Technical information

I
i
O
RADIO
RETAILING'5
",
e2de
MAJESTIC
50.
Set
dead,
no
plate
voltage
on second
detector
but
all
other
voltages
only about
l5 volts
below nor-
mal Do
not remove
bottom
plate
from chassis. Instead,
relnove
the small
plate
at back
of chassis
directly
below
the
deck upon
which is
mounted
the 80
and 45
tubes. Look for
a charred
25,-
000 ohm resistor.
Replace
it and
the
associated I
mike condenser.
which
has
shorted, causing
the resistor
to turn
out.
MAJESTIC
55
Crackling, noisy
oscillator
pri-
mary winding
breaking down.
Replace
with new unit
(I.F.
275KC).
MAJESTIC
55, 15.
Oscillation
not
traceable
to
filter
condensers
or re-
sistors
lteplace
detector
coupling
condenser
behind
resistor
board
rear
*'all
with
05, 400 volt
type.
MAJESTIC
55. Fading
arrd inter-
mittent
reception
Usually
due to
high
leakage
condensers
in
block, lo-
cated
on
outside
of chassis, uear
speaker.
Also
check
tubular corrdensers foi
opens
as sonre
have loose
ends
that cause noise
rvhen
srvitch
is first
turned
on.
MAJESTIC
60.
Set stops
playing
suddenly,
tunir.rg
nreter
pointer
swings
clear
over to stop.
Cause is
shorting
of
by-pass condenser
in
plate
circuit of
i.f.
tube.
Unsolder
leads from
i.f.
trans-
former,
remove
it fronr
chassis
and
heat
to
melt wax.
Remove
can and melt
wax
from
red lead
with iron.
Cut
this
lead.
re-assemble
the
transformer
with
it
pro-
jecting
from
case
and mount
reptace-
ment
by-pass
unit
externally.
MAJESTIC
60
Dead
. .
Check
for
shorting
of lead
from
80 filament
terminal
to
giound
or
to the
ll0-volt
line. The
rubber
cover-
ing
of this
wire
softens from
heat or
the
line
voltage
taps
cut through
it
The
set may
test
ok when
checking
with
an
analyzer
and
still not
play.
MAJESTIC
60,
70, 80.
To increase
sensitivity
and volume
. . . Place
a 250
mmf. mica
condenser
between
the
con-
tact arm
of the
10,000
ohm
volume
con-
trol
and the low
end
of
the variable
r.f.
coil
in the first
r.f.
stage.
Noise
will
also
be reduced
by this
addition,
MAJESTIC
66. Vibrator
adjustment
.
. . Connect d.c. ammeter
(0-5
or
0-10,
low resistance)
in series
between
pigtail
terminal
on
vibratoi
and battery
wire
which
was connected
to this terminat.
Connect
0-300 d.c. voltmeter,
1,000 ohms
per
volt
type,
between
ground
and
the
B
side
(red
lead)
of audio
output trans-
former.
Connect 0-100
d.c. milliameter
between
ground
and
grounded
end of ts
filter
choke
(which
is 6rst removed
from
ground).
Now,
with
a
good
A
battery
at 7.3 volts
there should
be'5.7
volts at
the
vibrator terminals.
With normal
tubes
which have
been heated
for
at
least
one minute
the
following
values
should be read
when
the vibrator
is
properly
adjusted:
Input:
5,7
volts
at
from
3.8
to
4.1
amperes.
Output: 200
volts
at
53 milliamperes.
If
voltage
measured
at
vibrator
is
higher
or tower
than 5.7 then
the other
reidings
will
be
corespondingty
morc
or
less.
Readjust-
mcnt
of the vibrator
will be
nccessarv
if, for
the above input
values,
the
outpui
current
and voltage
are
down
or
if
the
input
current is
over 4.1 amperes.
Vibrators
which have
seen
any ap-
preciable
amount
of service
will not re-
tain readjustment
unless
the
points
are
dressed
or
replaced
with new
ones.
Ex-
perience
has
shown
that it
is
much
cheaper
for
the
average
service
man
to
replace
the vibrator
head
with
a new
head
which
has been
adjusted
and run-in
at
fhe
factory.
