"

and

the

cable

pre¬

pared

as

shown

in

Figure

12.

Solder

alligator

clips

to

both

the

inner

conductor

and

the

shield

braid.

ACCURACY

Any

signal

generator

is

designed

as

a

convenient

and

controllable

source

of

modulated

or

unmod¬

ulated

signals.

No

signal

generator

is

designed

as

a

frequency

standard

Expensi

/e

standard

signal

generators

have

fairly

accurate

(3

to

20%)

attenuators

which

control

the

output

voltage

and

the

calibration

accu

acy

is

rarely

closer

than

1%.

The

Heathkit

Signal

Generator

may

be

expected

to

fall

within

2

to

3%

of

the

frequency

calibration,

which

is

quilt

satisfactory

for

ser¬

vice

work

and

alignment.

In

receiver

adjustment,

the

frequency

at

which

the

particular

adjust¬

ment

is

made

is

rarely

critical

but

the

adjustment

itself

for

maximum

signal

output

from

the

Page

15

receiver

is

frequently

quite

critical.

For

accurate

calibration

of

home

built

receivers

or

eq

iip-

ment,

pi

*ce?d

as

follows.

Make

a

rough

calibration

with

the

signal

generator.

Then,

with

a

receiver,

tu

le

in

W

VV

(Bureau

of

Standards)

at

2.5,

5,

or

10

me.

Set

the

signal

generator

to

a

suitable

sub-harmo

lie,

such

as

500

or

1000

kc,

and

adjust

the

generator

for

zero

beat.

Now

lurmonics

of

the

sh

nal

generator

occur

every

500

kc

or

1

megacycle,

and

these

harmonics

may

be

used

to

give

acci

rate

calibrations

at

points

500

or

1000

kc

apart,

such

as

2500

kc,

3000

kc

,

3500kc,

4000

kc,

etc.

These

known

frequency

points

can

be

marked

on

the

dial

of

the

equipment

being

calibrated.

T

le

object

of

the

rough

calibration

is

merely

to

furnish

a

means

of

identifying

for

example,

the

3(00

kc

point

from

the

2500

kc

or

3500

kc

points.

For

calibration

of

higher

frequency

equipmei

t,

a

choice

of

higher

sub-harmonic

will

reduce

the

confusion

between

the

n

ultitude

of

harmoi

ics

and

will

also

insure

adequate

signal

strength.

When

checking

the

cali¬

bration

accuracy

of

the

Heathkit

Signal

Generator,

the

most

convenient

standards

of

comparison

of

sufficient

accurac

/

are

broadcast

stations

of

known

frequency.

Crystal

oscillators

of

standard

frequency

when

zero

beat

against

WWV,

are

also

convenient

to

use

if

available.

The

use

of

re-

c

:iver

dial

calibrations

is

frequently

not

of

sufficient

accuracy

to

warrant

consideration.

Output

Voltage:

Tha

RF

signal

strength

going

into

the

output

control

depends

upon

the

strength

oi

oscillation

of

the

12.AU7

oscillator.

In

all

variable

frequency

oscillators

the

amplitude

will

vary

with

the

tunini

condenser

setting.

With

careful

design

the

variation

may

be

minimized.

In

theHeathkit

Signal

Generator,

the

variation

is

kept

down

to

a

ratio

of

about

2

1/2

to

1

on

each

band

except

band

E,

where

the

L/C

(inductance

to

capacitance)

ratio

becomes

sufficiently

un¬

favorable

that

oscillation

may

drop

off

rapidly

in

strength

when

the

condenser

is

near

maxi¬

mum

capacity.

Hov

ever,

even

on

this

band,

the

output

of

the

SG-8

is

in

excess

of

100,000

mi¬

crovolts

which

is

mare

than

sufficient

for

the

average

application

in

which

this

generator,

will

be

used.

IN

CASE

OF

DIFFICULTY

1.

Recheck

the

en

ire

wiring.

Follow

each

lead

and

color

it

on

the

pictorial

with

a

colored

pencil.

If

possible,

have

a

friend

recheck

the

wiring

for

you.

Most

cases

of

difficulty

re¬

sult

from

wrong

or

reversed

connections.

