Realistic Marine Radio Dx 75 Users Manual

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Ltstlc-

COM

MUN

I

C

AT I ON

REC

E

IV

E

R

OPERATING

AND

SERVICE

INSTRUCTIONS

M(IDEL

DX.I5

RADIO

SHACK

CORPORATION

DIVISION

OF

TANDY

COR,PORATION

#

INTRODUCTION

The Realistic DX

-75

Communications Receiver is desig'ned

to I rvideboth

the usual "long

wave" standard broadcast

recei)tion and'short wave' international

broadcast

recep-

tion. Therefore, it allows the listener to span the oceans

ald travel around the world by means of radio waves.

of radio waves.

Short wave radr,r signals

arcused forlong distance

trans-

nission becausc

of the way they are reflectcd back to

earth by the ionosplx'rc. Radiation frorn space

(primarily

Ironr thc sut)causes ioniz:ltioll olthe loycrs oI gascs higlt

above thc carth. Shott

wrr,rt

r-aclio signals rvill not pcne-

trate t.hcse tonized gascs; rnst.ead,

they bounce back

to

earth much like a stone skips

across the surface

of quiet

watcr. Variations in thc reflccting charactcristics of tlre

ionosphere due to sun spots, scasons,

time of day, etc.,

producc periods when the skipping of short wave signals

is espccially effective. Sincc nrany of these

periods

oc-

cur h regular cycles the listener may develop a sched-

ule of the best times to listen for sisnals from distant

Darts

of the world.

Listed below are sone of the many types of broadcasts

[hat can be heard on the short wave bands:

Amateur Radio (Ham)

Mobile Radio - Telepirone

Military

Citizens

Band

(CB)

lnt. Short Wave

(Voice

of America, etc.

)

Standard Time Sigrnls (WWV)

GENERAL

Thc Realistic DX-75 is a four band

AM receiver which

covcrs the standarcl broadcast frequencies in one band:

550 to 1600 KC; and the short wave frequencies in

tlrree

bands: 1.6

to 4.4 MC; 4.5 to fl MC; ll to 30MC.

Utilizing four tubes (one multipurpose tube affords five

tube perf

o rmance

)

plus rec tif ie

r, the supe rhetrodyne c i r -

cuit is designed to operate from a 105 to l25volt, 60 cycle

power source. A power transformer eliminates the haz

-

ard of a hot chassis. Housed in a vinyl clad steel taple

model cabinet, the receiver features an eight inch "slide

rule" type dial with continuous tuning of all four bands,

plus bandspread for precise location of signals on tie

busy short wave bands.

SPECIF'ICATIONS

6-5/16 x 14-I/4

x Lt)-17/32

1

5 pounds

550

to 1600

KC - 1.6

to

30

MC

3.5prv

at 20 MC (6

db signal-to-

noisc ratio with 30/s

mocl .

)

6 db

dorvn,

14.5

KC;

60 db

dorvn,

I 25

KC

I

.5 warrs

105 to 125 volts, 60

cps

35 watts

OPERATION

VOLUME Ciockwise rotation of t]le Volurne control

knob turns on powcl and increascs

volume.

BAND SE,LECTOR Rotation of the Band

Selector knob

switches antenna and local oscillator circuits for the var-

ious tuning bands. Index numbers are located near the

knob and at each end of the diai.

TUNING Rotation of the Tuning knob causes

the main

tuning indicator (red) to move across the dial .

BANDSPREAD Rotation of the Bandspread

loob affects

a fine tuning adjustmcnt of the reception frequency. Nor-

mally the indicator should be adjusted to the SET position.

After the approximate frequency has been tuned by use of

the rnain tuning lcrob, tl-rc bandspread

adjustrnent gradually

reduces the frequency for pinpoint selection of signals,

BFO Clockwise rotation of the BFO control turns on a

Beat !-requency

Oscillator and increases the % of modu-

lation of the IF signalby tlris oscillator. A CW signal, as

usecl

fol single side band or code telegraphy purposes,

contains no modulation and must be modulated in the re-

ceiver for proper reception (Note: settings in the lov/er

range of this control may also improve reception of weak

signals other than CW type).

