GENERAL RADIO COMPANY 1231-B Operating Instructions Manual

OPERATING

INSTRUCTIONS

TYPE

1231-B

AMPLIFIER

AND

NULL

DETECTOR

GENERAL

RADIO

COMPANY

OPERATING INSTRUCTIONS

TYPE

1231-B

AMPLIFIER

AND

NULL

DETECTOR

Form 634-H

May,

1961

GENERAL

RADIO

COMPANY

WEST

CONCORD,

MASSACHUSETTS,

USA

TABLE OF CONTENTS

Section

1. INTRODUCTION •

1.1

Purpose

.

1.2

Description.

1.2.1

General

1.2. 2

Controls

1.2. 3

Connections

1.2.4

Accessories

.

Section 2. PRINCIPLES OF OPERATION.

2.1

General

.

2.2

Linear

Amplifier

.

2.3

Semilogaritlunic

Null

Detector

2.4

Use

with

Type

874-LBA

Slotted

Line

2.5

Frequency

Response.

1
1

1

1

1
2

3
3
3

3

3

4

4

Section 3. INSTALLATION 4

3.1

Battery

. 4

3.2

A-C

Power

Supply. 4

3.3

Relay-Rack

Model 5

Section 4. OPERATING PROCEDURE. 6

4.1

General

. 6

4.2

Use

as

an

Amplifier

. 6

4.3

Use

as

a Null

Detector

6

4.4

Operation

as

Standing- Wave

Indicator

• 6

4.4.1

Frequency

Selection

. 6

4.4.2

Test

for

Adequate

R-F

Input

for

Low VSWR

Measurement

Assuming

50%

Modulation. 7

4.4.3

Measuring

Standing-Wave

Ratio

7

Section 5. ACCESSORIES 7

5.1

Tuned

Circuits.

7

5.2

Adjustable

Attenuator

9

5.3

Adjustable

Filter

. 9

Section 6. SERVICE

AND

MAINTENANCE . 12

6.1

General

.

6.2

Cabinet

Removal

6.3

Tube

Voltages

and

Resistance

Measurements

6.4

Zero

Coincidence.

6. 5

Meter

Sensitivity

.

PARTS LIST

12
12
12
12
12

14

SPECIFICATIONS

TYPE

1231-B AMPLIFIER

AND

NULL DETECTOR

Input Impedance:

1 megohm

in

parallel with

20J.Lj.Lf;

alternate

10-megohm input

available.

Maximum Gain: Greater than 83

db

at 1 kc

with 1-megohm load.

Meter

Scales:

NORM

scale,

calibrated

in

volts

with

accuracy

of ±5%

of

full

scale;

SENS

scale,

calibrated

in

db

with arbitrary zero.

DB

ratios

accurate

within

30%

of

correct

value

in

db, if one reading is above holf

scale.

Null-Detector

Sensitivity:

Less

than

25J.Lv

input

gives

1%

indication

on

meter

at

1 kc.

Amplifier

Sensitivity:

Less

than

8j.Lv

input

at

1 kc for

1%

indication on SENS range

of

meter.

Output Impedance: Approximately 50,000 ohms.
Maximum

Output Voltage: 5

volts

into 20,000 ohms; 20

volts

into one megohm.

Open-Circuit Noise and

Hum

Level:

Less

than

0.5

volt

at

full gain, battery operated;

less

than

one

volt, a-c operated with

Type

1261-A Power Supply.

Battery

Life: 200 to 250 hours

at

8 hours a day.

Dimensions: Height, 8 in.; width,

12-1/4

in.; depth,

10-3/4

in.; over-all.

Weight:

23-3/4

pounds, including

batteries,

{cabinet model).

TYPES

1231·P2

AND

-P3

TUNED CIRCUITS

Tuning

Accuracy:

±2%

at

normal

voltage

levels.

Attenuation: At

least

25 db to second harmonic.

Dimensions: Height,

4-1/8

in.; width,

3-9/16

in.; depth, 4 in.; over-all.

Weight:

3-7/8

pounds.

TYPE

1231-P4 ADJUSTABLE ATTENUATOR

Source Impedance:

30 kfl, about equal

to

output impedance of

crystal

detector

in

slotted

line.
Lood

Impedance: At

least

1 megohm.

Insertion

Loss:

3 db.

Attenuation Range:

80 db,

readable

to

nearest

tenth db.

Attenuation

Accuracy:

±0.3

db when

operated

between

rated

source

and load impedances.

Additional

errors

caused

by

source

between

14

kfl and

60

kfl

are

less

than

±0.3

db.

Frequency

Error: Negligible below 2 kc.

Maximum

Input Power:

1/2

watt.

Terminals:

Input,

Type

938-W

Binding

Posts;

output,

shielded

cable

with

Type

274-NK

shielded

plug to fit

Type

1231-B input terminals.

Accessories

Required: One

Type

874-R34

Patch

Cord for

connections

between

slotted

I ine and attenuator.
Dimensions: Height,

4-1/2

in.; width,

5-1/2

in.; depth,

5-1/2

in.; over-all.

Weight: 2 pounds,

11

ounces.

Figuro I, Typo 1231

-B

Amp

lilior and Null Ootoctar.

SPECIFICATIONS

<COHT)

TYPE 1231.P5

ADJUSTABLE

Fll

TER

Fr•queney Collbratlon: 50, 100, 200, 500

cps,

1,

2,

5,

10, 20,

SO

,

100

kc.

%2%

ot

minimum

voltogu.

lnurtlon

Gain:

.7

to +15 db, depending upon ftoquoncy. Soeond·hormonic rojoction: 28

to

46

db.

Termlnols: Shielded cord and plug

for

connection

to

Typo 1231

·6

jock·top terminals for

external

capacitor

s.

Acceuorln

Availabl

e:

Type 219 Decode

Copoeitou

for

tuning

filter betwoon frequencies

provided.

Dimensions:

Front P

anel: heig

ht, 7 in.;

width,

6-1/8

in,,

Cabinet: depth,

9-3/4

in.

Internal shiold box: hoight, 6-1/A in

.;

width,

4-1/2 in.;

depth, 9 in.

W•lght: 9 poun

ds,

12

ounces.

TYPE

1231-B

AMPLIFIER

AND

NULL

DETECTOR

Section 1

INTRODUCTION

1.1 PURPOSE.

The

Type

1231-B

Amplifier

and

Null

Detector

(Figure

1)

is

designed

for

use

asa

high-gainamplifier,

as

asensitive

nullindicator

for

bridge

measurements,

and

as a standing-wave

indicator

for

measure-

ments

with

the

Type

87 4-LBA

Slotted

Line.

Used

with a suitable

crystal

detector,

it

will

indicate

amplitude-modulated

high-frequency

voltages,

and

is

also

useful

as a preamplifier

for

crystal

microphones,

vibration

pickups,

and

oscilloscopes.

1. 2 DESCRIPTION.

1.2.1 GENERAL.

The

Type1231-BAmplifierand

Null

Detector

is

avail-

able

in

cabinet

and

relay-

rack

models,

operated

by

either a battery

(Burgess

6TA60,

Army

Signal

Corps

BA48)

or

an

a-c

power

supply

(Type

1261-A

Power

Supply).

Type

numbers

used

todesignatethevarious

mod-

els

are

indicated

below:

1231-BM

Cabinet

model,

battery

operated

1231-BMA

Cabinet

model,

a-c

operated

1231-BR

Relay-rack

model,

battery

operated

1231-BRA

Relay-rack

model,

a-c

operated

1231-BRF

Relay-rack

model,

battery

operated

with

Type

1231-PS

Filter

1231-BRFA

Relay-rack

model,

a-c

operated

with

Type

1231-PS

Filter

1.2.2

CONTROLS.

The

following

controls

are

on

the

panel

of

the

Type

1231-B Amplifier

and

Null

Detector:

1

GENERAL

RADIO

COMPANY

Name

Type

FuncUon

GAIN

Continuous

Varies

gain

of

amplifier

or

rotary

control

sensitivity

of

null

detector.

ZERO

Cap-covered

Makes

the

zero

of

the

SENS

COINCIDENCE

screw-driver

meter

range

coincide

with

the

adjustment

zeros

of

the

NORM

meter

ranges

and

the

null

detector.

ZERO

SET

Continuous

Sets

electrical

zero

at

meter

rotary

control

zero.

AMPL

METER

Push

buttons

(2)

Provide

choice

of

range

for

linear

amplifier

operation:

NORM

range

for

monitoring

output

during

amplifier

oper-

ation,

SENS

range

for

input

voltages

too low

for

NORM

range

or

NULL

DETECTOR.

NULL

Push

button

Causes

output

stage

to

function

DETECTOR

as a logarithmic

amplifier

for

null-detector

operation.

BATT CHECK

Push

buttons

(2)

Check

condition

of

the

plate

and

filament

batteries.

OFF

Push

button

Turns

off

battery

power

supply.

INPUT

Push

buttons

(2)

~0.03

v -

sets

approximate

maximum

no-load

gain

at

85

decibels

with

maximum

input

voltage

of

less

than

0.

03

volt.

<1

v -

sets

approximate

maximum

no-load

gain

at

55

decibels

with

maximum

in-

put

voltage

of

less

than 1 volt.

1MO-

10MO

Toggle

switch

Selects

input

impedance

of

the

amplifier.

1.2.3

CONNECTIONS.

The

following

connections

are

on

the

pane1of

the

Type

1231-B

Amplifier

and

Null

Detector:

Name

Type

Function

INPUT

Jack-top

binding

posts

(2)

Input

terminals.

FILTER

Telephone

jack

Provides

for

connecting

a

filter

to

the

output

stage

of

the

instrument.

OUTPUT

Jack-top

binding

posts

(2) Output

terminals.

