HP 492A, 494A Operating And Service Manual

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HEWLETT-PACKARD

COMPANY

4.2A/4.4A

TRAVELING-VVAVE
AMPLIFIER

)

)

)

00144·2

OPERATING

AND

SERVICE

MANUAL

MODEL

492A

AND

MODEL

494A

SERIALS

PREFIXED:

010-

TRAVELING-WAVE

AMPLIFIERS

Copy,;gh'

HEWLETT.'ACICA.D

COM'

ANY

1962

lS01

'AGE

MILL

ROAD,

'ALO

ALTO,

CALlFO.NIA,

U.S.A.

Printed:

JAN

1962

Model

492Aj494A

Table

of Contents

ListsofIllustrations

and

Tables

TABLE

OF

CONTENTS

Section

Page

Section

Page

I

GENERAL INFORMATION

1-1

IV

PRINCIPLES OF OPERATIO

(cont'd)

1-1.

Description

1-1

4-10.

Traveling

Wave

Tube

4-1

1-6.

Instrument

Identification

1-2

4-15.

Grid

Modulation.

4-4

1-8.

Traveling

Wave

Tube

Warranty

1-2

4-17.

Helix Modulation

·

.

4-4

4-22.

Constant-Amplitude,

Linear

II

INSTALLATION

2-1

Sawtooth

Generator

4-5

2-1.

Mechanical

Inspection

2-1

2-3.

Power

Requirements.

2-1

V

MAINTENANCE.

5-1

2-5.

Power

Cable.

2-1

5-1.

Introduction.

·

5-1

2-8.

Installation

2-1

5-3.

Cleaning

the

Air

Filter·

5-1

2-12.

Repackaging

for

Shipment

2-1

5-5.

Test

Equipment .

5-1

5-7.

Repair.

5-3

III

OPERATING INSTRUCTIONS

3-1

5-8.

Cabinet

Removal

5-3

3-1.

Introduction

.

3-1

5-10.

Tube

Replacement

.

.

5-3

3-3.

Preliminary

Operating

Procedure

3-1

5-12.

Traveling

Wave

Tube

Capsule

3-6.

Helix

Control

3-1

Replacement

5-3

3-8.

Saturation

Power

Output

3-1

5-17.

Changing

the

Frequency

Range

3-12.

Bandwidth

Considerations

.

3-1

of

the

492Aor494A

5-5

3-14.

Constant

GainorConstant

Output

5-21.

Adjustments

5-5

Amplification

3-3

5-22.

Excessive

Helix

Current

5-5

3-18.

Buffer

Amplifications

3-3

5-24.

Chassis

Helix

Control

5-5

3-20.

Amplitude

Modulation

3-3

5-26.

Anode Voltage

Control

.

5-5

3-24.

Pulse

Modulation.

3-6

5-28.

Regulated

Power

Supply

5-5

3-27.

Limited

Phase

Modulation.

3-6

5-30.

Troubleshooting.

·

5-6

3-29.

Unlimited

Phase

Modulation and

5-32.

Performance

Checks

5-7

Frequency

Shifting .

3-6

5-33.

Gain

Check.

5-7

3-34.

Homodyne

Detection

3-7

5-36.

Output

Power

Check

5-7

3-37.

Frequency

Modulation

3-9

5-39.

Noise

Figure

Check

5-7

5-42.

Hum and

Spurious

Modulation Check·

5-8

)

IV

PRINCIPLESOFOPERATION.

4-1

4-1.

Introduction

.

4-1

VI

REPLACEABLE

PARTS

.

6-1

4-3.

Magnet

Power

Supply.

4-1

6-1.

Introduction

6-1

4-5.

Regulated

Power

Supply

4-1

6-4.

Ordering

Information

6-1

LIST

OF

ILLUSTRATIONS

AND

TABLES

Number

Illustration

Title

Page

4-3.

CutawayView

ofaTWT

Capsule

andMagnet

Showing

the

Important

Elements·

. . .

4-3

4-4.

Cutaway View of an

Encapsulated

TWT·

.

4-3

4-5.

Simplified

Circuit

ofa

Constant

Amplitude,

Variable

Slope Sawtooth

Generator··

4-5

5-1.

Top

ViewofModels 492A and 494A

.,

5-2

5-2.

Bottom ViewLooking

Towards

the

Front

PanelofModels

492A and 494A .

..

5-4

5-3.

Rear

View of Models 492A

and

494A"

5-4

5-4.

Test

Setup

for

Gain, Output

Power,

and

Noise

Figure

Performance

Checks

5-7

5-5.

Test

Setup

for

Hum and

Spurious

Modulation

Performance

Check . .

5-8

5-6.

Models 492A and 494A

Schematic

Diagram'

5-9

Number

Illustration

Title

Page

1-1.

Model 492A

Traveling

Wave

Amplifier

1-1

1-2.

Traveling

Wave

Tube

Warranty

1-2

3-1.

Operating

Controls

.

3-0

3-2.

Typical

Gain

and

Power

Output

Characteristics

.

3-2

3-3.

Block

Diagram

of a

Circuit

used

to

Maintain

Constant-Level

Output

Power

fromaTWT

Amplifier

3-3

3-4.

Block

Diagramofan

Automatic

Gain

ControltoMaintain

Constant

Ampli-

fication

from

a TWT

Amplifier

3-3

3-5.

Typical

PlotofOutput VoltagevsGrid

Voltageofa Model 492A

3-4

3-6.

Typical

PlotofOutput VoltagevsGrid

Voltageofa Model 494A.

3-5

3-7.

RF

Phase

Shift

Produced

by Helix Mod

3-7

3-8.

Offset

Frequency

Produced

by Sawtooth

Modulationofthe

Helix .

3-7

3-9.

Block

Diagram

of a

Linear

(Homodyne)

)

Detection

System.

3-8

3-10.

Block

Diagram

of a

CircuittoProduce

an FM Signal with a

TWT

Amplifier

3-8

4-1.

Block

Diagram,

Models 492A and 494A

4-0

4-2.

TWT

and

HowitWorks

.

4-2

00144-2

1-1.
3-1.

5-1.
5-2.

5-3.
6-1.
6-2.

Table

Title

Specifications.

. . . . .

Maximum

Operating

Currents

for

Models

492A and 494A . . .

Recommended

Test

Equipment

Tube

Replacement

List

Troubleshooting

Chart

. . •

Reference

Designation Index

Replaceable

Parts·

. . . .

1-0
3-1

5-1
5-3

5-6
6-2
6-5

iii

Section I
Table

1-1

Model 492A/494A

Table

1-1,

Specifications

~ Model 492A

<Fj!

Model 494A

Frequency

Range:

4

gc

to 8

gc

7gcto

12,4

gc

Maximum

Output

Power:

20 mw

minimum

into

50 ohm

load

20 mw

minimum

into

50 ohm load

Modulated

Pulse

Delay:

Approximately

20 ns

Approximately15ns

Helix Modulating Voltage:

Approximately40volts

peak-to-

peak.

Provides

3600phase

shift.

Input

impedance

lOOK

Approximately50volts

peak-to-

peak.

Provides

3600phase

shift.

Input

impedance

lOOK

Hum and

Spurious

Modulation:

At

least

45 db below

signal

level

At

least

45 db below

signal

level

Weight:

Power

Supply:

66

lb

net,

85 Ib shipping

US

volts

±10%, 50to60

cps,

approximately

200

watts

63 Ib net, 84 Ib

shipping

U5

volts

±10%, 50to60

cps,

approximately

225

watts

Accessories

Furnished:

AC-16Q

cable

assembly

AC-l6Q

cable

assembly

For

Both Models

Small

Signal Gain:

30 db

minimum

Meter

Monitors:

Cathode

current,

anode

current,

helix

current,

collector

current.

Input Impedance: 50

ohms,

swr

less

than 2

Output

Internal

Impedance: 50

ohms,

swr

less

than 3

Dimensions:

Cabinet

Mount:

7-3/8

in.wide,

U-l/2

in.high, 20

in.deep.

TypeN
Less

than 30 db

t

:0:

IU]

REAR

,~,,".

:0:

'.1&

1.----19---.,

492AR/494AR

Rack

Mount:

Noise

Figure:

Connectors,
RF

Input and Output:

Pulse

Rise

and Decay

Time:

Amplitude Modulating Voltage:

Approximately15ns
Approximately50volts

peak

positive

pulse

will

produce

a 40 db

change

inrfpower

output.

Sensitivity

approximately1db/volt

1-0

00144-2

Model 492A/494A

SECTION

I

GENERAL

INFORMATION

Section I

Paragraphs

1-1to1-4

1-1.

DESCRIPTION.

1-2.

Thet$Models 492A and 494A

Traveling

Wave

Amplifiers

are

broadband,

linear

amplifiers

provid-

ing

adjustable

amplification

up toatleast

30 db,

be-

tween 4 and 12.4 gc, and

haveamaximum

power

out-

put ofatleast20milliwattstoan

external

load

of 50

ohms.

The

frequency

rangeofthet$Model 492A

is

4

to

8 gc; the

frequency

rangeofthe

Model 494A

is

7

to

12.4 gc.

These

traveling

wave tube (twt)

ampli-

fiers

are

designed

to be

used

alsoasbuffer

amplifiers

or

modulators

for

any

signal

within

their

frequency

range.

As

buffers,

their

input

impedances

remain

constant

with any

reasonable

load

changeatthe output

terminal;

the

attenuation between input andoutput

sig-

nalsisat

least

60 db,

minus

the

gain of

the

amplifier.

As

modulators,

they

can

be

usedtoamplitude,

fre-

quency,

pulse,

or

phase

modulate

the

signal

being

amplified

with no

interaction

on

the

signal

source.

The

gain and

power

output of

the

amplifiers

are

con-

tinuously

adjustablebythe

front

panelGRID BIAS

con-

trol.

Hum and

spurious

modulation

generated

within

the

amplifiers

areatleast

45 db below

the

output

sig-

nal

level

and

the

noise

figure

is

less

than 30

db.

1-3.

Thet$Models 492A and 494A

Traveling

Wave

Amplifiers,

amplify

any type ofrfsignal:

cw, swept,

sine-modulated,

pulsed,

multiple

signalsondifferent

frequencies,

etc.

A twt

amplifier

usedasa

modulator,

in conjunction with a

signal

generator,

canbeused

to

amplitude

modulate

anrfcarriertoapproximately

30%

with

less

than 2.5%

harmonic

distortion

and upto50%

with

less

than

5%

distortion.

Amplitude modulation

sensitivityisapproximately1db/volt.

Pulse

modula-

tion

is

excellent;

the

rise

timeisless

than15ns.

Phase

modulation up

to

3600with

less

than 1 db

amplitude

modulation

is

also

possible.

Wide-band

frequency

modulationissimulated

by a

step-wise

phase

modulation

describedinsection

Ill.

1-4.

The

front

panel

meterisprovided

for

checking

and

adjusting

electrode

currentsinthe

traveling-wave

tube.

The

meter

helpstoobtain

desired

operating

characteristics

during

normal

operationofthe

ampli-

fier

and

also

assists

with

preventive

maintenance

and

troubleshooting.

An

anode

voltage

adjustment

on the

instrument

chassis

prOVided

to

adjust

the

cathode

current

of the twt backtonormal

duetotube ageing.

)

00144-2

Figure

1-1.

Model 492A

Traveling

Wave

Amplifier

1-1

Section

I

Paragraphs

1-5to1-9

1-5.

The~Model 492A and 494A

are

similarinthat

one

model

maybechangedtothe

other,byreplacing

the

twt,ascoveredinparagraph

5-17.

1-6.

INSTRUMENT

IDENTIFICATION.

1-7.

Hewlett-Packard

usesatwo-section

eight-digit

serial

number

(000-00000).

If

the

first

three

digits

of

the

serial

numberonyour

instrument

do not

agree

WA••ANTY

CLAIM

AND

ADJUITMINT

'IOCIDUU

Model 492A/494A

with

those

on

the

title

pageofthis

manual,

change

sheets

supplied

with

the

manual

will

define

differences

between

your

instrument

and

the

Model 492Aor494A

describedinthis

manual.

1-8.

TRAVELING

WAVE

TUBE

WARRANTY.

1-9.

The

Traveling

Wave

Tube

Warranty

is

illus-

tratedinfigure

1-2.Asheet

for

your

useisincluded

in

the

appendixofthis

manual.

MICROWAVE

TUBE

WARRANTY CLAIM

INFORMATION FORM

IMPORT

ANT:

Please

ans

....erall

questions

fully--InsuHlclent Information may

delay

processing

of

your

claim.

-

for

microwave

tubes suppliedby[he

HEWLETT·

PACKARD

COMPANY

for

use

In*Instruments

Microwave

tubes

suppliedbythe

Hewlett-Packard

Company.

either88originalorreplacement.

for

use

in8instruments

are

actually

warrantedbythe

tube

manufaclUrer

and

not

by

9.

However, S

will

process

warranty

claims

for

you, and will

promptly

passonall

allowances

grantedbythe

tube

manufacturer.

In

the

event

that

your

tube Is (ound

toberepairable,

the tube

manufacturer

reserves

the

right

to

repair

and

return

the tube in lieu of

Issuing

pro--Tata

credil.

For

your

convenience,

warrantyclalms(orall

microwave

tubes

supplied

by the

Hewlett-Packard

Company

maybemade on

this

sIngle

form;

merely

fJII

out the

lnfonnallon

on the

reverse

side

and

rerurn

this

fonn.

along

....

lth

thedefectlve

rube.toyour8engineering

representallve.

or

tO~.

Pleasebesure

each

space

on the formisfilled

In··lackofcomplete

infonnation

may

delay

processingofyourcTiim.
Each

tube

manufacturer

has

his

own

warranty

policy.

Copies

of Individual Conditions of

War-

ranty

are

available

from

your*engineering

representativeorfrom Ihe He

....

len·Packard

Company.

SHIPPING

INSTIUCTIONS

FROM:

(rube

Owner)

Company

Address

Tube

type

Tube

serial

No.

_

Tube

mfr.

Use

in~Model _

Instrument

serial

no. _

Date

FOR FURTHER INFORMATION CONTACT:

Name

_

Title

_

Company _

Address

_

Tube

purchased

from

OnP.O.

number

The

following

instructions

are

includedtoaid youInpreventing

damageintransit.

Package

your

tube

carefully••no

allowance

canbemade on

broken

tubes.

TubeisOriginal ( )orReplacement

(

1.

Carefully

wrap

tube in

1/4

inch thick

"klmpack".

Cotton batting.orother

sofl

padding

material.

2. Wrap the

above

in heavy

kraft

paper.

3.

Pack

in a

rigid

container

....

hlch Isatleast4inches

larger

than the lube In

each

dimension.

4.

Surround

the

tube

withatleast2inches

of shock

absorbing

material.Becenaln

that the

packing Is tight

all

around

the tube.

Date

tube

received

_

Date

first

tested

Date

placedinservice

_

Dateoffailure

_

Hours

use

per

day

(average)

_

NumberofdaysInservice

_

Total

hours

filament

operation

5.

Tubes

returned

from

outside

the continental

UnltedSrates

shouldbepackedIna wooden box.

6.

Mark

container

FRAGILE and

ship

prepaid

via

Air

FreightorRailway

Expreu.Donot

ship

via

Parcel

POStorAJr

Parcel

POSt

since

experience

has

shown that

fragile

Items

are

more

apttobe

damaged

when

shippedbythese

means.

Tubes

returnedtothe

Hewlen·Packard

Company should be

addressed

to:

SYMPTOMS:

(Please

describe

conditions

priortoandattimeoffailure.

along with

description

of

lube's

defect,

If known) _

CUSTOMr.

snvlcr

H.~".,.d.rd

COfftpel'ly

]95

,.~

Mil

R_d

1'.

Alto. C.lifomi.,

U.S.A.

01

II.W....

,..I.r.,.J

H_lett·,.d.,dS.A.
kvedIiVifillli",dNo.l

G.I'l......S

...

itter!Mtd

Were

there

other

circuit

component

failuresattimeoffailure?

Which ones?

Signature

_

Title

9/12/61

1-2

Figure

1-2.

Traveling

Wave

Tube

Warranty

00144-2

)

Model 492A/494A

SECTION

II

INSTALLATION

Section

II

Paragraphs

2-1to2-13

/

2-1.

MECHANICAL

INSPECTION.

2-2.

Unpack

the

instrument

upon

receipt

and

inspect

it

for

signs

of

phy

ical

damage

such

as

scratched

panel

surfaces,

broken

knobs,

etc.

If

thereisany

apparent

damage,

fileaclaim

with

the

carrier

and

refertothe

warranty

pageinthis

manual.

2-3.

POWER

REQUIREMENTS.

2-4.

The

Model 492A and Model 494A

requireapower

source

of

115

volts

± 10%,

single

phase,50to 60

cps,

which

can

deliver

approximately

225

watts.

2-5.

POWER

CABLE.

2-6.

For

the

protection

of

operating

personnel,

the

ational

Electrical

Manufacturers'

Association

(NEMA)

recommends

that

the

instrument

panel

and

cabinet

be

grounded.

This

instrument

is

equipped

with a

three-prong

conductor

power

cable

which, when

plugged

into

an

appropriate

receptacle,

grounds

the

instrument.

The

offset

pin on

the

power

cable

three-

prong

connectoristhe

ground

pin.

2-7.

To

preserve

the

protection

fearure

when

opera-

ting

the

instrument

fromatwo-contact

outlet,

use

a

three-prong

to

two-prong

adapter

and

connect

the

green

pigtailonthe

adaptertoground.

2-8.INST

ALLATION.

2-9.

The

only

special

precaution

necessary

for

in-

stalling

the

twt

amplifiers

is

that

they

should

not be

operated

closetovery

large

magnetic

fields,

such

as

60-cycle

fields,

unless

externally

shielded.

While

the

twt

amplifiers

are

shielded

within

the

cabinet,

complete

protection

against

large

low-frequency

fields

would

require

more

shielding

thanispracticaltoin-

cludeinthe

design.

2-10.

To

operate,

connect

the

instrument

to a

115-

voltacpower

source,

check

and

adjust

rube

operating

00144-2

currents

as

described

in

preliminary

operating

pro-

cedure,

section

1Il, and

connecttothe

external

equip-

ment

with

coaxial

cables

terminatedinstandard

UG-

21D/U,

type

connectors.

2-11.

In

section

V, beginning with

paragraph

5-32,

isalistofperformance

checks

for

this

instrument.

These

procedures

make

a good

testaspartofincom-

ing

quality-control

inspection

following

initial

rurn-on.

2-12.

REPACKAGING

FOR

SHIPMENT.

2-13.

The

following

listisa

general

guide

for

re-

packaging

an

instrument

for

shipment.

If you

have

any

questions,

contact

your

authorized

Hewlett-

Packard

sales

representative.

a.

