Technical information

O
RADIO
RETAILING'S
"Sezuire
SPARTON
69, 79, 79A, E9.
(Number
terminal
strip
posts
I
to
9, from front
to back.) Detector
plate
voltage,
ter-
minals
I to 2, should
be
180
with
pick-
up inserted in
jack
. . .
If
90 to 135
check 20,000
ohm resistor
and
its by-
pass
between
a.f.
transformer
primary
rnd 6lter
choke.
Detector
bias, ter-
minals 2
to 9, should be 14 to 20 . .
.
If not check
1,200 ohm resistor from
phono
jack
to
terminal 2.
With
pickup
in use voltage
should be frgm 3
to 5
. . .
If
not c[eck 1,000 ohm
iesistor
be-
tween
jack
and terminal
2. R.F.
plate
voltage,
terminals 5 to
6, normally 90
to
135
. . Check 3,000 ohm
resistor
or
its bypass between filter choke
and
terminal
6, in
filter
block. R.F. bias volt-
age, terminals 5 to 9, voltage
normal
be-
tween 3 and 5...When otherwise
check 110 ohm resistor between
ter-
minals.5
and
7. A.F.
plate
voltage,
nor-
mal between 145 aad 185. A.F.
bias,
normal
between 27 and. 4l . , .
Trouble
sometimes develops in 1,700 ohm resistor
bchrecn
ground
and c.t.
of filament
wind-
ing. Lack of voltage at any
terminal
that can be
restored by removing
cable
wire
is
caused by
shorted bypass con-
denser in associated circuit
of r.f.
amoli-
fier, Adjust screw on top'of tuner,
ieft
side,
for
best
response
between
1,250
and
1,500 kc.
SPARTON
74
Dead,
plate and screen
voltages
okeh
.
look
for
open
200 ohm
bias
resistor
feeding cathodes
of
i.f. and
r.
f.
SPARTON
79A,
89A,
930,
931,
301,
109'
ll0, 740, 75O,
589,25,26.
Partial
or
complete
open-circuit
in
r.f. chokes
com-
pose
d of
very
small
enamelled
wire
wound
on
bobbin
in all band-pass
selec-
tor
and
fixed
r.f. amplifier
models
Break
most often
occurs
at
point
where
winding
is soldered
to
ferrules
at end
of bobbin.
This is detectable
with
an
ohmmeter
and
small
pocket magnifier.
Remove
a
few turns
of wire,
clean
with
fine sandpaper,
than warp
a
half dozen
turns
around
the
ferrule
and solder
with
rosin core.
Most of
the
chokes
have
a d.c.
resistance
of
about 3,000
ohms
and
a
hundred
turns
more
or
less seenls
to
make
no
difference.
SPARTON 79A,
109, ll0, 930. Oscilla-
tion
"growl"
while tubes
are
heating
when using
485's
in r.f. stages,
Place
quick-heaters
in first and second
r.f.
sockets
and detector socket,
using stow
heaters
in
third,
fourth and
fifth.
If
only
one
quick
heater is used
place
it
in
the
detector socket. If more than
three are available
ptace
them in third,
fourth and fifth.
I
SPARTON
80,
83, 84. Burning
out
oi
3,000 ohm resistor
part
8-6061-3
(5,000
ohm
part
8-6060-5 in
later serial
numbers) . Usuatly due
to
failure
of
.2 mfd.,
200 volt condenser
connected
from
plate
of
a.v. controlled tubes to
ground,
shown
as
C8
in
diagrams.
Re-
place
resistor and replace
condenser with
600
volt unit.
SPARTON
E0, E3,
E4, EsX,
66X,
104,
E35.
Improving
tone
of
cabinet
modelg,
.
. Remove
screws
hotding
speaker
bafre in
place.
Insert
I
inch
spacers
under
screws,
replacing
only
those
at
four corners.
SPARTON 89A,
79A.
R.f.
oscillation
in
serial numbers using
485
tubes. Re-
adjust
trimmers to exact resonance. If
trouble
persists
replace .5 m.f.d. B bypass
in r. f.
amplifier with .25 mfd.,
400
volt
tubular unit.
Some
late
chassis have it.
SPARTON 3O
I
Flunr
clean
and tighten
the
grouud
courrectiotrs
on
the large
7,000
rrhnr
resistor
located
in back
of the 50
trthes.
SPARTON
30 I
If hunr
still
retrrains
aftrr
cvet'1'-
trhing
is
checked, clean
attrl
tig'hten
gloutrd
connectiorl
oi the
l:Llqe
rvit'c-
woutrd
7,0{X)
ohrrr
ie-sistot'.
SPARTON 333
Spurir-rus oscillations at.
higlr
f re-
(1renc),
entl
of
dial
.
.
.
