Technical information

O
RADIO
RETAILING'S
",
e)'de
ZENITH
BATTERY MODETS
1F227,
EFa?I,
5F25 |
Complaints
of short
"B"
battery
life
and
poor
tone
quality
after
battery volt-
age has dropped below
120 volts may
be corrected by
eliminating
"C"
bat-
tery
and converting
circuit to automatic
bias. Also by bypassing
plate
voltage
with
4-8 mfd
electrolytic
condenser.
To
accomplish
this, disconnect nega-
tive
"B"
lead where it
connects
inside
chassis
and
connect
a 300 ohm
I
watt
carbon resistor
in
series to chassis. Run
the bias
leads from the 1H4G
grid
and
lK6G
grid
to the
"B"
lead
(yellow).
Disregard
green
lead as
"C"
battery
is
omitted.
ZENITH 4K,IOI
Oscillation
replace
defective
lA7
tube. X{otorboating
poor
ground
connection
on electrolytic
con-
denser
at rivet
which fastens
to
chas-
sis.
Solder connector
to
chassis.
ZEN
ITH
4K3
IO
Dead
disconnect
cliode
of
1H5G
and
check for
leakage
fronr
tube
prong
to
ground.
This
condition
is
prob-
ably caused
by soldering
fluid
between
wafers-
ZENITH
4P26
Low
volume,
oscillation, signal cuts
out u'hen volume
control
is
opened
nrore
than half rvay
open 2 ntfd.
screen
bypass conclenser
on the 647.
zENtTH
,rT-26,
56
Oscillation, hunr
replace
con-
denser
block 22-407. Shorted
or open
condenscrs
are
very
colllnion
at
this
point.
zENtTH
.tvl3
t. 483
r
Inoperative.
This
set
will not
operate
if
pilot
light is
burned
out.
It
is
connccted
in series
with the
trr.o 15
trrbes.
Replace
rvith
a
2.9
volt bayonet
type
bulb. Must
be exact
replacement
for
proper
operation.
Noisy.
Replace
15
tube in
first
r.f.
stage. Many times
this
tube
tests
perfect,
replacement
is
only
rvay
trouble
can be found
ZENITH 5MI9I
Intemrittrnt
s'lrrn
cal
is in nrotion.
noisr',
poor
<1ua1itr-,
jarrirrg
the set \\'ill
cure the trouble for :r :hort
tinre
tuning
cable is in.elterl
too iar into
conden.er
coupling.
'.1'he
result
cause:
the concleuser to
he
htltl
solid
instea(l
of lcsting
on
'tlre
rubbcr
utounting
u-ashers.
-\lso
check thc itnterrnri
con-
Irectol's
for noi.c.
zEN ITH
68
| 29
Distortion.
. . .
Replace 8 mfd. filter
condenser in
power pack.
Capacitv oi
this
unit
has
decreased.
64
ZENITH
6D. 70
Weak
signals
A.C.hum...
across
speaker
ZENITH 6D-I66
accompanied
by strong
half
of filter
condenser
field
shorted:
replace.
Dead check
.02 mfd.
tubular
condenser connected to one end
of the
volume
control.
Replace
condenser,
leaving
enough
slack in
the lead
to
prevent
pulling
the
condenser lead
loose
by,
a slight
movement
of the
control.
ZENITH 6-M-90, 6-M-91,
7-M-91
Noisy, inoperative at
times .
.
. Check
the
600
k.c.
padder
and tuning
con-
denser.
The
ground
lead
to these
units
often breaks
loose, Resolder for
a
permanent
cure.
ZENITH
6M-90, 6M-9r,
7M-tl
Dead, intermittent
or noisy when
jarred
. .
.
Look
for broken
connection
from bottom
of
condenser gang
to
oscillator
or
first
detector coil.
zENITH 6Mr92,
6Mr93,
6M194
Noisv rvhen
jarred
i.f.
shields
grounded
through
one
eve-bolt on
can.
Solder
ground
lead to cross-b:rr
on
top of
can, rnaking
sure the nuts
holding this
are secure. Also check
soldering lugs on tuning
gang
stator'
for
good
corrtact.
zENfTH 69f
2t,
t37, t17, 152, tS7
Inoperative
.
