Technical information

A
RADIO
RETAItING'S
"Seufiw
ZENITH
I93' MODELS
Strong
motor-boating
with switch
in
distance
position
.
.
. replace screen
grid
and
plate
bypass condensers
marked
C
4
in schematic.
zENtrHs
t938
Noisy tuning
on short
wave band
. . remove
dirt
and
grease insulating
the condenser
drive shaft from
ground.
This can
be accomplished
by removing
condenser and switch
shaft
and clean-
ing with
carbon
tetrachloride.
Also
clean shaft
bearing.
In the
5 tube
a.c.
models
a common
trouble
is
no reception
below 1200 kc.
This
is
due
to
an open
primary
in
the
oscillator coil. Shunt this
winding with
a
10,000 ohm resistor
and
circuit
re-
turns
to normal.
In 15
tube
models,
distortion
at
low
volunre
is
sometimes
encountered. This
is due to a
small amount
of r.f.
getting
through
to the
audio
system. To
remedy:
insert
a .0005 mmf
condenser
in series
with
a
150,000
ohm resistor
from first
audio
grid
to
ground.
Battery
Sets. In receivers
of this
type
using
a lA6 or 1C6 pentagrid
converter
it
is
common that
this tube
refuses
to oscillate
or has
short
life.
A
simple
remedy
is to
drop
the screen
voltage by insertipg
a 50,000 ohm
re-
sistor
in
series
with
the screen. A
.l
n.rfd
condenser
shoul<i
then
be connected
from screen
to
ground.
Care should
be
used
to
see that
the resistor is
not
placed
in
a circuit
that
will
drop the
screen
voltage
on all
tubes.
ZENITH I9.tO MODELS
Noisy operation
of' autonratic
tun-
ing rrray
be caused by
the leads to
the
autonratic assembly
or coils laying
against nretal
frame
of assen-rbly.
Care should
be taken
that
leads
from
the tone control
condenser
and all
other
leads
in the 6
tube bakelite models
be
kept
away from
the 6Q7
tube, other-
wise
the
tone
will
be affected.
Cutting
out in
portable
receivers
will
usually be
due to
poor
connections
at the battery
pack plugs.
Slight
bending
of
the
prongs
will correct
this.
ZENITH
BATTERY
SETS
Hash
.
Loose
cover on
power
pack.
Hash
on
automatic
tuning
.
. .
automatic
tuning touching
power pack.
Insulate
at
point
of contact.
ZENITH
FORD AUTO
RADIQ
Dead,
tubes.do not heat,
switch must
be snapped
several
times to
start ,
replace
volume
control
and switch.
The
trouble
is in the
srvitch
only, but
the
control
is
usually
s'oru
also. Use a
D.P.S.T.
switch
for longer
life.
Con-
nect
the
poles
in
parallel.
zENtTH
CHASSTS s709
Dead
on
broadcast
band,
alright on
short
waves
l0
mmf
.
condenser
shorted
in
antenna transformer.
This is
part
#22-601,
CZl
in diagram.
ZENITH AUTOMATIC
SETS
Some
automatic
buttolls,
espccialll'
those
f
or
the
lorv f
retluetrc-v
r;ttrge,
will
not tune
iu a station
abovc 700
K.C.
'l'his
is
apparerrtly
drte to
the iron core
of
tl.re
permeability coil
not
going
far enough
into the coil
clue to
insufficient
threading
of the
ad-
justing
screrv.
IIowever,
it is easily
taken
care
of
by
adding a
vely
srtlall
anrount of
capacity
to the
contpensat-
ing
corrdenser,
tnarked C9
in
the
dia-
grarn, part
No. 22-738.
This
blittgs
up
the
frequency range
of the auto-
ruatic
coils to any
range desired,
brrt
since it is
onll'
a
nratter of a couple
of
hundrcd K.C., a very snrall
capacity
is required, not nrore than 50
rnnfd.
Sinrply
twisting
two insulated No.
18
rvires about 6 inches
long around eaclt
other and
conhecting one
end
of each
lvire across the cor-npensating
coutlen-
ser, will
give
one
the corlect capacity.
