Philco 48-141 Service Manual

PHTLCO RADTO
'nODEtS
4g-t4t
AND 4g-t45
Circuit Description
Philco Models
48-L4L and 48-145
are
four-tube,
battery-operated superheterodynes, providing
reception
on the
standard broadcast
band,
540-L720
kc.
Manual tuning
is
employed.
Both models are identical
except
for the
cabi-
nets, knobs, and
dial
scales, as
indicated
in
the
parts
list. A
100-foot (over-all), outdoor aerial,
such as Philco
Part No.
45-1469,
is
recom-
mended.
The
converter stage employs a tytrle 1LA6
pentagrid converter tube; in this tube, the oscil-
lator signal is fed to the mixer
section through
the electron stream
within
the
tube.
A
type 1LN5
pentode tube is
used
in
the
i-f
amplifier stage. The diode
section
of
the
1LH4 tube
provides detection and a-v-c volt-
age,
and the triode section functions
as
the ftrst
audio
amplifter.
The ffrst audio
stage
is
resistance-coupled
to the type 3LF4 output tube, which drives the
permanent-magnet dynamic loud-speaker.
Philco
TROUBTE-SHOOTING Procedure
For rapid trouble shooting, the radio circuit
is
divided into four
sections,
with
test points
spec-
iffed
for
each section; these sections and test
points are indicated
in
the
schematic diagram.
The trouble-shooting procedure given for
each
'
section includes
a
simplifted test chart and
a
bottom view
of
the
chassis showing
the
loca-
tions
of the test points and the components of
that
section.
In
each chart, the first step is
a
master check
for
determining whether trouble
exists
in
that
section,
without going through the entire
test
procedure.
Failure
to obtain "NORMAL INDICA-
TION"
in any given step indicates trouble
with-
in
the
circuii inder
te3t.
After
isolating the trouble to a single
stage,
the defect is located
by:
ftrst, testing the tube;
second, measuring
tube
electrode
voltages;
MODEr
48-t4r
MODET
48-r45
SPECIFICATIONS
CABINET
Model
48-l4l
. .
.
Plastic, walnut
finish
Model
48-145
....Plastic,
ivory
finish
CIRCUIT
....Four-tube
superheterodyne
FREQUENCY
RANGE....
540-1720
kc.
AUDIO
OUTPUT
.
.220
mw.
POWER
SUPPLY
Battery pack, Philco P-608-6L
PLATE VOLTAGE AND CURRENT.
.
9O
volts,
lO
ma.
FILAMENT
VOLTAGE AND
CURRENT,
1.5 volts, .25
amp.
POWER CONSUMPTION
(total,
plate and
filament)
I
watt
AERIAL
. .
.
.
External,
Philco Parr
No. 45-1469
INTERMEDIATE
FREQUBNCY
..
....455
kc.
PHILCO TUBES
(4).
.
. .
.
.tLA6, lLNs, lLH4,
3LF4
third,
measuring
circuit
resistances; fourth,
substituting condensers. The trouble
revealed
should be corrected before testing further.
Preliminsry
Checks
The following preliminary
checks should
be
made before
turning on the
radio:
1. Carefully
inspect the top
and bottom of
the chassis.
Vtike si,r"
that
alliubes
are
secure
in
the proper
sockets, and look
for
any broken
or
shorted
cennections,
burned
resistors, or
other obvious
sources
of trouble.
2.
Disconnect the battery, and measure the
resistance between
B+
(red
lead
of
battery
plu_g
)
-and
_cha,ssis,
with the
ohmmeter polarity
such
that the
highest resistance reading is ob-
tained.
If
this reading is lower
than-
10,000
ohms, check condensers C100, C208, and
C404
for
leakage
or
shorts.
Copyright, 1947, Philco
Corporation