2

TYPE

1231-B

AMPLIFIER AND NULL DETECTOR

1.2.4

ACCESSORIES.

The

following

table

lists

accessories

supplied

with

the

various

models

of

the

Type

1231-B

Amplifier

and

Null

Detector:

Type

Accessories

Supplied

1231-BM

Cabinet

1231-BMA

Cabinet,

Type

1261-A

Power

Supply

1231-BR

Type

1231-

P7

Connecting

Panel

1231-BRA

Type

1261-A

Power

Supply,

Type

1231-P7

Connecting

Panel

1231-BRF

Type

1231-P5R

Filter

1231-BRFA

Type

1261-A

Power

Supply,

Type

1231-P5

Filter,

Type

1231-

P6

Connecting

Panel*

*for

Type

1610-A

Capacitance

Measuring

Assembly,

use

Type

1231-P6-2

Connecting

Panel

Section 2

PRINCIPLES

OF OPERATION

2.1 GENERAL.

The

simplified

circuit

diagram

(Figure

7)

shows

that

the

amplifier

has

three

stages

and a built-in

vacuum-tube

voltmeter,

which

consists

of a

diode

rectifier, a d-e

amplifier,

and

the

panel

meter.

2.2

LINEAR AMPLIFIER.

During

linear-amplifier

operation,

there

is

a

choice

of

maximum

no-load

gain

of 55

or

85

decibels,

as

selected

by

the

input

attenuator

buttons

at

< 1

volt

or < 0.03

volt

respectively.

A

tapered

wire-wound

gain

control

allows

continuous

variation

of

the

gain

over a wide

range.

2. 3 SEMILOGARITHMIC NULL

DETECTOR.

During

semilogarithmic

null-detector

operation,

rectified

de

from

the

vacuum

-tube

voltmeter

diode

is

applied

as

gain-controlling

bias

to

the

last

amplifier

stage

to

produce

the

desired

characteristics.

An

attenuator

in

the

grid

circuit

allows

meter

current

to

be

zero

with

no

signal

at

the

instrument

ter-

minals.

3

GENERAL RADIO COMPANY

2.4

USE WITH TYPE 874-LBA SLOTTED LINE.

The

Type

1231-B Am-

plifier

can

be

used

with

the

Type 1231-P2

Tuned

Circuit

and

the

Type

1231-

P4

Attenuator

as a standing-wave

indicator

for

the

Type

87 4-

LBA

Slotted Line. Since

the

amplifier

should

be

tuned

to

the

frequency

of

the

oscillator,

choose a filter

that

selects

the

modulating

frequency

used

(refer

to

Section 5).

Wit.'1

the

amplifier

gain

setat

maximum

and

theat-

tenuator

set

at

30 db,

full-scale

deflection

on

the

amplifier

meter

extends

to

r-f

inputs

with

50-percent

modulation.

For

most

accurate

results,

the

ratio

of

the

inputs

obtained

at a maximum

and

at a minimum

on

the

line

should

be

measured

on

the

Type

1231-

P4

Attenuator,

rather

than

on

the

meter

scale.

To

determine

this

ratio,

measure

the

difference

in

at-

tenuation

required

to

produce

the

same

meter

reading

for a voltage

min-

imum

as

for a voltage

maximum.

If

the

crystal

is

operating

in

the

square-law

region,

the

actual

decibel

difference

in

r-f

voltage

is

half

the

decibel

difference

measured

by

the

attenuator

or

meter.

2.5 FREQUENCY RESPONSE.

The

maximum

open-circuit

voltage

gain

is

over

70

decibels

at

10

cycles,

over

45

decibels

at

100

kilocycles,

and

greater

than 83

decibels

at

midband.

The

frequency

characteristic

is

shown

in

Figure

2.

~

0

I

lll-1

0/

~-20

"'

a:

OJ•3

>

j::

5·40

II!

·5

0

.....-

IOc

20c

SOc

-~---~

.........

""-

"""",

""'

IOOc

200c 500c

Ike

2kc

5kc

IOkc

20kc 50kc

IOOkc

FREQUENCY

Figure

2.

Frequency

Response

Curve.

Section

3

INSTALLATION

3.1 BATTERY.

Battery-operated

models

are

shipped

with

the

battery

in

place.

To

install

or

replace

battery

(Burgess

6T A60,

Army

Signal

Corps

BA48,

or

equivalent),

first

remove

the

instrument

from

the

cab-

inet

(refer

to Section 6.2).

Install

the

battery

on

the

hangers

at

the

rear

of

the

chassis

and

plug

the

battery

cable

into

the

socket.

3.2 A-C POWER SUPPLY.

For

a-c

operation

the

Type 1261-A

Power

Supply

is

provided

in

place

of

the

battery.

The

115-volt

socket

is

in-

stalled

above

the

hole

in

the

base

of

the

cabinet,

where

the

line

cord

is

4

TYPE

1231-B AMPLIFIER

AND

NULL DETECTOR

inserted.