In

this

unit,

there

is

also

the

possibility

of

shorts

to

the

chassis

o

xurringon

some

of

the

bare

wire

connections

from

the

coils.

These

wires

should

be

carefi

lly

spaced

away

from

the

chassis

when

the

instrument

is

assembled.

2.

Check

the

test

load

with

an

ohmmeter

to

be

sure

there

are

no

shorts

between

the

inner

and

outer

conductor

caused

by

overheating

during

the

soldering

process.

3.

If

the

wiring

is

found

to

be

correct

and

the

signal

generator

still

refuses

to

work,

try

chang¬

ing

tubes.

It

is

possible

that

one

of

the

tubes

is

defective.

4.

Check

the

voltages.

A

voltage

chart

is

included

showing

the

normal

voltage

to

be

expected

at

the

pins

of

the

tube

sockets.

These

voltages;

were

measured

with

an

11

megohm

input

vacuum

tube

voltmeter.

A

normal

variation

of

±15%

is

to

be

expected.

With

regular

volt¬

meters,

readings

may

be

very

much

lower.

All

voltages

are

DC

unless

otherwise

indicated

.

5.

If

only

one

band

on

the

signal

generator

is

inoperative,

it

is

very

likely

that

the

coil

associ¬

ated

with

that

band

has

become

damaged.

An

ohrr

meter

connected

between

the

terminals

of

the

coil

should

show

continuity.

If

it

does

not,

one

section

of

the

winding

is

open.

VOLTAGE

CHART

TUBE

Pin

1

Pin

2

Pin

3

Pin

4

Pin

5

Pin

6

Pin

7

Pin

8

Pin

9

6C4

65

NC

6.3

AC

0

65

-0.5

1

12AU7

78

*-

2

to

-15

3.5

6.3

AC

6

3

AC

*75-85

o

CO

1

o

CO

*

■

0

0

♦

Dependent

upon

frequency.

NC

-

no

connection.

BIBLIOGRAPHY

Marcus

and

Levy;

E

lements

of

Radio

Servicing

Kiver,

Milton

S.;

How

to

Understand

and

Use

TV

Test

Instruments

Johnson,

J.

Richard;

How

to

Use

Signal

and

Sweep

Generators

Page

16

USE

OF

THE

I

F

SIGNAL

GENERATOR

This

signal

generator

can

be

used

to

align

radio

receivers.

It

furnishes

a

source

of

radio

fre¬

quency

or

modulated

radio

frequency

by

means

of

signal

generator

fundamental

frequencies

be¬

tween

160

kc

and

100

megacycles

(1

megac?

cle

equals

1000

kilocycles)

e

nd

useful

harmonics

of

the

signal

generator

may

be

used

to

over

200

megacycles.

The

RF

Signal

Generator

will

be

found

a

most

valuable

aid

to

the

radio

service

man

as

well

as

the

hobbyist.

The

day-to-day

"bread

and

b

itter"

job

of

the

signal

generator

is

receiver

align¬

ment.

To

save

time

and

money,

the

servic

e

man

or

hobbyist

should

us<

a

technique

which

can

be

applied

to

the

majority

of

sets

encountered

in

normal

work.

After

us

ing

the

technique

a

few

times,

it

becomes

virtually

a

matter

of

"second

nature"

and

so

easily

used

that

the

average

set

may

be

completely

aligned

in

a

matter

of

minutes.

The

majority

of

single

band

radio

receivers

have

nowadays

become

quite

standardized

and

there¬

fore

it

is

seldom

necessary

in

alignment

o

receivers

to

refer

to

the

specific

manufacturer's

alignment

instruction.

In

the

average

rec<

iver,

it

is

generally

only

necessary

to

take

note

of

the

IF

frequency

(most

home

radios

and

aul

Dmobile

radios

employ

a

455

KC

IF

frequency).

Figure

13

is

a

schematic

diagram

of

a

small,

single-band

superheterodyne

radio

receiver.

The

majority

of

single-band

sets

use

a

circuit

similar

to

this

one.

Variations

likely

to

be

found

are

as

follows:

(1)

Use

of

an

antenna

coil

rather

than

a

rod-type

or

loop

antenna.