ANL ON ln rfie up position this slide switch activares

the Automatjc Noise Limiter circuits designed to mini-

mize background noise, static, etc. Operation in the

downposition may benecessary for reception of the very

weak signals since the noise limiter suppresses all low-

er level signals.

REC

/ STBY The receiver may be silenced by moving

this slide switch to the STBY position witiout actually

turning off power to the nrbes. Switching back to tfie REC

position instantly returns tlle receiver to normal opera-

tion without warTn-up or retuning.

PHONE This jack provides aconnectionforheadphones

(50 to 1000 ohms) which automatically silences tlre inter-

nal speaker. The Volume control functions as usual to

vary the volume at tie headphones.

Ditncnsions

Wcight (net)

Frequency Rangc

Sens itivity

Selectivity

Audio Orltput

Input Voltage

Power Consumption

INSTALLATION

Choice of a location for tlrc rece iver may bc subject to

several considerations. Tlrese include the arrangement

oI lurnitur-c in thc roon, thc comfort ancl convicncc of tl'rc

listencr, and acccss to a good electrical ground and an

outside antenna. MarT hours of listening enjoyrnent arc

available from a short wave ll:cciver soitis recommend-

ed that the selection of a location for the DX-75 be

be carefully made,

The antenna for standard broadcast is self-contained,

however, an outside antenna is required for distance re-

ception on the short wave bands. As a general rule an

outside antenna should be as high as practical and as long

as possible (up to I00 ft.) for best reception of short wave

signals. The antenna should be mounted away from power

lines, trees, buildings, etc. , and should be attached to

its supports by glass orceranric insulators. No. 12 to

16 ga. copper covered steel wire (uninsulated) is best for

both the antenna and the down lead. A lightening arrestor

should be connected to the down lead for protection against

storm damage. For additional information on antenna

design refer to 'A. R. R. L. Antenna Book" published by

American Radio Relay League, or to any of the many other

antenna handbooks currently available.

Connect the down lead from the antenna to the #2 termi-

nal on the rear of the receiver and connect the #l termi-

nal to a good earth ground such as a water pipe. Plug the

power cord into a standard receptacle providing ff7 VAC

power.

t

,l

2

SET TUNING

CAPACITOR

FULLY CLOSEO

SPRING

HERE

3_LooP coRD

3_t/2

TURt{S

AROUNO

SHAFT

LOOP

CORD

FAST

E

FASTE

Fig. IDial Stringing Diagram

SET TUNING

CAPACITOR

FULLY

CLOSEO

G'

MAIN TUNING

DIAL

CORD

(REAR

VIEIV) BAND

SPREAD DIAL

CORD

(

REAR

VIEIY)

LooP coRD 2-t/2-''

TURNS AROUND

SHAFT

,ffit

s

c3

2-25

c4

4-40

c5

4-40

c6

4-40 c7

220

ct5

.OO5Pf

ALL RESISTOR

VALUES

ARE

IN

OHMS

A I/2WATT

UNLESS

OTHERWISE SPECIFIED,

ALL CAPACITOR

VALUES ARE

IN MICROMICROFARADS UNLESS OTHERWISE SPECIFIED.

f3-

){

R2

t.5K :

g.F.o.

Ic27

30 "/ sw

.{ oN

I

{as

I 470

=

4

B.F.O.

VIB

lz,

eCuea

clo

t.o

R3

roo

R4

47K

---

I

I

I

7 lc24

I

reov i

L--

R7

looK

c22 L

.olpt

I

R22

IK

v2

I28A6

c38

rt .oo5l

s

V3

I2AV6 V4

6AQ5A

I c26

I.otpt

- R24

o, sw

3 IOOK

.1 ST8Y.

I REc.

= Rll

2.2M

cRl

EO

3004

R23

4.7K

Rt9

250

stv

4

8.F.O.