If

possible,

use

the

original

container

designed

for

the

instrument,

b.

Wrap

the

instrument

in

heavy

paperorplastic

before

placingitin

the

shipping

container.

c.

Use

plentyofpacking

material

around

all

sides

of

the

instrument

and

protect

the

panel

with

card-

board

strips.

d.

Use

heavy

cardboard

carton

or

wooden box to

house

the

instrument

and

use

heavy

tape

or

metal

bandstoseal

the

container.

e.

Mark

the

packing

box with

"Fragile",

"Delicate

Instrument",

etc.

Note

If

the

instrumentistobeshippedtoHewlett-

Packard

Company

for

service

or

repair,

at-

tachtothe

instrumentatag

identifying

the

owner

and

indicating

the

service

or

repair

to

be

accomplished.

In

any

correspondence

be

sure

to

identify

the

instrument

by

model

number,

serial

prefix,

and

serial

number.

2-1

Section

III

Figure

1-3

POWER

1.

Turns

on

all

circuits

of

the

amplifier

(allow

IS

minutes

warmup).

2.

Meter

selector

switchisused

for

selection

of

circuittobe

checkedonthe

front-panel

meter.

3.

Pin

jackisfor

measuring

grid

bias

(measures

E

k

;

grid

grounded).

4. GRID BIAS

controlisusedtoadjust

fordesired

tube

current.

Normal

cathode

currentisindi-

cated

on

the

meter

plate.

Do not

exceed

maxi-

mum

operating

currents,

refer

to

table

3-1.

Model 492A/494A

~-~--;3

MAG

C1RJD

Il100

8

7

L

S. HELIX

controlisusedtoadjust

for

best

broad-

band

response,

position

5,

or

for

maximum

gainatanyone

frequency.

6.

INPUTrfconnectoriswhere

therfsignaltobe

amplifiediscoupled

into

the

instrument.

7.

OUTPUTrfconnectoriswhere

the

amplified

rf

signaliscoupled

from

the

instrument.

8. GRID MOD.

connector

is

the

input

for

ampli-

tude

modulation

signals.

9. HELIX MOD.

connectoristhe

input

for

phase

and

frequency

modulation

signals.

3-0

Figure

3-1.

Operating

Controls

00144-2

)

Model 492A/494A

SECTION

III

OPERATING

INSTRUCTIONS

Section

III

Paragraphs

3-1to3-13

3-1.

INTRODUCTION.

3-2.

This

section

contains

operating

instructions

for

theModels

492A and 494A

Traveling

WaveTube

Ampli-

fiers.

Figure

3-1

gives

basic

operating

instructions.

The

remainder

of

this

section

supplements

these

in-

structions.

3-3.

PRELIMINARY

OPERATING

PROCEDURE.

3-4.

The

front

panel

controls,

indicator,

and

con-

nectors

for

the

492A and 494A

are

showninfigure

3-1.

This

figure

also

shows

the

uses

for

the

controls,

indi-

cator,

and

connectors.

Whenever

the

twtisturned

on,

use

the

front

panel

metertomeasure

the

current

to

each

electrode

in

the

traveling-wave

tube with

the

GRID BIAS

control

set

for

zero

bias.

The

safe

maxi-

mum

current

for

each

electrodeisshown in

table

3-1.

ormal

cathode

current

for

your

instrumentisindi-

cated

on

the

plate

attached

to

the

meter

face.

Cur-

rents

are

usuallyalittle

high when

the

instrument

is

first

turned

on, but

decreasetonormal

during

warm-

up. Allow IS

minutes

warmup

before

making

final

reading.

The

GRID BIAS

control

maybeusedtore-

duce

the

tube

currents

during

warmup.

Table

3-1.

Maximum

Operating

Currents

for

Models

492A and 494A.

Adjusting

the

HELIX

voltage

control

for

maximum

gainatthe

upper

frequency

limit

usually

produces

the

flattest

frequency

response

over

the

band.

Maximiz-

ing

the

gainatfrequencies

below

the

upper

frequency

limit

usually

resultsinadditional

gain

and

power

out-

put

over

that

obtained

when

adjusted

for

flattest

broad-

band

operation.

The

final

settingofthe

HELIX

con-

trol

is

independentofthe

typeofsignal

amplified.

3-8.

SATURATION

POWER

OUTPUT.

3-9.

Saturation

power

outputisthe

maximum

output

power

obtainable

with a

given

collector

current

and

optimized

helix

voltage.

As

the

input

signal

is

increased

from

the

noise

level,

the

output-vs-input

characteristic

is

linear

until

saturationisapproached

and

the

gain

beginstodecrease.

Eventually

the

output

reachesapeak

whichisthe

saturation

power

output

and any

further

increase

in

the

input

causes

the

outputtodecrease.Ifthe

collector

currentisreduced,

the

power

outputatwhich

saturation

occurs

will be

decreased.

The

primary

effects

which

lead

to

saturation

are:

1)

the

forces

between

the

electrons

in

the

beam

begin

to

limit

the

electron

density

in

the

bunches2)the

energy

transfer

from

the

electron

beamtothe

helix

causes

the

beam

velocitytodecrease

and

gradually

lose

synchronism

with

the

wave on

the

helix.

These

effects

become

more

pronounced

as

saturation

is

approached,

and

cause

the

gainofthe

twttodecrease.

3-6.

HELIX

CONTROL.

3-7.

The

HELIX

voltage

control

on

the

front

panel

maximizes

the

gain

and

power

outputofthe

twtata

selected

frequency

or

optimizes

the

gain

and

power

output

over

the

entire

band;

see

figures

3-2Aand

3-2B.

3-5.

If,

following

tube

replacement,

or

for

some

other

reason,

the

cathode

current

can

be

increased

with

the

GRID BIAS

controltoslightly

above

the

safe

maximum

current

(see

table

3-1),

readjust

the

anode

voltage

control,

paragraph

5-26.

The

anode

voltage

control

is

settolimit

the

twttoits

normal

cathode

current

when

the

bias

voltageonthe

twtiszero.

If

the

cathode

current

is

limitedtoits

normal

value,

but

the

currenttoanother

electrodeisexcessive,

the

amplifier

requires

service

or

adjustment,

see

para-

graphs

5-21or5-30.

)

CAUTION:

DO

NOT EXCEED:

Cathode

current

Helix

current

Collector

current.

Anode

current

3

ma

0.5

ma

3

ma

SO

/la

3-10.

Operating

the

492A

or

494A

near

saturation

power

output will

produce

second

harmonic

content

in

the

output.

To

obtain

maximum

power

output

from

the

twt without

excessive

second

harmonic

contentinthe

output,

increase

the

input

signal

level

until

satura-

tionisreached,

then

reduce

the

input until

the

out-

put

decreases

approximately

6 db (an

input

reduction

of

10

to

15 db).Ifsecond

harmonic

contentisun-

important,

operation

at

saturation

is

usually

very

satisfactory.
3-11.

One

advantageofoperating

the

twt

near

satura-

tionisthe

constant

output

characteristic

exhibited

by

a twt

at

saturation.

At

saturation

the

gain

of a twt

varies

inversely

with

the

input

level

and

input

varia-

tions

of

10 to 15 db

cause

the

outputtovary

only

4

to

6 db.Ifa

more

nearly

constant

outputisdesired,

see

paragraph

3-14.

3-12.

BANDWIDTH

CONSIDERATIONS.

3-13.

The

graphsinfigures

3-2A

and B show

typical

gainvsfrequency

and

saturation

power

output

curves

for

the

492A and

the

494A

amplifiers

using

two

differ-

ent

conditions

of

helix

voltage.

One

setofcurves

shows

the

gain

and

saturation

power

output when

the

helix

voltageisoptimizedateach

frequency.

The

other

setofcurves

shows

the

gain

and

saturation

power

out-

put when

the

HELIX

controlissettothe

broadband

00144-2

3-1

Section III
Figure

3-2

Model 492A/494A

GAIN:

GAIN AT

SATURATION

POWER

OUTPUT.

VHOPTIMIZED

AT EACH

FREQUENCY.

~

SMALL

SIGNAL

GAIN: VHOPTIMIZED

AT

EACH

FREQUENCY.

SIGNAL

GAIN;

VHOPTIMIZED

FOR

BROADBAND

OPERATION.

SATURATION

POWER

OUTPUT:

VHOPTIMIZED

AT

EACH

FREQUENCY

492A

-rr

a.

15

+-----+-----+-----+--------""'1-----+-----+-------1

50

30

A

V

H

:

HELIX

VOLTAGE

E

o

= 0

VOLTS

4

5

6 7

8

G-L-248

FREQUENCY

KMC

49'4

A

SMALL

SIGNAL

GAIN:

VHOPTIMIZED

AT

EACH

FREQUENCY.

VHOPTIMIZED

FOR

BROADBAND

OPERATION.

SATURATION

POWER

OUTPUT:

VHOPTIMIZED

AT

EACH

FREQUENCY,

GAIN:

GAIN

AT

SATURATION

POWER

OUTPUT

•

V

H

OPTIMIZED

AT

EACH

FREQUENCY.

rr

15

-1-----+-----+-----+-----+----""""""

......

-..---+-------1

25

45

.c

."

I

35

z

«

(9

B

V

H

:

HELIX

VOLTAGE

E

g

:

0

VOLTS

7 8

9 10

II

12

G-L-248

FREQUENCY

KMC

Figure

3-2.

Typical

Gain and

Power

Output

Characteristics

3-2

00144-2

Model 492A/494A

Section

III

Paragraphs

3-14to3-22

is

developed

whichisthen

appliedtothe

twt

grid

to

hold

its

amplification

constant.

)

pOSltlOn.

To

obtain

the

most

nearly

constant

amplifier

gain

over

the

full

frequency

range

set

the

HELIX

con-

trol

to 5,

the

setting

which

yields

the

optimum

broad-

band

helix

voltage.

Since

noise

powerisdirectly

proportional

to bandwidth,

it

may

be

desirable

to

limit

the

bandwidth and

therefore

noisebymaximizing

the

gain

ataparticular

frequency

with

the

HELIX

control

and by

installing

suitable

filtersatthe output.

3-14.

CONSTANT

GAIN

OR

CONSTANT OUTPUT

AMPLIFICATION.

SIGNAL

GENERATOR

TRAVEL

ING

-WAVE

TUBE

ANPLIflER

TO

GRID

MOD

INPUT

) (

DIRECTIONAL

COUPLER

Rf

OUTPUT

":>--------o------=<o-----+--

OUT

LO-l-66

00

L=J-=-~/~

__

,"""",,---_--,

BALANCE

CONTROL

(SETTOOBTAIN0VOLTSTOTWT

GRID

MOD.

CONNECTOR,ATDESIRED

AMPLIfiCATION)

3-19.

The

492A and 494A

serve

as

very

effective

buffers

to

isolateamicrowave

signal

source

from

a

load.

Mismatches,

changesinexternal

circuitry,

or

the

introductionofmodulation

do not

affect

the

con-

stant

50-ohm

input

impedanceofthe

twt and

thus

will

not

affectasignal

source

connectedtothe

input.

The

attenuation

between

the

output and

input

terminals

is

60 db

duetoattenuators

placed

along

the

helix.

How-

ever,

when

the

output

signalisreflected

fromamis-

matched

load

backtothe

input,

the

effective

signal

isolationisthe

60 db

minus

the

gainofthe

amplifier.

For

example:

withanamplifier

gain

of 25 db,anopen

or

short

circuitonthe

twt

output

can

result

in a

maxi-

mum

reflected

signal

35 db below

the

input

level

(approximately

1/56ofthe

input

signal),

which

corre-

spondstoa

swrofless

than 1.04.

Note

The

GRID MOD.

connectorisdirect-coupled

to

the

gridofthe

twt

amplifier.Ifadcpoten-

tial

accompaniesamodulating

voltage

applied

to

this

connector,

the

grid-bias

voltage

will

be

altered.

The

GRID BIAS

control

may

be

usedtocompensate

for

the

changeingrid

bias

voltage

due

to a

dc

componentatthe

input.

Figure

3-4.

Block

Diagram

of an

Automatic

Gain

ControltoMaintain

Constant

Amplifica-

tion

fromaTWT

Amplifier

3-18.

BUFFER

AMPLIFICATIONS.

3-20.

AMPLITUDE

MODULATION.

3-21.

To

amplitude

modulate

anrfsignal

applied

to

the

twt

amplifier

with a

minimumofenvelope

distor-

tion in

the

output

signal,

carefully

establish

the

opti-

mum

rf

drive,

grid

bias,

and

modulating

signal

amplitude

for

a given

setup.

3-22.

For

minimum

distortion,

the

twt

grid

voltage

must

not

leave

the

linear

regionofthe

grid

voltage

vs

rf

output

characteristic

(see

figures

3-5

and

3-6).

Also,

therfdrive

mustbeadjustedsothat

the

modu-

lation

peaks

areatleast

2 db below

saturation

power

DIRECTIONAL

COUPLER

LO-L-'2

00

TRAVELING-WAVE

TUBE

AMPLIfiER

TO

AMPLITUDE

MODULATION

SIGNAL

INPUT

GENERATOR

!

3-15.

Although

the

traveling

wave tube

amplifier's

saturated

power

output

characteristic

canbeused

to

provide

nearly

constant

output

power,

installing

suit-

able

feedback

circuitry

providesaconstant

output

for

input

signal

variationsasgreatas20 db.

Figure

3-3.

Block

Diagram

of a

Circuit

usedtoMaintain

Constant-Level

Output

Power

fromaTWT

Amplifier

3-16.

An

arrangement

for

obtainingaconstant-level

output

signal

from

the twt, in

spiteofvariations

in

input

signal

level

or

variationsinamplifier

gain,

is

illustrated

in

figure

3-3.

In

this

circuitaportion

of

therfsignaliscoupled

from

the

traveling-wave

tube

output,

throughadirectional

coupler

to a

detector

such

asacrystal

rectifier.

The

rectified

voltage

is

then

amplified

in a

dc

coupled

amplifier

and

applied

to

the

GRID MOD.

connectoronthe

twt. Any

tendency

for

the

output

level

from

the

twttoincreaseisimmed-

iately

detected,

amplified,

and fed

backtoreduce

the

gainofthe

traveling

wave tube

amplifierinproportion.

Conversely,

any

reduction

in output

level

increases

the

gainofthe

amplifiertohold

the

output

level

con-

stant.

The

flatnessoftherfoutput

power

level

will

be

affectedbythe

frequency

responseofthe

detector,

directional

coupler

and

the

amplifier

gain.

The

band-

width of the

amplifier

must

be

great

enoughtopass

any

rateofchangeatwhich

the

output

level

may

vary.

3-17.Avariation

of

the

basic

automatic

power

level

control

circuit

canbeusedtoobtain

constant

ampli-

fication

with a twt

even

though

the

gain

changes

with

frequency,

power

line

voltage

and tube

characteris-

tics.

This

circuit

is

illustrated

in

figure

3-4.

The

circuit

operates

as

follows:

Therfinput and output

signals

are

sampled,

rectified,

and

the

resulting

dc

voltages

amplified

and

compared.

The

gainoroutput

from

each

halfofthe

circuit

canbeadjustedtoestab-

lish

the

desired

ratioofinputtooutput

level.Ifthe

rf

input

to output

ratio

changes,adifference

voltage

)

)

00144-2

3-3

Section

III

Figure

3-5

Model 492A/494A

\

\,

INPUT

-

13

DBM

-24DBM

-27.5DBM

-30.0DBM

-34.0DBM

-36.0DBM

:

6000

Me

:

OPTIMIZED

AT E

g

=0

FOR

EACH

CURVE.

DB

BELOW SATURATION

OUTPUT AT

Eg=O

OUTPUT

---------

0

DB

-'--'-'

2DB

-_..__

__..- 4

DB

-,,-,,-,,-6

DB

----IODB

----12

DB

OUTPUT

FREQUENCY

HELIX

VOLTAGE

dJp--

MODEL

492

A

TYPICAL

MODULATION

CHARACTERISTICS

\ • I I ,

\\

'\\

'!

I

: .,

\

\'

:

~

\

'\T\TT

\\\\

\\

\'

::

I'

\ !

\ \

~

:

.,

\; \ ,

\ \\\

~

. i ,

\

: ,

I \

1\

,

: ! . ,

"

.~k.

,

r···,

,

I ,

, ,

."

I ,

r,

I

1700

1600

I

1500

1400

0

et

1300

0

..J

~

1200

%:

0

0

11.00

\t)

1000

C/)

~

..J

900

0

>

..J

800

..J

~

700

z

600

~

::)

500

0.

~

::)

400

0

300

200

100

0

+10

+5

o

-5

-10

-15

-20 -25

-30

-35

-40

-45

-50

-55

G

RID

B I A S

VOL

T S

G-

M-36

Figure

3-5.

Typical

Plot

of Output

VoltagevsGrid

Voltageofa Model 492A

3-4

00144-2

Model 492A/494A

Section III

Figure

3-6

)

1600+-----+-----1

-.::..bp--

MODEL

494A

TYPICAL

MODULATION

CHARACTERISTICS

INPUT

-6

OBM

-21

OBM

-250BM

-280BM

-31

OBM

OUTPUT

-------

0

DB

-'-'-'30B

............- _ 6

DB

-,,-,,-9

DB

----12

DB

FREQUENCY

:

9000

Me

HELIX

VOLTAGE:

OPTIMIZED

AT

Eg=O

FOR

EACH

CURVE.

OUTPUT:DB

BELOW SATURATION

OUTPUT

AT

E

g

=0

\

\

\

\

\

\

\

\

\

,

\

,

,

.

\

\.

\.

,.

.....

,.

,

,.

,

\ \

\

::::".

\'\

" \

\

\

\ \

800

-fI<--------t--\-----J'l---t---1

~\.\

',\

\

I \ \ \ \

6

00

+--4-~.____--+-.:,.-----4---;.-+-----l..-____,r----__r___---......,.....---_+---__l

'.'.

\ \

\>\\

\\

400+-------''rl-----T---'';---+-ir----1-----+-----+-----+----~

\

\.\

..•

',\

\\

.....

1\\

'.

'.

~~

\.

'\

\

..

\

200+------+------>,r-"""'d-....:...;-"""\r----11-----+-----+-----+----~

~~"

.•..

,~~

'~

"~

~

.............

~,.

~:.-.:.:..~

0~---_+_---_+_----1f_--==:..::.!!!~---_+_---_+---___l

1400+------+--~

1200

0

<

0

.J

:E

:I:

0

1000

0

It)

z

V>

~

.J

o

>

.J
.J

)

+10

o

-10

GRID

-20

-30

BIAS

VOLTS

-40

-50

G-M-37

-60

Figure

3-6.

Typical

PlotofOutput

VoltageVBGrid

Voltage

of a Model 494A

00144-2

3-5

Section

III

Paragraphs

3-23to3-30

output.