The

panel

switch

of

the

instrument

must

be

left

ON

and

the

switch

in

the

line

cord

used

to

turn

the

power

supply

ON

and

OFF.

With

both

the

panel

switch

and

line

cord

switch

ON,

measure

the

filament

volt·

age

by

pushing

the F IL

button. Note

the

meter

reading.

Push the button

on top

of

the

power

supply

and

again

note

the

meter

reading.

Tum

the

screw-driver

adjustment

on top

of

the

power

supply

until both

meter

readings

are

equal.

To

keep

the

hum

level

low,

do

not

ground

the

case

of

the

power

supply

to

the

instrument

shield.

3.3 RELAY- RACK MODEL.

The

Type

1231

·P7

Connecting

Panel

is

in-

stalled

to

fit

the

standard

19 - ln.

relay-rack

. When the Type 1231-PSAd-

justable

Filter

is

included,

the

Type

1231-P6

Connecting

Panel

Is

used.

(See F

lgure

3.)

Figure 3o. Typo 1231-P7 Connecting Panel.

Figure

3b.

Type 1231-P6 Connecti

ng

Panel

and Type 1231-PS Filter.

5

GENERAL RADIO COMPANY

Section 4

OPERATING

PROCEDURE

4.1 GENERAL.

The

following

procedure

should

be

followed

when

the

Type

1231-B

is

first

set

up.

a.

Turn

the

power

on

by

pushing

either

the

NULL

DET

button

or

one

of

the

AMPL

METER

buttons.

b.

Zero

the

meter

by

turning

the

ZERO

SET

knob

with

the

INPUT

terminals

short-circuited.

If

the

zero

of

the

SENS

range

does

not

coin-

cide

with

the

zero

of

the

NORM

and

NULL

DET

ranges,

remove

the

ZERO

COINCIDENCE

cap

and

set

the

screw-

driver

adjustment

until

there

is

no

change

in

meter

indication

as

the

meter

is

switched

between

the

SENS

and

NORM

ranges.

c.

To

check

the

battery,

push

the

BATT CHECK PL

and

FIL

but-

tons,

and

note

the

meter

indications.

If

the

indication

with

either

button

pushed

is

below

the

BATT

mark

on

the

meter,

replace

the

battery.

d.

Select

the

input

impedance

by

means

of

the 1 MQ

- 10

MQ

switch.

4.2

USE

AS

AN

AMPLIFIER.

For

ordinary

use,

operate

with

the

NORM

button

pushed;

then

meter

deflection

is

approximately

linear,

and

full

scale

corresponds

to

20

volts.

When

the

input

voltage

is

too

low

to

give

satisfactory

meter

indications,

operate

with

the

SENS

button

pushed.

The

meter

deflection

is

approximately

linear,

and

full

scale

corresponds

to 2 volts.

4.3

USE

AS

A NULL DETECTOR. When

using

the

Type

1231-B

as

a

null

detector

first

remove

all

load

from

the

OUTPUT

terminals.

Then

select

maximum

no-loadgain

by

means

of

the

INPUT

attenuator

buttons.

With

the

<:

1 v

button

pushed,

maximum

no-load

gain

is

55 db. With

the

< 0.03 v button

pushed,

maximum

no-load

gain

is

85

db

and

the

meter

is

more

sensitive.

Increasing

the

gain

setting

also

increases

sensitivity.

Use

the

NULL

DET

button

for

preliminary

balances,

the

SENS

but-

ton

for

final

balance.

4.4

OPERATION

AS

STANDING-WAVEINDICATOR.

(Refer

to

Operating

Instructions

for

Type

87 4-LBA

Slotted

Line.)

4.4.1 FREQUENCY SELECTION.

Tune

the

amplifier

to

the

modulation

frequency

with

an

appropriate

filter

(refer

to

Section

5).

6

TYPE 1231-B AMPLIFIER

AND

NULL DETECTOR

4.4.2

TEST

FOR

ADEQUATE

R-F

INPUT

FOR

LOW VSWR MEASURE-

MENT

ASSUMING 50% MODULATION.

a.

Find

the

voltage

maximum

on

the

line.

b.

Set

the

Type

1231-B

for

maximum

sensitivity

and

set

the

Type

1231-

P4

Attenuator

for

attenuation

less

than

30

db.

c.

Find

the

voltage

minimum

on

the

line.

d.

If

the

meter

reading

at

the

minimum

is

greater

than

one-fourth

of

full

scale,

the

r-f

input

to

the

line

is

adequate.

If

the

meter

reading

is

less

than

one-fourth

of

full-scale,

increase

the

r-f

input

or

the

probe

coupling.

4.4.3

MEASURING STANDING-WAVE RATIO.

For

most

accurate

re-

sults,

the

ratio

of

the

outputs

obtained

at a maximum

and

at a minimum

on

the

line

should

be

measured

on

the

Type

1231-P4

Attenuator,

rather

than

on

the

meter

scale.

a.

