McMartin TR-66A Manual

www.SteamPoweredRadio.Com

1-fCMartin

industries.

inc.

• I

I

i

INSTALLATlCN

AND

SERVICE

MANUAL

TR-66A

SCA

TRANSISTORIZED

MULTIPLEX

RECEIVER

www.SteamPoweredRadio.Com

TABLE

OF

CONTENTS

UNPACK

ING

. . . . . • . . . . . . • . . . . . • 1

WARRA.NT'l

.••

SPECIFICATIONS

•

SPECIAL

FEATURES

.

. . .

..

1

• • • 2

• • 4

GENERAL

DESCRIPTION

...•.........•

S

INSTALLATION

PROCEDURE

.......•..•.•

6

FIELD

ADJUSTMENTS

TROUBLESHOOTING

..

• • • 7

TRANSISTOR

AND

DIODE

COMPLEMENT.

SCHEMATICS

• 11

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www.SteamPoweredRadio.Com

UNPACKING

Remove

the

receiver

from

the

carton

and

examine

it

for

signs

of

external

physical

damage.

Remove

the

top

cover

by

loosening

the

four

screws

at

the

sides.

Examine

transistors,

crystal

and

etc.,

to

see

that

they

are

properly

seated

in

their

sockets.

If

any damage

is

noticed,

ilIDllediately

notify

the

shipping

agency

and

advise

McMartin

Industries,

Inc.

of

such

action.

Contents

of

Carton:

l McMartin

Multiplex

Receiver

l

Instruction

Manual

l Cover Nut

(for

MN-MX

Switch)

WARRANTY'

McMARTIN

Broadcast

and Audio

Products

are

warranted

to

be

free

from

defects

in

workmanship

FOREVER.

At

our

discretion,

we

will

exchange

or

repair

any

defective

unit

or

components,

at

any

time,

without

charge.

Material

and components

are

guaranteed

for

a

period

of

ninety

days

from

the

date

of

original

purchase

.

Return

authorization

should

be

obtained

and

transportation

char~es

must

be

prepaid

on

equipment

returned

for

warranty

service.

This

warranty

does

not

extend

to

any•of

our

products

which

have

been

subjected

to

misuse,

neglect,

accidents,

incorrect

wiring

not

our

own,

improper

installation,

or

to

uni

ts

that

have

been

used

in

violation

of

the

instructions

furnished

by

us;

nor

to

units

that

have

been

altered

outside

our

factory.

- 1 -

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'

i ..

Main

Channel

Range

Sensitivity

Selectivity

Capture

Ratio

RF

Input

Antenna

Distortion

Subchannel

Range

Sensitivity

Selectivity

De-emphasis

Cross

Talk

Frequency

response

Distortion

Hum

and

noise

General

Outputs

SPEC;[FICATIONS

88-108

mHz,

crystal

controlled

·

1

microvolt

for

30

db

of

quieting,

complete

limiting

at

3

microvolts

Fixed

250

kHz

at

3

db

points,

553

kHz

at

50

db

points

Better

than

1.25

db

50-72

ohms

(solderless

coax

connector)

Less

than

0.5%

at

1007.

modulation

(400

Hz)

41, 42,

65

or

67

kHz

at+

6

kHz

deviation

-

other

frequencies

special

order.

(Must

specify

frequency

when

ordering.)

(20%

Inj.)

(10'1..

Inj

.)

5

microvolt/45

db

quieting

5

microvolt/30

db

quieting

~

7.5

kHz

at

3

db

points

150

microsecond

standard,

75

microsecond

on

special

request

Main

to

SCA

to

SCA

Stereo

to

SCA

-55

db

-55

db

-55

db

30-8,000

Hz~

2

db

at

150

microsecond

de-emphasis

Less

than

1.07. + 6

kHz

Dev.,

400 Hz.

G~•ater

.

than

60

db

below

full

output

Main

and

sub-channel

switched

l.OV

at

600

ohms

unbalanced

(phone

jack).

Optional:

Balanced

25

and

70.7

volt

(terminal

board)

with

LT-lOA

or

LT-20

plug-in

amp.

- 2-

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Front

Panel

Controls

Rear

Chassis

Under

Chassis

Power

Supply

Dimensions

and

finish

Shipping

weight

Pilot

Light

Lamp

SPECIFICATIONS

(continued)

Main/sub-selector

switch,

volume

control,

power

ON-OFF

AC

convenience

outlet

(unswitched)

Antenna

connector

Antenna

B+

switch

Fuse

holder

Mike preamp

input

(4

Jones

plug)

Adjustable

automatic

main

channel

muting

105-120V

AC

50/60

Hz

fused

at

0.5

amp;

normally

5

watts,

with

LT-lOA -

15

watts,

with

LT-20 -

22

watts.

11"

wide

x 4

1/2"

high

x 8

3/4"

overall

depth,

gray

cover

and

brushed

chassis

7

lbs.

Neon

assembly

-3-

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SPECIAL

FEATURES

*

The

elimination

of

tunable

IF

transformers.

The

IF

transformers

have

been

replac~

by a

single

10.7

mHz

solid

state

filter.

The

bandwidth

remains

constant

at

all

signal

levels

and

is

phase

linear

over

220 kHz.

*

All

transistors

operate

at

less

than

501.

of

their

rated

dissipation

for

increased

long

life

through

cool

operation.

* The

sub-carrier

uses

a

phase

linear

bandpass

filter

with

steep

sided

skirts

for

rejection

of

stereo

and

second

sub-carrier.

*

Noise

rejection

is

excellent

due

to

the

elimination

of

time

constants

in

the

limiters.

*

A

pulse

counting

detector

is

used

eliminating

drift

and

the

necessity

for

tuning.

Near

perfect

linearity

is

also

obtained.

*

Convenient

test

points

for

easy

aligmnent

of

the

RF

section.

*

Integrated

circuitry

is

used

in

both

the

main

channel

and

sub-channel

limiter

amplifiers.

*

RF

shielding

meets

FCC

requirements.

*

Unit

is

supplied

with

an

RF

solderless

connector,

both

male

and

female

for

72

ohm

coax.

*

There

is

a

front

panel

switch

for

MN

(main)

and

MX

(sub-channel).

This

switch

simplifies

servicing

and

enables

a

customer

to

switch

to

the

main

channel

for

special

announcements,

such

as

historical

events

or

local

distress

notices.

A

cover

nut

is

supplied

with

all

units

and

can

replace

the

knob

if

it

is

desired

that

the

customer

be

prevented

from

using

the

switch.

*

1"'10

plug-in

amplifiers

are

available:

LT-lOA,

5-watt

amplifier;

LT-20,

12-watt

amplifier.

A

socket

is

provided

for

these

plug-in

amplifiers

and

all

wiring

is

·

rincorporated

1n

the

receiver.

The

25

and

70.7

volt

outputs

are

available

on a

terminal

strip

on

the

rear

of

the

chassis.

* A

plug-in

mike preamp

is

also

available

for

connecting

a mike

to

either

the

tuner

or

tuner-amplifier

combination.

This

preamp

employs

solid

state

switching

to

mute

music

when a

push-to-talk

mike

is

used.

- 4 -

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GENERAL

DESCRIPTION

The TR-66A

multiplex

receiver

is

desi

g

ned

for

continuous

duty

r_

eception

of

commercial

FM/SCA

multiplex

programming.

The

TR-ooA

is

built

on a

modular

construction

basis

utilizing

five

glass

epoxy

printed

circuit

boards

..

These

consist

of

an

RF

amplifier,

IF

amplifier

and

demodulator,

subchannel

demodulator,

dual

gate

squelch

and

audio

amplifier,

and

power su

pply.

The

RF

amplifier

board

uses

two

silicon

field

effect

transistors

(FET's)

in

a

cascade

configuration

for

excellent

AGC

with

minimum

cross-modulation

The

local

oscillator

is

crystal

controlled

.•

k~silicon

bipolar

transistor

is

used

for

a

mixer

which

is

suitable

for

driving

the

low impedance

solid

state

10.7

mHz

filter.

A

10.7

mHz

IF

trap

is

used

in

the

mixer

input

to

improve

the

conversion

gain.

The main

channel

IF

board

consists

of

two

high

gain,

wide band

integrated

circuits

(IC's),

an

AGC

and

squelch

circuit,

pulse

counting

demodulator

and

an

audio

amplifier.

The

subchannel

demodulator

uses

1

integrated

circuit

(IC)

for

an

amplifier

and

limiter,

a

pulse

counting

detector,

a

squelch

voltage

amplifier

and

a

one

stage

audio

amplifier.

·

The

dual

gate

squelch

board

and

audio

amplifier

consists

of

a main and

subchannel

gate

which

requires

both

main and

subchannel

squelch

voltage

for

operation.

Positive

squelch

will

occur

in

case

of

main

channel

failure.

The

audio

amplifier

has

an

unbalanced

low impedance

output.

