National Horizon 20 Instruction Manual

INSTRUCTION

BOOK

FOR

The

National

The

latest

in

audio engineering techniques, plus

careful

attention

to

design

details,

make

the

Hqrizon

20

an

instrument unparalleled

for

superb

performance

and

operating efficiency.

Its

excellent characteris-

tics

are

due,

in

large measure,

to the

unique output

stage

in

which

the

coupling between

the

output tubes

is

unity, independent

of the

output transformer.

This

permits

the

use of

high efficiency

class

ABj

operation

without

the

impulse distortion

commonly

associated

with

conventional

circuits

which rely upon

the

output

transformer

for

coupling between

the

tubes.

Unity

coupling

has the

additional

advantage

of

requiring

a

TWENTY

WATT

AMPLIFIER

far

lower impedance

ratio

between

the

output tubes

and

the

load

with

attendant reduction

in

leakage

in-

ductance

and

increased

power

bandwidth.

In

addition

to its

superlative

performance,

the Na-

tional Horizon

20

incorporates

the

unique

plug-in

faci-

lity

for the

accommodation

of the

Horizon 5 Preampli­fier — Control Unit. This feature alone exemplifies
the

advanced design

of the

National

high

fidelity

line

resulting

in

optimum

flexibility

of

installation

and

operation.

The

following

specifications

indicate some

of

the

other outstanding features

of the

Horizon

20.

Please

use

this

manual.

It has

been

prepare*/

with

the

prime p urpose

of

enabling

the

user

to

obtain

full

satisfaction

from

this product.

NATIONAL

COMPANY,

INC.,

MAIDEN & MELROSE, MASS.

FEATURES

HARMONIC

DISTORTION: 0.3%

at

rated output

of

20

watts.

0.6%

at 25

watts.

INTERMODULATION

DISTORTION:

1% at 20

watts,

measured

with

400

cps.

and 7 kc. at a

ratio

of

4:1.

FREQUENCY

RESPONSE: ±0.1

db

from

20

cps.

to

20

kc. ±1 db

from

10

cps.

to 100 kc.

POWER

RESPONSE

AT 20

WATTS:

±0.15

db

from

20

cps.

to 20 kc. ±1 db

from

10

cps.

to 60 kc.

HUM

AND

NOISE:

80 db

below

20

watts output.

SENSITIVITY:

1.6

volts

for 20

watts output.

OUTPUT IMPEDANCE: 8 and

16

ohms

nominal.

INPUT

IMPEDANCE:

500,000 ohms.

INPUT LEVEL CONTROL: accommodates a wide

range

of

input

signal

levels.

RUMBLE

FILTER: built

in to

minimize turntable

rumble

and

noise.

ACCESSORY

OUTLET:

117

volt

AC, 3

amp. con-

venience outlet

for

energizing

associated

equipment.

PREAMP

COMPARTMENT: contains

multiconnector

wired

to

associated

rear-panel jacks

to

convert

the

Horizon

20 to a

single-unit equipment

when

the

Hori-

zon 5 preamp

is

plugged

in.

POWER

INPUT:

117

VAC, 50-60 cps, 1 amp,

110

watts.

PREPARING

TO

OPERATE

Examine

the

amplifier

immediately

after

unpacking

to

make

certain that

no

apparent damage

has

been

in-

curred

during shipment. A cardboard

pad is

placed

around

the

tubes

to

protect

them

in

transit.

This

must

be

removed.

To do so it is

necessary

to

remove

the

cabinet.

Since

the

Horizon

20 has no

operating con-

trols,

it may be

installed

in any

convenient location

so

long

as

there

will

be a

free

circulation

of air to

allow ventilation.

The

above

would

hold true

when

the

Horizon 5 preamp

is

used

with

the

amplifier,

pro-

vided

that

the

preamp

is

located

at a

point remote

from

the

amplifier.

When

the

National Horizon 5 preamp

is

plugged

into

the

Horizon

20, the

unit must

be

installed

with

con-

trol

accessibility

in

mind.

The

attractive

overall

appearance

of the

amplifier makes

it

well

suited

for

use on a

table top, shelf

or any

convenient

location.

Once

the

input, power

and

speaker connections have

been made,

the

Horizon

20

with

the

Horizon 5 preamp

becomes a versatile

control center

for the

custom

high

fidelity

installation.

If it is

desired

to

make

this

combination

part

of a

custom

installation,

refer

to the

paragraph

on

Cabinet

Installation.

ELECTRICAL

CONNECTIONS

All the

input

and

output connections

of the

Horizon

20

amplifier

are

located

on the

back drop

of the

chas-

sis.

See

Figure

1.

Connections

to the

various jacks

and

terminals should

be

made

in the

following

manner:

1.

HORIZON

20

AMPLIFIER

WITHOUT

HORIZON

5

PREAMP

PWR.

