National Horizon 20 User manual

INSTRUCTION BOOK FOR
The
National
The latest in audioengineeringtechniques,plus
careful attention to design details, make the Hqrizon
20 an instrumentunparalleled for superb performance
and operatingefficiency. Its excellentcharacteris-
tics are due, in largemeasure, tothe uniqueoutput
stage in which the couplingbetween the outputtubes
is unity,independent ofthe outputtransformer. This
permits the useof highefficiency class ABj operation
without the impulsedistortion commonly associated
with conventional circuits whichrelyupon the output
transformer for couplingbetween the tubes. Unity
coupling hasthe additional advantage of requiring a
TWENTY WATT
AMPLIFIER
far lowerimpedance ratio between the outputtubes
and the load with attendantreduction in leakage in-
ductance and increased power bandwidth.
In addition toits superlative performance, theNa-
tionalHorizon 20 incorporates the unique plug-in faci-
lity forthe accommodation ofthe Horizon 5 Preampli-
fier — ControlUnit.Thisfeaturealoneexemplifies
the advanceddesign ofthe National high fidelity line
resulting in optimum flexibility of installation and
operation. The following specifications indicatesome
of the other outstandingfeatures ofthe Horizon 20.
Please use this manual. Ithas 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 ratedoutput of
20 watts. 0.6% at25 watts.
INTERMODULATION DISTORTION: 1%at20 watts,
measured with 400 cps. and7 kc.ata ratio of 4:1.
FREQUENCY RESPONSE:±0.1 db from 20 cps. to
20 kc.±1db from 10 cps. to100kc.
POWER RESPONSE AT20 WATTS: ±0.15 db from
20 cps. to20kc.±1db from 10 cps. to60kc.
HUM AND NOISE: 80db below 20 wattsoutput.
SENSITIVITY: 1.6 volts for20 wattsoutput.
OUTPUTIMPEDANCE: 8 and 16 ohms nominal.
INPUT IMPEDANCE: 500,000ohms.
INPUTLEVELCONTROL:accommodates a wide
range of input signal levels.
RUMBLE FILTER:built into minimizeturntable
rumble and noise.
ACCESSORY OUTLET: 117 volt AC,3 amp.con-
venienceoutlet for energizing associated equipment.
PREAMP COMPARTMENT:contains multiconnector
wired to associated rear-paneljacks to convert the
Horizon 20toa single-unitequipment when the Hori-
zon 5 preamp is plugged in.
POWER INPUT: 117 VAC,50-60cps, 1 amp, 110
watts.
PREPARING TO OPERATE
Examine the amplifier immediately after unpacking
to make certainthat no apparentdamage has been in-
curred duringshipment. A cardboard padis placed
around the tubes to protect them in transit. This must
be removed. Todosoitis necessary to remove the
cabinet. Since the Horizon 20hasno operatingcon-
trols, itmaybe installed inany convenientlocation
so long as there will bea free circulation ofairto
allowventilation. The above would holdtrue when
the Horizon 5 preamp is used with the amplifier, pro-
vided that the preamp is located ata pointremote
from the amplifier.
When the NationalHorizon 5 preamp is plugged into
the Horizon 20,the unitmust be installed with con-
trol accessibility in mind. The attractive overall
appearance ofthe amplifiermakes it well suited for
useona tabletop,shelf orany convenient location.
Once the input,power and speakerconnectionshave
beenmade, the Horizon 20 with the Horizon 5 preamp
becomes a versatile controlcenter forthe custom
high fidelity installation. Ifitis desired to make this
combination part ofa custom installation, refer tothe
paragraph on Cabinet Installation.
ELECTRICAL CONNECTIONS
Allthe input and outputconnections ofthe Horizon
20 amplifier are located onthe backdrop ofthe chas-
sis. See Figure 1. Connections tothe variousjacks
and terminalsshould be made inthe following manner:
1. HORIZON 20 AMPLIFIER WITHOUT HORIZON
5 PREAMP
PWR. AMP.INPUT: The output ofthe National
Criterion or similar AM-FM tuner orthe output ofa
preamp otherthan the Horizon 5 is connected to this
jack.Singleconductorshielded cable must be used,
the lengthdictated bythe recommendationsaccompany-
ing the particularequipment. Associated equipment
should have an output level of1.6 volts or more. All
other jacks are unused.
SPEAKER OUTPUT: A highfidelityloudspeaker
system having an impedance of either 8 or16 ohms
may be connected to these terminals. The terminal
marked G isthe common connection andmaybe
grounded if desired. Shieldedcable isnot required
for speakerconnections andthe length isnot critical.
Number 18 wire (size of ordinarylampcord), or larger,
is recommended.
117V 3A OUTLET: This convenienceoutlet is
supplied forthe purpose of providinginputvoltage
for otherunits ofthe system as desired. Itis ener-
gized when the amplifier is pluggedinto 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, eitherpluggedinto the
unit or connected by means ofan interconnecting
cable, the Pwr.Amp.Inputjack isnot used. The
interconnectingcablecompletewithmatingconnec-
tors maybe procured in either 4 or 15-footlengths.
When the interconnecting cable is used, remove one
of the thumbscrews from the preamp compartment
coverplate and thread the screwinto the tappedhole
atthe rightedge ofthe preampcompartment. This
must be done in order to close the interlockswitch.
TV INPUT: AnyTV tunerhaving an output of1.6
volts or more maybe connected to this jack. This
jack will also accommodate the standardhigh-level
ceramic or crystaltypephonopickup.Shieldedcable
must be used.
TAPE PLAYBACK INPUT: A tapereproducing
unit maybe connected to this jack, orany 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. Thisjackwill also accommodate the cera-
mic or crystalpickup.
TUNER INPUT: The NationalCriterion AM-FM
tuner orany high qualitytuner maybe connected at
this point. When the Criterion is used, the four-foot
length of audiointerconnectingcable maybe used.
If another tuner is employed, the cableusedshould
be ofthe single-conductor shieldedtype. The length
must be determined bythe instructionsaccompanying
the tuner.Cables in excess ofthe recommended
length may cause serious attenuation ofthe higher
frequencies.
PHONO INPUT:This jack accommodates all types of
high fidelitylow-levelphonopickup cartridges.Shield-
ed cable ofthe type and length recommended bythe
pickup manufacturer should be used. A slide switch
is incorporated in the Horizon 5 to select the proper
circuitry for either the10mv.or30mv. type of cart-
ridge.(Seeinstruction manual supplied with the
Horizon 5 preamp).
SPEAKER OUTPUT AND 117V, 3A OUTLET: The
instructionsgiven in paragraph 1. also apply when
the preamp is used.
OPERATING INSTRUCTIONS
When the Horizon 20 amplifier is usedwithout the
preamp installedthere areno operationalcontrols to
be adjusted. The linecordshould be pluggedinto a
117-volt sourcethatwill be switchedwithsomeother
unit ofthe highfidelity installation. No ON-OFF
switch is provided onthe amplifier since itmaybe
installed inan inaccessible location.
If the Horizon 5 preamp is installed inthe preamp
compartment ofthe amplifier or connected tothe am-
plifier by means ofthe interconnecting cable; all
the operational functions ofthe amplifier-preamp com-
bination are handled atthe controlpanel ofthe pre-
amp. Thisincludes the ON-OFF switch, program Se-
lectorswitch,Loudness-Volumecontrol, Bass and
Treble controls andthe full range of phonoequaliza-
tion selection. The function of thesecontrols, to-
gether with instructions for their proper adjustment,
is described inthe Horizon 5 instructionmanual.
-3-

