Technical information

A
RADIO
RETAILING'S
,,,
ehuie
ll
g
PHILCO 20.
Bad
tone,
pitchco
higher
than normal. Rcplace
old cone
using solidified
disc with new spider
tyPe conc.
PHILCO 20
Oscillation
connect.l
rnfd
condenser across entire.voltage
clivider.
PHTLCO
20
Oscillation n'hen volunre
'is
in-
creased . cl-rcck .05 nrfcl
screen
by-
pass
on 2-1
r.f. for
open.
PHILCO 20,
70,
90.
Tuning
shaft
wears
grooves
where
bathtub serves as
end bearing
for rotor
.
.
. The
back
bearing
may be
given
a
new
working
surface by
beating
in
the end of the tub
for about
l./16 inch. The
front
bearing
is not so easily
fixed. Take
the old
dial
(a
new one is usually needed anyway)
and cut out a
piece
as shown in the ac-
companying
drawing.
Drill holes in
the
front
end of the bathtub.
(taking
care
not to
damagie the
stator) and
fasten
this
piece
over the shaft in such
a
posi-
tion that
the shaft
runs
true and
does
not
bind when
rotated.
The machine-
screws
holding this bearing
in
place
must be
secured
with lock
washers,
Of
course, the
rotor and tubes
must be
re-
moved during all this
violent treatment.
Greater
precision
may be
secured
if
the
holes in the
piece
of
dial supporting
the
new bearing
are drilled after
the
part
is
in
place.
This can
be done by
aligning
all
the
parts
in their
final
position
and
using
one or
small C clamps to
hold the
parts
while the
dritling
is in
process.
?HILCO 29
Fading after slrort
periorl
of opcra-
tion.
Check 350,000 ohm
volume
control; may
vary
up
to several meg-
ohms intermittently.
PHTLCO 29.
Audio whistle and bubbling
hum
. . .
Common
bias by-pass, a ,09,
for the
two 39's
opens.
PHTLCO
30
I-ou' volunre
sistance in
i.f.
coils.
coils
rvitl-r nerv units
PHTLCO 30
look
for high re-
Replace
defective
Intermittent broken
flexible wire
under
cover of
grid
control
leads.
Check
from condenser to
ground
shows
good
conbact
but a check from
inside
of
rub-
ber
control
grid
caps shows open.
PHTLCO 30
Dead, no
screen
voltage
Com-
mon
cause
is shorting of
,25
condenser
connected
from choke
to chassis.
This
is
one section
of
a
dual
unit
in a
metal
can near
the choke
terminals.
40
PHILCO
30.
Thin,
metallic
qualitY
.
.
.
If circuit, tubes
and
speaker
seem
to
be
functioning
as well
as
sets
known to
be
in
good
condition
trouble
is
probably
characteristic
"stiftness"
of speaker
cone.
This
may be
remedied,
if the
cus-
tomer
will
pai
for it, by
a little careful
cone-cutting.
Free edge
by cutting
out
between
points
where screws
are neces-
sary
for support.
Cut
slots
in
the
apex
member of
thc voice
coil
to
give
it
greater
flexibility.
Spiral
slots, starting
at the center
and winding
out
near th€
edge are
suggested.
Three
are usually
sufficient.
PHILCO
37-38
Excessive ir-nage
interference and
low volume replace defective an-
tenna coil.
PHILCO
37-10
Intermittent
oscillation check
32,000 ohm resistor
under
the oscillator
coil
section
for increase in value. Re-
place
with nerv
32,000 ohm unit.
PHILCO
37-33, 37-38
Retttc.rr
e
1500 oltrrr
t'csistor lLcl'()ss
"C"
battery
ln
37-33
rnodel and 900
ohur
lesistor
irt the
37-38.
Replace
rvith
6000
ohnr vlrlue.
l-ow value
short-
6n5
ly211g1y
life.
PHTLCO 37-604
Distortion
and
birdies
oPen .1
mfd
bypass
across 3(i0
ohm
cathode
resistor
on 6K7G.
?HtLCO 37-6r0
No
short
wave
reception
. . .
small
mica condenser
(part
No 20)
soldcrcd
to
tuning
condenser workcd loose.
Rc-
solder and bend to
clear
plates
of
gari-
able condenser.
PHTLCO
37-650
Dead replace C 51
and C
48
twin
.003
1000 volt
condenser
con-
nected from
plate
of 6F6G's
to chassis.
Also replace
C
25 a.1 mfd. connected
from
B
plus to
chassis.
PHILCO
37-660
Intermittent distortion
after set
heats
up second'section of
candohm
re-
sistor
(15
ohms)
has increased to 30
ohms. Replace
with 15 ohms
rvire-
wound unit.
PHTLCO 38
Oscillator
dead
.
.
Remove
oscilla-
tor coil and
heat thoroughly
to drive
out
moisture.
Dip
in
a 50/50
preparation
of beeswax
and
paramn,
when
cool re-
place.
PHILCO 38
Distortion
after
replacing leaky
coupling conclenser
on first
audio
.
check battery
pack
for
positive
charge
at nrinus
7]
"C"
terminal.
This is
probably
caused by
discharge
and
snrall recharge
from
"B"
plus
through leaky
condenser.
PHTLCO 38
Intermittent, dead . . .
in
this
model
the i.f.
transformers
are wound on
wood dowels.
Small
staples are
used
to
fasten the leads
to the dowel.
In
some
cases
it has
been
found that
the staples
were
driven
so
far into the
dowel
that the
insulation on the
wire
was cut.
At
the
same
time the ends
of two
staples
met inside the
dowel,
shorting
the
coil.
The
most effective
method
for
finding this
trouble
is to
use a
low-range
ohmmeter.
PHTLCO
38-2
And
other
models
using
phase
in-
verter-poor tone-both output tubes
must
check
O.K. Unbalanced output
tubes will
cause distortion
in
this
model.
PHTLCO 38-5
Noisy, internrittent
or dead
check screen dropping rcsistor No. 2l
in
diagram. This
is
a
10,000
ohnr I
watt unit. Replace
with
wirewountl
type.
PHtlco 38-8
Oscillation
at high
volume
.
shunt
.0005
mfd condenser
from
grid
of 6K5G
to
ground.
PHTLCO
38-12
Intermittent
look
f or shorted
oscillator
trimtner
locatcd
on
top
o[
gang
condenser.
PHILCO 388
Noisy volume
control
bias volt-
:rge flows through
contl'ol
causit-tg
noise.
Change
circuit
as shown
below.
Old Woy
Ncw Wqy
c-1h
PHTLCO 39-tl
Insensitive
on
B.C. band,
calibra-
tion off
check
band
switch stop
to see
if
this
allows
full movement
of srvitch
arm.
PHTLCO 39-307
Crackling,
noisy
check 250
nrnrf. r-nica condenser
bypassing
plate
of the
75 tube.