At

the

voltage

maximum,

note

the

attenuation

and

the

ampli-

fier

meter

reading.

b.

At

the

voltage

minimum,

vary

the

attenuation

of

the

Type

1231-

P4

Attenuator

until

the

amplifier

meter

reading

is

the

same

as

that

noted

in

step

a.

c.

If

the

crystal

is

operating

in

the

linear

region,

the

difference

in

attenuation

at

these

two

points

is

the

standing-wave

ratio

(SWR = 20

E

log

10

Em~x)

expressed

in

decibels.

m1n

d.

If

the

crystal

is

operating

in

the

square-law

region,

the

actual

db

difference

in

r-f

voltage

is

half

of

the

db

difference

measured.

Section

5

ACCESSORIES

5.1 TUNED CffiCUITS.

Types

1231-P2 (400

and

1000

cycles)

and

-P3

(60

cycles)

Tuned

Circuits

(Figure

4)

can

be

used

as

interstage

filters

with

the

Type

1231-B

for

suppressing

harmonics,

noise,

and

hum

in

sin-

gle-frequency

measurements.

A

telephone

plug

on

each

filter

plugs

into

a

panel

jack

on

the

Type

1231-B

Amplifier

and

Null

Detector.

Filters

thus

connected

are

isolated

by

amplifier

stages

from

the

effects

of

vary-

ing

input

and

output

impedances

and

at

the

same

time

are

at a high

7

0

1/1

I 0

..J

llj

0

~

20

!':

i5

30

Si

~

1-

4 0

!<i

50

/

GENERAL RADIO COMPANY

Figure 4. Type

123

l.P3 Tuned Circuil

(ldenlical

in App

earance

ro

Typo 123l.P2).

TVI'E

TVPE

1231-

P3

1231·P2

J \

~

\

I

1/

-\

1/

v

/

'\

1'\.

1-

v

r-/

"'

""'

v

/

""'

1'.::::

-

K

10

20

50

1

00

200

500 1,000

2POO

5poo

10,000

FREQUENCY

IN

CYCLES

PER

SECOND

FigureS

. Attenuat ion Curve, Types 1231

-P2

and

-P3

Tunod

Circ

uit

s.

enou

gh

voltage level

along

the

amplifying chain

to

withstand

effects

of

external

fields.

Figure 5 shows

the

attenuation

vs

frequency

for

the

Types 123l

·P2

and

· P3 TUned

Circuits.

5.2

ADJUSTABLE ATIENUATOR. When

used

with

the

Typel231-B

am·

pllfier

and Null

Detector

and

the

Type

874-

LBA

Slotted

Line

to

measure

standing

-wave

ratio,

the

Type

1231-P4

(Figure

6)

Adjustable

Attenuator

8

TYPE

1231-B

AMPLIFIER

AND

NULL

DETECTOR

Fi

;U<o

6. Ty.,- 1231-P4 Adjuuablo Allonuarar.

Increases

both the

range

and

accuracy

of

measurement

over

that obtain-

able

with the

ampll!ler

alone. Thls high-Impedance

resistive

voltage

divider

covers a range

of

80

decibels,

with

three

20-db

steps

and a 20-

db

potentiometer.

5.3

ADJUSTABLE FILTER.

The

Type 1231-PS Adjustable F

ilt

er (Fig-

ure

3)

Is a

paro

Jiol

-resonant, shielded

!liter

tor reduci ng

ha

rmon

ics

and background

noise

In

bridge

measurements.

Designed primaril

y to

plug Into the Type 1231-B

Ampll!ler,

the Type 1231-PS

Filter

can

be

used

as

an

anti resonant

L-C

element

In

the

grid

circuit

of any

Class-A

am-

plifier

where

It

Is

not

subjected

to

direct

current.

The

Adjustable

Filter

can

be

set

to

any one of

11

frequencies: 50, I 00, 200, and 500

cycles,

and

1, 2, 5,

10, 20, 50, and 100 kc. In

order

to obtain high

selectivity

with

low

lnsenlon

loss,

!our

sepsrate

Inductors

are

used:

L1

(20

henrys)

for

50 and 100

cycles,

centrlcore

;

L2 (2

henrys)

for

200 and 500

cycles,

duet

core;

L3

(300

millihenrys)

for

1,

2,

and 5 kc,

dust

core;

L4 {IS

millihenrys)

for

10, 20, 50, and 100

kc,

dust

core.

The

selector

switch

has

eleven frequency positions, four Induct

or

posl-

tlons, and an OFF position. Maximum

accuracy

of the Indicated resonant

frequencies will

be

attained

only when the CUt

er

Is u

sed

with the

Type

1231-B Amp l

liler

and Null Detecto

r,

and only when

operating

at

vanish-

Ingly low l

eve

ls In balancing

bridges

or

oth

er

null

circ

uits.