CONT

clD

40pl

350v

crc

lOpf

350V

DX

-75

T-

I

I

l

rC

t28

+7ovj JI

PHONE

/ii-\

ey/ ,ri-3-l

t'_J .t@

,-.@

.o@

cs@

cq@

cs@

ceO

L6@

L8@

15@ cu@

crz@

u

z

(O gs@

qq@

o

Fig. 2 Chassis Layout Diagram

*

A LIC;NMENT INSTITIJC'f

IONS

Equiptnr:nt rcquirccl :

l. Oscilloscopc with calibratcd vcrtical scalc

2, RF Signal gcncrator- capablc of:

a, Oprcratiol fronr 455 KC to 30 MC

b. Attenuation below lpv output

c. Modulation at I KC wich variablc modula-

tron pcrccnt.rges

IF Alignnrent

1. Looscly couplc a 455 KC, 50/u

modulatcct signal

into thc antenna temrinals (Bancl

Sclector in po-

sition #l)

2. Corulcct oscilloscopc to spcaker tcrminals

3. With signal gcncr.rtor:'sct to lowcstu.scablc sig-

nal levcl, 1rcak all IF-

transfomrers for nrexi-

rnunl recovcred audio.

RF Alignmcnt

l. Prcliminary set up

a, Bcgi,ruring

with all tr-imnrer calrecitors

tightly closcd, o1r:n

thc trinrn)crs as fol-

Iows:

C3 I

/4 'I'urn

C4 3/4 Ttrn

C5 l/4 Tuln

C6 7

/8 Turn

Crl 1/'2

1-urn

Clz l/4'furn

Cl3 l/4'furn

C 14 l,z4

'furn

b. llcginnirg $itlr ail slugs at top of fonn ad-

just as follotvs:

L2

L3

L4

L6

L7

L8

l5 Turns

22 Turns

l5 Turns

30 Turns

22 Turns

30 Turns

15

'I'urns

NO|E:

These settings

RF Alig'nmcnt (con't.)

Z. Final A-lig'nrncnt

ln t-lrc

following proccdurc, a signal of thc spcc-

ilicd frcqucncy (ltJ/u ntoclulat-ctl) is {cd into thc

antenna tcrminal. Thc antcnna and local oscil-

Iator tuncd circuits arc adjustcd for maximum

rccovcrcd audio, always adjusting thc oscillator

cornlxrncnts first.

Iland

Signal Frcq.

and

Dial Sctting

Adjust

for

Maximunr

600 KC

1400

KC L5, LI

cll, c3

2I,8

MC

4.3 MC

L6, L2

ctz, c4

5.0 MC

lr.0 Mc

L7, L3

c13, c5

4lr.0

MC

30.0

MC L8, L4

c 14,

c6

NOTE: The atrovc adjustrncnts should bc madc in tlrc

ordcr shown, anrl shoukl bc rcg.:atc-d scvcral [inrcs on

caclt band, until propcr trackfurg and calibration arc ob-

taincd.

7

are approximate and are NOT final-

PARTS

LIST

I'TEM

NO. DESCRIPTION PART NO. ITEM NO. DESCRIPTION PART

NO.

VI

v2

V3

V4

TUI]ES

6CL8A

128A6

I2AV6

6AQsA

CAPACITORS

40

-20

-10 -4Oprfl350V

-350V

-350V

-150V

Electrclytic

.0lpf GMV

Z5U

500V Cerarnic

2-2Spf

Ceramic Trirnmer

4

-40pf

Ceramic Trimmer

4-40pf

Ceramic Trimmer

4-40pf

Ceramic Trimmer

22Opt tl\/o NPO 500V

Ceramic

-? I

t- 2)

c33

c34

r.?c

c36

c37

C3B

c39

c40

RI

R2

R3

R4

t(5

R6

R7

R8

R9

RIO

Rtl

R12

Rl3

R14

Rl5

R16

11

r7

R18

Rl9

R20

R2 l

a),

R23

R24

CAPACITORS

(CONT.)

22opt

t20J,

Z5lr 500V Ceramic

00lpf t20fi ZSU 500V Ceramic

NOT USED

.001pt

!2ffi Z5U 500V Ceramic

NOT USED

.0lpf CMV ZsU 500V

Ceramic

.()05

CMV ZsU 500V Ceramic

.005

GMV Z5U 5U0V

Ceramic

40ttf.

/ 250Y Elcctroiytic

.0lpf GMV Z5U 500V

Ceratnic

RESISTORS

2M Variable

l.5K Variable

l00ft

tl0% l/2W Carbon

47K

tlj% l/2W Carbon

3.3M 110%

1/2W Carbon

lM t10% 1/2W

Carbon

l00K tt0% 1/2W Carbon

4.7K !10% I/2W Carlrcn

4700

tl0% l/2W Carbon

27in 1l0t; l/2W Carbon

2.2M tl0T 1/2W Carbon

47K t10% l/2W Carbon

47OK

!I}a/(.

t/2W Carbon

10M

tl0% I/2W Carbon

270K !10% I,/2W Carbon

470K

!1070 l/2W Calllon

47Gt

lI0To I/2W Caitx>n

l&A

tlO% i/2W Carbon

25A1!n% sW W.W.

lK 110%

l/2W Carbon

4.7K !rO%

l/ZW Carbon

rK tl0% l/ZW Carbn

4.7K ! l07o I/2W Carbon

i00Ktl0% r/2W Carbn

CI

C2

C5

C6

C7

rra

rro

cr0

cll

CT2

c13

c14

cl5

c16

c17

cl8

cl9

c20

rtt 1

c22

c23

c24

a)E

c26

c27

c28

c29

c30

300

-268

-

l8

rot -7

34

-6

Main Truring

Bandspread

301

-338 -

r

301

-338 -2

l.Opf t10/6

500V

Composition

/

-

luuill ueramlc I rlmmer

4-4opf

Ceramic Trimmer

4-4opf

Ceramic Trimmer

4-4Opf

Ceramic Trimmer

.005uf GMV Z5U 500V Ceramic

Bzpf

- l0!i N750 600V

Ceramic

.Olpf

GMV

Z5U

500V

Ceramic

560pf

t5lo 125V

Polystyrene

1800pf

15% 125V

Polystyrene

3900pf

t5[ l25V Polystyrene

.0lpf CMV ZSU

500V

Ccramic

.0lpf GMV ZSU

500V

Ceramic

.Olpf GMV

Z5U

500V Ceramic

SEE

T3

SEE

T3

.0lpf GMV ZsU 500V

Ceramic

30pf

t5% NPO

500V

Ceram.ic

SEE

'T4

SEE T4

30pf t57"

NPO

500V

Ceramic

I

PARTS LIST (CON'T.)

ITEM NO. DESCRIPTION PART

NO. ITEM NO. DESCRIPTION PART NO.

TI

lz

.r?

T4

TRANSFORMERS

Power Traasformer

Outprt Transformer

IF 455KC

IF 455KC

COILS

RF Band

#l

RF Band

#2

RF Band

#3

RF Band

#4

Osc, Band

#l

Osc. Band

#2

Osc. Band

#3

Osc. Band

#4

SWITCHES

Power Switch

(On Volume Control)

ANL (On - Off)

STBY-REC

BFO Switch

(On BFO Control)

Band Switch

500

-685

301

-335

1655-6

1655

-6

MI

M2

CRl

cR2

J1

SPK

T

Diode 400PIV 500 MA. ED-3004

Diode 400 PM00 MA. ED-3004

MISCELLANEOUS

Dial Light

Dial Light

Phone

Jack

Speaker

Cabinet

Panel

(Front)

Panel (Back)

Knob (BFO)

Dial Glass

Feet

#1813

#1813

I6-2

14826

600-r73-3

5W-787

soo-629-2

26600P-r

301

-336

r00-435-1

l

LI

L2

LJ

L4

L5

L6

L7

L8

301

-340

301

-34

l

30L-342

30r

-343

30r-344

301

-345

30i

-346

30r-347

Knob (Bandspread

-Tuning) 27

OO2

- L

Knob (Band-Volume) 27OO2P-1

swl

sw2

sw3

sw4

sw5

300

-268

-

18

ss-32

SS.32

LOr

-7

34-6

301

-339

9