Two

plug-in

audio

modules

are

available

to

transform

the

TR-66A

into

a

tuner-amplifier

combination.

A mike preamp

is

also

available

for

the

TR-66A.

The power

supply

board

has

a

regulated

13V

output

for

operating

the

receiver

and

the

optional

plug-in

mike

preamp,

and

an

unregulated

36V

output

to

operate

either

of

the

two

optional

plug-in

power

amplifiers.

Straight

line

design

with

test

points

make

the

TR-66A

a

very

easy

unit

to

-

align.

There

are

no

tuned

circuits

past

the

RF

section.

With no

LC

tuned

circuits

in

the

IF,

the

problem

ot

drift

need

not

be

considered.

The main

channel

is

crystal

controlled

to

receive

an

FM

frequency

between

88 and 108

rnHz.

An

extremely

well

regulated

power

supply,

utilizing

electronic

control,

assures

circuit

stability.

The

subcarrier

is

fixed

at+

6

kHz

deviation

and

may

be

ordered

on

41,

42,

65

or

67 kHz.

Other

subcarrier

frequencies

are

available

upon

special

request.

The

frequency

must

be

specified

when

ordering.

-5-

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INSTALLATION

PROCEDURE

Inspection

Upon

receipt

of

your

TR-66A remove

it

from

the

packing

material

and

inspect

carefully

for

any

damage

caused

in

transit

due

to

rough

handling

or

vibration.

If

damage

is

found,

notify

the

shipping

agency

and

advise

McMartin

Industries,

Inc.

of

such

action.

Receiver

Location

Sufficient

space

should

be

allowed

for

proper

circulation

of

air

to

aid

in

the

cooling

of

the

unit.

Keyhole

slots

are

provided

in

all

bottom

plates

to

facilitate

mounting

the

receiver

on

a

wall.

This

is

important

in

order

to

increase

air

circulation

and

also

to

prevent

use

of

the

recaiver

as

a

"shelf"

for

paper,

books,

etc.

It

will

also

eliminate

the

possibility

of

your

customer

moving

the

receiver

and

shorting

or

breaking

connecting

wires.

The

receiver

should

be

located

as

near

to

the

entrance

of

the

antenna

coaxial

cable

as

possible.

Antenna

A

properly

selected

and

installed

antenna

is

one

of

the

most

important

factors

for

satisfactory

multiplex

reception.

Good

directional

char-

ac

.

teristics

are

very

important

in

the

reduction

of

"multipath"

(cross

talk)

reception

and

only

proper

antenna

installation

can

eliminate

this.

This

condition

is

most

c011111on

in

large

metropolitan

areas

and

mountainous

country.

High

gain

antennas

normally

have

the

best

directional

pattern

and

although

signal

strengcb

may

be

high

at

a

given

location,

it

may

still

be

necessary

to

use

this

type

to

eliminate

multipath.

The

antenna

should

be

o~iented

for

a

combination

of

best

signal

and

lowest

multipath.

For

all

installations

we

recormnend

the

use

of

either

a McMartin

outside

(A-·72-SF) 3

or

S

element,

72

ohm,

cut-to-frequency

directional

antenna

or

indoor

(A-72PA)

transistor,

fixed-frequency

antenna.

For

proper

location

and

orientation

of

the

antenna

.,

we

recommend

using

the

McMartin TX-200

Field

Strength

Meter.

Antenna

Connection

An

RF

coaxial

receptacle

is

provided

on

the

rear

of

the

chassis

for

the

re.commended

outside

antenna.

A

solderless

connector

plug

is

furnished

with

the

receiver

for

connection

to

the

cable.

The

coaxial

lead-in

eliminates

receiving

ignition

and

other

man-made

noises

by

the

antenna

line.

The reconwne~ded

input

impedance

is

72

ohms,

however,

a 50

ohm

impedance

may

be

used

with

little

mismatch.

Additional

antenna

connector

plugs

may

be

obtained

from McMartin

Industries

by

ordering

part

#173009.

- 6 -

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FIELD

ADJUSTMENTS

A

considerable

aroount

of

time

has

been

spent

aligning

your

receiver

to

your

exact

center

frequency.

Normally,

the

only

field

alignment

that

should

be

necessary

is

to

peak

the

antenna

coil

to

match

the

receiver

to

your

antenna.

The

following

procedure

can

be

used

if

a

frequency

change

is

required

or

for

touch

up

alignment

under

field

conditions.

It

should

be

noted

that

it

is

very

easy

to

peak

the

RF

section

to

an

adjacent

station

so

extreme

care

should

be

taken

in

the

RF

alignment.

Local

Oscillator

and

RF

Alignment.

1.

Reroove

only

the

receiver

top

co

v

er.

CAUTION:

Do

not

remove

the

bottom

plate

in

high

RF

signal

areas.

2.

Connect

a

volt

ohmmeter

(20k

ohm/volt

VOM)

,

or

preferably

a

VTVM

to

test

point

11

AH

(TP-A)

and

ground.

(-3.0

VDC

scale).

3.

Turn

the

oscillator

sl

ug

counterclockwise

(out)

as

far

as

it

will

go.

4.

Insert

the

proper

crystal

into

the

crystal

socket.

Crystal

frequency=

Operate

Freque

ncy

-10o7

mHz

2

S.

Slowly

turn

the

oscillator

slug

clockwise

(in)

until

the

ne~ative

voltage

rises

abr~pt

ly

,

in

di

cating

oscillation.

Continue

clockwise

until

the

voltage

drops

1/10

to

2/10

of

a

volt

below

the

peak

to

insure

positive

starting.

T

his

voltage

should

be

at

lea

st

one

volt

de

~ith

a 20 k

chm/volt

VOM.

6.

~E

::

h

the

meter

on

TP-A,,

tun~

the

do

ubler

coil

fo

r a

sharp

d

ip.

Min

imum

meter

reading

with

a

rap

id

voltage

r

i=~

when

the

core

is

turned

right

or

left

indicat

es

proper

tuni~

g.

7.

Connect

an

antenna

to

the

TR-~

6~.

8.

Connect

a

VTVM

to

TP-C

or

TP-

B

1

-3

.,

0

VDC

scale)

(

see

::ote

) .

9.

Tune

the

mixer

coil

for

maximum

negative

voltage

readin

g.

If

two

peaks

are

noted

,

tune

tc

the

peak

producing

the

highest

voltage.

10.

With

a

VTVM

connected

to

TP-C

or

TP-B,

tune

the

RF

coi_

for

maximum

negative

voltage.

'

-7

-

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FIELD

ADJUS'IMENTS

(Continued)

11.

With

a

VTVM

connected

to

TP-C

or

TP-B,

tune

the

doubler

coil

for

maximum

negative

voltage.

12.

With

the

VTVM

connected

to

TP-C

or

TP-B,

tune

the

antenna

coil

for

maximum

negative

voltage.

13.

Repeat

steps

8,

9,

10,

11,

and

12,

until

no

further

improvement

can

be

made.

NOTE:

Since

there

are

no

tuned

circuits

in

the

rest

of

the

'ra-66A

you

may

listen

for

quality

on

both

the

main

channel

and

the

SCA

multiplex

channel.

Test

point

"C"

should

be

used

in

areas

where

there

is

more

than

SO

microvolts

of

signal

available.

In

strong

signal

areas

the

signal

must

be

attenuated

during

alignment

to

minimize

the

AGC

action

of

the

front

end,

especially

in

a

metropolitan

area

with

a

strong

adjacent

or

alternate

channel.

If

the

TR-66A

is

installed

in

a

fringe

area,

and

no

voltage

is

present

at

test

point

"C",

test

point

"B"

should

be

used

for

alignment.

(In

very

weak

signal

areas

the

voltage

may

be

positive

and

the

receiver

should

be

tuned

for

minimum

positive

or

a

negative

going

voltage)

.

For

steps

5,

6,

8,

9,

10,

11,

and

12,

it

is

PREFERABLE

to

USE

a

VTVM.

This

completes

the

oscillator

and

RF

align~ent.

*

On

units

with

screw

driver

adjusted

oscillator

slug

-

steps

3

and

5

should

be

as

follows:

3.

Turn

the

oscillator

slug

clockwise

(in)

as

far

as

it

will

go

.

5.

Slowly

turn

the

oscillator

slug

counterclockwise

(out)

until

the

negative

voltage

rises

abruptly,

indicating

oscillation.

Continue

counterclockwise

until

the

voltage

drops

l/10

to

2/10

of

a

volt

below

the

·

p,eak.

~

This

voltage

should

be

at

least

-1.5

volts

DC

with

a

20

K

VO~.

De-Emphasis

The

TR-66A

subchannel

has

a

standard

de-emphasis

of

150

microseconds.

To

change

this

de-emphasis

to

75

microseconds,

change

capacitor

C-12 on

the

subchannel

demodulator

board

from

.001

mfd

to

.00075 mfd.

-8-

McMartin TR-66A Manual

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