Technical information

O
RADIO
RETAILING'S
fI
eUioo
?H[CO 60
Intermittent
or low volume
. . .
Check
for
high resistance
opcn in secondary
of antenna
coil.
PHILCO 60. Intermittent loud
buzzing similar to outside motor intcr-
ference but
originating
in set .
. . Re-
place
6A7 oscillator-first dctector even
though
it tests ok.
PHTLCO
60, s05
Noisy
check
.18 nrfd
cathocle
bypass
on 6.47
tube.
PHttco
65
Fading
intermittent
open in
speaker
field.
This
field
should
have a
resistance
of approximately
3000 ohms.
PHTLCO 70
When
replacing
the filter
condensers
be sure to insulate the can from
ground,
otherwise the
47
tubes will be
without bias.
PHTLCO
70
Ifum
on
stations
near the
center of
the
band
Look
for
trouble
in
tlre
coniensers
seriesed
across
the
power
transforrrrer
prirnary.
PHTLCO
70
Dead
except
on strong
stations.
.
. .
Check
coupling
condensel between
second
detector
and 47
grid
for
open.
PHTLCO 70
Distortiorr.
[;Lrlcs
out cornlrlt'tcl-v
rcplace,2.5
rrrg rcsistor irr
gritl
cir-cuit
r.tf.
47.
PHTLCO 70
Loud howl
. .
. on receivers with
a
serial
number
belorv 22,000
suspect
an
open
circuited
detector
plate
by-
pass
on
B
plus
side of r.f.
choke,
PHILCO
70
Oscillation that cannot
be cured
by
the
usual
methods
bypass
the 61a-
nrents of the r.f.
and
i.f.
tubes with
capacities
ranging
betrveen .005 and
.?5 mfd.
The
correct value
must be
iound
by
experiment.
PHILCO 70
Hou'ling caused
by
vibration of
cr,rnrlenscr
plates
due
to dried
rubber
nrountings under
condenser.
If
the rub-
bers cannot be
removed easily
a simple
remedy is to
float
the chassis
from
the.
cabinet by
placing
rubber
g'rommets
uncler the
chassis.
PHILCO 70.
Howl or microPhonics
when tone
control
is in left countet-
clockwise
position
. .
Inspect .00025
mfd.
phone
condenscr
connected
to
platc
of second
detector.
It
has
a
ycllow
dot
on one
side
and frequently
opcns
or
changcs
value.
42
PHILCO
70. Set impossible
to bal-
anc€
so that stations come in
on
proper
dial settings .
.
.
When all else fails re-
move
gang
condenser. It
will usually
be found
that the
front
end of
the
shaft
has
dropped a
fraction
of
an inch al-
though this is not
visible
from
the top.
Replace
with
new
gang
unit.
PHTLCO 70,
70A
Dead,
with recti6er
plates
red hot
. if
filter condensers check
okeh,
inspect filament
leads of tubes at rear
of chassis at
points
where
leads
pass
under
primary
trimmer
condensers of
I.F.
transformers.
Leads
sometimes
come
in contact
with edges of con-
denser
plates,
the latter
in time
cuts
through the
insulation
on the wire
sl'rortening of
entire
"B"
supply,
PHILCO
70,
7OA.
Replacing
dual
volume
control with
single, tapered unit,
giving
even
smoother control.
Circuit
is
self-explanatory.
The
200 ohm fixed
resistors
are I watt
types.
PHILCO
70, 7OA,
370. Ir:rpossible
to align
circuit
at
1400
kc.
, . . Look for
open
.00011 condenser
between
oscillator
coil
and
plate
of oscillator.
Replace
with .0005
and the
set will align and
be
more selective
than
originally.
Where
this trouble exists reception
will be
ok
below 850 kc.
but will fall
off
rapidly
at
higher frequencies.
PHILCO
70,90, Feedback
not
trace-
able
to
nrissing
rubber
cushions
or
floating
condenser
gang
.
Drop
wad
of
paper
into
oScillator
coil form,
mounted
on the
chassis by means
of a
bracket,
and,
with set upside
down,
drop
catacomb
wax onto
paper
off
soldering
iron
point.
Feedback
is due
to vibra-
tion
of oscillator
coil itself.
PHILCO
70, 90.
Slipping dial drive
shaft
. . . Pull
shaft down
tight.
Solder
thin washer
to
bracket.
PHILCO
70,90. Il oirfort
beacons
o|erating on 260
kc. cause interfrence,
readjust the i.f.
compensating
condensers
and the osci'llator
compensating
condenscr
to eithcr 250
or
270 hc.
Philco
70, 71,90, 91. Fading
of locals
is usually due to failure
of a I mfd. con-
denser. Use sharpty
pointed
test
probes
to
locate
the
defective
unit,
gentty
lifting
up the
wires that come
out of the hard-
rubber
case which houses
the condensers.
PHILCO
7l
Distortion
replace
70,000 ohrn
plate
resistor
on first audio
rvith
50,000
ohms.
PHTLCO 7l
Broken
dial cable On
tl.ris
set
a
woven dial cable is used.
On
the dial
where the cable fastens there will
usu-
ally be
found a sharp edge. If
a
cable
is
too
tight
this
edge cuts
the
strands.
To remedy:
place
a small section of
Scotch Tape over the edge. This tape
is
flexible, transparent and may
be ob-
tained
at almost afiy stationery store.
PHTLCO 7l
Cuts
out or1 strong
locals, lorv
porv-
ercd
stations
conle
through
rveakly
. change resistor
in
oscillator
circuit
fronr
15,000 to
10,000 ohnrs.
PHILCO
MODEL 7I
Sometimes
in
order to mal<e the os-
cillator
tube in
these
sets
work over
the
entire band the cathode resistor
was lowered,
if this is
too
low the
set
will lack volume
on
the 600
KC
end
of the dial. The
correct value of
this
resistor
for
best
operation shoulcl be
about 10,000
ohms.
PHTLCO 7l
Cuts
out on strong
locals,
low-
powered
stations
can
be
heard in
the
background . change the bias
re-
sistor on the oscillator from
15000
to
10000
ohms.
PHTLCO
7t.
Intermittent
operation,
volurie drop-
ping
50
per
cent,
proper
operation
re-
stored
,the
instant
an analyzer
plug
is
in-
serted for
test
. . . Check
voltage
divider
section between
screen
grid
and cathode
of second
detector.
PHTLCO 76
Intermitterrt
volunre, opening anc
closing line
srvitch
restores operatior
.
replace
R19 and R20
plate
drop-
ping
resistors
rvith
nerv 100,000
ohn:
units.
PHTLCO
76
Fading
cl'reck
ground
strap
from
ground
post
to chassis for
poor
contact.
Sol<ler leatl {roru
oost to
chassis.
PHILCO
76.
Hum starts about
15
minutes
after
set
is
turned on,
then all
reception
stops
, . .
Look at
r.f.
coils.
Wire
comes toose on
form
and drops
on
soldering lugs at bottom coits, shorting
primary
to
secondary.
Loosen wire
with thinner and
push
back
in
place
then cement-
PHILCO 76, 77
Hiss
on all stations May be re-
duced by raising
the
value
of the detec-
tor
cathode resistor.
PHrrco
80.
To improve volume
and
quality,
espe-
cially in models with a star
stamped
on
chassis . .
.
Change
I meg.
grid
resistor
to 0.5.
gOOO
ohm.
Ant lapr.d
Ncw
Singh Conlrcl