FRONTPANEL
OF CABINET
BRACKET
NOTE:
FELT FEET
DIMENSIONS OF OPENING IN
FRONTPANEL 14"X 4"
Figure 2. Custom Cabinet Installation
-4-

CABINET INSTALLATION
If desired, the Horizon 20 Amplifier maybe mounted
ina woodencabinet as part ofthe custom installation.
Thisrequires a shelf and cutout as illustrated in
Figure 2. Locate the14by4 inchhorizontalcutout,
making certainthat itis square with the sides ofthe
cabinet. Prime consideration should be given tothe
location in regard to accessibility of controls and
sufficient clearancebetween thetopofthe amplifier
and the inside ofthe cabinet topto allowventilation.
A 12by15 inchshelf must be installed within the
cabinet, with itstop surface flush with the bottom
edge ofthe cutout.Thisshould be made of stock at
least 1/2 inchthick and supported by shelf mounting
brackets sufficiently rigid to maintain the weight of
the Horizon 20.
Remove the metaldustcover from the amplifier as
described inthe followingparagraph. Before placing
the amplifier inthe cabinet it must be equipped with
the ornamental bezel. Thisbezel maybe procured
from your Nationaldealeralong with the necessary
brackets, mounting hardware and A.C. linecord. The
bezel hastwo mounting holes onthetop flange and
three holes onthe bottom flange. Thetop flange is
securedusing the brackets, screws, washers and nuts
suppliedwith the bezel. The bottomflange is secured
by first withdrawing thetwo feltfeet and self-tapping
screw atthe front ofthe amplifier and thenreplacing
them through the flange.
Slide the Horizon 20 through the cutoutuntil the
bezelmeets the front ofthe cabinet. The weight of
the amplifier is sufficient to hold the unit inthe
cabinet.
REMOVALFROMCASE
The Horizon 20 amplifier is enclosed ina ventilated
protective metal dust coverequippedwith a safety
interlock. The cover must be removed to gain access
tothe tubesand/orcomponents. Todoso, remove
thetwo hex-headscrews atthe front corners ofthe
bottom plate and remove thetwo Phillips-headscrews
atthe ends ofthe reardrop ofthe dustcover. Slide
the coverstraightback far enough to disengage the
interlockplug and then lift the cover from the ampli-
fier. Thisprocess is reversed when replacing the
dustcover. Use care in engaging the interlock to
prevent distortion ofthe plug.
HUM BALANCE ADJUSTMENT
Thehum balancingadjustment has beenmade atthe
factory for satisfactoryperformance ofthe power am-
plifier itself butmay requirereadjustment after the
input equipment(Horizon 5 preamp etc,) has been
connected. To accomplish this, turn onthe equipment
and turn the loudness or volume control ofthe preamp
to maximum. Any tonecontrols,such asthe Bass
and Treblecontrols ofthe Horizon 5, should beset
atthe Flat position. With no signal input,adjust the
Hum Balancecontrol onthe rear chassis drop ofthe
Horizon 20for minimum hum from the loudspeaker.
GAINADJUSTMENT
The Gaincontrol atthe back ofthe chassis requires
no adjustment when the Horizon 5 preamp is used
with the amplifier. Itis always left atthe maximum
clockwiseposition (full gain).
When the Horizon 20is usedwithout a preamp, the
Gain control is adjusted toseta limit of maximum
volume level as follows:
Setthe volume control ofthe deviceconnected to
the amplifier at maximum. Setthe Gaincontrol of
the amplifier to provide the maximum volume forthe
specific installation. Make this adjustment using
program material with a high audio level. Thereafter
the level is controlled bythe volumecontrol onthe
associated device.
-5-