AMP. INPUT:

The

output

of the

National

Criterion

or

similar

AM-FM

tuner

or the

output

of a

preamp

other than

the

Horizon

5 is

connected

to

this

jack. Single conductor shielded

cable

must

be

used,

the

length dictated

by the

recommendations accompany-

ing

the

particular equipment.

Associated

equipment

should

have

an

output

level

of 1.6

volts

or

more.

All

other

jacks

are

unused.

SPEAKER

OUTPUT: A high fidelity loudspeaker

system

having

an

impedance

of

either

8 or 16

ohms

may

be

connected

to

these

terminals.

The

terminal

marked

G is the

common

connection

and may be

grounded

if

desired.

Shielded cable

is not

required

for

speaker connections

and the

length

is not

critical.

Number

18

wire

(size

of

ordinary lamp cord),

or

larger,

is

recommended.

117V

3A

OUTLET:

This

convenience outlet

is

supplied

for the

purpose

of

providing input voltage

for

other units

of the

system

as

desired.

It is

ener-

gized

when

the

amplifier

is

plugged into

the

117-volt

line.

2.

HORIZON

20

AMPLIFIER

WITH

HORIZON

5

PREAMP

PWR.

AMP. INPUT:

When

the

Horizon 5 preamp

is

used

with

the

Horizon

20,

either plugged into

the

unit

or

connected

by

means

of an

interconnecting

cable,

the

Pwr. Amp. Input jack

is not

used.

The
interconnecting cable complete with mating connec­tors

may be

procured

in

either

4 or

15-foot lengths.

When

the

interconnecting

cable

is

used,

remove

one

of

the

thumbscrews

from

the

preamp

compartment

cover plate

and

thread

the

screw into

the

tapped hole

at the

right edge

of the

preamp compartment.

This

must

be

done

in

order

to

close

the

interlock switch.

TV

INPUT:

Any TV

tuner having

an

output

of 1.6

volts

or

more

may be

connected

to

this

jack.

This

jack

will

also

accommodate

the

standard high-level

ceramic

or

crystal type phono pickup. Shielded cable

must

be

used.

TAPE

PLAYBACK

INPUT: A tape reproducing

unit

may be

connected

to

this

jack,

or any

piece

of

-2-

II7VAC

60

~

GAIN

HUM

BALANCE

TAPE

PHONO

PLAYBACK

OUTPUT

REAR

VIEW

Figure

I.

Electrical

Connections

audio

equipment

having

an

output

of

approximately

1.6

volts.

This jack will

also

accommodate

the

cera-

mic

or

crystal pickup.

TUNER

INPUT:

The

National Criterion

AM-FM

tuner

or any

high

quality tuner

may be

connected

at

this

point.

When

the

Criterion

is

used,

the

four-foot

length

of

audio interconnecting cable

may be

used.

If

another

tuner

is

employed,

the

cable used should

be

of the

single-conductor

shielded type.

The

length

must

be

determined

by the

instructions accompanying

the

tuner. Cables

in

excess

of the

recommended

length

may

cause

serious

attenuation

of the

higher

frequencies.

PHONO

INPUT: This

jack

accommodates

all

types

of

high

fidelity low-level phono pickup

cartridges.Shield-

ed

cable

of the

type

and

length

recommended

by the

pickup

manufacturer

should

be

used. A slide

switch

is

incorporated

in the

Horizon

5 to

select

the

proper

circuitry

for

either

the 10 mv. or 30 mv.

type

of

cart-

ridge. (See instruction

manual

supplied

with

the

Horizon 5 preamp).

SPEAKER

OUTPUT

AND

117V,

3A

OUTLET:

The

instructions given

in

paragraph

1.

also

apply

when

the

preamp

is

used.

OPERATING

INSTRUCTIONS

When

the

Horizon

20

amplifier

is

used without

the

preamp

installed there

are no

operational controls

to

be

adjusted.

The

line cord should

be

plugged into

a

117-volt

source that will

be

switched with some other

unit

of the

high fidelity

installation.

No

ON-OFF

switch

is

provided

on the

amplifier

since

it may be

installed

in an

inaccessible

location.

If

the

Horizon 5 preamp

is

installed

in the

preamp

compartment

of the

amplifier

or

connected

to the

am-

plifier

by

means

of the

interconnecting

cable;

all

the

operational

functions

of the

amplifier-preamp

com-

bination

are

handled

at the

control panel

of the

pre-

amp.

This includes

the

ON-OFF

switch,

program

Se-

lector switch, Loudness-Volume control,

Bass

and

Treble

controls

and the

full

range

of

phono equaliza-

tion

selection.

The

function

of

these controls,

to-

gether

with

instructions

for

their

proper

adjustment,

is

described

in the

Horizon 5 instruction manual.

-3-