(2)

Use

of

a

separate

oscillator

rather

than

a

pentagrid

converter.

(3)

Trimmer

tuning

of

IF

and

RF

stages

in

place

of

iron

core

slugs.

(4)

Use

of

an

RF

stage

ahead

of

the

mixer.

(5)

More

than

one

IF

stage.

These

variations

do

not

appreciably

affect

the

alignment

technique

and

the

following

step-by-

step

procedure

may

be

used

directly

in

most

cases:

(1)

Turn

both

the

signal

generator

and

the

receiver

on

and

allow

severa

minutes

for

both

units

to

reach

normal

operating

temperature.

(It

is

a

good

idea

to

leave

the

signal

generator

on

during

all

working

hours.)

»4

P0<NT

*C*

«00

ANTENNA

Figure

13

i

2

a€©

1ST

DETECTOR

&

OSCILLATOR

OUTPUT

TRANSFORMER

HO

-

125V

AC

-D

POWER

TRANSFORMER

SWITCH

BLACK

_I_

.05

MfO

—WvVv-

4700A.

-2W

»

5

k-

2

W

I

20

MfO

~

~20

MFO

I

.OS

*ro

MIEN

TUNER

WIRING

0

0"

•

?|E$

W

I2IAC

I2AV6

Y*2AS

1-

SPUR.

B*

POINT

V

Page

17

(£)

.

Connect

an

output

indicator

to

the

receiver.

This

may

be

an

AC

voltmeter

connected

di¬

rectly

across

the

loudspeaker

voice

coil;

however,

a

VTVM

connected

to

measure

AVCvol-

tage

is

by

far

the

most

desirable

method.

(3)

Short

ou

the

local

oscillator

tuning

circuit

temporarily.

The

simplest

way

to

accomplish

this

is

merely

by

clipping

a

short

piece

of

wire

across

the

rotor

and

stator

plates

of

the

oscillator

section

of

the

tuning

condenser.

Set

the

receiver

dial

to

the

low

frequency

end,

somewhere

near

550

KC.

(4)

Connect

the

signal

generator

to

the

antenna

terminals

of

the

receiver

or

if

the

receiver

employs

a

loop

antenna

or

rod

antenna,

couple

the

output

of

the

generator

to

the

antenna

sys¬

tem

through

a

one

or

two

turn

loop

of

wire

around

the

antenna.

In

cases

where

an

RF

stage

is

used

ahead

of

the

mixer,

connect

the

signal

generator

to

the

injection

grid

of

the

mixer

stage.

Set

the

signal

generator

to

the

IFvalue

o!

thi

set.

(455

KC

is

generallythe

accepted

standard.)

Use

a

modulated

signal

if

an

AC

voltmeter

is

employed

as

an

output

indicator.

An

unmodulated

signal

is

used

provided

the

AVC

voltage

is

used

as

an

output

indication.

(5)

Using

the

lowest

range

of

the

output

indicator,

increase

the

output

of

the

signal

generator

until

a

reading

can

just

be

obtained.

(.6)

Adjust

the

IF

transformers

for

maximum

reading

on

the

output

indicator.

Reduce

the

sig¬

nal

generator

output

as

necessary

to

keep

a

low

reading

on

the

output

indicator.

Repeat

the

adjustments

at

le

ast

once

to

correct

for

any

interaction

between

primary

and

secondary

windings

on

the

individual

transformers.

Interaction

is

most

likely

to

occur

in

sets

where

adjustment

is

by

means

of

iron-core

slugs

rather

than

trimmer

condensers.

(7)

Next,

remove

the

short

across

the

local

oscillator

and

tune

the

receiver

to

its

-highest

fre-

quenc/

setting

(somewhere

around

1600

KC).

Set

the

signal

generator

to

the

same

frequency

^

and

adjust

the-

os<

illator

trimmer

for

maximum

out

out.

(8)

Now

tune

the

rec<

iver

and

signal

generator

to

1400

KCand

adjust

the

RFtrimmer

formax-

imum

output.

(0)

Turn

.he

signal

generator

to

600

KC

and

tune

the

receiver

to

the

low

frequency

end

of

the

dial.

