Technical information

O
RADIO RETAILING'5
ff,
ehde
TRUETONE
5K
Crackling, vibrator
and ignition
quiet.
.
.
Antenna
transformer
shield
can
ungrounded.
This
condition may be
remedied
by removing
chassis and
in-
serting
a
phosphor
bronze
spring be-
tween
the coil can
and chassis bracket
with
a long-nose
pliers.
Most
stores
hatdling
this set
have these springs
on
hand.
TRUETONE 7J
Weak Shorted
.25
mfd by-
pass
in
screen
of output
tube.
This
usually burns the
20,000
ohm
re-
sistor in same
circuil
TRUETONE
657
High
background
noise
on local sta-
tions . .
look
for broken lead on
r.f.
section of
gang
condenser.
TRUTONE
D.689
Mushy
tone, unstable
performance
.
check 6A7G for
gas.
TRUETONE D726
Static
but
no reception . . . check
first i.f.
coil in
plate
circuit of
6A7,
TRUETONE 57I9
Oscillation, especially at high
fre-
quency.
The 57 tube
shield
base
rivets
corroded and
practically insulat-
ing shields from
chassis.
Drill
out
rivets and replace
with
bolts after
thoroughly cleaning
rust
or corrosion
around
holes.
TRUTONE AUTO RADIO
(wilh
remole
permability
luning
)
Noisy on
remote
control open
head
and
bond r.f.,
osCillator, and
nrixer coil cans
to
nrounting
strap
rvith braid.
TRUETONE AUTO
RADIOS
Noisy look for
defective first
i.f.
transfornrers.
UNITED MOMRS
UNITED
If,OTORS 2035.
Vibra-
tor test . . ,
Connect 8
volts to battery
leads, remove
5
ampere fuse in
84
6la-
ment lead
and shunt an ammeter across
the
fuse
terminals. Place
a
good
it4
in the
rectifier
socket. The meter
should
jump
to
10
amperes and
thcn
drop back to 4.5 if
unit
is normal.
Volt-
age from
plate
of 84 to
ground
is
300 a.c.
UNTTED
MOTORS
4038
(CHEVRO-
LET 600249,
600565, BOP
9E0459).
Low or intermittently
low volume
ac-
companied
by
poor quality
and
missing
bass notes . . . Check
primary
of
push-
pull
input
transformer carefully. Trouble
is deceptive
as
voltages
are not
affected.
62
UNITED MOTORS 4037
Weak or inoperative
.
.
. .
this
trouble
can
often be
traced to
shorted turns on
the
primary
of
the
vibrator transformer.
Primary
winding consists of 4 layers
of
heavy
wire, can easily be rewound.
Check secondary for short also before
attempting
any repair.
Also
check buffer condenser and r.f.
filtcr condensers for shorts
or
leaks.
U. S. AIRCELL
US lu.
Overloading.
.
Check200,000-ohm
resistor
in
plate
circuit
of a,v.c. tuh,
also
condenser from
plate
of this
tube
to
cathode. Erratic
reception
.
.
Examine resistance
strip mounted
tight
against side
of cardboard
electrolytic
upon
which
the a.v.c. ciicuit
resistors
are mounted.
There
is
often sufficient
leakage
between the
resistance
strip
and
the
condenser to cause trouble.
Insulate
with
cardboard.
u.
s. RADIO
24
Weak
or
no reception
on
low fre-
queney
half of
band open
4 mfd.
electrolytic
condenser, connected
be-
tween
chassis
and
high
voltage center
tap
of
power
transformer,
(across 500
ohn.r
bias resistor of
47
tube)
is often
cause,
not any defect
in oscillator.
-\lignment
this receiver,
hav-
ing
but four tubes, utilizes
regenera-
tion. tb
increase sensitivity, Accord-
ingly,
alignment
procedure
differs
somervhat
from usual
method. Before
adjusting
i.fs., oscillation control
con-
denser
is set to
minimum capacity
by
turning
adjusting
screw
counter-
clockwise.
The i.fs. are then
peaked
at
455 kc. Next
follows
adjustment
of
oscillation
control condenser
to
point
of
oscillation
and
"backing
off" a
quarter
turn
below squealing
point.
The
i.fs.
are
now repeaked and oscil-
lation
control
condenser again
ad-
justed
to
squeal
point
and
"backed
off"
a ouarter
turn as
before. This com-
pleies the
i.f. alignment.
Adjustments
on the
r.f.
and
oscil-
lator circuits
are
carried out
in ortho-
dox
fashion.
In event
oscillation
re-
appears,
oscillation
control
condepser
is
"backed
off"
further till oscillation
ceases.
The
i.f. trimmers, however,
are
not
to
be touched again.
Location
of trimmer
condensers
l
r.f.,
on
front
gang
condenser;
oscil-
lator
high frequency,
on
rear
gang
condenser;
i.f. secondary,
forward
screw
atop
i.f.-oscillator
assembly;
oscillation
control, rear screw atop
assembly;
i.f.
primary,
forward
screw
on base
of assembly,
oscillator
padder,
(for
adjustruent
at 600
kc.) rear
screw
on base
of assemblv.
u. s. 24
Intermittent...check
former at
rear of
chassis
nection
between trimmer
ing
lug.
U.
S. 2r
top i.f. trans-
for
poor
con-
and
ground-
Volume control ineffective
on
strong
signals
Replace
control with
good
left hand tapered 5000 ohms
car-
bon control and reverie
center and
high leads. In
the original the
antenna
went to
center arm.
u. s. RADto 26,
26-?
Oscillation
. loose
or dirty
rotor
wipers
on
condenser
gang
repeatedly
cause
this trouble.
Remove
wipers,
clean, bend
slightly
to
give
better
ten-
sion,
replace.
us. 2t
Intermittent .
leakage in wet
elcc-
trolytics. Liquid on
top of
can
causes
short
between
positive
terminal and can,
Mount
with
vents
on
top. If boiling
still
persists
replace both 8
mfd
sections.
UNIVERSAL
UNIVERSAL 'IO
Bad
hum. both tunable and constant
.
. . .1 mfd condenser,
from
the
high
side
of the
400
ohm
chbke omitted
but
shown in diagram.
WELLS.GARDNER
WELLS.GARDNER
O2AA
Volunre
control
rvill
tlot
lcdttcc
vol-
urrle
contpletely,
distortion
at
lorv
sct-
tings
.
-.
disconnect
suppressol
grids
of
l.f. tube-*
irour
se ries
resistor
(
Rl3
in schematic
)
antl contrect
stlpprcssol's
to
cathode.
,'\dtl
5
rrrf<l ot' ttrorc
itt
o:rrallel
rvith
C5,
the
cathode
bypass
for the 55
tube.
'Ihese
changes
cause
the
turring
nteter'to
deflect
somervhat
further
to
the
riglrt than
usual,
but
this
itrcrca.c
is
rrot
olrjectionable.
WELLS
GARDNER
2DL, AIRLINE 62-,+13
Intermittent crackling
defective
contact in
Candohnr
resistalrce
contain-
ing
bias
for
avc and audio tubes.
Resistance of this section is 156.5 ohms.
znd
l.F,
f,d
[:r-
FlI
J.l