The

linear

modulation

region

extends

from

approximately

+4

volts

(where

beam

de-focusing

occurs)toapproximately

-15

volts

(where

therfout-

put

becomes

an

exponential

function of the

grid

volt-

age).

This

linear

operating

region

permits

upto30%

modulation

with

less

than 2.5%

envelope

distortion

and upto50%

modulation

with

less

than5%distortion.

Envelope

distortion

increases

rapidly

above

50%

modu-

lation.

In

pulse

work

the

twt

maybebiased

near

or

below

cut-off

and

therfdrive

adjusted

for

saturation

outputatthe

peak

amplitudeofthe

modulating

pulse.

However,

the

grid

voltageatthe

peakofthe

modu-

lating

signal

must

not

cause

de-focusing

(approxi-

mately+4to

+ 8

volts)

nor

excessive

average

electrode

current,

see

table

3-1.

The

transient

responseofthe

492A

or

494A to a

step

function

appliedtothe

grid

is

approximately15nsec.
3-23.

Amplitude

modulationisaccompaniedbysome

incidental

phase

modul'btion of

therfsignal,

amount-

ingtoapproximately

90

phase

shiftoftherfcarrier

for

a 10 db

changeinthe

modulatedrfoutput

level.

In

practice

this

phase

modulationisunimportant

when

using

the

conventional

square-law

crystal

detectors,

butisimportantindetection

systems

where

the

out-

putisa functionoftherfcarrier

phase.

3-24.

PULSE

MODULATION.

3-25.

Thereisconsiderably

latitudeinthe

adjustment

of

modulation

characteristics

when

pulse

modulating

anrfsignal

using

the

492Aorthe

494A;

see

figures

3-5

and

3-6.

The

cw

input

level,

the

modulation-

pulse

amplitude,

and

the

grid

bias

determine

the

characteristics

of

the

rf

output

pulse

as

follows:

a.

The

cw

input

signal

primarily

determines

the

maximum

possible

leveloftherfoutput

pulse

and

whetherornot

the

twt

canbeoperated

into

saturation.

b.

The

peak-to-peak

amplitudeofthe

modulating

pulse

primarily

determines

the

on-off

ratioofthe

rf

output

pulse.

c.

The

grid

bias

level

primarily

determines

the

rf

output

levels

attained

during

the

pulse-on

and

pulse-

off

times

and

also,inconjunction

with

the

modulating

pulse,

determines

the

rf

input

level

necessary

to

saturate

the

twt.

The

GRID BIAS

control

always

should

be

set

so

that

the

twt

grid

will not

draw

cur-

rent

(approximately4volts

positive)

during

the

pulse-

on

period.

3-26.

To

pulse

modulate

therfsignal

being

amplified

in

the

492A

or

494A,

refer

to

figures

3-5or3-6

and

proceedasfollows:

a.

Determineifthe

twtisto be

driven

into

satura-

tion

andiftherfoutput

mustbeataspecific

level.

b.

Set

the

GRID BIAS

control

for

zero

bias.

c.

Connect

therfinput

signaltothe

twt and

adjust

its

leveltoproduce

the

desiredrfpulse

output

level.

d.

Determine

the

on-off

voltage

ratio

required

in

therfoutput

pulse.

3-6

Model 492A/494A

e.

Using

the

graph

in

figure

3-5

determine

the

magnitudeofmodulation

pulse

requiredtoproduce

the

desired

on-off

ratio.

f.

Set

the

GRID BIAS

controltoobtain

the

voltage

determined

in

step

e.,

Le.,

the

peak

voltageofthe

modulating

pulse.

The

bias

VOltage

maybemeasured

at

the

pin

jackonthe

front

panel.

g.

Connect

the

modulating

pulsetothe

GRID MOD.

connector

and

adjust

its

amplitudetothe

voltage

de-

terminedinstep

e to

produce

the

desired

on-off

ratio

in

therfoutput

pulse.

Since

the

gridofthe

twtiscon-

nected

directly

to

the

GRID MOD.

jack,adc

com-

ponent

in

the

modulating

signal

will

affect

the

grid

bias.

Also,ifcapacitive

couplingisused

the

modu-

lating

signal

will

drive

the

gridofthe

twt

above

and

below

the

dc

level

established

by

the

grid

bias,

an

amount

determined

by

the

duty

cycleofthe

modulating

signal.

The

GRID BIAS

control

mustbeadjusted

to

compensate

for

both of

these

effects.

h.

To

increase

the

on-off

ratiooftherfoutput

pulse,

increase

the

amplitudeofthe

modulation

pulse,

at

the

same

time

adjust

the

grid

biassothat

the

grid

will not be

driven

beyond 4

volts

positive,

see

the

Note

paragraph

3-21.

Note

Large

input

modulating

pulses,

above

15

volts,

tendtoshock-excite

the

helix,

produc-

ing

ringing

on

the

top of

therfoutput

pulse

and a slow

rise

time.Ifthe

traveling-wave

tubeisoperated

near

saturation

this

effect

is

minimized

and

better

pulse

characteristics

are

obtained.

3-27.

LIMITED

PHASE

MODULATION.

3-28.

The

signal

being

amplifiedinthe

492Aor494A

can

be

phase-modulated

by applying

voltagetothe

HELIX MOD.

connector.

This

voltage

varies

the

electron-beam

velocity

by

changing

the

potential

be-

tween

the

cathode

and

the

helix--a

positive

voltage

change

accelerates

the

electron

bunches

and

advances

the

phaseoftherfoutput

signal;anegative

change

slows

them

and

retards

the

phaseofthe

output

signal.

The

resultant

phase

deviationinthe

output

signal

is

directly

proportionaltothe

applied

voltage.

The

de-

gree

of

phase

deviation

producedislimited

by

the

range

of

helix

voltages

that

produces

amplification,

and

by

the

amountofincidental

amplitude

modulation

permissible

in

therfoutput.

Phase

deviation

of 360

0

is

possible

with

the

output

amplitude

heldtovariations

of

approximately

1-1/2

db andisobtained

with a

helix

voltage

variationofless

than 50

volts.

The

actual

voltage

required

foraphase

shiftof3600varies

with

the

operating

frequency

and

from

tube-to-tube.

3-29.

UNLIMITED

PHASE

MODULATION

AND

FREQUENCY

SHIFTING.

3-30.

Although

the

limited

phase

deviation

described

in

paragraph

3-27isusefulinsome

applications,

un-

limited

phase

deviation

hasamuch

wider

range

of

usage.

Itisparticularly

useful

because

the

frequency

00144-2

Model 492A/494A

Section III

Paragraphs

3-31to3-36

G-l-7

TIM

E

DESIRED OUTPUT

(Ftl

FR

EQU

ENCY +-

__

-'---_----'

__

---A.

__

--L.._---l

--

---

---1---

INPUT FREQUENCY

(Fl

UNDESIRED OUTPUT ( F )

FREQUENCY

2

HIGH

Figure

3-8.

Offset

Frequency

Produced

by

Sawtooth Modulation of

the

Helix

LOW

SAWTOOTH MODULATION

APPLIED

TO

HELIX

3-31.Inpractical

applications,aconstant

amplitude

linear-slope

sawtooth

generator

is

used to

produce

the

sawtooth

waveforms.Ifthe

amplitude8fthe

saw-

tooth

voltageisadjustedtoproduce

a 360

shift,

one

cycle

of

the

cw

signal

will be addedorsubtracted

during

each

sawtooth, and

the

frequency

shift

pro-

duced in

the

output will be

equaltothe sawtooth

repe-

tition

rate.

Sawtooth

voltages

having

negative

slopes

(see

figure

3-7)

produceadecrease

in the output

fre-

quency (delay in

phase).

Conversely,

sawtooth

volt-

ages

of the

opposite

slope

causeanincreaseinoutput

frequency.

of the input

signal

canbeshifted

by a

predetermined

amount. Unlimited

phase

deviationiseffectively

sim-

ulated

by continuously

repeating

exact

3600phase

deviations.

Thisisaccomplished

by modulating

the

traveling

wave tube

helix

wiSh

a sawtooth

waveform,

each

sawtooth

producing

360

phase

shift,asshown

in

figure

3-7.

Anrfoutput

frequency

thatisshifted

in

relationtothe input

frequencyisthus produced,

as

shown in

figure

3-8.

O·

HIGH

SAWTOOTH

MODULATION

APPLIED

TO

HELIX

LOW

PHASE DIFFERENCE
BETWEEN

INPUT AND

OUTPUT WAVES

frequency

shift

with

its

relatively

small

power

content

would

be

rejected

by

most

narrow

band

circuits.

In

systems

where

the

undesired

frequency

shift

falls

within

the

pass

band of the

equipment

under

test,

a

negative

pulse

canbeappliedtothe

GRID MOD.

con-

nectortocut

off the twt

beam

current

during

the

fly-

back

time.

This

method

reduces

the

undesired

fre-

quency

shift

althoughitproduces

some

small

tran-

sients

and

leaves

small

time

intervals

during

which

thereisno

signal

output.

Practical

applications

of

offset

frequencies

include

the

measurement

of

ex-

tremely

high

swr's

accurate

calibrationofattenu-

ators

over

wide

amplitude

ranges

(paragraph

3-34),

frequency

shiftingofmicrowave

radio

relay

channels

for

retransmission,

productionofmixer

frequencies

for

radar

and

other

microwave

receivers,

etc.

G-l-I

TI

ME

..

3-34.

HOMODYNE

DETECTION.

Figure

3-7.

RF

Phase

Shift

Produced

by

Helix Modulation

3-32.

With sawtooth modulation,

the

desired

output

frequency

shift

(F

in

figure

3-8)

occurs

during

the

sawtooth

formatioJ

time,

andisproportional

to

the

rate

of

change

of voltage.

During

the sawtooth

fly-

back

time

the output

phaseisshifted

in the

opposite

direction

producinganundesired

frequency

shift(F2

in

figure

3-8).Ifthe

flyback

timeismade

extremely

short,

this

frequencyisfar

removed

from

the

desired

frequency

since

the

degreeoffrequency

shiftisin-

versely

proportionaltothe

flyback

time.

In

addition

to

being

far

removed

from

the

desired

frequency

the

powerinthe

undesired

frequencyisvery

small

since

itisproportionaltothe

ratio

of flyback

timetosaw-

tooth

time.

3-33.Ina

typical

case

involving a

desired

50-kc

fre-

quency

shift,

a

I-microsecond

flyback

time

would

produceaI-megacycle

frequency

shiftinthe

opposite

direction

and would

contain

only5%of

the

total

power

in

the

output wave.

In

practice,

this

undesired

3-35.

The

ability

of a twttoproduce

an

offset

fre-

quency

thatisstable

with

respecttothe

signal

source

makesitan

ideal

instrument

to

use

in a homodyne

(linear)

detection

system.

The

difference

frequency

will be dependent upon

the

stability

of the sawtooth

generator

usedtomodulate

the

twt helix, a

problem

ofnoconsequenceatthe

low modulating

frequencies

involved.
3-36.Atypical

linear

detector

system

suitable

for

calibrating

microwave

attenuators

is

illustrated

in

figure

3-9.

The

signal

generator

suppliesasignal

(f) both

toacrystal

mixer

andtoa

traveling

wave

tube

amplifier.

The

traveling

wave tube

amplifier

is

sawtooth modulated to

produce

an

offset

frequency

(f-f

) whichisapplied to

the

attenuatortobe

cali-

brated.

The

output

signal

from

the

attenuatoristhen

combined

with the

original

signal

(f) in

the

mixer

to

produceabeat

frequency

(f ) whose

amplitudeisdi-

rectly

proportional

to

the

ahtplitudeof(f-f

j

)

so

long

as

the

amplitudeof(f-f

j

)

remains

within

the

square-

law

region

of the

cryStal.

This

beat

frequency

is

amplified

by

the

tuned

amplifier

and

the

outputisin-

dicated

by an

ac

voltmeter.

The

lower

sensitivity

01144-2

3-7

Section III
Figures

3-9

and

3-10

Model 492A/494A

SAWTOOTH

GENERATOR

f,

OFFSET

FREQUENCY

SINGLE

SIDEBAND

GENERATOR

-------------1

I

A

TTENUATORBEING

CALIBRATE"

/ I

I

I

I

I

I

I

f-f, I

I

I

I
I

I

_

_J

L_

I-

I

TRAVELING

WAVE

TUBE

TUBE

AMPLIFIER

SIGNAL

GENERATOR

COUPLER

/

f

VOLTMETER

TUNED

AMPLIFIER

LO-l-'"

Figure

3-9.

Block

Diagram

of a

Linear

(Homodyne)

Detection

System

INT.

SWEEP

OSCILLOSCOPE

MI

XER

30

DB

PAO

'T'

CONNECTOR

TWT

AMPLIFIER

)20OB(

DIRECTIONAL

COUPLER

SIGNAL

GENERATOR

4TO8

KNC0USE

-hp-

MODEL

492

A

7TO12.4

MC.

USE

·hp·

MODEL

494

A

USE

APPROPRIATE

DIRECTIONAL

COUPLERS.

ATTENUATORS.

MIXERS.

ETC.

TO

HELIX

SLOPE-MODULATED

SAWTOOTH

GENERATOR

.h

p

'

202A

FUNCTION

GENERATOR

M.O.P.A.

MICROWAVE

FREQUENCY

MODULATION

SYSTEM

LD-L-40B

Figure

3-10.

Block

Diagramofa

Circuit

tc?

ProduceanFM

Signal with a TWT

Amplifier

3-8

00144-2

)

Model

492A/494A

limitisdetermined

by

the

crystal

and IF

amplifier

noise

andisapproximately

-100

dbm.

ote

When a

swr

indicator

(suchasthe

<[j)

Model

4158)

calibrated

for

use

with a

square-

law

detector

is

usedinplaceofthe

tuned

amplifier

and

voltmeter,

the

db

readings

mustbedoubled.

3-37.

FREQUENCY

MODULATION.

3-38.

Narrow-band

frequency

modulation

canbeob-

tained

by

applying

the

modulation

signal

directly

to

the

helixofthe

twt;

however,tofrequency

modulate

with an

appreciable

frequency

deviationitis

first

necessarytoproduceanoffset

frequencyasdescribed

in

paragraph

3-29.

The

deviationofthe

offset

fre-

quency

shouldbeslightly

greater

than

1/2

the

total

frequency

deviation

desired.

The

offset

frequency

is

then

varied

by

varying

the

slope

of

the

sawtooth.

3-39.Asawtooth

waveform

produced

by

the

special

generator

describedinparagraph

4-20

canbeslope-

00144-2

Section

1II

Paragraphs

3-37to3-40

modulated

by any

waveform

before

being

applied

to

the

traveling

wave

tube

helix.Inthis

manner

complex

signals

canbeusedtofrequency-modulate

the

signal

applied

to

the

twt and

the

center

of

the

output

fre-

quency

will

be

fixed by

the

sawtooth

repetition

rate

without

slope

modulation.

Innocase

should

the

p~ase

shift

duetoa

single

sawtooth

cycle

exceed

360

so

that

the

amplification

propertiesofthe

traveling

wave

tube

amplifier

will notbeadversely

affected

regard-

less

of

the

magnitudeofthe

apparent

phase

deviation

when

the

sawtooth

waveismodulated.

3-40.

Figure

3-10isa

block

diagram

of a

system

for

the

generationoffrequency-modulated

offset

signals.

In

this

arrangement,

the

slope-modulated

sawtooth

voltage

whichisappliedtothe

twt

helix

produces

an

offset

frequency,

the

instantaneous

frequencyofwhich

is

proportionaltothe

slopeofthe

sawtooth.

Varying

the

slopeofthe

sawtooth

voltage

varies

the

offset

fre-

quency.

Thus

the

output

signal

from

the

twtisan

fm

signal.

The

detected

fm

signal

(the

difference

between

the

signal

generator

frequency

and

the

fre-

quency-modulated

offset

frequency)

is

shown on

the

oscilloscope.

3-9

"'"

,

o

'rjC/)

.....

CD

OQ

n

c:

~.

'i

0

CD

::s

"'"-

,<

......

3::

8.

CD

>-

"'"

'Cl

N

;>

-....

"'"

'Cl

"'"

;>

J4

rG'iiiDl

l!QQJ

J5

PIN

JACK

ON

FRONT

PANEL

FOR

MEASURING

BIAS

J2mD

J3m

(

~Jll

HELlXI

MOO.

Figure

4-1.

Block

Diagram

~

Models

492A and 494A

~

-

SRI

HALF

WAVE

RECTIFI

ER

+

SR2

~

VI

V5A

SR3

SERIES

HELIX

VOLTAGE

REGULATOR

MODULATOR

I

DOUBLER

6BQ6

V4

1126BQ7A

REFERENCE

ew

I

-

VOLTAGE

I

HELIX

~

0

OA2

STRAY

CAPACITY

'--c.--

T1

V2

V5B

..,-

,,'

-",

CONTROL

DISCHARGE

I I

POWER

TUBE

TUBE

,

,

I

i

~

TRANSFORMER

6AU6

1

12

6BQ7A

IWI

~

I

I

elY

-

:

~

u

> <

@

HELIX

e>

elY

I

-

--

I

""

ANODE

\~.J

~

, "

'--

""

~

<

V3

~o

I

GRID

BIAS

I

<:>

BIAS

eIY~

REGULATOR

OB2

80-

L-44B

JF1

I.SA

F2

1.6

A

~

SR4

~

TIT

MAGNET

SI

SUPPLY

L----J

L-

o

o

......

"'"

"'"

,

N

)

Model 492A/494A

SECTION

IV

PRINCIPLES

OF

OPERATION

Section

IV

Paragraphs

4-1to4-13

)

)

4-1.

INTRODUCTION.

4-2.

The

twt

amplifier

contains

very little

signal

cir-

cuitry

external

to

the

twt

itself.

The

electrical

cir-

cuitsinthe

instrument

provide

the

operating

voltages

and

the

means

for

modulating

the

twt,asshown in

the

block

diagram,

figure

4-1.

4-3.

MAGNET

POWER

SUPPLY.

4-4.

The

492A and 494A

utilizea400-gauss

electro-

magnet

(surrounding

the

traveling

wave tube

capsule)

to hold

the

emitted

electrons

in a

very

narrow

beam.

The

power

supply

for

the

magnet

consists

of a

full-

wave

selenium

bridge

rectifier

connected

directly

across

the

US-volt

line

andacapacitive-input

filter,

and

supplies

approximately

0.7

ampere

at

an output

voltage

of 120

voltsdcwith

less

than 1 volt

rms

ripple

when

connectedtothe

magnet.

The

magnetiscovered

by a

shield

asaprotection

against

stray

magnetic

fields.

4-5.

REGULATED

POWER

SUPPLY.

4-6.