Now

"rock"

the

receiver

tuning

condenser

while

at

the

same

time

adjusting

the

trim-

mer

c

mdenser

for

maximum

output.

In

sets

using

especially

shaped

plates

in

the

oscillator

^section

of

the

tuning

condenser,

generally

no

trimmer

condenser

will

be

found.

Also,

in

some

jets,

the

lew

frequency

oscillator

adjustment

will

be

through

means

of

an

iron-core

slug

in

the

oscillator

coil

rather

than

a

trimmer

condenser.

(10)

Steps

7

,

8

and

9

t

hould

be

repeated

if

it

was

found

necessary

to

readjust

the

trimmer

con¬

dense!'

(or

iron-c

>re

slug)

as

directed

in

Step

9.

The

alignment

procedi

re

for

multi-band

AM

superheterodyne

receivers

is

essentially

the

same

as

outlined

above

fora

single-band

set.

First

the

IF

stages

are

aligned

using

the

same

technique

as

given

in

Steps

1

through

6.

Next,

each

RF

band

is

aligned

separately,

starting

with

the

high¬

est

frequet

cy

band

an

l

working

towards

the

lowest.

The

technique

given

may

be

used

but

with

corresponding

frequercy

settings

for

each

band.

&

If

the

oscillator

and

I

F

trimmer

condensers

for

the

different

bands

are

not

well

identified,

a

simple

technique

may

be

employed

to

locate

the

proper

adjustment

screws.

Turn

the

receiver

band

switch

to

the

highest

frequency

band

and

tune

in

a

signal,

using

a

short-.wave

station

or

a

signal

from

the

RF

generator.

Using

an

insulated

alignment

tool,

try

compressing

the

different

oscillator

trimmers

until

one

is

found

that

changes

the

tuning

of

the

signal.

Do

not

compress

the

oscillator

trimmer

condensers

by

turning

the

adjustment

screws,

just

press

the

leaves

of

the

condenser

togethei

temporarily.

This

method

will

identify

the

trimmers

for

each

band

with¬

out

drastically

changii

g

their

original

setting.

After

identifying

the

oscillator

trimmer

for

the

band

in

this

manner,

epeat

the

technique

to

identify

the

RF

trimmer.

Turn

to

the

next

band

and

reoeat

the

method

being

careful

not

to

touch

the

trimmers

already

identified.

Page

13

Should

the

oscillator

trimmer

of

the

short-wave

band

have

a

wide

tuning

range,

it

may

>e

pos¬

sible

to

pick

up

and

"peak"

a

signal

with

two

different

settings

of

the

trimmer.

Should

ihisthe

the

case,

use

the

setting

with

the

least

capacity

to

insure

that

the

oscillator

is

tuned

ai

)ve

the

incoming

signal.

FM

RECEIVER

ALIGNMENT

It

is

the

standard

practice

to

align

the

IF

amplifier

of

an

FM

receiver

(tuner)

before

aligning

the

RF

and

oscillator

sections

just

as

in

AM

receivers.

However,

the

exact

technique

of

alignment

depends

on

whether

a

limiter

discriminator

or

a

ratio

detector

is

used.

Where

a

limiter

and

discriminator

are

used,

usual

practice

is

to

align

the

IF

section

up

to

(he

input

of

the

limiter

first.

Then

align

the

discriminator

as

a

separate

step.

When

aligning

the

IF,

RF

and

oscilla¬

tor

sections,

the

grid

current

of

the

limiter

may

be

used

as

an

output

indicator.

Althougl

the

voltage

across

a

limiter

grid

resistor,

measured

with

a

VTVM,

willser/^e

in

many

cases,

it

is

not

an

ideal

indication.

A

typical

limiter

and

discriminator

stage

is

shovn

in

Figure

4.

>ro-

per

alignment

technique

for

the

complete

FM

receiver

is

as

follows:

LIMITER

Figure

14

(1)

Connect

an

output

indicator

by

(1)

attaching

a

VTVM

across

the

limiter

grid

resistor,

or

(2)

b

reaking

the

circuit

at

the

grid

of

the

limiter

and

inserting

a

microammeter

with

a

max¬

imum

range

of

around

150

microamps.

