Technical information

O
RADIO
RETAILING'S
,,.
ehube
&
.
check
of
this
unit
STEWART.WARNER
STEWART-WARNER,
Loss
of vol-
unle
or sensitivity
after
defective
by-ptrss
condenser
is
replaced
Sets are criti-
cal as
to by-pass
condenser
values.
IJse
exact original
value
of
tubular type
con-
denser,
avoiding
mctal-cased
replacement
units.
STEWAR,T-WAR,NER.
Some
models
of auto-radios
have
loud hum when volume control
is at
low setting
Looser. the r.f. coils
and
shield
wire
from
volume
control
to
e
coupling condenser
located
under
these
coil cans on the bottom of the
chassis. The
shield should
be soldered
to the
grounded
terminal
of the
volume
control.
Hum is
caused
by
inductive
pickup
frorn the A wire to the
vibrator
being alongside the
wire to
be shielded.
Loud
hum and chattering of
relay,
weak,
distorted
reception Open
plate
circuit
to
one
plate
of
84. May be
bad socket contact.
STEWART-WARNER
Bad hunr
replace
th:
.grid
re-
sistor in the output
stage
\\'ith 100,000
ohms.
Also
tighten
spring
holding
grid
bias
cell.
STEWART WARNER 9I.62
Sensitivitv
rlrops
aftcr
pllving
a
short
tinre, turrirrg eye lill
not opcr-
ate.
. . . I-iqrrirl
lclLl<s
out of
clectrolvtic
cotrrlcnscr :rrrcl
partially
sltorts avc
systenl.
STEWART-WARNER
Rl00A,
RlooB,
R10OE.
Distortion .
.
. . Check2T-plate
current and
voltage, which shoutd
bc
about 3
mils.
at
115 volts. If
low volt-
age and higher
mils., replace .1-mfd.
tubular
coupling
condenser,
probably
lcaking.
Regular lfl),(DO-ohm
ohmmeter
will
not show
it up. Condenscr
is con-
nected
between detector
ptate
choke
and
first audio
grid.
It is also a
good
idea to
replace 45,fl)0-ohm
(red),
l-watt
carbon
resistor connected
between r.f.
plates
and
ground
(bleeder)
with
a
2-watt
carbon
job
while
the
chassis is
open,
as this
is a
common
cause of
low
voltage and
weak reception,
STEWART WARNER
I02
\\'errk.
rli*tor'leri
clreck
f,rr
t-,peIt
or
sltorted .l
nrftl cottdcnser
connected
lrt'tweetr
the
purplc
and
yellow
rcsistors
orr
the resistor
strip.
STEWART
WARNER
R-IO2A
Overload
on strong
signats
trY
different
values
cathode
resistor
(orig-
inal
45,000) as
this
valtte often
critical.
STEWART-WARNER
102A.
Quat-
ity
poor,
no volume
. . .
Check
.l mfd.
condenser
near 5l tube socket,
detector
audio
couplin
g
.02 and. 2
megohm screen-
grid
second detector
resistor.
STEWART-WARNER
ll0.
Loud
crackle
when
set is
first
turncd
on
(early
production
models)
Don't look
for
death and destruction
in the
powerpack.
The noise is normal, emanates
from clcc-
trolytic condenser
film breakdown
on
high starting voltages
and the
film
quickly
reforms.
STEWART-WARNER
ll2. Noise
after
standard suppression
has been
in-
stalled. Shield
tone control
and
pilot
leads
from
tuning
head to chassis
with
metal braid,
grounding
at head.
Bond
shield of
ant€nna lead to
metal case
of
chassis,
STEWART
WARNER
116. Hum
. . .
Check
for
following
possibilities:
Poor
contact at
grounding
lug of
vitreous
voltage divider
resistor.
To cure, tighten
screw used to
hold down the
grounding
terminal
and solder it in
place.
If this
does
no
good
cut
the 230 ohm
negative
section out
and use a separate
230 ohm
unit.
To cut out section unsolder
from
the negative terminal
of the divider
both
the wire
leading
from the
power
trans-
former and the
small,
red resistor
within
the insulated
sleeving.
Re.solder
these
wires to one end of
the 230 ohm resistor.
Sotder the other end
of the
resistor to
ground.
The
groundinc
lug located
be-
low the shortwave
switch is convenient
for
grounding.
Keep
power
cord
away
from
the .05,
100 volt
isolating
con-
.denser.
See
that
green
speaker
field
coil lead
goes
to
the front etectrolytic
condenser.
the white
lead to
the
rear.
STIWART-WARNER
R1I6AH. I.f.
trimmer requircs frequcnt
adjustmcnt
.
. .
.
Caused
by
expansion
and contrac-
tion drte to temperature.
Readjustment
required
every 2 to 3 months where
weather
varies widcly.
STEWART-WARNERRl16.
Setgets
oft
calibration
and
loses
power
on
lower
end of dial
. . .
. Trimmers
on
gang
are
soldered,
poor
connections develop
here.
I-ook for opens or
high-resistance,
re-
solder
and
balance.
STEWART
WARNER
R-II5X
Weak
and distorted
Shorted
0.1
mfd. cottrlt'nscr
betwcen
positiv€
ternrinals
of dlectrolytic
contlensers
shorting
spelker fielcl.
Replacc with
600
volt
unit.
STEWART-WARNER
RII6X
Deacl replace oscillator
plate
resistor with
20,000 ohnts, also replace
the condenser
at
B
plus
end oi this
resistor with .1
mfd.
STEWART
WARNER
RI2OA
Weak
. sltort
out
cttllo(le
l'e-
sistor
of
oscillator
tube'
STEWART-WARNER
R,I36, RI37, RI3E.
Poor sensitivity at
low frequency
end of broadcast band,
inability'to align
or calibrate at
600 kc., oscillation
at
low frequency end of
broadcast band
.
. .
Almost
always
due
to
large
change
in
capacity
of small bakelite
fixed
con-
denser connected across
oscillator
shunt
padding
trimmer. Unit colored brown,
brown, black.
Replace
with
.000011
original
replacement number 85434.
STEWART
WARNER
R-I274
Poor
tone,
oscillates
t()ne
control,
often
lralf
operrs.
STEWART-WARNER
R.I36, R-I37,
R-138.
lnsensitive
above
12
mc.
despite
perfect
alignment and
corrcct
voltages,
shadow-meter
on
last
two
chas-
sis
mentioned
contracts
as if station
was
tuned
in when set
is switched
to
this
high-frequency
range
.
.
Due
to
stray
coupling
within
set
wiring. Sets
up spu-
rious oicillation
of
the 6,{8,
causing the
control
grid
to
draw current,
producinig
an a.v.c.
voltage
and reducing
sensitivity.
To eliminate
trouble
isolate
grid
return
of the
6A8
from the
a.v.c.
sYstem bY
returning it directly
to
ground.
The
grid
coil of this
tube
is tuned
by trimmer
condenser
ll in the
136, by
trimmer
15
in model
137 and trimmer
16 in the
138,
referring to the
diagram.
Shortwave
sec-
tion is the
one
wound with
heavy,
bare
coDDer
wire
and
grid
return
id at
the
toi, the
lead
running down
the
full
lencth of
the coil
before
it is
soldered
to its terminal
lug.
The simplest
way to
isotate
the
grid
return
circuit
is to
cut
the heavy
coil
wire as close
to
the lug
as
oossible.
Be careful
not to
cut
the
6ni
wire
from another
winding
soldered
to this same
terminal.
After
cutting
the
heavy wire
merely
re-solder
it to
the
grounded,
threaded
support
lug of the
ioit.
Re-align the
set
after change
is
made.
STEWART
WARNER
R.I45
Severe
distortion,
excessive
bias
on
the 6F5
tube
Trouble
may
be
checked
to
25 ohm
resistor section
shown
above.
A
change of onlY
a
few
ohm
in this
resistor
will
cause
the
trouble.
Dead
.
. . Check
for open
circuit
in
one
of
the
resistors
shown
above.
Mo-
torboating
can
usually be stopped
by
bypassing
the
25 ohm
section with a
10
or
l5
mfrl
electrolytic.
STEWART
WARNER
Rl'17
Station
hum
replacc .'l
mfd.
screen
bypass
on
6,4'8
with .5
mfd.
unit.
STEWART
WARNER, R I,t9
Hunr on stations
conncct
6KZ
and
6J7 screen
gri(ls
together.
Retrtove
.01 rufd. contlenscr
antl
110,000 ohnt re-
sistor
corrrrt'cted to
i.f. circuit.
STEWART WARNER
R.I6I-D, R.I6..tD
Burned out
driver
transformers
Check
.0011
mfd condenser
from
plate
to
ground
for leak or short.
If this
condenser shorts
it
places
135 volts
directly
across
the driver transformer
primary.
STEWART-WARNER
RI73
Dead check
for
leakv audio
coupling
condenser rvhicl'r
puts
a
posi-
tive
voltage
on the 6F6
,rutput
tube
grid.
59