By

the

addition of

external

capacitance,

this

filter

can

also

be

tuned

to

any

other

frequency

from

20

cycles

to 100

kc.

Both

terminals

of

the

9

GENERAL

RADIO

COMPANY

filter

are

available

on

the

front

panel

for

attaching

external

capacitors.

To

choose

the

proper

inductor

for

any

operating

frequency,

take a com-

promise

point

of

tolerable

insertion

loss

and

desirable

discrimination

against

the

second

harmonic.

Data

for

determining

this

point

for

any

frequency

are

given

in

the

graphs

of

Figure

7.

For

convenience,

the

ranges

of

external

capacitance

needed

to

tune

over

the

indicated

ranges

of

frequency

are

given

in

the

following

table.

In

most

cases

these

values

could

be

obtained

with

the

Type

1419-A

Dec-

ade

Capacitor.

Resonance

for

any

specific

frequency

is

then

indicated

by

a

maximum

of

observed

gain.

To

Tune

Down

Set

Switch And

Add

External

From

To

At

Capacitance

(!Jf)

50 c

20 c

50 c 0

to

2.66

100c

50

c

100

c

0

to

0.381

200 c

100

c

200

c 0

to

0.951

500 c 200 c

500 c

0

to

0.266

1

kc

500

c

1

kc

0

to

0.238

2

kc

1

kc

2

kc

0

to

0.0634

5

kc

2

kc

5kc

0

to

0.0177

10

kc

5

kc

10

kc

0

to

0.0507

20

kc

10

kc

20

kc

0

to

0.0127

50

kc

20kc

50

kc

0

to

0.00354

100

kc

50

kc

100

kc

0

to

0.00051

Typical

low-level

characteristics

of

the

Type

1231-P5

Filter,

when

used

with

the

Type

1231-B

Amplifier

and

Null

Detector,

are

given

in

Table

1.
TABLE 1.

Inductor

Resonant

Resonant

Insertion.

Discrimination

Frequency

Used

ZMn

Q

db

vs

Second

Har-

monic

db

50 c L1 0.28 45

6.4

loss

33

100

c L1

1.02

81

2. 7

loss

31

200 c

L2

0.070

27.6

15.0

loss

30

500

c

L2

0.47 75

7.3

loss

32

1

kc

L3

0.26 138

7.8

loss

42

2

kc

L3

0.86 228

3.0

loss

40

5kc

L3

2.70

287

1.9

gain

34

10

kc

L4

0.17 175

3.8

loss

46

20

kc

L4

0:50 262

2.2

gain

44

50

kc

L4

1.06

214

5.6

gain

37

100

kc

L4

2.13 192

7.4

gain

28

10

TYPE

1231-B

AMPLIFIER

AND

NULL DETECTOR

Figure

7a.

Insertion

Loss,

Type

1231-PS

Filter.

48

0

44

~

~

40

"0

tG

36

i5

32

!;i

~

28

~

0 24

..c

"0

20

I

/

.......

"\i

v

/\

1\

\

~

z

0

i=

8

0

4

8

ffi

12

(/)

~

,g

16

20

/

/

I

I

/LI

/

-

I

L2

v

I

I

)'

/

/

/

v

/ I

/

v

v

L

I

I

I

I

/_

/L3

i/L4

I

02

.05

0.1

0.2

0.5

I 2 5

10

20 00

100

/

/

~

1\

\

'\

L2

\

RESONANT

FREQl£NCY-

KILOCYCLES

v-

"'

~

~3

\

\

\

\

L4\

Figure

7b.

Second Harmonic

Discrimination,

Type

1231-PS

Filter.

02

.05

.10

.20 .50 I 2 5

10

20

50

100

RESONANT

FREQUENCY

KILOC'ICLES

11

GENERAL

RADIO

COMPANY

Section

6

SERVICE

AND

MAINTENANCE

6.1 GENERAL.

The

two-year

warranty

given

with

every

General

Radio

instrument

attests

the

quality

of

materials

and

workmanship

in

our

prod-

ucts.

When

difficulties

do

occur,

our

service

engineers

will

assist

in

any

way

possible.

In

case

of

difficulties

that

cannot

be

eliminated

bythe

use

of

these

service

instructions,

please

write

or

phone

our

Service

Department,

giving

full

information

of

the

trouble

and

of

steps

taken

to

remedy

it.

Be

sure

to

mention

the

serial

and

type

numbers

of

the

instrument.

Before

returning

an

instrument

to

General

Radio

for

service,

please

write

to

our

Service

Department

or

nearest

district

office

(see

back

cover),

requesting a Returned

Material

Tag.

Use

of

this

tag

will

insure

proper

handling

and

identification.

For

instruments

not

covered

by

the

warranty, a purchase

order

should

be

forwarded

to

avoid

unne-

cessary

delay.

6.2

CABINET REMOVAL.

To

remove

the

instrument

from

the

cabinet,

remove

the

black

thumbscrew

from

each

comer

of

the

panel

and

slide

the

instrument

out

of

the

cabinet.