The

operating

voltages

appliedtothe

twt

are

obtained

fromavoltage

doubler

followed by a

voltage

regulator,

VI,

V2, and V4.

The

regulationisaccom-

plished

by

varying

the

plate

resistance

ofVIin

ac-

cordance

with

the

output

voltageinthe

following

man-

ner,

see

figure

4-1.

V4isa

constant

voltage

tube

which

holds

the

voltageatthe

gridofV2

constant

with

respect

to

the

cathodeofVI.

The

cathodeofV2

is

connectedtoa

voltage

divider

between

the

cathode

of

VI

and

the

minus

sideofthe

supply.Ifthe

cathode

voltageofVI

increases,

the

grid

voltageofV2

will

also

increase

the

same

amount.

However,

the

cath-

ode

voltage

of

V2

will

increase

only by

an

amount

equaltothe

ratioofresistance

below

the

potentiom-

eter

arm

to

the

total

resistance

times

the

total

voltage

change.

Thus,asignal

appears

on the

grid

of

V2

whichisproportionaltothe

riseofvoltage

on

the

cathodeofVI.

This

signal

on the

grid

of V2

is

amplified

and

inverted

by

V2

and

appliedtothe

grid

of V1,

increasing

the

plate

resistance

of V1 and

low-

ering

the

voltageatthe

cathodeofVI

which

results

in

a

substantially

constant

output

voltage.Ifthe

voltage

at

the

cathodeofVI

tendstodecrease,

the

plate

re-

sistanceofVI

decreases,

holding the

voltageatthe

cathode

of V1

substantially

constant.

4-7.

The

chassis

Helix

control

(R25)

adjusts

the

level

of

the

regulateddcoutputtocompensate

for

the

varia-

tions

in twt

characteristics.

The

switch,

52,

and

the

associated

voltage

dividers

permit

the

useofthe

same

power

supply

with two twt

types

and

allows

the

opera-

tor

to

use

the

same

instrumentasa 492A

(4-8

gc)

or

as

a 494A

(7-12.4

gc) by

changing

the twt. Changing

the

tube typeisno

more

difficult

than

replacing

the

twt

with

another

tube of

the

same

type

(see

para.

5-17).

00144-2

4-8.

The

bias

voltage

for

the

twtissuppliedbyV3

and

controlled

by the GRID BIAS

controlonthe

front

panel.

The

grid

of

the

twtisgrounded

through

a

3900-ohm

resistor,

and

the

voltageonthe

cathode

is

varied.

The

circuit

is

arranged

so

that

all

the twt

electrode

voltages

except

the

control

grid

varyasthe

cathode

voltageisvaried

and

therefore

remain

con-

stant

with

respecttothe

twt

cathode.Ifthe

grid

were

not

grounded,

but

connectedtoa

sourceofvariable

negative

voltage

a blocking

capacitor

wouldberequired

which would

impair

the

response

of the twttolow-

frequency

modulating

signals.

A pin

jackonthe

front

panel

allows

the

bias

voltagetobe

measured;

an

ex-

ternal

voltmeter

haVing 20,000

ohm/volt

sensitivity

or

higher

shouldbeused.

4-9.

The

anode

voltageiscontrolled

by a

potentiom-

eter

on

the

chassisofthe

instrument

andisadjusted

to

obtain

normal

cathode

current

for

the

twt

amplifier;

see

paragraph

5-26.

The

front

panel HELIX

control

adjusts

the

helix

voltageofthe

twt to obtain

either

maximum

gain and

powerata

particular

frequency

or

optimum

broadband

response.

4-10.

TRAVELING

WAVE

TUBE.

4-11.

The

basic

traveling

wave

tube

consists

of an

electron

gun which

projectsafocused

electron

beam

throughahelically-wound

coiltoa

collector

electrode,

shown in

figure

4-3.

The

focused

electrons

are

held

inapin-like

beam

through

the

centerofthe

helix

by

a powerful

magnet

around

thefull lengthof

the

capsule.

4-12.

A cw

signal

coupled

into

the

input

end of the

helix

travels

around

the

turnsofthe

helix

and

thus

has

its

linear

velocity

reducedbythe

amount

equaltothe

ratio

of

the

length of

wire

in the

helixtothe

axial

lengthofthe

helix.

The

electron

beam

velocity,

de-

termined

by the

potential

difference

between

thecath-

ode

and

the

helixisadjustedsothat

the

electron

beam

travelsalittle

faster

than the cw

signal.

The

electric

field of

the

cw

signal

on the

helix

interacts

with

the

electric

field

created

by

the

electron

beam

and

in-

creases

the

amplitudeofthe

signal

on the

helix,

thus

producing

the

desired

amplification.

4-13.

Figure

4-2isa

diagram

showing the

principal

elements

of a

typical

traveling

wave

tube

in the

upper

portion

and

the

important

stepsinthe

amplification

processinthe

lower

portion.

The

steps

shouldbefol-

lowed by

referring

to

the

numbered

captions

below.

(1)

An

electron

beamisdirected

through

the

center

of

the

helix.

(2) A cw

signaliscoupled

into

the

helix.

Arrows

in

the

detail

show the

direction

and

magnitudeofforce

exerted

on

the

electron

beam

by

the

cw

signal.

4-1

"'"

I

t-;)

BEAM

FORMING

ANODE

200V

TO

300

V

,.---

HELIX

MOUNTING

AND

SHIELD

VOLTAGE

SANE

AS

COLLECTOR

LOSSY

-

WIRE.

HELIX

-COUPLED

ATTENUATOR

COLLECTOR

FRON

500

V

TO

1500

V

(DEPENDING

ON

TUBE

TYPEl

'TjUl

....

(1)

OQO

C M

I-l ....

(1) g

"'"

......

~<

INPUT

DIRECTIONAL

COUPLER

SINGLE

-

WIRE

HELIX

OUTPUT

DIRECTIONAL

COUPLER

CATHODE

OV

MODULATOR

GRID

I

OV

TO

-50V

TYPE

'N'

INPUT

!lh

I =

I

JACK--~

fjjjjjjjjjfjjjjjjjjjjf

ril1

I I

TYPE

'N'

OUTPUT

JACK

~

8.

~

"'"

-.0

t-;)

»

........

"'"

-.0

"'"

»

,I

II

,•..-.n

@----I

Figure

4-2.

Traveling

Wave

Tube

and

How

It

Works

CD--

'\

! \ !

~!

..

!",/

1-1

"/1.>_

.....

~~

o

o

.-

"'"

"'"

I

t-;)

Model 492A/494A Section

IV

Figures

4-3

and

4-4

Figure

4-3.

Cutaway Viewofa

Traveling

Wave

Tube

Capsule

and Magnet Showing

the

Important

Elements

OUTPUT

COUPLER

)

COAXIAL

CONDUCTOR

CATHODE

OUTPUT

Figure

4-4.

Cutaway Viewofan

Encapsulated

Traveling

Wave

Tube

00144-2

4-3

Section

IV

Paragraphs

4-14to4-21

(3)

Electron

bunching

causedbythe

electric

field

of

thecwsignal

(see

detail).

(4)

Amplification

of

the

signal

on

the

helix

begins

as

the

field

formedbythe

electron

bunches

interacts

with

the

electric

fieldofthe

cw

signal.

The

newly

formed

electron

bunch

addsasmall

amountofvoltage

to

the

cw

signal

on

the

helix.

The

slightly

amplified

cw

signal

then

producesadenser

electron

bunch which

in

turn

addsastill

greater

voltagetothecwsignal,

and

so

on.

(5)

Amplification

increases

as

the

greater

velocity

of

the

electron

beam

pulls

the

electron

bunches

more

nearlyinphase

with

the

electric

fieldofthecwsignal.

The

additive

effectofthe

two

fields

exactlyinphase

produces

the

greatest

resultant

amplification.

(6)

Attenuators

placed

near

the

beginningofthe

helix

reduce

all

the

waves

traveling

along

the

helix

near

to

zero.

This

attenuator

prevents

regeneration

and

possible

oscillation

duetoundesired

backward

waves,

such

as

reflected

waves

from

mismatched

loads.

(7)

The

electron

bunches

travel

through

the

attenu-

ator

unaffected.

(8)

The

electron

bunches

emerging

from

attenuator

induce

a new cw

signalonthe

helix.

The

new cw

sig-

nalisthe

same

frequency

as

the

originalcwsignal

applied.
(9)

The

fieldofthe

newly

induced

cw

signal

inter-

acts

with

the

bunched

electrons

to begin

the

amplifi-

cation

process

over

again.

(10)

Forashort

distance

the

velocityofthe

electron

bunchesisreduced

slightly

duetothe

large

amount

of

energy

absorbedbythe

formationofthe

new cw

signal

on

the

helix.

(11)

Amplification

increases

as

the

greater

velocity

of

the

electron

beam

pulls

the

electron

bunches

more

nearlyinphase

with

the

electric

fieldofthecwsignal.

(12) At

the

point

of

the

desired

amplification

the

amplified

cw

signaliscoupled

outofthe

helix.

Note

that

the

"amplified"

cw

signalisa new

signal

whose

energy

is

wholly

supplied

by

the

bunched

electron

beam.

4-14.

The

traveling

wave tubeiscompletely

enclosed

in

the

capsule

showninfigure

4-4.

The

capsule

sup-

ports

and

shields

the

tube

and

rigidly

mounts

the

cap-

sule

attenuator

and

the

input-output

couplers,

cables

and

connectors.

The

capsule

attenuator

prevents

energy

from

being

propagated

down

the

capsuleina

coaxial

mode

using

the

helix

asacenter

conductor

and

the

shield

as

the

outer

conductor.

The

front-

panel

INPUT

connector

connects

throughacoaxial

cabletothe

helically-wound

directional

coupler

atthe

gun endofthe

helix;

the

OUTPUT

connector

connects

throughasimilar

cable

to an

identical

coupleratthe

collector

endofthe

helix.

Impedance

matching

over

the

extremely

wide

frequency

range

of

the

twt,

is

obtained

by

cavity-coupling.

For

an

explanation

of

4-4

Model 492A/494A

cavity-coupling

refer

to

"The

UseofQuasi-Static

Mode

Approximations

in

the

Design

of

Slow Wave

Structure

Impedance

Matches"

by Wayne E. Raub,

dated

August 1961.

Manual

number

27-3.

Reprints

available

from

Microwave

Electronics

Laboratory,

4061

Transport

Street,

Palo

Alto,

California.

4-15.

GRID

MODULATION.

4-16.

The

signal

being

amplifiedinthe

traveling

wave

tube

is

amplitude-modulated

by

applying

the

modula-

ting

signal

between

the

cathode

and

first

grid.

Making

the

potential

on

the

grid

more

positive

increases

the

current

passing

through

the

centerofthe

helix

without

changing

the

velocity

and

resultsingreater

density

of

the

electron

bunches

whichinturn

contribute

more

energy

to

therfwave being

amplified

on

the

helix,

and

correspondingly

increases

the

levelofthe

output

signal.

Conversely,

making

the

grid

more

negative

decreases

therfoutput.

4-17.

HELIX

MODULATION.

4-18.

The

Helix

Modulator,

V5A,isa

cathode

follower

connected

between

the

regulated

voltage

and

the

helix.

The

front

panel

HELIX

control

varies

the

bias

on V5A,

and

hence

the

voltage

appliedtothe

helix.

When

the

twt

amplifierishelix-modulated,

the

modulating

sig-

nal

is

connectedtothe

grid

of

the

helix

modulator

from

the

front

panel

BNC

connector

labeled

HELIX

MOD.
4-19.

Therfsignal

on

the

helixisphase-modulated

by

superimposing

the

modulating

signalonthe

normal

dc

helix

voltage.

Changing

the

helix

voltage

changes

the

velocityofthe

electronsinthe

beam

through

the

helix

without

changing

beam

density.Anegative

volt-

age

slows

the

beam

down and

retards

the

phaseofthe

output

signal;apositive

voltage

speedsupthe

beam

and

advances

the

phase.

Since

the

final

signal

taken

from

the

helixisthe

resultofelectron

bunchinginthe

beam,

altering

the

velocityofbeam

alters

the

relative

position

of

the

bunches

and

resultsina

phase

shift

between

the

input

and output

signals.

4-20.

Since

the

amountofenergy

transferred

from

the

electron

beamtothe

wave on

the

helixisin

part

a function of

the

phase

difference

between

the

fields

of

the

helix

and

the

electron

bunches,

altering

the

electron

velocity

has

some

effect

upon

the

energy

giventothe

signalonthe

helix

resultinginsome

inci-

dental

amplitude

modulation.

Special

tubes

are

avail-

able

which

sacrifice

gaintominimize

this

incidental

amplitude

modulation,

see

paragraph

5-14.

4-21.Acertain

amountofstray

and

wiring

capacity

exists

between

the

helixofthe

twt and

chassis

which

mustbecharged

and

dischargedasthe

helixismodu-

lated.

When

the

helix

modulating

signal

goes

positive

this

capacity

canbecharged

very

rapidly

through

the

low

impedanceofthe

helix

modulator

tube,

V5A, and

the

power

supply.

However,ifthe

modulating

signal

wereafast

negative-going

signal,

V5A

couldbecut

off and

the

stray

capacity

would

discharge

through

the

insulation

(leakage)

resistance

which

exists

between

the

helix

and

the

chassis.

Thisisa

relatively

long

01144-2

Model 492A/494A

Section

IV

Paragraphs

4-22to4-25

)

time

constant

circuit.

The

discharge

tube, V5B,

is

connected

between

the

helixofthe

twt and

chassis

to

formalow-impedance

and

thereforearapid-discharge

circuit

for

this

capacity.Anegative-going

modulating

signal

appliedtothe

HELIX MOD.iscoupledtothe

helix

through

the

cathode

follower,

V5A, and

simul-

taneously

inverted

by V5Aand

appliedtothe

grid

of

V5B.

The

stray

capacityisthus

abletodischarge

rapidly

through

V5B,

allowingarapid

decay

time

when

fast

pulses

are

appliedtothe

HELIX MOD.

jack.

4-22.

CONSTANT-AMPLITUDE,

LINEAR

SAW-

TOOTH

GENERATOR.

4-23.

To

shift

the

phaseorfrequencyoftherfsignal

inatraveling

wave tube

amplifier,asawtooth

such

as

is

used

in

oscilloscope

sweep

circuits

can

be

appliedtothe

traveling

wave tube

helix.Iftherfout-

put

signalisto

be a

nearly

pure

offset

frequency

and

containaminimumofspurious

components,

the

saw-

tooth

waveform

appliedtothe

helix

mustbeconstant

in

amplitude,

must

be

linear,

must

not

contain

noise

or

ripple

and

must

haveafast

flyback

time.Inaddi-

tiontofrequency-modulate

anrfsignal,

the

sawtooth

amplitude

and

the

sawtooth

repetition

rate

must

be

completely

independent

and

separately

adjustable

and

the

repetition

rate

shouldbeadjustable

over

a wide

range.

To

frequency-modulate

anrfsignal

with a

traveling

wave tube

amplifieritis

necessarytomod-

ulate

the

slopeorrepetition

rateofthe

sawtooth

wave

without

affecting

the

sawtooth

amplitude.

4-24.Asawtooth

generator

having

these

character-

istics

is

shown in

simplified

form

in

figure

4-5.

This

generator

consists

ofanadjustable,

regulated

power

supply,acharging

capacitor,

a blocking

oscil-

latortocharge

the

capacitor,apentode

tubetodis-

charge

the

capacitor,

and a

cathode

followertoisolate

the

generator

from

the

output.

4-25.

The

broken

line

in

figure

4-5

indicates

the

capacitor-charging

circuit,

the

solid

line

the

discharge

circuit.

When

powerisappliedtothe

generator,

the

grid

bias

on

the

blocking

oscillator

tubeiszero

and

the

oscillator

goes

through

one

cycleofoperation.

During

the

oscillation

cycle,

the

tube

conducts

heavily

and

rapidly

charges

the

capacitortothe

B+

voltage,

t----@

SAWTOOTH

OUTPUT

SAWTOOTH

SLOPE

CD

PENTODE

DISCHARGES

CAPACITORATA

RATE

DETER~INED

BY

GRID

BIAS

-I-----4~t------@

SLOPE

MODULATION

INPUT

o

VOLTS

B+r-----

I

~

CD

BLOCKING

OSCILLATOR

;I

CHARGES

CAPACITOR

I

RAPIDLYTOTHE

Bt

I

VOLTAGE

I

I I

I
I
I

VARIABLE

Bt

ADJUSTS

+

A~PLI

TUDE

OF

OUTPUT

SAWTOOTH

B-

...

......-----4....--------J

L0-L-41

Figure

4-5.

Simplified

Circuitofa

Constant

Amplitude,

Variable

Slope Sawtooth

Generator

00144-2

4-5

Section

IV

Paragraphs

4-25to4-27

producingarapid

flyback.

The

chargeonthe

capaci-

tor

biases

the

blocking

oscillator

tube beyond

cutoff

and

prevents

further

operation

until

the

charge

is

removed.

4-26.

The

instant

the

blocking

oscillatorisbiased

to

cutoff,

the

capacitor

beginstodischarge

through

the

pentode

tubeata

rate

determined

by

the

grid

bias.

The

capacitorisdischargedata

linear

rate

due to

the

constant

current

characteristic

of

the

pentode

and

thus

producesanoutput

voltage

with a

linear

slope.

As

the

capacitorisdischarged,

the

grid

biasonthe

blocking

oscillator

returns

toward

cutoff

andatsome

value

the

4-6

Model 492A/494A

tube

conducts

sufficientlytostart

the

blocking

oscilla-

toronanother

cycleofoperation,

thus

again

recharg-

ing

the

capacitor.

4-27.

The

amplitudeofthe

output

sawtooth

waveform

is

adjusted

by

changing

the

regulated

B+

to

vary

the

charge

placed

on

the

capacitor.

The

repetition

rate

or

slopeisadjustedbychanging

the

pentode

grid

bias

to

control

the

rateatwhich

the

capacitorisdischarged.

Modulating

signals

appliedtothe

control

gridofthe

pentode

modify

the

nominal

grid

bias

level

and

change

the

capacitors

discharge

rate,

andinturn,

the

saw-

tooth

slope

and

repetition

rate.

00144-2

)

Mcx:lel

492A/494A

SECTION V

MAINTENANCE

Section V

Paragraphs

5-1to5-6

5-1.

INTRODUCTION.

5-2.

This

section

provides

maintenance

and

service

information

for

Mcx:lels 492A

and

494A

Traveling

Wave

Tube

Amplifiers.

The

section

includes

replacement

procedures

for

tubes,

recommended

test

equipment,

adjustment

procedures,

and

troubleshooting.

This

section

also

includes

performance

checks

which

veri-

fy

proper

instrument

operation.

5-3.

CLEANING

THE

AIR

FILTER.

5-4.