Untwisting or tu'isting
nrore or less
of the wires
will
give
sufficient
change
in
capacity
to
get
the
range
just
right.
Noisy autornatic buttons.
.
.
'l-his
is
due either to
poor
contact oi
the
spring contacts rvlrich is actuated bv
the
button itself, or to the key
bar
in
the switch,. which slips out of
posi-
tion,
In
the
first case,
that of
poor
contact; simply clean
the
spring
switches with carbon tetrachloride,
and if necessary,
bend
them over so
that they make
better contact. In the
second case,
that of the key bar
slip-
ping
out of
position,
the
best thing
to
do
is to
drop a bit of
solder on each
end
of
the bar, where it
goes
through
the
guiding
slots,
which
will
prevent
it
shooting
out of the slot and losing
its
position.
ZENITH
MIDGETS
Due
to the'small
baffie area,
lack
of
bass is apparent. To increase bass re-
sponse the
following notes apply.
On model 5R312
add an
.02
mfd
con-
denser across
the .02
mfd coupling con-
denser already
in
the circuit.
Also,
a
.01 600 volt
across the .002
connected
between
plate
and
B
plus
of the
power
output tube.
In
the 6D312 model, add a .01
con-
denser
across the .002 in the circuit.
Also,
a .02
across the .02 already
con-
nected
from
plate
to
ground.
In
both of the
above models, in
order
that
the speaker
fits
closer to the
cabinet,
replace
the 3 hexagon
speaker screws
rvith
flat head screws.
A
common complaint in the
6D3ll
and 6D312
models
is
poor
tone and
loss
of
volume
after
playing
a
while.
This
is
usually due
to
a
defective
25L6
output
tube.
When these
models are dead
yet
all
components check okeh
and set lights,
check the two 50 ohm
resistors con-
rrected from
the switch
to
ground.
To determine if the a.v.c. of a
receiver
is
working,
try
grounding
the
grid
re-
turn
of the
first
i.f. secondary.
If sen-
sitivity does not
increase, look for
defect
in
this circuit.
ZENITH
PORTAILES
When the a.c.-d.c.-battery
portables
work
on the battery
but are dead
on
the line,
check
the l17Z6G
tube
first.
If
this checks
O.K. then look for
an
open resistor
next
to the
cathode
of
the 17726G which
feeds
the filaments
of
the other
tubes. The
filaments
of
these
tubes
are all in
series
and
get
their filament
voltage
from the
recti-
6ed
plate
voltage
of
the
rectifier
tube.
The
resistor
is in
series with
the fila-
ments
ancl frequently
opens
up, being
only of
I watt
capacity.
When set
operates
weakly
and
everything(else
checks
O.K. change
the
speaker.
The
permanent
nagnet
on
these sets
seems
to deteriorate
rather
rapidly
and
produces
the
above
effect.
Another
thing
to look
for with
weak
reception
is
a moist
loop
cable.
The
covering
of
the loop
cable is
made
of
sonre material
which
readily
absorbs
nroisture,
causing
high radio
leakage.
Later
models
of this set have
changed
the
covertng.
When
sets work
O.K. on the line
but
are dead
on battery,
look
for
poor
switch
contact
at
the back
of
the
plug
receptacle
on
chassis. The
regular
electric
plug
has
to
be
plugged
into
this receptacle
on back
of
set before
it will
work
on the batteries.
ZENITH RADIORGAN
No control of tone
. insulation
on 33,000 ohm resistor
cut through,
shorting to cathode lug.
Too much
tone control on some
buttons,
none
on others
.
.
. tone con-
denser
or switch
leads
shorted.
Tone
changes
with
different settings
of volume
control
defective
volume
control or
shorted
terminal,
either
of tone switch
or volume
con-
trol, Poor
volume
control
contacts or
shorted
taps.
Noisy
when tuning
dirty
con-
denser gang
wipers
or
plates;
fly-
wheel touching
band
switch lug;
vol-
ume
control or drive
shaft not
making
good
contact
to
ground.
Volume
control has two
peaks
and
distorts
at low
volume
.
.
.
iiolate
6F5
grid
circuit
from
i.f.
plate
leads.
(Later
sets have
this lead
shielded.)
67