Replace 50,000
ohm oscillator
gli<l
leak
conttectecl
front
grid
to catlrorle of socket u'ith
I
sirtt
-10,()00
ohrns. Original unit has incrcased
r
;Llrte
causing
oscill;rtor to sr.lpcr-
rcgenerate.
SPARTON
333. Reception
of
code
or
police
signals . . Often
caused by
breaking
of
wire
which runs from
an-
tenna equalizing
condenser
to r.f. sec-
tion of
'the
condenser
gang.
To
correct,
remove lrroken
wires and solder in 6
inch length of flexible wire. Form
a
loop in this wire
by
winding a
few
turns around a lead
pencil.
This
rvill
allow slack
and avoid further difficulty.
In the event that
the wire connecting
the
grid
cap
of the 6F7
6rst detector-os-
cillator to the antenna
equalizer breaks
replace
with
longer
flexible rvire rutr
fronr the
grid
cap
down under the
gang
condenser
arrd thence to the equalizer.
SPARTON
333. Intermittent or noisy
reception Frequently caused by
breaking of stator
connections
under-
neath condensers. Replace such
leads
with stranded
push-back
wire.
(I.F.
456
kc.)
SPARTON
333.
Hum
r\tay
be
a floating
ground
at
the eyelet
of
the
.12
tube,
One
side of the
heater cir-
cuit
is
grounded
at this
point
anti
if
the
eyelet loosens
an intermittent or
fading
\um
of the
same
pitch
as the
vibrator
will
result.
Correct
by soldering
two
additional
ground
connections
of the
same type
and in
the
same
circuit, one
at the 6F7
socket
and one
at the 78
socket.
A
grounding
wire should also
be run
from
the
gtound
circuit
heater
terminal of the
75
socket
over to the
resistor
mounting
ptate,
which should
be
grounded.
SPARTON
4OO
Intermitterrt noise caused by
poor
contiict
of
r.f.
gritl
returtr uhich
c()nuects to casting on
bottonr
of coil.
Sol<ler
lead frour tlris lug to
ground.
SPARTON
4IO
Nlicroplronic
horvls and
fa<ling
checl<
vitrcous cnameled
voltage
di-
virler
liveted
to
shiclding
panef Rivets
ale used
to secure the
divider
to the
shielcl, also to
make contact
to
the
circuit
lrrgs. To repair,
solder
resistor
lugs to
circrrit
lrrgs, also solder
pumper
to
shieldinc.
Since trvo
of the divider
ternrinals
irre
insulated from
the
chassis,
cale should be
exercised
when
solrlcring the
lue.s not to
thertr to
the
shicld
pancl.
SPARTON
410.
No
plate
voltage
on
i.f, tubes and oscillator. Replace
tubular
condenser attached to front
panel
with
.5 or I mfd.,
400
volt capacity.
SPAPTON
410.
Type 45
power
tubes
n.ray
be substituted
for the
183's by
re-
wiring the output
stage filaments
in series,
including a
half-ohm
resistor in the circuit.
SPARTON
410.
Set
breaks into
oscillation after warming
up although
all
voltages,
bypasses
and
ground
con-
nections are ok
. .
.
Try
two
new 183
type tubes.
SPARTON
1t0,
120
Interinittent.
inspcct
the
resistor
hlock
iol loose
conncctions.
SPARTON
5r7,
557, 567
.l)istortiorr,
disappears
n'hen fitrger
is
placcd
on
grid
cal)
of 75 tube
chcck for leaky
bypass
at
junction
o{
220,000
and
100,000
ohnt
resistor in
pllte
circuit of 75.
SPARTON
537, 577
Dcad
or rve:lli
arrtl tlistor-terl
tcst ior
short
or lerrliagt' in
0. 1 urfrl.
conclcttsrr, b-ylrarsirrg
jurrcture
ol 270.-
000 ard 100,00() olrrrr
rc:istors irr
platc
cilcuit
o[ 6Q;G.
(
)r'ia'inal ratctl
at
-{{)0
r',rlts; repl:rcc
,,rith
6t)0
volt rrnit.
SPARTON 537, s77
High noise
level
at
all
sc-ttings oi
volume corrtrol
check
i.f.
trans-
formers,
particularl.v
thc
primarics,
for
high
resistance
ope'ns.
Test
lrv
both
voltage
and continuity
methods
as sometimes
one
procedrtrr
rvill shorv
the coil as bcius okeh
nlrercas thc
other
rvill
clisclose
the
troulrle.
Oscillation
rvith vt,lurue control ad-
justed
to about
nricl-point
push
control
grirl
of 6Q7G
an'ay
f
lonr
6F6G
output tube. Spealier cable
rvires
shoultl also
bc renrovcd
fronr
vicinity
of
botlr
tubes.
(i.f.
-1.56
l<c.)
SPARTON
589. Weak reception
and
low
speaker
field
current
.
. .
Replacc
defective resistor with brown and
sil-
ver
ends,
connecting
primary
of a.f.
transformer
to
ground.
57