Technical information

O
RADIO
RETAILING'5
,,,
eUie
AC.DC
SETS
HUM IN
AC,/DC
SETS
\\'lrt'rr :tlnornr:rlly
high
hum nrodula-
tion
is
prr.rser-rt
in
a-c/cl-c rcccivers, it
is
suggcste<l
that
the heater
of
the
penta-
grid
convertcr
be located
as near
chassis
potcntial
as
possible.
In
several
cases
s
herc this
condition
rvas invcstigated,
hunr nrodulation
rvas
reduced
consider-
:rbly
by
rearranging
heater
connections
irr
such a nranner
that
the heater
of thc
pentagrid
converter
was
second front
the
chassis.
'I'he
heater of
the first a-f
tulre
was located
at chassis
ootential in
oltlr.r'
to reduce
hum introcluced
in
thc
grid
circuit
of this tube.
AC.DC MIDGETS
Oscillation
Most
oscillation
troubles
in
this type
set can
be
reduced
by
slightly increasing
the
bypass from
detector
plate
to
chassis.
The
tone is
usudlly
improved
by this
change.
A.C.
SETS
Occasionally an
old set turns up that,
even
after
a
new
filter is installed,
hums
badly.
In
most
cases
it will be found
that these
sets have
the speaker in
the
negative
tead. Miscellaneous
bias volt-
ages are
taken from the voltage
drop
across
the field.
Additional filtering
at
this network
is
of
little
value.
An
effective cure is
to
remove
the
field f.rom its
original position
and con-
nect
in
the B* lead,
as
shown
in
the
diagrarn.
An
8 mfd
condenser, each
side
of the field
will then
be sufficient
to
remove
all hum.
The
disadvantage
of
this
system is
tl-rat another
bias
netrvork must
be de-
vised. This
may be
accomplished by
grounding
the B-
lead
through a re-
sistance
of a few
hundred
ohms.
The
exact
value
of the resistance
deoends
on
the
total current
drawn
by tlte
set an,l
the amount
of bias voltage
required.
Speaker field
To powen
lube
qnound
To
€-firsl
oudio
AC-DC SET
The
older models
of this type
often
give
trouble
at
the
connections
of the
high-rvattage dropping
resistor.
To
prevent
the leads
from working loose
due
to
heat,
bolt
the
lead
securely.
6
AC.DC SETS
Considerable
increase
in
sensitivitv
results
when
rhe antenna coil
is movei
up
closer to the
secondary
winding.
Of
course
this
means readjusting
the bal-
ancing
condenser
on
the
first
section of
the
tuning
gang.
ACRATONE
ACRATONE
2
No reception
due to the shal-
low sub-base
of chassis,
Jrarts
mounted
close
together frequently
short to
one
another.
Inspect
first {or fhis
trouble.
ACRATONE
9A
Oscillation
turn sccontl
r.f.
coil
at right
arrgles
to
antcuna
coil
or
vlsa
versa.
ADMIRAL
ADMIRAT
BA4t
Dead
.
.
.
Check for
shorted .01 mfd
condenser
in
power pack
can
connected
from
one
side
of vibrator
prong
to
ground.
ADMIRAL
AM 787. AM
,T88
Dial
dlive
belt slips
off
guide
pul-
leys . remove flywheel
from shaft,
tin exposed sides
of
guide pulleys,
sol-
der
f
in. washer
to each side of
pu1-
leys.
Washer is made
from
l/32 in.
copper
or brass rvith
{
in. hole drilled
in
center.
AIR CASTLE
AIR CASTLE
Dead
on
part
of dial. . . Replaces
6D8G
cr-rrrverter
with 6A8G.
AIR CASTLE
ALL WAYE
Oscillator
tube
cuts
on
and off
inter-
mittently.
Changing the tube,
grid
con-
denser, resistor
did
not
cure the
trou-
ble. Check the
tuning condenser for
leakage
in the oscillator
section. If
a
resistance reading
is obtained
replace
the
condenser.
AIR KING
AIR
KIN6
909
Turntable
slips
. .
replace rubber
rvasher
between turntable
and
motor.
This
gets
oil soaked from motor.
ATR
LINE
AIRLINE
BATTERY
5.
ImProv-
ing sensitivity
and
tone
.
. .
Replace de-
teitor
34.
unshietded,
at
rear
of chassis,
with a
32
connecting
the
grid
return
directly
to
minus C9
volts.
(Brown
lead.)
This
eliminates
the
I
meg
re-
sistor in
this
lead.
The
grid
lead
is
originally
connected
to the
plus
fila-
melrt.
AIRLINE 05BA.
Oscillation aftcr sev-
eral months of use . . . Substitutc
.01
condenser for .N2 dctcctor
platc
ca-
pacitor.
If
still troublesome
conncct
another .01
from
choke coil to chassis.
AIRLINE
33
Intermittent.
Wcak
contact
spring on back
c,f three
gang
con-
denser
permits
end-play in rotor.
AIRLINE 40,
,t0A.
Whistlc near 8(X)
kc. .
. .
Replace
oscillator
grid
teak
with
J0,000
ohms.
A
lower
resistance causes
cutoff rrear 1,400
and
a higher
value is.
the cause of
the origirral trouble at 800.
AIRLINE
.IO
Intermittent
.
..
open half
megohm
resistor
in
plate
circuit
of
24
avc tube.
Replace
with new
unit.
AIRLINE
62-22. Distortion
and
over-
loading
on locals, receives
dx ok,
a.v.c.
plate
voltage
somewhat high
when
6rst
turned on Look for
open circuited
resistor
between oscillator
and r.f.
screens to
plate
of
a.v.c.
tube, also took
for
open
in
"localizer."
It
sometimes
lets
go
on the cathode
side
of the con-
trol. The
divider should
be
4,300
ohms
overall, tapped at I,100.
Tests
should
be made
to cathode instead
of from
sus-
pected point
to
ground.
Fading,
inter-
nrittent reception
Check
for
open
cathode
bypass condenser
in i.f.
stage.
AIRLINE
62-,f25
Hum,
no
receptiorr
.
.
. open section
in
dual 8
mfd.
electrolytic
condenser
in
cylindrical
container
atop
chassis.
IJse common
positive
type replace-
ment.
AIRLINE 62-68.
Intermittent re-
ception . Due to
periodic
opening of
3,200 ohm
candohm resistor
furnishing
cathode and
suppr'essor
grid
bias to the
57 first detector-oscillator.
Replace
with I watt unit,
AIRUNE 62-72
Dead, no voltage
on
screens.
. , .
Open
field
coil, screen voltage supplied
through field. As this
set has
two
speakers it may
be
made
to
operate by
bridging field
(red
and
yellow
wires)
with
l0
watt 10,000
ohm
resistor.
AIRLINE 62-76. To improve
bass
response and
avoid
overloading of
paralleled
47's , ..
Change
resistor
in
plate
circuit of 57
first
a.f, stage frorn
50,000
to
25,000 ohms. This
will
prob-
ably
make
set screech when volume
is
full on and tone control is
in treble
position,
so
shunt a condenser of from
.005 to .01 capacity
(a
.006
is usually
best)
from
the
variable
arm of
the
marrual
tone cbntrol
potentiometer
tc
the high
potential
end of
this
same
po
tentiometer.
AfRtfNE
52-70,
U2-t2
Intermittent
fading . . .
Replace .04
coupling
condenser between 56 dete'ctor
and,
47.