6.3

TUBE VOLTAGES AND RESISTANCE MEASUREMENTS.

Table

2

gives

the

normal

d-e

voltages

and

d-e

resistances

from

various

tube-

socket

pins

to

ground. A deviation

of

10

percent

from

any

of

these

val-

ues

is

not

necessarily

abnormal.

6.4

ZERO

COINCIDENCE.

If

either

the

battery,

V3, V4,

or

the

Type

1N56-A diode

is

replaced,

or

as

the

battery

ages,

the

ZERO

COINCI-

DENCE

control

should

be

readjusted

to

make

the

electrical

zero

of

the

AMPL

METER

SENS

range

coincide

with

the

zeros

of

the

NORM

and

NULL

DET

ranges.

The

ZERO

COI1'JCIDENCE

control

is a screw-driver

adjustment

accessible

through

a

~ble

in

the

front

panel

behind a snap

button

cover.

With

the

instrument'

INPUT

terminals

short-circuited

or

with

the

GAIN

control

turned

to

sero,

adjust

the

ZERO

COINCIDENCE

potentiometer

until

there

is

no

change

in

meter

indication

as

the

instru-

ment

is

switched

between

the

SENS

and

NORM

ranges.

6.5

METER

SENSITMTY.

R19

is a factory-adjusted

control,

which

normally

does

not

require

readjustment.

If

its

setting

has

been

disturbed

it

may

be

reset

as

follows:

a.

Push

the

AMPL

METER

NORM

button.

Turn

the

GAIN

control

to

zero

and

adjust

the

ZERO

SET

control

for

zero

reading

on

the

NORM

meter

scale.

12

TYPE 1231-B AMPLIFIER

AND

NULL DETECTOR

b.

Reset

the

GAIN

control

to

maximum

(10). Apply a

1-kc

signal

to

the

INPUT

of

the

amplifier

and

increase

the

input

voltage

to

give

ex-

actly

20

volts

at

the

amplifier

OUTPUT

terminals,

measured

with a vacu-

um-tube

voltmeter.

c.

Adjust

potentiometer

R19

(mounted

above

ZERO

COINCIDENCE

potentiometer)

until

the

amplifier

meter

reads

exactly

full

scale

for

a

20-volt

reading

on

the

voltmeter.

TABLE 2

TEST

VOLTAGES AND RESISTANCES

TUBE

(TYPE)

V1

(1U4)

V2

(1U4)

V3

(1U4)

V4

(1U4)

NOTES:

Batteries:

A

+1.5

v

B

+90v

PIN

1

2

3
6
7

1
2
3
6
7

1
2

3
6
7

1
2
3
6
7

No

batteries

for

resis-

tance

measurements.

Panel

controls

and

switch

settings:

GAIN = 0

VOLTS

RESISTANCE

TO

GROUND

TO GROUND

0
+38
+37

0

+1.5

0
+42.5
+26

0

+1.5

0
+53
+90

-1.1

+1.5

0
+90
+90

-1.1

+1.5

0

160

k

350 k

30 k

3.5

0

660

k

2.3 M

0

3.5
0

50

k

0

2.2 M

3.5

0

1.6k

1.6k

4.7 M

3.5

For

resistance

measurements,

short

terminal

2 to 4

and 1 to

5

on

PLl.

INPUT = 1

v,

1 MU

AMPL = NORM (20 v)

Voltmeter

input

resistance

should

be

at

least

10

times

the

value

given

in

the

RESISTANCE

column.

13

GENERAL RADIO COMPANY

PARTS

LIST

PART

NO. (NOTE

A)

RESISTORS. k =

kilohms,

M

=Megohms

Rl

1M

±

5%

1/2

w

REG-20BF

RIA

10M

±

5%

1/2

w

REC-20BF

R2

30 k

±

5%

1/2

w

REC-20BF

R2A

300 k

±

5%

1/2

w

REC-20BF

R3

270 k

±10%

1/2

w

REC-20BF

R4

56 k

±10%

1/2

w

REC-20BF

RS

47 k

±

5%

1/2

w

REC-20BF

R6

100 k

±

2%

976-400

R7

2.2 M

±10%

1/2

w

REC-20BF

R8

lOOk

±10%

1/2

w

REC-20BF

R9

560 k

±10%

1/2

w

REC-20BF

Rl2

2.2

M

±10%

1/2

w

REC-20BF

Rl3

2.2 M

±10%

1/2

w

REC-20BF

Rl4

47 M

±

5%

1/2

w

REC-20BF

Rl5

47

M

±10%

1/2

w

REC-20BF

Rl6

4.7

M ±10%

1/2

w

REC-20BF

Rl7

50 k

POSC-11

Rl8

l.SM

±

5%

1/2

w

REC-20BF

Rl9

50

POSC-11

R20

9.1 k ±

1%

1/2

w

REF-70

R21

680 k ±

1%

1/2

w

REF-70

R22

Sk

±

5%

973-410

R23

1 k

±

5%

1/2

w

REC-20BF

R24 4.7 k

±10%

1/2

w

REC-20BF

R25

12

k

±

5%

1/2

w

REC-20BF

R26 82 k

±

5%

1/2

w

REC-20BF

R27 47 M

±

5%

1/2

w

REC-20BF

R28

47 M

±

5%

1/2

w

REC-20BF

R29 2.7

±10%

1/2

w

REW-3C

CAPACITORS. All

capacitances

are

in

fJf

unless

otherwise

indicated.