Inspect

the

air

filter

regularly,

and

clean

it

beforeitbecomes

dirty

enough to

restrict

air

flow.

a.

Remove

filter

from

instrument

rear,

and

wash

itinwarm

water

and

detergent.

b.

Dry

filter

thoroughly and

coatitwith

filter

ad-

hesive.

We

recommend

Filter

Coat

No.3

from

Re-

search

Prcx:lucts Company, Inc.

This

adhesive

comes

in

"Handi-Koter"

sprayer

cans

andisavailable

from

most

heating

supply

stores

or

from

your

authorized

Hewlett-Packard

sales

representative.

5-5.

TEST

EQUIPMENT.

5-6.

Test

equipment

recommended

for

useinmain-

taining

and

checking

performanceofthe

Mcx:le1s

492A

and 494A

is

listed

in

table

5-1.

Equipment

having

similar

characteristics

can

be

substituted

for

the

equipment

listed.

)

)

Table

5-1.

Recommended

Test

Equipment

Instrument

Type

Required

Characteristics

Use

Mcx:lel

AC

Voltmeter

Voltage Range: 1.0mvto

1 volt

Power

supply

ripple

~

Mcx:lel

4000

Voltage

Accuracy:

2%

Spurious

mcx:lulation

check

Input Impedance:

10

megohoms

DC

Voltmeter/

Voltage

Range:

to 1000

volts

Power

supply

~

Mcx:lel

4108

Ohmmeter

Voltage

Accuracy:

3%

measurements

Imput Impedance: 100

megohms

Crystal

Detector

Frequency

Range:to12.4

gc

Spurious

mcx:lu1ation

check

~

Mcx:lel

420A

Sensitivity:

approximately

0.1 V

/mw

Power

Meter

Power

Range:

upto10 mw Gain

check

~

Model 430C

Scale

must

readindbm

and

milliwatts

Power

check

Noise

figure

check

DC

Voltage

Division

ratio:

100: 1or3:

1

Power

supply

~

Mcx:lel

459A

Divider

Input Impedance: 12,000

megohms

measurements

Maximum

Voltage:

2000

volts

Thermistor

Mount

Power

Range: to 10 mw Gain

check

~

Mcx:lel

4778

Frequency

Range:to10

gc

Power

check

Noise

figure

check

Signal

Generator

Frequency

Range: 4to12.4 gc

Power

source

for

~

Mcx:lels

6188

Output Amplitude:

at

least

1 mw

performance

checks

620A,626A

Waveguide Coax

SWR

less

than 1.25

With

all

checksat10 gc

~

Mcx:lel

X281A

Adapter

and

above

Waveguide

Power

Range:

to

10 mw Gain

check

~

Mcx:lel

X4878

Thermistor

Mount

Frequency

Range:to12.4

gc

Power

check

Attenuator

10 db

power

attenuation

Power

check

Weinschel

210-10

00144-2

5-1

Section

V

Figure

5-1

Model

492A/494A

SR4----....:;:;..=

S2----f--=-.:::::.!

C2

C1

RT1----...;...:,,...;-d~.:

SR2-----;:'

SR3----

~~-'i..:.-...,---

MEASURETWl

1t:;~~~~}

__

~H~E:A~T:E:R

VOLTAGE

~

R47

ir-------

C8

r-----r.14

C3A/B

V3

~~5.-----V4

---7-r---';O',.....--------C

10

MP-S-5558

Figure

5-1.

Top

ViewofModels

492A

and

494A

00144-2

)

Model 492A/494A

5-1.

REPAIR.

5-8.

CABINET REMOVAL.

5-9.

To

remove

the

instrument

chassis

from

the

cabinet

proceedasfollows:

a.

Place

the twt panel down on a

soft

pad.

b.

Remove

the

two 10-32 round head

machine

screws

which

secure

the

rearofthe

cabinettothe

in-

strument

chassis.

c.

Lift

the

cabinet

up and off

the

chassis.

The

panel

bezel

remains

attachedtothe panel.

5-10.

TUBE

REPLACEMENT.

5-11.Alist

of tubes in the 492A and 494A and

the

checks

and

adjustments

that

mustbemade

following

replacement,

areintable

5-2.

Table

5-2.

Tube

Replacement

List

Tube

Function Adjustment

Type
VI

Series

Regulator

Check

voltage

range

of HELIX

control

(see

sChematic)

Adj. R25ifnecessary

see

paragraph

5-24.

V2

Control

Tube

SameasVI.

V3

Bias

Regulator

Check

range

of GRID

BIAS

control.

V4

Reference

Tube

SameasVI.

V5A,

a.

Helix

Modulator

SameasVI.

B b.

Discharge

Tube

V6

Traveling

Wave

Tube

See

para.

5-12.

5-12.

TRAVELING

WAVE

TUBE CAPSULE

REPLACEMENT.

5-13.

Because

the

traveling

wave tubeisfragile

and

adjustment

of

the

coupling

helicesiscritical,

re-

placement

tubes

are

furnishedinthe

complete

cap-

sule

assembly

which

includes

the tube, coupling

hel-

ices,

coaxial

cables,

and

panel

connectors

complete

in a

single

unit.

Refer

to the

"ConditionsofWar-

ranty"

pageinthe

manual.

5-14.

Special

traveling

wave

tubes

in which gain

has

been

sacrificed

to obtain a

more

constant

output

over

the

full

frequency

range

and a

very

low value of

inci-

dental

amplitude

modulation

during

phase

modulation

are

availableonspecial

order.

5-15.

REMOVAL.

To

remove

the

encapsulated

traveling

wave tube

from

the

492Aor494A

proceed

as

follows:

00144-2

Section V

Paragraphs

5-7to5-16

a.

Remove

the

instrument

from

the

cabinet.

(See

paragraph

5-8.)

b.

Disconnect

the

twt

collector

lead

connector

at

the

rearofthe

capsule,

shown in

figure

5-3.

c.

Remove

the

screws

mounting

the

INPUT and

OUTPUT

connectorstothe

panel.

d.

Loosen

all

the

capsule

alignment

screws.

The

front

alignment

screws

are

shown in

figure

5-2

and

the

rear

alignment

screws

are

shown in

figure

5-3.

e.

Remove

twt plug

from

socket.

This

plug

is

located

on bottom of

instrument.

Refertofigure

5-2.

Grasp

the

rearofthe

capsule

and

carefully

pullitout

of

the

magnet.

5-16.

INSTALLATION

AND

ALIGNMENT.

To

install

and

alignatraveling

wave tube

capsule

proceed

as

follows:

a.

Hold

the

twt

capsule

so

the

recessed

hole

in

collar

is

turned

upward;

insert

the

capsule

into

the

magnet

and be

sure

the

spring-loaded

ball

(bullet

catch)

seats

into

the

recessed

hole.

b.

Plug

the

collector

lead

into

its

connector

as

shown in

figure

5-3.

c.

Reconnect

twt plugtosocket

as

shown in

fig-

ure

5-2.

d.

Turn

the

GRID BIAS

control

completely

clock-

wise

for

the

most

negative

bias

voltage (cathode

posi-

tive);

turn

the

power

ON.Ifnecessary

adjust

R47

to

obtain

correct

heater

VOltage.

Refertotwtdata

sheet

(supplied with new

tubes)

and

figure

5-1.

e.

The

alignment

screws

determine

the

position

of

the

capsule

in the

magnet.

When

the

capsuleiscor-

rectly

positioned

the

helix

current

will be

minimum

(near

zero).

Therefore

the

relative

levelofthe

cur-

rent

flowing in the

helixisan indication of

correct

capsule

positioning.

f. Set

meter

switch

to HELIX.Ifthe

meter

indi-

cationisnear

zero,

thereisinsufficient

current

flow

to

check

the

alignment.

Reduce

the

grid

bias

voltage

until

the

meter

indicates

some

small

readable

helix

current;

at

the

same

time

be

sure

that

the

cathode

current

is

below

its

safe

maximum

for

continuous

operation

after

warmup,

see

table

3-1.

g. Adjust

the

alignment

screwstothe

setting

which

minimizes

the

helix

current.

h.

Reduce

the

cathode

current

with

the

anode

con-

trol

and

turn

the GRID BIAS

controlto0, then

adjust

the

anode

control

to obtain

the

normal

cathode

current

(see

the

meter

plate

that

came

with

the

new tube).

i.

Readjust

the

alignment

screws;

note

the

elec-

trode

currents.

If

any

currents

are

abnormal

see

paragraph

5-30.

j.

Lock

the

alignment

screws,

at

the

same

time

watching

the

metertosee

that

the

helix

current

does

not

increase.

Note

the

meter

reading.

5-3

Section V
Figures

5-2

and

5-3

INPUT
RF CABLE

FRONT

ALIGNMENT
SCREW

Model

492A/494A

PLUG

,'""==----;:!!I---0 UT

PUT

RF

CABLE

FRONT
ALIGNMENT

SCREW

Figure

5-2.

Bottom

View Looking

Towards

the

Front

Panel

of Models 492A and 494A

REAR
ALIGNMENT

SCREW

INPUT

_----,

RF"CABLE

COLLECTOR

LEAD

TWT

CAPSULE

MP-S-I020

REAR
ALIGNMENT

SCREW

5-4

Figure

5-3.

Rear

ViewofModels 492A and 494A

00144-2

)

Model 492A/494A

k.

Remove

the

meter

plate

which

indicates

the

normal

cathode

current

for

the

old tube and

install

the

new

plate.

m.

Perform

the

chassis

Helix

control

adjustment,

see

paragraph

5-24.

n.

Turn

the

power

off and

install

the

cabinet.

p.

Set

the

meter

switch

to

HELIX and

turn

the

power

ON.

The

meter

reading

shouldbethe

same

as

in

stepj;if

not,

the

settingofthe

capsule

was

dis-

turbed

when the

cabinet

was

replaced.

Turn

off

the

power,

remove

the

cabinet,

and

reposition

the

capsule

as

before,

starting

with

stepf.Replace

cabinet;

again

measure

the

cathode

and

helix

currents,

which should

be

the

sameaswith

cabinet

removed.

5-17.

CHANGI G

THE

FREQUENCY RANGE

OFTHE

492A

OR

494A.

5-18.

The

t$j)

Models 492A and 494A

are

identical

ex-

cept

for

the

traveling

wave

tube type

supplied

and

the

operating

voltage

adjustments.

The

proper

range

of

dc

operating

voltages

for

one

tube

typeorthe

other

is

selectedbyS2onthe

instrument

chassis

(figure

5-1).

5-19.

To

change

a 492Atoa 494A

proceedasfollows:

a.

Remove

the

cabinet;

see

paragraph

5-8.

b.

Remove

the

twt

capsule;

see

paragraph

5-15.

c.

Turn

S2tothe

494A position;

see

figure

5-1.

d.

Install

the

typeM2201-K(HPI952-0009)installa-

tion

procedure

is

the

same

as

type M2207-A

except

S2

should

be in 494A

position.

(See

paragraph

5-16.)

5-20.

To

change

a 494A to a 492A

proceedasfollows:

a.

Remove

the

cabinet;

see

paragraph

5-8.

b.

Remove

the twt

capsule;

see

paragraph

5-15.

c.

Turn

S2

to the 492A

position,

see

figure

5-1.

d.

Install

the

typeM2207-A

(HPI952-0012)

installa-

tion

procedure

is

the

sameastype

M2201-K,

except

S2

shouldbein 492A

position.

(See

paragraph

5-16.)

5-21.

ADJUSTMENTS.

5-22.

EXCESSIVE HELIX CURRENT.

5-23.Ifexcessive

helix

current

is

indicated

on

the

front

panel

meter

with

normal

currentsinthe

other

twt

electrodes,

the

electron

beamisnot

being

focused

accurately

through

the

centerofthe

helix.

Measure

the

dc

voltage

and

current

suppliedtothe

magnet

at

115

volt

line,

which shouldbeapproximately

120

volts

at

700

mao

Theacrippleonthe

magnet

supply should

be

less

than 1 volt

rms.

If

these

measurements

do

not

reveal

the

cause

of

the

trouble,

check

the

align-

mentofthe

twt in the

magnet.

See

paragraph

5-16.

00144-2

Section V

Paragraphs

5-23to5-29

5-24.

CHASSIS HELIX CONTROL.

5-25.

The

chassis

Helix

control,

R25,

determines

the

range

of the

front

panel HELIX

controlbygovern-

ing

the output

voltageofthe

regulated

power

supply.

This

adjustment

shouldbeperformed

whenever

a new

twt

capsuleisinstalledorthe

gain of

the

amplifier

is

less

than 30 db.

To

adjust,

proceed

as

follows:

a.

Remove

the

cabinet,

see

paragraph

5-8.

b. Set twt HELIX

controltoposition

5, and

adjust

GRID BIAS

controltoobtain

normal

cathode

current.

c.

Connectatest

setup

as

shown in

figure

5-4.

d. Set the

generator

for

the

Model 492Ato4 gc,

for

the Model 494Ato7 gc.

For

both

models

set

the

generator

attenuator

to

-30

dbm, in cw

operation.

e.

Adjust the

chassis

Helix

control,

R25,

for

maxi-

mum

gain,asreadonthe

430C.

f.

Change

the

frequencyofthe

generator,

for

the

Model 492A to 8 gc,

for

the Model 494Ato12.4 gc,

maintaining

the

same

power

level.

g.

The

430C should

read

greater

than 0

dbm.

If

the

430C

doesn't

read

greater

than 0

dbm,

readjust

the

chassis

Helix

control,

R25, to obtain

from

0 dbm

to

+2

dbm.

Recheck

the

gain

for

the

Model 492A

at

4 gc,

for

the Model 494Aat7 gc, and

readjust

R25,

if

necessary,

to

obtain

nearly

equal

gainatboth

fre-

quencies.

5-26.

ANODE VOLT

AGE

CO

TROL.

5-27.

The

Anode

control,

R30, on the

chassis

of the

instrument,

(see

figure

5-1),isprovidedsothat

the

two

cathode

current

canbemaintainedatits

normal

level

(as

indicated

on

the

plate

attachedtothe

meter

face)asthe

tube

ages.

To

adjust

proceedasfollows:

a.

Place

meter

selector

switchtoCATH.

position

and GRID BIAS

control

to

O.

b.

Rotate

Anode

control

adjust,

R30,

to

obtain

normal

cathode

current.

Also

note

that

other

tube-

element

currents

do not

exceed

their

safe

maximum

limits

(see

table

3-1).

5-28.

REGULATED POWER

SUPPL

Y.

5-29.

To

check

the

regulated

power

supply,

proceed

as

follows:

a.

Set

GRID BIAS

control

to

O.

b.

Connectadc

voltmeter

to

the

output of

the

power

supply,atpin 3 of

VI.

c.

Adjust

the

line

voltage

from

low to high

line

(103 - 127

volts).

Power

supply

voltage

should not

change

more

than 10

volts.

5-5

Section V
Paragraphs

5-30to5-31

d. Connect an

ac

voltmeter

to the output of

the

power

supply,atpin 3 of

VI.

e.

Adjust

the

line

voltage

from

lowtohigh

line

(103 - 127

volts).

Ripple

voltage

should not be

greater

than 7

mv.

5-30.

TROUBLESHOOTING.

5-31.Ifthe

twt

amplifierissuspectedofunsatisfac-

tory

operation,

proceedasfollows:

Model 492A/494A

a.

Remove

all

the

external

connectionstothe

in-

strument

and

set

GRID BIAStozero.

b.

Measure

the

electrode

currentsofthe

twt

using

the

front

panel

meter.

c.Ifthe

electrode

currents

are

abnormal,

remove

the

instrument

from

the

cabinet

(see

paragraph

5-8)

and with

the

indication

observed,

determine

the

possible

cause

and

action

from

table

5-3.

Table

5-3.

Troubleshooting

Chart

Indication

Possible

Cause

Action

Check

Cathode

current

low

Regulated

voltage low

Replace

VI

Table

5-2

Check

regulation

Para.

5-28

Loworno

helix

voltage

Replace

V5

Table

5-2

Low anode voltage

Adjust anode voltage

Para.

5-26

Low twt

emission

Replace

capsule

Para.

5-12

Cathode

current

high

High anode VOltage

Adjust anode voltage

Para.

5-26

Gassy

twt

Replace

capsule

Para.

5-12

Anode

current

high Low

helix

voltage

Adjust

chassis

helix

voltage

Para.

5-24

Replace

V5

Table

5-2

Gassy

twt

Replace

capsule

Para.

5-12

High anode voltage

Adjust anode voltage

Para.

5-26

Helix

current

high

Misalignmentofthe

twt

Align

capsule

Para.

5-16

Collector

current

Low,orno twt

magnet

current

ReplaceF2(iffan

does

not

turn)

low

(low field).

Replace

defective

magnet

power

supply

components.

No

voltageoncollector

(discon-

nectedatconnector),

Fig.

5-3

Noorlittle

control

of High

impedance

path between

the

Replace

capsule

Para.

5-12

Cathode

current

with

anode

and

grid.

May be 40

meg-

GRID BIAS

control.

ohmsormore.

Low gain.

Misadjustment

of anode

voltage.

Adjust anode VOltage

Para.

5-26

The

anode

may

have

been

ad-

justedtoobtain

the

COrrect

cathode

current

with

some

grid

biasonthe

tube.

Wrong

valueofhelix

voltage

Adjust

chassis

helix

voltage

Para.

5-24

Low

cathode

current

See

cathode

current

low

(in

indication

column)

Oscillation

Defective

Helical

Attenuator

Replace

capsule

Para.

5-12

Excessive

cathode

current

See

cathode

current

high

(in

indication

column)

5-6

00144-2

Model

492Aj494A

Section I

Paragraphs

5-32to5-44

5-32.

PERFORMANCE

CHECKS.

5-33.

GAl

CHECK.

5-34.

For

Model 492A

proceedasfollows:

d. Set the two HELIX

control

to

position

5, and

position

the

GRID BIAS

controltofull

counterclockwise.

e.

Adjust

the

output

powerofthe

generator

until

the

430C

reads2miIIiwatts.

a.

Set

the

twt HELIX

controltoposition 5, and

position

the GRID

BIAS

controltofull

counterclockwise.

f.

Repeat

steps

c through e throughout the

fre-

quency band of the twt

amplifier,upto

8 gc.

b. Connect

test

set

up

as

showninfigure

5-4.

c.

Set

the

generator

attenuator

to

-30

dbm, with

a

frequency

output of 4 gc, in cw

operation.

d.

The

430C should

read

greater

than 0

dbm.

5-38.

For

Model 494A

as

for

Model 492A, except,

generatortobe

usedinfigure

5-4tohaveafrequency

range

from7to

12.4 gc, and

the

test

should

start

at

7 gc and endat12.4 gc.

e.

Change

the

frequency

of the

generatorto8 gc,

maintaining

the

same

power

level.

5-39.

NOISE FIGURE CHECK.

f.

The

430C should

read

greater

than 0 dbm.

5-40.

For

Model 492A

proceedasfollows:

a.

Connect

test

set

up

as

shown in

figure

5-4.

5-35.

For

Model 494A

proceedasfor

Model 492A,

except,

generator

to

be

usedinfigure

5-4

to have a

frequency

range

from

7 to 12.4 gc, and

the

test

should

be

madeatthese

frequencies.

b. Set

generator

to 6 gc, in cw

operation.

c.

With

generator

output

power

turned

off,

adjust

the

twt HELIX

control

foramaximum

dbm

indication

on

the

43OC.

Record

this

reading.

5-36.

OUTPUT POWER CHECK.

5-37.

For

Model 492A

proceedasfollows:

a.

Connect

test

set

up

as

shown in

figure

5-4

and

insert

a 10 db

attenuator

between the twt

amplifier

and

the

477B

Thermistor

Mount.

b. Set

the

430Ctothe 3 mw

range.

c.

Set

the

generator

to a

frequency

output of 4 gc,

in cw

operation.

d. With

generator

output

power

turned

on,

adjust

the

generator

attenuator

to obtain a

reading

on

the

430C

thatis3 db

greater

than

that

recordedinstep

c.

e.

Record

the

readingonthe

generator

attenuator

dial.

f.

Take

the

reading

obtainedinstep

e and

sub-

tractitfrom

-78

dbm,

for

the

Model 492A.

The

re-

sultisthe

noise

figure

for

this

492A.

~

MODEL
430C
POWER

METER

~

MODEL
492A/
494A
TWT

AMPLIFIER

~

MODEL

6188/

620A!

626A

SIGNAL

GENERATOR

§]

rg

©

Mo!l

© ©

©

a

©

4778

THERMISTOR

MOUNT

~

0

(0

INPUT

OUTPUT

RF

OUTPUT

(

0 0

RO

)

MODEL

X281A

ADAPTER

MODEL

X4878
THERMISTOR

TO

REPLACE

477B

AT

FREQUENCIES

ABOVE IOGC.

Figure

5-4.

Test

Setup

for

Gain, Output

Power,

and

Noise

Figure

Performance

Checks

00144-2

5-7

Section V

Paragraphs

5-41to5-44

~DEL

618B/
620A/

~DEL

492A/
494A
TWT AMPLIFIER

Model 492A/494A

~DEL

4000

VACUUM

TUBE

VM

626A

SIGNAL

GENERATOR

§]

g

@

!DEV~

© ©

©

a

co

420A

CRYSTAL

DETECTOR

=

(()

~r

OUTPuT

INPUT

ouTPUT

(8)

RF

OUTPUT

(

RO

Figure

5-5.

Test

Setup

for

Hum and

Spurious

Modulation

Performance

Check

5-41.

For

Model 494A

proceed

as

for

Model 492A,

except,

the

generator

to

be

usedinfigure

5-4isto

be

setata

frequencyof9.7

gc.

The

value

from

which

the

attenuator

dial

reading

istobe

subtracted,

is

-76.7

dbm

for

the

Model 494A.

5-42.

HUM

AND

SPURIOUS MOOULATIO CHECK.

5-43.

For

Model 492A

proceedasfollows:

a.

Connect

test

setup

as

shown in

figure

5-5.

b.

Set

the

generatorto8gcand

to

square

wave

modulation,

1000

pps.

5-8

c.

Set

the

twt HELIX

control

to

position

5, and

position

theGRID BIAS

controltofull

counterclockwise.

d. Adjust

the

generator

attenuator

until

the

output

is

indicatedasa

-20

db on

the

4000.

e.

Switch

the

generatortocw

operation.

f.

Record

the

readingonthe

4000.

g.

Take

the

difference,

in

db's,

in

the

readings

in

steps

d and f and add

toit8 db.

The

sum

of

these

two

numbers

should

be

greater

than 45 db.

5-44.

For

Model 494A

proceed

as

for

Model 492A,

except,

the

generator

tobeusedinfigure

5-5isto

be

setata

frequency

of 12.4

gc.

00144-2

8

......

>I>-

>l>-

I

N

J'

I

o~

"41

~

100.

~

8.

CD

.....

>I>-

'0

N

>

'-

>I>-'0>I>-

>

-

II

+

+--IZOY~

:--~--~

I M

...

GNET I

~----

I

..

[!;!!]

~

Slo·eLO

lUCK

J 1

OPAl.

V6

1952-0012

(492A)

1952-0009

(494

A)

TWT

~

=

IOU7PVTI

J>

o 1"·PUTI

W

~--

=~

JS

PIN

JACK

ON

PANEL

FOR

MEASURING

liAS

l..m

1

r-OOZlJ.F

R44

.

3.9k

CI.

2O~'

~

I

S3""'-:.~

__

!3!~"1

-JVV\r--

'.0

'0

'CATHODEI

'00

3301<

.

..

3301(

C13...L

O.IIJ,--r

so

ICOLLECTOR'

~

'.OOE

I

IHELIX'

'.Hood

...

CW(AOJ.FOR

MAX.CATH

CUR)

<2

~~

~

T

.0

<;>

NOTES

l

DC

VOLTAGES MEASURED FROM CHASSIS WITH VTVM.

GRID

BIAS

SET

TO

ZERO.

CH"'$SIS~

CONTROL

SET

TO

CENTER,

II'

VOLT

•

60

I'\;

LINE. VOLTAGES

ADJUSTED

FOR

INDIVIDUAL

V6,

LIMITS

MAY

VARY:t,O

WLTS.

2. UNDERLINED VOLTAGES

ARE

FOR

hp

MODEL

494A.

... VOLTACE RANCE

WHEN

FRONT PANEL HELIX, A21, IS

VARIED

BETWEEN LIMITS

• VOLTACE RANGE WHEN CHASSIS HELIX CONTROL,

RlS,

IS

VARIED BETWEEN LIMITS

1. RESISTANCE

IN

QHMS

UNLESS OTHERWISE NOTED

4

WHEN

REPLACING

V6,

ADJUST

ill

AS

REQUIRED

TO

OBTAIN THE CORRECT

HEATER

VOLTAGE

FOR

v6

.

5 HEAVY

90X

INDICATES

FRONT

PANEL ENGRAVING.

.

..

'.OK

•

••

,"".

V3

C.-l

'''f

OB2

.047~f

SOl(

cw

BIAS

-."

~

RECULATOR

1'12

BIAS

27.

-.,.

l..co C

7...L

(j)

r-.2'~'

,0·~·T

."

,

..

.,.

,..

."

,

..

t-

.16

".

"7

,..

.,.

,

..

."

,

..

"0

,

..

COf'YlIGHl

I'~

IY

HlWlm

PACltAiD CO/llU'ANT

lhlo

....

wl

..

, I.

"'

••

IOlI

...

,

..

1h

••

_

..

Ie

..

.....

_.".,,

__

.1

""wi."

••

do

~

....

'

.OMII

,.

..

••

,....1

__

,.1,...

H

...

'"'"

~

c.

,

,.,.

1

__

vo

'(jJ

AMPERITE

0-

•

1I

C2

'S

IH

~l~'

...,

YELLOW

C,

00\1'

51.

%

-518l21J

I

POWE.j

.,

I.'.

SLO-8LO

,r-------

...

~

P'

;

; /

/

CJ1

I

'0

'-

CJ1

I

......

o

Figure

5-6.

Models

492A and 494A

Traveling-Wave

Amplifiers

'T1

....

UJ

oq

CD

C n

"1

M

CD

....

o

CJ1::l

6-<

Model

492Aj494A

Section

VI

Paragraphs

6-1to6-7

)

SECTION

VI

REPLACEABLE

PARTS

6-1.

INTRODUCTION.

6-4.

ORDERING

INFORMATION.

6-2.

This

section

contains

information

for

ordering

replacement

parts.

Table

6-1

lists

partsinalpha-

numerical

order

of

their

reference

designators

and

indicates

the

description

and ~

stock

numberofeach

part,

together

with any

applicable

notes.

Table

6-2

lists

partsinalpha-numerical

orderoftheir~stock

numbers

and

provides

the

following

information

on

each

part:

6-5.

To

orderareplacement

part,

address

order

or

inquiry

either

to

your

authorized

Hewlett-Packard

sales

representative

or

to

CUSTOMER SERVICE
Hewlett-Packard

Company

395

Page

Mill

Road

Palo

Alto,

California

a.

Descriptionofthe

part

(see

listofabbreviations

below).

b.

Manufacturer

of

the

part

in a

five-digit

code;

see

listofmanufacturersinappendix.

c.

Typical

manufacturer's

stock

number.

d.

Total

quantity

usedinthe

instrument

(TQ

column).

e.

Recommended

spare

part

quantity

for

complete

maintenance

during

one

year

of

isolated

service

(RS

column).

6-3.

Miscellaneous

parts

not

indexedintable

6-1

are

listedatthe

endoftable

6-2.

or,inWestern

Europe,

to

Hewlett-Packard

S.A.

Rue du Vieux

Billard

o. 1

Geneva,

Switzerland.

6-6.

Specify

the

following

information

for

each

part:

a.

Model and

complete

serial

numberofinstrument.

b.

Hewlett-Packard

stock

number.

c.

Circuit

reference

designator.

d.

Description.

6-7.

To

orderapart

not

listedintables

6-1

and

6-2,

giveacomplete

descriptionofthe

part

and

include

its

function

and

location.

A

B

C

CR

DL

DS

E

=

assembly

=

motor

=

capacitor

=

diode

=

delay

line

=

device

signaling

(lamp)

=

misc

electronic

part

F

FL

J
K

L

M

=

fuse

=

filter

=

jack

=

relay

=

inductor

=

meter

REFERENCE

DESIGNATORS

P =

plug

Q =

transistor

R =

resistor
RT=thermistor
S =

switch
T =

transformer

v =

vacuum

tube, neon

bulb,

photocell,

etc.

W =

cable

X =

socket
XF=fuseholder
XV=tube

socket

XDS=lampholder

~

=

bandpass

bwo =

backward

wave

oscillator

c =

carbon
cer=ceramic
cmo=cabinet

mount

only

coef =

coefficient
com=common

comp=composition
conn=connection
crt=cathode-ray

tube

lin=linear

taper

log=logarithmic

taper

m =

milli

= 10- 3

M =

megohms

rna =

milliamperes

minat=

miniature

mfg =

metal

film

on

glass

mfr

=

manufacturer

ABBREVIATIONS

mtg

= mounting

my=mylar

td

=

time

delay

Ti0

2

=

titanium

dioxide

tog=toggle
tol=tolerance
trim=trimmer
twt=traveling

wave

tube

var=variable

wi

= with

W =

watts

ww

=

wirewound

wlo

= without

• =

optimum

value
selectedatfactory,
average

value

shown

(part

may

be

omitted)

rot=rotary
rms=root-

mean-

square

rmo=rack

mount

only

s-

b = slow - blow

Se =

selenium

sect=section(

s)

Si

=

silicon

sl

=

slide

=

normally

closed
= neon
=

normally

open
=

negative

positive

zero-zero

tem-

perature

coeffic

ient

= not

separately

replaceable

nsr

obd =

orderbyde­scription

p

=

peak

pc

=

printed

circuit

board

pf

=

picofarads

=

10-

12

farads

pp

=

peak-

to-

peak

piv

=

peak

inverse

voltage
pos=position(s)
poly =

polystyrene
pot=potentiometer

rect=rectifier

NC

Ne

NO

NPO

elect=electrolytic
encap=

encapsulated

impg=impregnated
incd =

incandescent

ins=insulation

(ed)

h =

henries

Hg =

mercury

Ge=germanium
grd=ground

(ed)

K =

kilo

f =

farads

fxd = fixed

=

deposited

=

detector

=

Tubes

and

transistors

selected

for

best

performance

will

be

suppliedifordered

by

~

stock

numbers;
tubesortransistors
meeting

Electronic

Industries'

Associa-

tion

standards

will

normally

result

in

instrument

operating

within

specifications

EIA

deli

det

co

,

....

0>

0-<
0-<

o

00144-2

6-1

Section

VI

Table

6-1

Table

6-1.

Reference

Designation

Index

Model 492A/494A

Circuit

~

stock

No.

Description

If Note

Reference

B1

3140-0010

Motor,

AC

B1A

3160-0014

Fan

blade

C1, 2

0180-0025

fxd,

elect,4sect,

20

j.L

f/sect,

450 vdcw

C3AB

0180-0012

fxd,

elect,2sect,

20

jJf/sect,

450 vdcw

C4,

5

0160-0082

fxd,

paper,

4

j.Lf

±1O%,

1000 vdcw

C6

0160-0097

fxd,

paper,

0.25

j.Lf

±1O%,

2000 vdcw

C7

0160-0037

fxd,

paper,

0.04

j.Lf

±20%, 1600 vdcw

C8, 9

0160-0005

fxd,

paper,

0.047

j.Lf

±10%, 600 vdcw

C10

0160-0037

fxd,

paper,

0.04

j.Lf

±20%,

1600 vdcw

C11

0150-0023

fxd,

cer,

0.002

j.Lf

±20%, 1000 vdcw

C12

0160-0040

fxd,

paper,

0.01

j.Lf

±1O%,

1000 vdcw

C13

0160-0001

fxd,

paper,

0.1

j.Lf

±10%, 600 vdcw

C14

0180-0011

fxd,

elect,

20

j.Lf,

450 vdcw

C15

490A-82

Cathode

Bypass

Assembly:O.002

j.Lf

DS1

2140-0009

Lamp,

incd: 6-BV,O.15

amp,

#47

F1,

2

2110-0005

Fuse,

cartridge:

1.6

amp

s-b

J1

1250-0083

Connector,

BNC:

female

J2,3

nsr;

part

of V6

J4

1250-0083

Connector,

BNC:

female

J5

1251-0073

Jack,

telephone

tip:

for

single

conductor

J6

1251-0027

Connector,

female

L1

9110-0019

Choke: 1

H

M1

1120-0060

Meter:

ammeter

P1

8120-0015

Power

cable

P2

thru

P5

Not

Assigned

R1

0690-2231

fxd,

comp,

22K

ohms

±10%, 1 W

R2

0693-4731

fxd,

comp,

47K

ohms

±10%, 2 W

R3

0690-4701 fxd,

comp,

47

ohms

±10%, 1 W

R4

0690-3941 fxd,

comp,

390K

ohms

±1O%,

1 W

R5

0690-3341 fxd,

comp,

330K

ohms

±10%, 1 W

R6

0690-8251

fxd,

comp,

8. 2M

±1O%,

1 W

R7

0690-2251

fxd,

comp,2.2M

±1O%,

1 W

R8

0690-1521 fxd,

comp,

1500

ohms

±10%, 1 W

R9

0690-3941

fxd,

comp,

390K

ohms

±10%,

1 W

R10

0687-1051

fxd,

comp,

1M ±10%,

1/2

W

R11 2100-0044

var,

comp,

lin,

50K

ohms

±10%

R12

0690-2731

fxd,

comp,

27K

ohms

±10%, 1 W

# See

introductiontothis

section

6-2

00144-2

Model 492A/494A

Section

VI

Table

6-1

Table

6-l.

Reference

Designation

Index

(Cont'd)

Circuit

<FiJ

stock

No.

Description*

Note

Reference

R13,14

,

15

0693-1831 fxd

,

comp,

18K

ohms

±10%, 2 W

R16

,

17

0693-1531 fxd,comp,

15K

ohms

±10%, 2 W

R18

,

19

,

20

0693-1831

fxd

,

comp,

18K

ohms

±10%, 2 W

R21

0693-2241

fxd

,

comp,

220K

ohms

±1O%,

2 W

R22

0693-1541 fxd

,

comp,

150K

ohms

±10%, 2 W

R23

0693-1841

fxd

,

comp,

180K

ohms

±1O%,

2 W

R24

0690-6831

fxd

,

comp,

68K

ohms

±10%, 1 W

R25

2100-0044

var1comp,

lin

,

50K

ohms

±10%

R26

0690-8231 fxd

,

comp,

82K

ohms

±10%, 1 W

R27

2100-0133

var1comp,

200K

ohms

±20%, 2 W

R28

0690-5641

fxd

,

comp,

560K

ohms

±1O%,

1 W

R29

0690-6831

fxd

,

comp,

68K

ohms

±10%, 1 W

R30

2100-0043

var1comp,

lin

,

500K

ohms

±10%

R31

0690-4721

fxd

,

comp,

4.7K

ohms

±1O%,

1W

R32

0687-1051

fxd

,

comp,

1M ±10%,

1/2

W

R33

0687-4741 fxd

,

comp,

470K

ohms

±1O%,

1/2

W

R34

0690-6821 fxd,

comp,

6800

ohms

±1O%,

1 W

R35

,

36

0690-3341 fxd,comp,

330K

ohms

±1O%,

1 W

R37

thru

R40

492A-26A fxd,

ww

1 50

ohms

R41

0690-1041 fxd

,

comp,

lOOK

ohms

±10%,

1W

"

R42

,

43

Not

Assigned

R44

0690-3921

fxd

,

comp,

3900

ohms

±10%, 1 W

R45

0693-1211

fxd

,

comp,

120

ohms

±10%, 2 W

R46

Not

Assigned

R47

0693-4701

*

fxd,comp,47ohms

±5%,

2 W

RT1

0852-0003

Ballast

tube,

Amperite

type

6-4

Sl

3101-0003

SWitch,tog:

DPST

S2

3100-0055

SWitch

,

rot:

4

pole

,

2

pos

S3

3100-0099 Switch,rot:

1

sect

,

4

pos

SR1

1882-0007

Rectifier,metallic:

620 rna

SR2

,

3

1880-0007

Rectifier

,

metallic:

1430 V

SR4

1880-0003

Rectifier,metallic:

130 V

T1

9100-0109

Transformer1power

V1

1923-0026

Tube

,

electron:

6BG6

V2

1923-0021

Tube

,

electron:

6AU6

V3

1940-0007

Tube

,

electron:

OB2

V4

1940-0004 Tube

,

electron:

OA2

)

# See

introductiontothis

section

00144-2

6-3

Section

VI

Table

6-1

Table

6-1.

Reference

Designation

Index (Cont'd)

Model 492A/494A

Circuit

r[j>

stock

No.

Description

'if

Note

Reference

V5

1932-0021

Tube,

electron:

6BQ7A

V6

1952-0012

encap

TWT, (492A only)

includes

.12,

3

1952-0009

encap

TWT, (494A only)

includes

.12,

3

MISCELLANEOUS

G-74D

Knob:

METER

SELECTOR

switch

G-74N

Knob: CATH. COL.

1200-0009

Socket, tube:

7

pin

1200-0020

Socket,

tube:

octal

1251-0044

Connector:

female

and

male

contacts

1400-0084

Fuseholder

1401-0006

Clip,

tube:

plate

and

grid,

cer,

ins

1450-0027

Lamp

holder,

bayonet

type

3150-0005

Filter,

air:

6X6"

9161-0005

Solenoid

Assembly

'if

See

introductiontothis

section

6-4

00144-2

Model

492A/494A

Table

6-2.

Replaceable

Parts

Section

VI

Table

6-2

)

~stockNo.

Description

#

Mfr.

Mfr.

Part

No.

TQ

RS

490A-82

Cathode

Bypass

Assembly:O.002 Ilf

28480 490A-82

1

1

492A-26A fxd,

WW,

50

ohms

28480 492A-26A

4

1

0150-0023

fxd,

cer,

0.002

Ilf ±20%, 1000 vdcw

91418

JF.002

1 1

0160-0001

fxd,

paper,O.11lf

±1O%,

600 vdcw

56289

160P10496

1 1

0160-0005

fxd,

paper,

0.047

Ilf ±10%, 600 vdcw

56289 160P47390

2

1

0160-0037

fxd,

paper,

0.04

Ilf ±20%, 1600 vdcw

14655

ST16S4-20

2 1

0160-0040

fxd,

paper,O.011lf

±1O%,

1000 vdcw

14655

TST-100

1 1

0160-0082

fxd,

paper,

4 Ilf

±1O%,

1000 vdcw

00656

JP09

2

1

0160-0097

fxd,

paper,

0.25

Ilf ±lO%, 2000 vdcw

00656 2009

1 1

0180-0011

fxd,

elect,

20 Ilf, 450 vdcw

56289

D32550

1 1

0180-0012

fxd,

elect,2sect,

20

Ilf/sect,

450 vdcw

00853

LPI

(obd)

1

1

0180-0025 fxd,

elect,4sect,

20

Ilf/sect,

450 vdcw

56289 D32452

2 1

0687-1051

fxd,

comp,

1M ±10%,

1/2

W

01121

EB-1051

2 1

0687-4741

fxd,

comp,

470K

ohms

±lO%,

1/2

W

01121

EB-4741

1

1

0690-1041

fxd,

comp,

lOOK

ohms

±10%,

1W

01121

GB-1041

1 1

0690-1521

fxd,

comp,

8.2M

±lO%, 1 W

01121

GB-1521

1 1

0690-2231

fxd,

comp,

22K

ohms

±10%, 1 W

01121

GB-2231

1

1

0690-2251

fxd,

comp,

2.2M±10%,

1W

01121

GB-2251

1 1

0690-2731

fxd,

comp,

27K

ohms

±10%, 1 W

01121

GB-2731

1

1

0690-3341

fxd,

comp,

330K

ohms

±lO%, 1 W

01121

GB-3341

3 1

0690-3921

fxd,

comp,

3900

ohms

±1O%,

1 W

01121

GB-3921

1 1

0690-3941

fxd,

comp,

390K

ohms

±lO%, 1 W

01121

GB-3941

2 1

0690-4701

fxd,

comp,47ohms

±10%, 1 W

01121

GB-4701

1

1

0690-4721

fxd,

comp,

4.7K

ohms

±10%, 1 W

01121

GB-4721

1 1

0690-5641

fxd,

comp,

560K

ohms

±1O%,

1 W

01121

GB-5641

1 1

0690-6821

fxd,

comp,

6800

ohms

±1O%,

1 W

01121

GB-6821

1 1

0690-6831

fxd,

comp,

68K

ohms

± 10%, 1 W

01121

GB-6831

2

1

0690-8231

fxd,

comp,

82K

ohms±10%,

1 W

01121

GB-8231

1 1

0690-8251

fxd,

comp,

8.2M

±10%, 1 W

01121

GB-8251

1

1

0693-1211

fxd,

comp,

120

ohms

±10%, 2 W

01121 HB-1211

1

1

0693-1531

fxd,

comp,

15K

ohms

±10%, 2 W

01121 HB-1531

2 1

0693-1541

fxd,

comp,

150K

ohms

±lO%, 2 W

01121

HB-1541

1 1

0693-1831

fxd,

comp,

18K

ohms

±10%, 2 W

01121 HB-1831

6

2

0693-1841

fxd,

comp,

180K

ohms

±lO%, 2 W

01121 HB-1841

1 1

0693-4701~fxd,

comp,47ohms

±5%,

2 W

01121 HB-4701

1

1

0693-4731

fxd,

comp,

47K

ohms

±10%, 2 W

01121 HB-4731

1 1

0852-0003

Tube,

ballast:

Amperite

type

6-4

70563

6-4

1 1

# See

introductiontothis

section

00144-2

6-5

Section

VI

Table

6-2

Table

6-2.

Replaceable

Parts

(Cont'd)

Model 492A/494A

~stockNo.

De

scription

ti

Mfr.

Mfr.

Part

No.

TQ

RS

1120-0060

Meter:

ammeter

55026

Model 182 1 1

1250-0083

Connector,

BNC:

female

91737

UG-1094/U

2

1

1251-0027

Connector,

female

08145 1700D

1

1

1251-0073

Jack,

telephone

tip:

for

single

conductor

74970 105-521

1

1

1880-0003

Rectifier,

metallic:

130 V

84970 Model

65

1 1

1880-0007

Rectifier,

metallic:

1430 V

89473

6RS2OGH55TED1

2 2

1882-0007

Rectifier,

metallic:

620

rna

89473 6RS22GB5BFD1

1

1

1923-0021

Tube,

electron:

6AU6

33173

6AU6

1 1

1923-0026

Tube,

electron:

6BG6

86684 6BG6

1 1

1932-0021

Tube,

electron:

6BQ7A

86684 6BQ7A

1 1

1940-0004

Tube,

electron:

OA2

86684

OA2

1 1

1940-0007

Tube,

electron:

OB2

86684 OB2

1 1

1952-0009

Encapsulated

TWT (494A only)

includes

J2,

3

11312 M2201-K

1 1

1952-0012

Encapsulated

TWT (492A only)

includes

J2,

3 11312 M2207

1

1

2100-0043

var,

comp,

lin,

500K

ohms

±10%

01121 JA4N0568504UA

1 1

2100-0044

var,

comp,

lin,

50K

ohms

±10%

01121

JA1N0565503UA 2

1

2100-0133

var,

comp,

200K

ohms

±20%, 2 W

11237 95CV

1 1

2110-0005

Fuse,

cartridge:

1.6

amp

s-b

71400

MDL1.6

2 20

2140-0005

Lamp,

incd: 6-8V,

0.15

amp,

#47

24455 #47

Frosted

1

1

3100-0055

Switch,

rot:4pole,2pos

76854

47809-F2

1 1

3100-0099

Switch,

rot:

1

sect,4pos

76854 161711-H1

1 1

3101-0003

Switch, tog:

DPST

88140 8908K434

1

1

3140-0010

Motor,

AC

73793

G5-CW-

ER-6667

1 1

3160-0014

Fan

blade

06812

(obd)

1 1

8120-0015

Power

cable

70903

KH

3981/PH70/7.

5ft

1 1

9100-0015

Transformer,

power

98734 8656 1 1

9110-0019

Choke, 1 h

98734

1010

1

1

MISCELLANEOUS

G-74D Knob:

METER SELECTOR

switch

28480

G-74D

1 0

G-74N

Knob:

Cath.

COL.

28480

G-74N

1 0

1200-0009 Socket,

tube:7pin

91662 316PH-3702 1 1

1200-0020

Socket,

tube:

octal

71785 51A12272 1 1

1251-0044

Connector:

female

and

male

contacts

OOOOL

PM6S

1 1

1401-0084

Fuseholder

75915

342014

2

1

1401-0006 Clip tube:

plate

and

grid,

cer

ins

76487 36002

1 0

1450-0027

Lamp

holder,

bayonet

type

72619 81OB-1

1

1

3150-0005

Filter,

air:

6X6"

82866 806340 1 0

9161-0005 Solenoid

assembly

98734 5016

1 1

# See

introductiontothis

section

6-6

00144-2

Model

492Aj494A

Appendix

APPENDIX

CODE

LIST

OF

MANUFACTURERS (Sheet 1

of

2)

The following

code

numbers are from

the

Federal Supply

Code

for Manufacturers Cataloging Handbooks

H4-1

(NametoCode)

and H4-2 (Code

to

Name) and their latest supplements. The

date

of revision and

the

dateofthe

supplements used

appear

at

the

bottomofeach

page.

Alphabetical codes have been arbitrarily assignedtosuppliers not appearingintheH4handbooks.

CODE

NO.

MANUFACTURER

ADDRESS

CODE

NO.

MANUFACTURER

ADDRESS

CODE

NO.

MANUFACTURER

ADDRESS

Fullerton,

Calif.

Quincy,

Mass.

Cleveland,

Ohio

Paramus,

N.J.

Precision

Thermometer

and

Inst.

Co.

Philadelphia,

Pa.

Raytheon

Company

Lexington, Mass.

Shallcro..Mfg.

Co.

Selma,

N.C.

Simpson

Electric

Co.

Chicago,

III.

Sonotone

Corp.

Elmsford, N.Y.

Sorenson

& Co., Inc. So. Norwalk,

Conn.

Spaulding

Fibre

Co.,

Inc.

Tonawanda,

N.Y.

Sprague

Electric

Co.

North

Adams,

Mass.

Telex, Inc. St. Paul, Minn.

Union Switch

and

Signal,

Div.

of

Westinghouse

Air Brake

Co.

Swissvale, Pa.

Universal Electric

Co.

Owosso, Mich.

Western

Electric

Co., Inc. New York, N.Y.

Weston

Inst. Diy.ofDaystrom, Inc.

Newark,

N.J.

Wollensak

Optical

Co.

Rochester, N.Y.

Allen Mfg.

Co.

Hartford,

Conn.

Allied

Control

Co.,

Inc. New York, N.Y.

Atlantic

India

Rubber

Works, Inc.

Chicago,

III.

New York, N.Y.

Chicago,

III.

Cleveland,

Ohio

New York, N.Y.

JohnE.Fast&Co.
Dialight

Corp.

General

Ceramics

Corp.
Girard-Hopkins
Drake Mfg.

Co.

Hugh

H. Eby Inc.

Gudeman

Co.

Erie Resistor

Corp.

Hansln

Mfg.

Co.,

Inc.

Helipot

Div.ofBeckman

Instruments,

Inc.

Hughes

Products

Division

of

Hughes

Aircraft

Co.

Newport

Beach,

Calif.

Ampere.

Electronic

Co., Diy.

of

North

Americ"an Phillips

Co.,

Inc.

Hicksville, N.Y.

Bradley

Semicondudor

Corp.

Hamden,

Conn.

Carling

Electric, Inc.

Hartford,

Conn.

GeorgeK.Garre",

Co., Inc.

Philadelphia,

Pa.

Cincinnati,

Ohio

Elyria,

Ohio

San

Jose,

Calif.

Winchester,

Mass.

Fischer

Special

Mfg.

Co.

The

General

Industries

Co.

Jennings

Radio

Mfg.

Co.

J.

H. Winns,

and

Sons

48

6 2 0

49

9 5 6

54294

55026

55933
55938

56t37

562

B9
59446
61775

71218
71

286

71313

70563
70903
70998
71002
71

041

621

1 9

649

5 9

65092
66346

70276
70309
7048

5

71450
71468
71471
71482

71

52

B

7 1 7 B 5

Cinch

Mfg.

Corp.

7 1

984

Dow

Corning

Corp.

72136

Electro

Motive

Mfg.

Co.,

Amperite

Co.,

Inc.

Bolden Mfg.

Co.

Bird

electronic

Corp.

Birnbach

Radio

Co.

80ston

Gear

Works

Diy.

of

Murray Co.ofTexas

Bud

Radio

Inc.

Camloc

Fastener

Corp.

AllenO.Cardwell

Electronic

Prod.

Corp.

Plainville,

Conn.

71

40aBunmann

Fuse Div.ofMcGraw.

Edison Co. St. Louis, Mo.

CTS

Corp.

Elkhart,

Ind.

Cannon

Electric

Co.

Los

Angeles,

Calif.

Cinema

Engineering

Co. Burbank,

Calif.

C.P.Clare&Co.

Chicago,

III.

Standard·Thomson

Corp.,

Clifford

Mfg.

Co.

Div.

Waltham,Ma...

71

590

Centralab

Div.ofGlobe

Union Inc.

Milwaukee, Wis.

71

700

The

Cornish

Wire

Co.

New York, N.Y.

7 1

744

Chicago

Miniature

lamp

Works

Chicago,

III.

7

I

753A.O.

Smith

Corp.,

Crowl~e~;V6range,

N.J.

Chicago,

III.

Midland,

Mich.

Inc.
Willimantic,

Conn.

Chicago,

III.

Brooklyn, N.Y.

Keasbey,

N.J.

Oakland,

Calif.

Chicago,

III.

Philadelphia,

Pa.

Chicago,

III.

Erie, Pa.

Princeton,

Ind.

73

29

3

73

445

73

5 0 6

73

5 5 9

73

6B 2

73743

73793

73905
7445

5

723

5 4

72

619
72656
72758
72765
72B25
729

2 8

72982

73

0

61

73138

Teterboro,

N.J.

General

Electric

Co.

G.E.,

Lamp

Division

Nela

Park,

Cleveland,

Ohio

General

Radio

Co.

Wist

Concord,

Mass.

Grobet

File

Co.ofAmerica,

Inc.

Carlstadt,

N.J.

Hamilton

Watch

Co.

Lancaster,

Pa.

Hewlett-Packard

Co.

Palo

Alto,

Calif.

G.E.

Rlceivin9

Tube

Dept.

Owensboro,

Ky.

lectrohm

Inc.

Chicago,

III.

P.R.Mallory&Co.,

Inc.

Indianapolis,

Ind.

Mechanical

Industries

Prod.

Co.

Akron,

Ohio

Miniature

Precision Bearings, Inc.

Keone,

N.H.

Chicago,

III.

Englewood,

Colo.

Skokie, III.

Cambridge,

Mass.

Muter

Co.

C.A.Norgren

Co.

Ohmite

Mfg.

Co.

Polaroid

Corp.

09026
091

34
09250
09569

40920

10411
10646
11236
11237

24446
24455

1171

7

1 1

870
12697
146

5 5

a7 1

17

Transistor Electronics

Corp.

Minneapolis,

Minn.

07138

Westinghouse

Electric

Corp.

Electronic

Tube

Div. Elmira, N.Y.

07261Avnet

Corp.

Los

Angeles,

Calif.

a7 2

'3

Fairchild

Semiconductor

Corp.

Mountain

View,

Calif.

a7 9 1 a

Continental

Device

Corp.

Hawthorne,

Calif.

a7 9 1 3

Rhelm

Semiconductor

Corp.

Mountain

View,

Calif.

07980

Boonton

Radio

Corp.

800nton,

N.J.

08145

U.S.

Engineering

Co.

los

Angeles,

Calif.

083

5 B Burge..Battery

Co.

Niagara

Falls,

Ontario,

Canada

oB

717Sloan

Company

Burbank,

Calif.

08718Cannon

Electric

Co.

Phoenix Div. Phoenix,

Aril.

a8 7 9 2 CBS

Electronics

Semiconductor

Operations,

Div.ofC.B.S. Inc.

Lowell, Mass.

Babcock

Relays, Inc.

Costa

Mesa,

Calif.

Texas

Capacitor

Co.

Houston,

Texas

Electro

Assemblils,

Inc.

Chicago,

Ill.

M~~o::d~~tt.~J:

CO'T:~onto,

Ontario,

Canada

Ti·Tal, Inc. Berkeley,

Calif.

Carborundum

Co.

Niagara

Falls, N.Y.

CTS

of

Borne, Inc. Berne,

Ind.

Chica90

TelephoneofCalifornia,

Inc.

So.

Pasadena,

Calif.

1 1312

Microwave

Electronics

Corp.

Palo

Alto,

Calif.

1 1

71

1

General

Instrument

Corporation

Semiconductor

Division Newark,

N.J.

Imperial

Electronics, Inc. Buena Park,

Calif.

Melabs,

Inc. Palo

Alia,

Calif.

Clarostat

Mfg.

Co.

Dover,

N.H.

Cornell

Dubilier

Elec.

Corp.

So.

Plainfield,

N.J.

1

5909

The Daven

Co.

livingston,

N.J.

1

675

B Delco

Radio

Div.ofG.M.Corp.

Kokomo, Ind.

1 8 B7 3

E.

I. DuPont

and

Co.,

Inc.

Wilmington,

Del.

1

931

5 Eclipse

Pioneer,

Div.

of

Bendix

Aviation

Corp.

I

9500

Thomas A. Edison Industries,

Div.

of

McGraw-Edison

Co.

West

Orange,

N.J.

Electra

Manufacturing

Co.

Kansas

City,

Mo.

Electronic

Tube

Corp.

Philadelphia,

Pa.

Fanst.el

Metallurgical

Corp.

No.

Chicago,

III.

2 1

335

The Fafnir Bearing

Co.

New Britain,

Conn.

21

964

Fed.

Telephone

and

Radio

Corp.

Clifton,

N.J.

Schenectady,

N.Y.

19701
201

83

21

520

246

5 5

26462

26992

2848

0

131

73

35

4 3 4

37942
39

5

43

421

90

439

9 0

446

5 5

47904

Colton,

Calif.

New York, N.Y.

Culver

City,

Calif.

Northlake,

III.

Chicago,

III.

Humidial

Co.

Westrex Corp.

Garlock

Packing

Co.,

Electronic

Products

Div.

Camden.

N.J.

A.rovol

Corp. New Bedford,

Man.

Amp,

Inc.

Harrisburg,

P,.

Aircraft

Radio

Corp.

Boonton,

N.J.

S.ng.mo

Electric Company,

Ordill

Division

(Capacitors)

Marion,

III.

Go.

Engine.ring

Co.

Los

AnQlles,

Calif.

CarlE.Holmes

Corp.

los

Angeles,

Calif.

Allen Bradley

Co.

Milwaukee,

Wis.

Litton Industries, Inc. Beverly Hills,

Calif.

Pacific

Semiconductors,

Inc.

Culver

City,

Calif.

Radio

Corp.

of America

Semiconductor

and

Materials

Div.

Somerville,

N.J.

Vocaline

Co.

of

America,

Inc.

Old

Saybrook,

Conn.

Hopkins

Engineerin9

Co.

San

Fernando,

Calif.

G.E.

Semiconductor

Products

Dept.

Syracuse, N.Y.

Apex

Machine

& Tool

Co.

Dayton,

Ohio

Eldema

Corp.

EI

Monte,

Calif.

Transitron

Electronic

Corp.

Wakefield,

Mass.

Pyrofilm Resistor

Co. Morristown,

N.J.

Air

Marine

Motors,

Inc. Los

Angeles,

Calif.