If

this

method

is

used,

be

sure

and

bypass

the

meter

with

a

.05

pfi

condenser

to

ground.

See

point

X

in

Figure

14.

(2)

Connect

a

signal

generator

to

the

input

of

the

mixer

stage

and

turn

on

both

the

signal

gen¬

erator

and

the

receiver.

A

sufficient

warm-up

time

must

be

allowed

to

permit

both

t

ie

re¬

ceiver

and

the

generator

to

reach

their

normal

operating

temperature.

In

the

case

of

FM

receivers

this

is

usually

15

to

20

minutes

before

complete

stabilization

can

be

ob

ained.

Adjust

the

signal

generator

to

the

IF

value

of

the

set.

This

is

usually

10.7

me.

1

he

un¬

modulated

RF

output

of

the

signal

generator

is

used.

(3)

P

eak

all

IF

trimmers

for

maximum

meter

readings.

If

the

IF

is

considerably

out

c

align¬

ment

so

that

very

little

meter

reading

is

obtained,

it

may

be

necessary

to

connect

t

ae

sig¬

nal

generator

to

t

ie

last

IF

stage

and

align

this

portion

of

the

circuit

first.

Then

wo-kback

toward

the

mixer

stage,

rechecking

previous

IF

adjustments

at

each

point;

Connect

a

VTVM

.etween

point

1

and

ground

as

shown

in

Figure

14.

Adjust

the

trim

neror

slug

"J"

for

max

aum

reading

using

a

low

VTVM

range.

(5)

Transfer

the

VT

VI

connection

to

point

2

and

adjust

trimmer

"H"for

a

minimumvol

meter

reading.

Page

19

(6)

Transfer

the

signal

generator

lead

to

the

antenna

terminals

and

align

the

RFand

oscillator

trimmers,

using

essentially

the

same

technique

as

is

outlined

for

AM

receiver

adjustment,

except

the

frequency

settings

will

fall

between

88

me

and

108

me.

The

output

indicator

for

this

adjustment

is

the

same

as

discussed

in

Step

1.

Lastly,

adjust

the

antenna

trimmer

for

maximum

indication

or

volume

using

the

receiver's

own

antenna

and

at

its

permanent

loca¬

tion.

'

RATIO

DETECTORS

The

following

technique

may

be

used

for

alignment

of

ratio

detector

FM

receiver

circuits.

Re¬

fer

to

Figi

re

15.

last

if

Figure

15

(1)

Connect

a

VTVM

or

high

resistance

DC

voltmeter

across

RC.

(2)

As

before,

both

receiver

and

signal

generator

should

be

allowed

to

warm

up.

The

receiver

-dial

should

be

set

to

the

low

frequency

end

(88

me)

and

the

signal

generator

adjusted

to

give

an

unmodulated

signal

at

the

receiver

IF.

Connect

the

signal

generator

to

the

input

of

the

mixer

stage

as

before.

(3)

Adjust

all

IF

trimmers

(or

slugs)

for

a

maximum

reading

on

the

meter,

using

a

low

range

and

the

least

signal

generator

output

possible.

Repeat

the

adjustments

at

least

twice

to

cor¬

rect

for

any

interaction.

Be

sure

slug

N

is

accurately

adjusted.

(4)

Connect

two

100,000

S2

1/2

watt

resistors

across

RC

(RA

and

RB)

and

connect

the

voltmeter

as

shown

in

Point

V

in

Figure

15.

(5)

Adjust

the

trimmer

(or

slug)

M

for

a

zero

output

indication

on

the

meter.

(6)

Align

the

RF

and

oscillator

stages

using

the

techniques

previously

described,

measuring

the

voltage

across

RC

as

an

output

indication.

SERVICING

BY

SIGNAL

INJECTION

THE

AUDIO

AMPLIFIER

-The

block

diagram

for

a

typical

audio

amplifier

is

shown

in

Figure

16.

Let

us

assume,

for

the

moment,

that

the

amplifier

is

"dead"

due

to

a

defective

second

audio

stage.

o

z

o

z

<L

SPEAKER

Figure

16

Page

20