Technical information

O
RADIO
RETAILING'S
ff,
erde
CROSLEY
Showbor. No r.f.
platc
voltage. Shorted 5 mfd.
condenser by-
passing
B-rupply lead
is reported
as
most common
cause.
CROSLEY
SHOWBOX.
Fading.
Try
soldering a
piece
of wire
on bottom
of aerial lug
and fastening
the other end
under
the screw at
the top
of the aerial
and
ground
strip.
Distortion
or dead
set. Apply
heat
with soldering
iron
to
the
case of
the a,f.
condenser. Then
push
back
high
potential
terminals.
CROSLEY.
Certain
N{ershon
con-
denser
models hum
and may
be repaired
by drilling
a
i
inch
hole
in
the bakelite
top
of
the electrolytic
unit,
being
careful
not
to damage
the
"innards,"
filling
with
distilled
u'ater
to a
point
about
I
inch from
the
top and
closing
up
the
hole
again
with sealing
wax.
Discharge
tlre
con-
denser
before drilling.
DETROLA
DETROLA 6W
\lreak
check 75,000
ohm
plate
resistor in i.f.
stage.
Distortion
Check
25 mfd electrolvtic
across 42
bias resistor
for short.
DETROLA
58
Distortion
after
about
l0
minute-s
operation
. look for
open
section
of candohrrr
resistor'
Iocaied
at the
right
of the
grouncl
connection. Re-
place
rvith l00
ohnr
5 rvatt unit.
DETROLA
IgIE
Porver
transfornrer heats
check
po\rier
transfornrer. leads for
short
u'here
they
pass
through
hole
in
chassis.
DETROLA
288
PORTABLE
Oscillation.
noisy, frequency
juurps.
Negative A
and B
terminals
grounded
to socket.
Solder socket frame
to
chassis as rivets make
poor
connection.
DELCO
DELCO
630, 500.
Comnron conr-
plaint
is
lack
of
reception
on stations
that are
not local, but which should
nevertheless
be
within
range Due
to blocking of weak signals by noise-
suppression circuit. To
correct make
the following
simple wiring change:
Remove
the wire connecting the
ground
end of the votume control
to the chassis
ground.
Connect this
ground
lug of
control
to cathode
of
6D6
tube. In
some instances
it is found that the
above change
results in the appearance
of
vibrator noise not
bothersome before.
To
eliminate
it after making
the sug-
gested
change connect
a 100-ohm re-
sistor in
series
with
the
275 ohm
com-
mon bias resistor
for
the 6D6
and
687
tubes. Put
it between
the
cathodes
and
the old resistor,
re-connecting
the
by-
pass
condenser.
across
both the
old
and
new resistors.
Connect
the tead
from
the
volume
control to
the
junction
be-
tween
the resistors.
20
DELCO
500'
No volume .
. Connect a
.001
mfd
condenser from
the
lug
on top of
r.f. section
of
gang
condenser to
grid
of first detector
stage.
DELCO 64t-654
Facling
ternrinals.
resolder oscillator
coil
DELCO 644
Fading check for
short to lug
on loacling coil
in
series with
antenna
coil.
DELCO
6,14
Fading . .
look for
short of sec-
ondary trimmer
lugs on second i.f.
DELCO
|
| 17
Poor tone
readjust
speaker
by
drilling out
riveted washer which
holds
spider
in
place.
Adjust
cone
with spaeers as usual;
fasten with
self
tapping screw and same washer.
oELCO
Rr
I r7
No tuning
eye action,
frequent 6G5
replacement, no
pep
ground
brown lead coming
from tuning
eye
socket.
DELCO
RIII9
Tuning
eye
inoperative,
no
plate
voltage
on 6L7 tube shorted
.01
bypass
condenser and burned 15,000
ohm resistor. Replace
both resistor
and conclenser.
DELCO
R-r r t9
Repeated
bl6wing
of
line
fuse during
warm
up
period
. . . Replace 3 mfd.
250
volt electrolytic
condenser
with 400
volt
unit.
DELCO RI I26
Oscillation
Replace
8-8
mfd
filter. If
a
high pitched
whistle still
persists
connect
a
.002 mfd unit
from
plate
of
output tube to
ground.
DELCO R-r
r29
Distortion and
hum when signals
are tuned in, 6E5
r.rot operating
replace
6E5.
DETROLA MIDGETS
Distortion
rcplace
.5
rrreg
plate
resistor
ol 6C6 detector rvith
.25
mee.
DELCO
'35, '37
Impossible to align
correctly
r.'u'ithout
squealing or
uncontrollable
oscillation.
This is
particularly
common
on
models
using
(rA7
and 687
tubes. Grid
and
plate prong
on
6A7
very close,
causing
feedback.
To remedy,
cut lead
to
plate
prong
to absolute
minimum
and shield.
Also,
insert
insulated
piece
of braid
between
grid
and
plate
prongs;
ground
braid.
DELCO
CHEVROLET 985200
Blows
fuses .
.
. look
for short
from
can to
ground
of
4-12 mfd electrolytic.
To
remedy: take can out
of
clamp
and insulate with
heavy
paper
and
cambric.
DELCO
AUTO SETS
Most of these
receivers
have a
1.-500
ohm resistor
in
series with
one of the
6D6
cathode
leads. Sensitivity
can
be
increased by substituting
a
300 to
500
ohm
unit.
Dead check
tone
coucletrser
for short.
Vibrator hash
defective
42
output tube. Also
try 8 mfd.
elec-
trolytic from orre
sicle of the
heater
to
ground.
EMERSON
EMERSON
5A AUTO
RADIO
Insensitive,
poor
a.v.c.
action
replace cathode
bias
resistor on 85
tube
with
14,000
ohm
unit.
Also replace
l0 mfd low voltage condenser
in
same
circuit.
EMERSON
5A
Insensitive
rePlace
14,000.
ohm
catlode
resistor
on
85
tube.
Resistor
has
greatly changed
value.
EMERSON DSs
Low volume
. . . Check
plate
voltage
ol 2B7; if
low, replace
100,000 ohm
plate
resistor.
EMERSON
H5
Loud hum;
filter condensers
and
tuber check
O.K.
. .
inspect the ballast
resistor for
leakage
from
taPS
to
ground. This
'resistor
is
covered
rvith
asbestos
then
protected
with a
metal
sheath.
If leakage
is found, insulate
sheath
from chassis.
EMERSON H5
Hum, condensers and tubes check o.k.
. check
for
leak between line drop-
ping
resistor and
ground.
This is
a
nretal
cased unit and very often a leak
through the asbestos occurs.
EMERSON U68
\\'eak or dead .
cl.reck
C7, .1
nrfd
647
scr:een
bypass.
Also .l
mfd
2525
plate
to
cathode
byPass.
EMERSON U6D
Frequency
drift,
requirrng constant
retuning
itr the
broadcast range
Frequently trouble
will
not appear
when
chassis
is removed
from cabinet and
placed
on bench
but will
reappear again
in
the
cabinet.
Trouble
is in midget
type compensating
con-
denser
in series with
broadcast
oscil-
lator coil.
Drill
I
inch
holes in
the cabi-
net
base near
this condeuser to
venti-
late it and drift,
due to
heating, will
tlis-
appear: