Harris MW-5 Reference manual

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HARRIS

COMMUN

CATIONS

AND

FORMAT

HANDLING

Equipment:

MW-5

A.M

Transmitter

MAINTENANCE AND MODIFICATION DATA

Broadcast Products Division

A."1-109-KDL

Bulletin

No.

Date

October

197

Subject:

Additional

Maintenance

and

Troubleshooting

Information

Neutralization:

The

MW-5

should

not

require

frequent

neutralization,

but

the

event

any

component

failure

the

grid

plate

circuits,

the

neutralization

should

checked

follows:

Measure

the

resistance

the

resistors

used

grid

(1A3Zl)

and

plate

(lZl)

parasitic

suppressors.

open

parasitic

suppression

resistor

can

upset

circuit

stability

and

make

neutralization

difficult.

These

failures

are

often

not

detectable

visually.

Disconnect

the

center

lead

the

coaxial

cable

attached

the

grid

transformer

input

tuning

capacitor

(1A3Cl2),

located

the

center

side

wall

the

grid/cathode

cavity.

Connect

signal

generator

(previously

zero-

beated

with

the

transmitter

oscillator

adjusted

assigned

carrier

frequency

using

counter)

between

capacitor

input

lug

and

ground.

Connect

oscilloscope

having

least

a 5MHz.

vertical

bandwidth

between

tube

plate

and

ground.

WITH

POWER

APPLIED

THE

TRANSMITTER,

adjust

the

generator

output

level

and

'scope

vertical

gain

for

convenient

display.

Adjust

neutralization

padder

capacitor

1A3C3

for

minimum

signal

amplitude.

Check

the

degree

mesh

the

plate

1A3C3.

1A3C3

fully

open

fully

meshed,

the

neutralization

procedure

not

yet

finished.

Should

reasonable

amount

mesh

exist,

neutralization

complete.

original

MW-Ss

(shipped

prior

October,

1976),

the

center

tap

grid

transformer

1A3Tl

moved

one

turn

time

until

minimum

signal

amplitude

and

within-range

mesh

the

plates

1A3C3

obtained.

later

MW-Ss

(identified

the

presence

grid

bias

choke

1A3L2),

the

value

1A3Cll

1A3C10

may

have

changed

achieve

within-range

mesh

1A3C3.

HARRIS

CORPORATION

ampsh

eet

Quincy

Illin

ois

62301

7 /

222-8200

www.SteamPoweredRadio.Com

-2-

proper

neutralization

cannot

achieved,

failure

neutralization

blocker

capacitors

1A3C9

and/or

Cl0

grid

transformer

secondary

tuning

capacitors

lA3ClA,B,

etc.

should

investigated.

When

adjustments

are

completed,

sure

remove

all

test

equipment

from

the

transmitter

and

restore

connection

the

driver

output

cable

center

conductor

1A3Cl2.

Restore

transmitter

operation

full

carrier

power

and

perform

normal

tuning

procedures

necessary.

Checking

Grid

and

Plate

Efficiency

Resonators:

Poor

efficiency,

wierd

tuning,

excessive

audio

distortion,

excessive

harmonic

output,

and

other

operational

instabil-

ities

may

caused

mis-adjusted

faulty

efficiency

reson-

ators.

When

these

symptoms

are

present,

the

resonators

must

thoroughly

examined

and

carefully

adjusted.

Perform

the

adjustment

procedure

outlined

sections

4.3(17)

through

(19)

page

4-6

the

MW-5

Instruction

Book.

tuning

and

operation

still

does

not

seem

normal

obvious

component

failure

has

occurred,

further

effort

required.

Drop

small

oscilloscope

probe

(connected

the

'scope

vertical

input)

through

the

grating

above

the

tube

and

connect

the

ground

clip

the

grating.

Observe

the

plate

waveform

sweep

rate.

should

look

something

that

shown

below

operation

normal.

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-3-

Find

the

setting

the

resonators

the

following

method:

Set

generator,

clip

leads,

resistors,

and

the

'scope

shown

the

diagrams

below.

Vary

generator

frequency

until

response

peak

noted;

determine

the

generator

frequency

that

point.

should

within

±200kHz.

the

third

harmonic

the

assigned

carrier

frequency.

not,

adjust

the

generator

the

third

harmonic

and

adjust

the

resonator

for

response

peak.

the

case

the

grid

resonator,

may

necessary

change

the

tap

coil

1A3Ll

one

turn

either

way

place

grid

efficiency

tuning

capacitor

1A3C2

within

range.