TABLE 1. TUBESOCKETVOLTAGES
CONDITIONS
All voltages measuredbetween tube pinand chassis except as noted.
VTVM used forall measurements.
117 VAC, 60 cycle input.
No input signal.
Tolerance ±1.0%.
TUBE
VI
V2
V3
V4
PIN
1
140
0
0
NC
2
0
32 #
32 #
400H
3
1.5
380
380
117V
tie point
4
32*
380
380
350AC
5
32*
-26
-35
NC
6
250
-26
-35
350AC
7
»*
32 #
32 #
5
8
-270
5
0
400 «
9
32*
—
—
—
*6.3 AC between pins 4 or5 and9.
**-3.6 betweenpins 7 and8.
#6.3 AC betweenpins 2 and7.
##5 AC betweenpins 2 and8.
I6db FEEDBACK-
PWR.AMP.,
INPUT
c
CONNECTED
WHEN
HORIZON 5
IS USED
TAPE
PLAYBACK
PHONO
TUNER0
•>0/60cps
SPEAKER
OUTPUT
Figure 3. Functional Block Diagram
-6-

PARTS LIST
5YMBOL
CR1
El
E2
Jl
J2
J3
J4
J5
J6
LI
PI
R3
R19
SW1
Tl
T2
Wl
XF1
DESCRIPTION
SeleniumRectifier
Dummy Panel
Terminal Panel, speakerconnection
Phono-jack, single, CinchMfg. Co. type8171
Receptacle, A.C. Alden Products type 402ACE
Receptacle, A.C.powercordinterlock;CordsLtd.,Inc.typeCC-2
Phono-jack, double,CinchMfg. Co. type8113
Jack, 16 contacts, Amphenol type 26-4200-16S modified
Phono-jack,double,CinchMfg. Co. type8113
Filter Choke, 1.5 hy, 200ma, StancortypeC2327
Dummy Plug
Variable,500,000ohms, C taper, IRC type RQ13-133
Variable,1,000ohms, A taper, IRC typeRQ11-108
Switch,interlock
Output Transformer, two primary windings
Power Transformer, primary 117v AC,60 cycles; secondaries 360-0-360 v at
120 ma,5 v at3 amps, 6.3v at3.5 amps
Power Cord, 2 conductor,interlock;Phalo Plastics typeCSR-606RTV or
equivalent
Fuseholder, Littlefuse type34201
NATIONAL CO.
DRAWING NO.
T657-1
T671-2
E259-6
T458-1
T452-1
L283-1
T579-1
T448-1
T579-1
T685-1
SB:2800
T013-1
T013-5
T755-1
T665-1
T658-1
A 10927
E510-1
Standard Form Warranty
Adopted by die Radio Manufacturers Association, Inc.
This equipment is warranted tobe free from defective material and workmanship and repair or replacement
will be made ofany part which under normal in stall at ion, useand service discloses defect, provided the unit
is delivered bythe owner tothe manufacturer or through the authorized radiodealer or wholesaler from whom
purchased, intact, for examination, with all transportation chargesprepaid tothe factory,within ninety days
from the date of sale to originalpurchaser,and! provided that such examination discloses in the manufacturer's
judgment that itis thus defective.
This warranty does not extend to any radio products which havebeen subjected to misuse, neglect,
accident, incorrect wiring, improper installation, ortousein violation of instructions furnished by the man-
ufacturer, nor extend to units which have been repaired or altered outside ofthe factory, norto cases where
the serial number thereof has been removed, defaced or changed, norto accessories used therewith of other
manufacture.
Any part ofa unit approved for remedy or exchange hereunder will be remedied or exchanged bythe
authorized radio dealer or wholesaler without charge tothe owner.
This warranty isin lieu ofall other warranties expressed or implied andno representative or person is
authorized to assume forthe manufacturer any otherliability in connection with the sale of theirradioproducts.
National Company, Inc.reserves the right to make any change in design orto make add' tanto, or im-
provements in,its products without imposing any obligations upon itself to install them inits productspre-
viously manufacturered.
-7-

Figure 4. Schematic Diagram
-8-
M-4000-ER418
10-54