Cl

0.047

±10%

600

dcwv

COL-71

C2

0.2

Part

of

COWB-6

C3

2

Part

of

COWB-6

C4

0.25

±10%

600

dcwv

COL-43

cs

0.2

Part

of

COWB-6

C6

1

Part

of

COWB-6

C7

0.05

±10%

600

dcwv COM-SOB

14

TYPE

1231-B

AMPLIFIER

AND

NULL DETECTOR

PARTS

LIST

(CONT)

CAPACITORS (Continued)

C8

o.os

±10%

600

dcwv

COM-SOB

ClO 0.01

±10%

600

dcwv COM-4SB

Cll

0.1

±10%

200

dcwv COW-16

Cl2

0.8

±10%

300 dcwv COW-4

Cl3

2

Part

of

COWB- 6

Cl4

soo

fJfJf

±10%

300

dcwv

COM-20B

CIS

16

ISO

dcwv

COE-4

MISCELLANEOUS

BATTERY

Burgess

6TA60

Bl

BATTERY,

1-1/2

v 2BAC-4

Dl

DIODE

1NS6-A

Jl

JACK CDSJ-820

Ml

METER,

200

f.la

MEDS-36

PLl

PLUG

CDMP-1344

Sl

SWITCH

SWPM-14

S2

SWITCH SWT-33SNP

Vl

TUBE

1U4

V2

TUBE

1U4

V3

TUBE

1U4

V4

TUBE

1U4

vs

REGULATOR

NE-2

NOTES

(A)

Type

designations

for

resistors

and

capacitors

are

as

follows:

COE -Capacitor,

electrolytic

COL -

Capacitor,

oil

COM -

Capacitor,

mica

COW -

Capacitor,

wax

POSC -

Potentiometer,

composition

REC -Resistor,

composition

REF -Resistor,

film

C-1

~~-~04~7--~~----~

INPUT

t

/OIL

<003v

R-20

9./k

C-4

.25

TYPE

1231-B

AMPLIFIER

R-24

4.lk

R-25

12k

105R

FIL

CHECK

PL

BATT

Figure 8.

Sche~

'LIFIER

AND

NULL

DETECTOR

I J-1

1:£

f

VI

ALTER

C-12

.05

2.

---+-1

-==

r----------t---------1~@

C-B

IUv-4·

3 2

V-4

.8

OUTPUT

R-24

4.7k

R-25

12k

R-8

lOOk

OFF

.05

IU4

3.

-=-

NULL

DET.

;'f'C-10

~01

-=

.,..

/J-:1

/N56A

cw

R-19

50k

SENS

METER

NORM.

METER

(DB) AMPL.

(20v)

NOTE.' RESISTANCES

IN

OHMS UNLESS OTHERWISE SP£CIFIEO

. Schematic Diagram.

k=IOOO

OHMS M= I

MEGOHM

CAPACITANCES

IN

MICROFARADS UNLESS OTHERWISE

SPECIFIEO. p

J1

f = MICROMICROFARAOS

15

-

0..

!

-;-

"=:"

v ?

Figure 9. Elementary Schematic Diagram

(Includes Tube Layout).

AMPLIFIER.

r---t

RECTlAER

1.._-~.)~UTPUT

!

~

+

.....

"

m

:z

m

:::0

>-

.-

:::0

,...

c

0

i

.,

>-

:z

-<

•

INPUT

C-1

.047

/OIL

<003v

V-1

/U4

----·

INPUT

<lv

2

R-20

9.1k

R-5

R-3

47K

2

C-15

16

903L

R26

82k

C-4

.25

R-4
56k

TYPE

1231-B

AMPLIFIER

AND

NULL DETECTOR

GAIN

R-6
lOOk

FIL

V-2

IU4

2

CHECK

PL

BATT

R-9

R-7'

560k

R-24

4.7k

R-25

B-1

R-21

680k

$-I

OFF

Figure

E.

Schematic Diagram.

ALTER

C-12

~----------~~------~~@

V-4

v..:..3

lU4

R-17'
50k

2

-

NULL

DET.

2

IU4

R27

R28

4l'M

47M

C-14~

-

-

R-19

50k

710R

-

SENS

METER

NORM.

METER

(DB)

AMPL.

(20v)

C-11

0.1

.8

OUTPUT

VIEWEO. FROM

PIN

SlOE

PL-1

NOTE.' RESISTANCES

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