Technical information

A
RADIO
RETAITING'S
ff,
ehui@ hptlcotll,"
d
PHILCO
9lX.
Hun.r, developing aftcr
few
hours of
use,
accompanied by dis-
tortion
.
. .
Replace
input
push-pull
audio
transformer. Secondaries
are sometimes
faulty.
PHILCO
95.
I
ntermittent recrp-
tion volume
increases to high
level and
drops back
to
normal when test
instru-
ments shock
circuit
Look
for in-
te rmittent trouble
in bypass condenser
on
low side of
volume control.
The
lead
to this condenser
goes
from control,
through
a
cable,
and
connects to
filter
block. Cut
oft
wire
at
both
ends
where
it emergcs
from
cable and
resolder
a .5
tubular between tow end of
volume
con-
trgl and
grounded
lug of
nearest
trrmmer.
PHltco
95,
96,
lt2
Blocking, similar
to very
slow
re-
covery
of avc,
set otherwise
normal
. .
. replace
volume control.
Ringing
sound
in
speaker
when
set is
removed
from cabinet .
Same
cause, volume
control.
Static
similar to
that
caused
by
bad a.
f. transformer
.
Check
same
control
PHTLCO 96
Intermittent
operation
for short
periods,
any attempt
to
make tests
restores operation replace 30,000
ohm metalized resistor in
plate
of first
audio.
PHILCO 96. Serious
oscillation
not
traceable
to open condenser or resistor
.
Replace screeu feeder resistor with
50,000 ohrn,
I watt replacement and
by-
pass
with 2
rnfd.
Bypass the
a.c.
line
with .001.
Add a .l mike to
center of
grid
resistor network
in
the
audio
chanrrel.
PHTLCO
96
Poor
scnsitivity aiter bypass
con-
densers, tubes
have
beeu
checkcd,
cspe-
cially
at 550
end of dial. Snspcct
antenrla coil
rvhich is conrposctl
of ap-
proxinrately
250 turns of
resistancc
rvilc at
appro-xiruately
l0 ohtrrs
pcr
foot.
Rcuind uith
100 turns
of No.
'fi
rrr
No. Jtl
coplrcr
l
irc.
PHILCO
f l1,
f l2. Poor sensitivity
and
tone . . .
Replace
resistor
number 8 with
75,000 ohms.
This
peps
up both
molels.
PHILCO
rr r, il
lA, 2ll,
2llA
Low
volume,
all voltages check
Change
*
meg.
resistor
(#44)
in
plate
circuit of
'27
detector.
PHILCO ilr, ilrA.
2il,
2llA
Cutting
off of signal
followed
bY
oscillation
intermittent
opening
of
.05
mfd.
condenser
between
cathode
and low
end of
first detector
grid
coil.
PHILCO
lll, lllA,
ll2, ll2A,
2ll,
2llA
Weak,
distorted,
noisY
suspect
audio
transfornrers
for open
in
these
receivers.
PHILCO il2
Distortion on
local
stations
. . .
re-
olace
the
a.v.c.
resistor
to the
first
r.f.
iube
rvith a 70,000
ohm
unit.
PHTLCO il2
Poor
tone
.
check
5 watt carbon
resistor
between
speaker
return and
ground
for drift
from
original
value
of
15 M, If
necessary to
replace use wire-
wound
unit.
PHILCO llzK.
Slight, continuous
whistle
Move
plate
wires away
from
compensating condenger,
PHILCO
il2, ll2A,
212,
?l2A
Oscillation
and
distortion
when sen-
sitivity
switch
snapped
to
maximum
. open
.5
nrfd.
condenser
located
in
fil,ter block
bypassing
screens
of
6rst
detector
and
i.f.
Weak
or
dead
.
. check
15,000 ohm
resistor between
minus
of
speaker
field
end
chassis
for decrease
in value.
Re-
place
rvith
5 rvatt
unit.
PHILCO il6
Internlittent
oscillation over entire
dial replace
10,000
ohm
resistor
in voltage
divider
section.
To test,
turn volume up full, tune off station
and
tap
resistor,.listen for crackle.
Tlris resistor is
diagram
#96
part
#3521.
PHILCO I 168
Oscillation
.
. .
push
hot
grid
lead on
volume
control
close to
chassis.
PHTLCO
il6RX, ssRX
Hum when tune<l
to strong statiolls
. Circuit
ground
returns
riveted to
chassis.
Solder
all
tlrese
points.
PHTLCO r 18
R.F. hash
repeats at twice
i.f. fre-
(luency
over entire
dial
one
side
of dual filter
(30-2045)
operr.
PHILCO l,[4
Shadowmeter
varies
itr
accordance
with loud signals
Replace triple
section
electrolytic
condenser.
PHILCO 200. 201
While
repiacing a
defective
fidelity
control
in this set
a
peculiar
case., of
trouble
was
experienced.
The coqtrol
is a three-section
wire-wound
varieble
resistor, having one
section
of
1500
ohms and two sections
of
8775 ohms
each.
The
sections are
insulated from
each other
and arranged
so to
be
con-
trolled by a common
shaft. This
is
shown
in
the drawing.
In
the
original control, the
part
num-
ber
is 33-5083.
The replacement
chart
specifies
part
number 33-5103
as
the
correct replacement.
(33-5083
evidently
bcing discontinued.)
Upon
installing
the
new control
trouble
was
encountered.
Instead of
operating
like
a
6delity control,
the
replacement
part
acted like a
volume
control.
The explanation
is this: the
fidelity
control circuit
for this set
is shown
in
Fig.
1. Notice
that the
1500 ohm
sec-
tion of
the control
is
in the
cathode
cir-
cuit of
the
first
and
second i.f.
tubes,
in
series
with the
200 ohm resistor
which
provides
the
fixed
bias.
The two
8775
ohm sections
are connected
to
the
ter-
tiary
windings
of the first
and second
i.f. stages
respectively. On
the
original
control
(33-5083)
the arrangement
of
the sections
is as shown
in
Figure
2.
In the
replacement
control
(33-5103)
the sections
are arranged
as
shown
in
Figure 3. Comparison
of
the two
fig-
ures
will show
that the
1500 ohm
sec-
tion is located
differently
in the
replace-
ment control,
than
it is in the
original.
It
is
this
difference
of
construction
which causes
the unwanted
volume con-
trol action,
because
if customary
repair
procedure is
followed
in replacing
each
wire
in its
original
position,
instead of
having
a
1500
resistance
in the cathode
circuit,
we
will have 8775
ohms.
As
the
control
shaft is
rotated
the bias
on
the 78
i.f. tubes will
gradually
be
in-
creased
to a
value
which will make
the
tubes
inoperative.
In order
to obtain
the
correct
replacement
for 33-5083
it is merely
nec-
essary to
transpose the
rviring on
sec-
tions
1 and
2. The control
will
then
operate
properly. Put the single
wire,
lug A section
1,
on
lug
A, section
2.
Put
the
two leads
from lug A
section
2,
on
lug A section
1.
Lug B is blank
on
both
controls.
Secl. I
6
/
r5JL
Sccf.2
1500
n
Scct.5
E?75.n
Sec*-
1
1500n
Secl.2
87-75n
Sccl.5
6775n
PHTLCO
2t2
Fading.
nected
to
low
This
is
a tone
for
increasing
volume.
.
Replace
bypass con-
side of
volume control.
compensator condenser
bdss response
at
low
o
o
!
.o
41