. .
section
between B
tap. Replace
with
unit.
ZENITH 7
open
voltage divider
plus
end and
screen
l0
watt
10.000
ohm
Internrittent
reception
.
look
for
faulty
voice
coil.
The
clearance
of
the
coil
is very
small and
care
ntust
be
used
when reptacing.
zENtTH
95262
Whistles rvhen
volunre
control is
advanced
replace 12 rnfd
elec-
trolytic
across
high
voltage divider
tap.
zENITH
95307
Distortion
similar
to avc blocking.
. Look
for
open output
filter
con-
derrser.
zENtTH
9S365
Howling
off
for
defective
^;-^..:..
a.v.L.
LrlLulL,
unit.
ZENITH
I2A57,
resonance
look
.05 rirf
d condenser ilr
replace u'ith
400
.r'olt
| 2457-58
c29, a
6116 to
zENtTH
t2Ut58-r59
Distortion
at
low
volume
. .
re-
place
I
watt
400
ohm cathode resistor
on
6F6
with
5
watt
wire-wound
unit.
Check
cathode
bypass
condenser
for
leakage.
No
reception on
lowest
wave
band
.
untwist
grid
lead wires
f rorn
screw
on
gang
condenser.
Realign,
using
.0001 mfd. mica
condenser
from
oscillator
to
antenna.
Weak reception,
high noise
level
.
check r.f
.
alignment,
also 6xed
condenser grouped
around volume
con-
trol
ZENITH
I5U269
To.reduce the
uunrber
of complaints
on the split-dial
nrechanisms
be sure
to
carefully
lubricate
all
bearings
and
tighten all set-screws; especially
the
two
that hold the lever on the wave
band switch.
If these work
loose,
the
entire dial assembly u'ill
jam.
ZENITH 33X. Reception
faint,
audio ok .
. Look
under chassis nc.r
thc
antcnna compensating coil
(mov-
able).
Here
you
will
find
a 2,000
ohm
resi3tancc from
ground
to coil.
It
ir
often open.
It nray
usually be
simply
left out.
Tone raspy
Change over
l7l
to
ll2 rube.
ZENITH
35-P,
4O-P.
Noisy
recep-
tion
Look
for
high
resistance
ground
on secondary
of original
a.f.
transforruer.
Green corrosion
is fre-
quently
found
under
the
terminal lugs.
()hrunreter
tests
rarely
show up this
grlel,
ZENITH
11
,
42, 422
Noisy,
fading
. check
local-dis-
tance
rsrvitch
for
poor
irrterual
contact.
This
connects
to
a .00025
rnfd
condcrrser
in
tlre
antenna
circrrit.
ZENITH 50 SERIES. Loud hum,
all
parts
and tubes checking ok
Connect
250,000 ohm resistor from
grid
to
srid
of
push-pull
second audio tubes.
ZENITH
50
SERIES.
Pronounced
hum
not due
to
trouble
in filtei
.
. . Ap-
parently
due
to
pickup
of hum
induc-
tively from
the
filter
choke
by the
a.f.
transformer
between
the first
and final
a.f
.
stages.
It
will be found
that first
a.f.
stage
plate
is fed
through.l
meg.
resistor,
a.f.
passing
from
this
plate
through
a blocking
condenser
to the
audio
transformer
primary,
the low
end
of
which is
connected
to the
cathode.
Remove
the
blocking
condenser
and
shunt
the
transformer
primary
with
a
.l
megohm
resistor.
Connect the low
end
of this resistor
to
ground
through
a
2 mike
by-pass.
Now feed
plate
volt-
age to the
low
end of
the transformer
primary,
through
an
additional
.l
megohm
resistor.
The
connection from
the B
plus
transformer
terminal
to
cathode
is,
of
course,
removed.
-
Too
deep over
all tone
control
posi-
tions.
Remove
.01 mfd
ClO
and
much
better
tone will result.
zENtTH
r2157,
t2158
Internrittent
r-epl:ice
.05
nrfd
condenscr
coupling
volunre
control
( R7).