General

Test

Circuit:

Generator

ohms

r :

Test

--,

Point

"A"

'Scope

----

----------,--------

Test

Point

"B"

Transmitter

Chassi

Plate

Resonator

Connections:

1Cl2

o,-----;1--

1Cl3

Test

Point

"A"

Grid

Resonator

Connections:

Test

Points

"B"

*all

components

have

1A3

prefix

for

grid

circuit

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-4-

Repeat

the

efficienc

optimization

procedure

sect

ons

4.3(17)

through

(19)

page

4-6

your

Instruction

Book.

waveform

similar

that

(2)

above

ould

now

noted

Optimization

Harmonic

Distortion

sys

ematic

procedure

adjustment

will

lead

reduction

audio

distortion

products

generated

the

transmitter.

Adjust

plate

tuning,

efficiency

resonator,

grid

tuning,

and

grid

efficiency

resonator

with

modulation

accordance

with

the

procedure

outlined

sections

4.3(16)

through

(19)

your

Instruction

Book.

Modulate

the

transmitter

into

the

normal

load

(antenna)

95%

positive

negative

(whichever

mes

first)

400

Hz.

Measure

and

note

harmonic

distortion

(T.H.D.).

Adjust

the

following

controls

for

minimum

T.H.D.:

Modulator

high-power

screen

voltage

1A4Rl0

Auxiliary

modulation

1AlR3

Auxiliary

driver

1AlA3R8

Several

repetitions

the

adjustment

cycle

above

may

necessary

assure

distortion

null.

Change

audio

generator

frequency

SkHz

•·

and

modulate

the

transmitter

95%

positive.

Measure

and

note

T.H.D.

and

plate

tuning

control

dial

counter

reading.

Adjust

the

plate

tuning

control

for

minimum

T.H.D.

and

note

both

distortion

and

dial

counter

readings.

Back

off

the

tuning

until

the

halfway

point

between

the

two

distortion

values

dial

counter

readings

reached.

Then

adjus

the

plate

efficiency

resonator

for

minimum

T.H.D.

Return

400Hz.

95%

modulation

and

repeat

step

(2)

above.

Note

distortion

with

modulating

frequencies

400Hz.,

lkHz.,

2.SkHz.,

and

SkHz.

may

possible

further

reduce

T.H.D.

SkHz.

through

adjustment

the

Auxiliary

Modulation

control.

However,

this

control

will

not

show

T.H.D.

null

high

audio

frequencies.

reduces

T.H.D.

minimum

value

and

further

rotation

the

control

will

not

change

T.H.D

The

auxiliary

modulation

control

should

adjusted

t he

poi

where

T.H.D.

just

the

verge

increasing.

Dist

rtion

should

checked

once

again

400Hz.

and

compared

with

results.

some

transmitters,

slight

trade-off

between

mid-band

and

high-frequency

T.H.D

necessary.

This

trade-off

should

not

typically

increa

mid-band

T.H.D.

than

0.2%

order

achieve

in-s

ec.

high

frequency

harmonic

distortion.

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-5-

slight

adjustment

the

grid

efficiency

resonator

may

lower

T.H.D.

slightly

older

MW-Ss.

Should

you

find

this

the

case

your

transmitter,

leave

the

resonator

set

just

the

verge

causing

T.H.D.

increase.

case

should

the

plate

voltage

all0wed

increase

than

volts

(½

division)

above

the

dip

obtained

(1).

Harmonic

distortion

problems

high

audio

frequencies

are

many

times

the

result

asymmetrical

reactive

antenna

sideband

impedances.

Transmitters

are

designed

all

manufacturers

around

industry

standard

for

"normal

load".

This

EIA

specification

calls

for

the

reactive

component

the

load

edance

adjusted

zero

the

transmitter

output

terminals

for

operation

assigned

carrier

frequency.

The

resistive

component

load

impedance

may

not

vary

than

±5%

the

carrier

frequency

resistance

value

sideband

frequencies

through

5kHz.

either

side

carrier.

The

reactive

components

cannot

exceed

±18%

the

carrier

resistive

value

over

the

same

frequency

range.

From

5kHz.,

through

l0kHz.

sidebands,

the

resistive

component

must

within

±10%

carrier

resistive

value

and

the

reactive

component

must

within

±35%

carrier

resistive

value.

Old

modulator

tubes

and

tubes

may

sometimes

affect

distortion

figures.

Also,

open-delta

primary

power

source

will

cause

low-frequency

distortion

problems

.•

T.H.D.

problems

exist

low

frequencies

{less

than

l00Hz.)

only,

keep

mind

that

the

transmitter

was

designed

for

connection

closed-delta

power

source

{as

spelled

out

the

instruction

book).

Take

appropriate

action

assure

closed-delta

primary

power

source.

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