Arrow,

Hart

and

Hegeman

Elect.

Co.

Hartford,

Conn.

Elm.nco

Products

Co.

New York, N.Y.

Hi-Q

DivisionofAerovox Myrtle Boach, S.C.

Eltl:c~r~t~icnsaID~is~~~

Co.,

Burbank,

Calif.

Dymec Division

of

Hewlett-Packard

Co.

Palo

Alto,

Calif.

Sylvania Electric Prods., Inc.

Electronic

Tube

Div.

Mountain

View,

Calif.

Motorola,

Inc.,

Semiconductor

Prod. Div. Phoenix,

Arilona

Filtron

Co.,

Inc.

Western

Division

Automatic

Electric

Co.

PM

Motor

Co.

Twentieth

Century

Plastics, Inc.

Los

Angeles,

Calif.

Westinghouse

Electric

Corp.,

Semi·Cbnductor

Dept.

Youn9wood,

Pa.

Illumitronic

Engineering

Co.

Sunnyvale,

Calif.

Barber

Colman

Co.

Rockford, III.

Metropolitan

Telecommunications

Corp.,

Metro

Cap.

Di..

Brooklyn, N.Y.

Stewart

Engineerin9

Co.

Santa

CruI,

Calif.

TheBa..

ick

Co.

Bridgeport,

Conn.

Beede

Electrical

Instrument

Co., Inc.

Penacook,

N.H.

Torrington

Mfg. Co.,

West

Div.

Van Nuys,

Calif.

00656

00779

00781
00853

00334

00335

00373

00866
00891

01121
01255
01

281

02735

02771
02777

04404

04651

0471

3

01295

Texas

Instruments,

Inc.

Transistor Products

Diy.

Dallas,

Tu.s

01

349

The

Alliance

Mfg.

Co.

Alliance,

Ohio

01

561

Cha..i-Trak

Corp.

Indianapolis,

Ind.

01

589

Pacific

Relays, Inc. Van Nuys,

Calif.

o1

930

Amerock

Corp.

Rockford, III.

019'

1 Pulse

Engine.ring

Co. Santa

Clara,

Calif.

021,..

Ferrolcub.

Corp.

of

America

Saugerties,

N.Y.

022B6Cole

Mfg.

Co.

Palo

Alia,

Calif.

02660

Amphenol·Borg

Electronics

Corp.

Chicago,

III.

047

73

048

7 0

05006
05277

05624
05729

05783
06004
06555

06812

03508

03705
03797
038

7 7

038

8 8

039

5 4

04009
04062

042

2 2

0429

8

05593

047

3 2

071

1 5

Corning

Glass

Works

Electronic

Components

Oept.

Bradford,

Pa.

Paudena,

Calif.

o7 1 2 6

Digitran

Co.

)

)

00015·19

Reviled:,December

1961

From:

F.S.C.

Handbook Supplements

H4-1

Dated October

1961

H4-2

Dated November

1961

00144-2

i-I

Appendix

Model

492A/494A

APPENDIX

CODE

LIST

OF MANUFACTURERS (Sheet 2

of

2)

CODE

NO.

MANUFACTURER

ADDRESS

CODE

NO.

MANUFACTURER

ADDRESS

CODE

NO.

MANUFACTURER

ADDRESS

Attleboro,

Mass.

Madison,

Wis.

Evanston, III.

Yonkers, N.Y.

New York, N.Y.

Waltham,

Mass.

Versailles,

Ky.

Providence,

R.1.

Palo

Alto,

Calif.

Mineola,

N.Y.

Burbank,

Calif.

New York, N.Y.

Palo

Alto,

Calif.

Chicago,

III.

Chicago,

III.

Sunnyvale,

Calif.

Olean,

N.Y.

Mt.

Carmel,

III.

los

Angeles,

Calif.

Chicago,

III.

Burlington, Mass.

Oakland,

Calif.

Danvers,

Mass.

Jamaica,

N.Y.

Pasadena,

Calif.

So.

Pasadena,

Calif.

Mamaroneck,

N.Y.

Redwood

City,

Calif.

Methode

Mfg.

Co.

Weckesser

Co.

Huggins

laboratories

Hi-Q

DivisionofAerovox

Thordarson-Meissner

Div.

of

Maguire

Industri-.s. Inc.

Solar

Manufacturing

Co.

Carlton

Screw

Co.

Microwave

Associates,

Inc.

Excel

Transformer

Co.

Automatic

and

Precision

Mfg.

Co.

CBS

Electronics,

Div. of C.B.S., Inc.

Axel Brothers Inc.

Francis

l.

Mosley

Microdot,

Inc.

Sealectro

Corp.

Carad

Corp.

Palo

Alto

Engineering

Co.,

Inc.

North

Hills

Electric

Co.

Clevite

Transistor

Prod.

Div.ofClevite

Corp.

International

Electronic

Research

Corp.

Columbia

Technical

Corp.

Varian

Associates

Marshall

Industries,

Electron

Products

Division

Pasadena,

Calif.

Control

Switch Division,

Controls

Co.

of

America

EI

Segundo,

Calif.

Delevan

Electronics

Corp.

East

Aurora,

N.Y.

Wileo

Corporation

Indianapolis,

Ind.

Renbrandt,

Inc. Boston, Mass.

Hoffman

Semiconductor

Div.

of

Hoffman

Electronics

Corp.

Technology

Instrument

Corp.

of

Calif.

Newbury

Park,

Calif.

96296
96

3 3 0

96341

96

5 0 1

97539

981

41
98220
98278
98291
98405
98734

95354
95987

96

0 6 7

96

0 9 5

96

2

56

97966

98821
98925

98978

99109
99

3 1 3

99

515

99

9 5 7

99

7 0 7

99

8 0 0
99848
99

9

34

99942

0000

N

OOOOP
OOOOT

THE

FOLLOWING

H·P

VENDORS HAVENONUM.

BER

ASSIGNEDINTHE

LATEST

SUPPLEMENT TO

THE FEDERAL SUPPLY

CODE

FOR MANUFACTURERS

HANDBOOK.
0000FMalco

Tool

and

Die Los

Angeles,

Calif.

a a a a J Telefunken

(c/o

American

Elite)

a a a a L

Winchester

Electronics,

Inc.

Santa

Monica,

Calif.

a a a a M

Western

Coil

Div.ofAutomatic

Ind.,

Inc.

Redwood

City,

Calif.

Nahm-Bros.

Spring

Co.

San

leandro,

Calif.

Ty·Car

Mfg.

Co.,

Inc.

Holliston,

Mass.

Texas

Instruments,

Inc.

Metals

and

Controls

Div.

0000

U Tower

Mfg.

Corp.

a a a a W

Webster

Electronics

Co.

Inc.

Now York, N.Y.

a a a 0 X

Spruce

Pine

Mica

Co.

Spruce

Pine,

N.C.

0000YMidland

Mfg.

Co.

Inc. Kansas

City,

Kans.

0000ZWillow

Leather

Products

Corp.

Newark,

N.J.

000

A A 8ritish

Radio

Electronics

Ltd.

Washington,

D.C.

oa a B B Precision

Instrument

Components

Co.

Van Nuys,

Calif.

000

C C

Computor

Diodo

Corp.

Lodi,

N.J.

a 0

aDD

General

Transistor

los

Angeles,

Calif.

a a 0 E EA.Williams

Manufacturing

Co.

San

Jose,

Calif.

a a a F F

Carmichael

Corrugated

Specialties

Richmond,

Calif.

a a a G G

Soshen

Die

Cutting

Service

Goshen,

Ind.

Plainfield,

N.J.

Loveland,

Colo.

Newark,

N.J.

Huntington,

Ind.

Festus, Mo.

New York, N.Y.

Rotron

Manufacturing

Co.,

Inc.

Woodstock,

N.Y.

Glendale,

Calif.

Cambridge,

Mass.

Darlington,

S.C.

Los

Angeles,

Calif.

Union,

N.J.

Red Bank,

N.J.

8rooklyn, N.Y.

Vector

Electronic

Co.

Carr

Fastener

Co.

Pyramid

Electric

Co.

Electro

Cords

Co.

Victory

Engineering

Corp.

Bendix

Corp.,

Red Bank Div.

Smith,

Herman

H., Inc.

Gavitt

Wire

and

Cable

Co.,

Div.ofAmerace

Corp.

Brookfield, Mass.

Burroughs

Corp.,

Electronic

Tube

Div.

Model

Eng.

and

Mfg.,

Inc.

Loyd

Scruggs

Co.

Arco

Electronics,

Inc.

A.

J.

Glesener

Co.,

Inc.

San

Francisco,

Calif.

Good

All

Electric

Mfg.

Co.

Ogallala,

Neb.

Sarkes

Tanian,

Inc.

Bloomington,

Ind.

Boonton

Molding

Company

Boonton,

N.J.

R.M.Bracamonte&Co.

San

Francisco,

Calif.

New

Haven,

Conn.

Chicago,

III.

Tung-Sol

Electric,

Inc.

Curtiss-Wright

Corp.,

Electronics

Div. East

Paterson,

N.J.

Tru

Ohm

Prod.

Div.ofModel

Engineering

and

Mfg.

Co.

Chicago,

111.

Worcester

Pressed

Aluminum

Corp.

Worcester,

Mass.

Miami,

Fla.

Woodside,

N.Y.
New York, N.Y.
Burbank,

Calif.

Sheridan,

Wyo.

Bridgeport,

Conn.

United

Transformer

Co.

U.S.

Rubber

Co.,

Mechanical

Goods

Div.

Passaic,

N.J.

Bearing

Engineering

Co.

San

Francisco,

Calif.

Connor

Spring

Mfg.

Co.

San

Francisco,

Calif.

Radio

Materials

Co.

Chicago,

Ill.

Augat

Brothers,'lnc.

Attleboro,

Mass.

Dale

Electronics,

Inc.

Columbus,

Nebr.

Elco

Corp.

Philadelphia,

Pa.

Gremar

Mfg.

Co.,

Inc.

Wakefield,

Mass.

K F

Development

Co.

Redwood

City,

Calif.

Minneapolis-Honeywell

Regulator

Co.,

Micro-Switch Division

Freeport,

III.

Universal

Metal

Products,

Inc.

Bassett Puente,

Calif.

Sylvania

Electric

Prod.

Inc.,

Semiconductor

Div.

Woburn,

Mass.

Robbins

and

Myers, Inc. New York, N.Y.

Stevens

Mfg.

Co.,

Inc.

Mansfield,

Ohio

lnsuline-Van

Norman

Ind.,

Inc.

Electronic

Division

Manchester,

N.H.

Raytheon

Mfg.

Co.,

Industrial

Components

Div.,

Receiving

Tube

Operation

Quincy,

Mass.

Raytheon

Mfg.

Co.,

Semiconductor

Div.,

California

Street

Plant

Newton,

Mass.

Scientific

Radio

Products,

Inc

Allies

Products

Corp.

Continental

Connedor

Corp.

Leecraft

Mfg.

Co.,

Inc.

Lerco

Electronics,

Inc.

National

Coil

Co.

Vitramon,

Inc.

82877

83594

82893

83058
83125

831

48

831

86
83298
83330
83501

83777
83821

841

71
84396

84411
84970

85454
85474

85660
8591

1

866

8 4

89665
90179

Koiled

Kords, Inc.

Seamless

Rubber

Co.

Radio

Corp.ofAmerica,

RCA

Electron

Tube

Div.

Harrison,

N.J.

8721

6 PhilcoCorp.

(Lansdalo

Division)

Lansdale,

Pa.

a

7473

Western

Fibrous

Glass

Products

Co.

San

Francisco,

Calif.

aa1 4 a

Cutler-Hammer,

Inc. Lincoln, III.

a9 4 7 3

General

Electric

Distributing

Corp.

Schenectady,

N.Y.

a9

/)3/)

Carter

Parts

Div.ofEconomy Baler

Co.

Chicago,

III.

Chicago,

III.

94144

94145

933

3 2

92196

9097

0
91260
91

41

8

91

506

91

637

91662

91737
91

827

91921

93369
9341

0

93983

94148

9431

0

941

54

941

97

946

8 2

95236
95238

9 S

26

3

95264
95265
95275

Newton,

Mass.

Du

Bois, Pa.

Clifton,

N.J.

Greenwich,

Conn.

Emporium,

Pa.

East

Newark,

N.J.

Chicago,

III.

Div.

of

Columbus

16,

Ohio

Defiance,

Ohio

Now York, N.Y.

Boston, Mass.

Wallingford,

Conn.

Chicago,

III.

Riverside,

Calif.

Industrial

Condenser

Corp.

Chicago. III.

R.F.

Products

DivisionofAmphenol-

Borg

Electronics

Corp.

Danbury,

Conn.

E.F.Johnson

Co.

Waseca,

Minn.

Int.rnational

Resistance

Co.

Philadelphia,

Pa.

Jones,

Howard

B.,

Division

of

Cinch

Mfg.

Corp.

James

Knights

Co.

Kulka Electric

Corporation

lent

Electric

Mftll.

Co.

litt.lfuse

Inc.

Lord

Mfg.

Co.
C.W.Marwedel
Micamold

Electronic

Chicago,

III.

Sandwich,

III.

Mt.

Vernon, N.Y.
Chicago,

III.

Des Plaines, Ill.

Erie, Pa.

San

Francisco,

Calif.

Mfg.

Corp.

8rooklyn, N.Y.

James

Millen

Mfg.

Co.,

Inc.

Malden,

Mass.

J.W.Miller

Co.

Los

Angeles,

Calif.

Monadnock

Mills San

Leandro,

Calif.

Mueller

Electric

Co,

Cleveland,

Ohio

Oak

Manufacturing

Co.

Chicago,

III.

Sendix Pacific Division

of

8endix

Corp.

No.

Hollywood,

Calif.

Phaostron

Instrument

and

Electronic

Co.

South

Pasadena,

Calif.

Pott.r

and

Brumfield, Div.ofAmerican

Machine

and

Foundry

Princeton,

Ind.

Radio

Condenser

Co.

Camden,

N.J.

Radio

Receptor

Co.,

Inc. Brooklyn, N.Y.

Resistance

Products

Co.

Harrisburg,

Pa.

Signal

Indicator

Corp.

New York, N.Y.

Tilley

Mfg.

Co.

San

Francisco,

Calif.

Stackpole

Carbon

Co.

St.

Marys, Pa.

Tinnerman

Products,

Inc.

Cleveland,

Ohio

Transformer

Engineers

Pasadena,

Calif.

Ucinite

Co.

Newtonville,

Mass.

Veeder

Root, Inc.

HarHord,

Conn.

Wenco

Mfg.

Co.

Chicago,

III.

Continental-Wirt

Electronics

Corp.

Philadelphia,

Pa.

New

Rochelle,

N.Y.

Zierick

Mfg.

Corp.

Mepco

Division

of

Sessions

Clock

Co.

Morristown,

N.J.

Times

Facsimile

Corp.

New

York, N.Y.

Electronk

Industries

Association

Any

brand

tub.

meeting

EIA

standards

Washington,

D.C.

Unimu

Switch, Div.

of

W.L.Maxson

Corp.

Oxford

Electric

Corp.

Bourns

Laboratories,

Inc.

Aero

Div.ofRobertshaw

Fulton

Controls

Co.

All

Star

Products

Inc.

Hammerlund

Co.,

Inc.

Stevens,

Arnold,

Co.,

Inc.

International

Instruments,

Inc.

New

Haven,

Conn.

Wilkor

Products,

Inc.

Cleveland,

Ohio

Raytheon

Mfg.

Co.,

Industrial

Components

Div.,

Industr.

Tube

Operations

International

Rectifier

Corp.

EI

Segundo,

Calif.

Watertown,

Mass.

Skokie, III.

Barry

Controls,

Inc.

Carter

Parts

Co.

Jeffers

Electronics

Division

of

Speer

Carbon

Co.

AllenB.DuMont

Labs.,

Inc.

Maguire

Industries,

Inc.

Sylvania

Electric

Prod.

Inc.,

Electronic

Tube

Div.

Astron

Co.

Switchcraft,

Inc.

Metals

and

Controls,

Inc.,

Texas

Instruments,

Inc.,

Spencer

Prods.

Research

Products

Corp.

76

48

7

16493
76

5 3 0
76545
76854
77068

75378
75382
7581

8

7591

5

76

0 0 5

76

210
76433

77221

80207

77

6 3 0

776

3 8

77764

78

2 8 3

78471
78488
78553
78790
78947
79142
79251
79727

7996

3

80031

77

3 4 2

748

6 1

74868

749

7 0
75042
75173

81

483

80248

80294
8041

1

80486
80583
80640
81

030

81

41

5

81453

81860
82042

82142

821

70
82209
8221

9

82376
82389

82647

82866

801

30

801

31

00015-19

Revised:

/)

December

1961

From:

F.S,C,

Handboo~

Supplements

H4-1

Dated

October

1961

H4-2

Dated

November

1961

i-2

00144-2

(ffj)

M.ANUAL

CHANGES

MODEL

492A/494A

TRAVELIl\G-WAVE

AMPLIFIER

M1\nual

Serial

Prefixed:

010-

Manual

Printed:

1/62

To

adapt

this

manuaitoinstruments

with

other

serial

prefixes

check

for

errata

below, and

make

changes

shown in

tables.

Instrument

Serial

Prefix'

ALL

Make

Manual

Changes

ERRATA

Instrument

Serial

Prefix

Make

Manual

Changes

492A

•••••••

O. 5

rna

494A

•••••••

1.0

rna

-

ERRATA:

'/a/63

Table

6-1.

SRI:

Change

to

rectifier.

metallic:

65

rna,

l;OV;

~Stock

No.

1880-0003.

SR4:

Change

to

rectifier.

metallic:

620

rna.

l30V;

!tStock

No.

1882-0007.

Page

3-1,'

Table

3-1.

'.

Change

HELIX

CU~RENT

to

read:

Table

6-1.

VI:

Change

descrip:ion

to

"tube.

clectro:l:

6BG6G".

Table

6-2.

'iStock

~o.

0690-1521:

Change

description

to

"fxd.

comp.1500

ohm.,

±.IO';'o.

1

W".

1j'Stock

No.

1923-0026:

Change

description

to

"tube.

electron:

6BG6G".

Under

lo-tlSCELLA1\"EOUS,

change

~Stock

1\"0.

1401-0084

to

1400-0084.

Section

V,

Paragraph

5-2ge.

Line3sh",uirl

read

33

folio'."3:

"~rc

t~r

thon

-0

m·.·

...

Table

I-I.

Specifications,

Hum

a:1d

SpUrim.l3

~lcdulation:

Char:geto"At

least

40db

below

signal

le';el"

forr"xlel

492A

and

494A.

S

:??:e':lle

.:

;.~

f::;r

-i

Q

2h,'

~').;;...

-~.-

•

PRINTED

IN

U.S.A.