In
dressing
the
points
re-
move
the
armaturc
from the
vibrator
as-
sembly. In
removing
the armaturc,
loosen
only
one
pivot
screw in order
that the other may
remain
in
position
and
properly
locate
the armature
when
it is
put
back in
the frame.
Before
re-
moving
the armature
take note
of
the
side
play
on the
pivots
as this
same
amount
of
side
play
must
be obtained
when
the unit is reassemblpd.
In
reas-
sembting,
be
sure that
the
pivots
do not
bind
the armature
and
that the
side
play
does
not
exceed
.003
in.
to .005
in.
A 6le
is
practically
useless for
dress-
ing
the contact
points,
especially
for
the
tungsten
on the brass
studs.
A fine
carborundum
stone
should
be used for
acquiring
a final
finish.
When work
on
the contacts
is finished
they
shoutd
be
washed
in
alcohol
(never
use Ethyl
gas)
as any
carborundum
dust
left
on the
contacts
will
cause
rapid failure
after
adjustment.
In
disassembling
the vibrator unit
never
disturb
the
spring tension adjust-
ing
screw,
as this
screw
has
been set at
the factory
at that
point
which
will
place
the spring
under a tension
of 30
grams.
It is
very hard
to
guess
what
this
tension is and if
spring
gauges
for
measuring
this tension are not
available
it
is apparent
that the
tension
adjust-
ment
ought not
to be disturbed.
The
contact
which is
opposite from
the
tension
spring
is
called
the
primary
contact,
that on the
same side
as the
tension
screw, the
secondary
contact. In
adjusting
the vibrator,
set
the
primary'
contact
all the way
out so that it
does
not
make
contact
to the
armature.
Con-
nect the
battery
and
after
the tubes
and
rectifier
are heated,
turn
the
priInary
down
until
the armaiure
begins
to cfitter
against
the
core,
then back
it
oft about
a half
turn
so
that
the clatter
stops.
Tighten
the lock
nut
on the
primary
con-
tact
and then
turn
down
the
secondarv
until
the ammeter
reading
begins
to
make
an
abrupt
rise
and at
this
point
ad-
just
to 3.8
to
4,1
amperes.
Note
that
a
point
witl
be reached
in
this
adjustment
at
which the
output curr€nt and
voltage
do
not'increase,
even
though
the input
current rises
as the contact
is
turned.
The
point
at
which input
current is
a
minimum
for
a standard
output voltage,
is
the
point
of correct
adjustment.
Do
not
attempt
to turn any
adjusting
screw
without'first
loosening
the lock
nuts
and
do not
try
any one adjustment
as
final
without
tightening the locknut
as
tightening__.the
nut is
apt
to
change
things.
When the
vibraior
is
orooeilv
adjusted,
clearance
of
the
iorrirallv
opened
contact
is
.010 in.
to
.015 in. I;
attempting
to measure
this clearance
qilh a feeler
gauge
one
must
rety
on
sight
and not
feel
because
if
the
gauge
is
thicker
than
the clearance
of
thJ
con.
tact,
it
will force
its
way
in
because
of
the
flexibility
of
the spring
on which
the
lower
contact
is mounted.
If
the
gap
is
too small,
turn
the
spring
tension
lciew
down
a
hatf
turn.
The
armature
may
now
clattcr
against
the core
and if
it
does,
turn
the
primary
contact
back
about
one-quarter
turn.
Recheck
ad-
i-ustment
of the
secondary
contact
as
described
before.
.
I.f,
on inspection
of
the vibrator
unit,
it
is
seen
that
the armaturc
spring
ij
badly
discolored,
it
is an
indicaiion-that
the
vibrator
has
been
operated
under
improper
conditions,
as follows:
A:
Tampered
adjustment,
B: Incorrect
battery
polarity.
C:
Operated
at no
ioad
condition.
D:
Operated
at
overloed.
E:
Oqerated
at
too high
a
primagy
voltage.-
MAJESTIC
66-
Fuse
blows regu-
larly,
voltagcs
test
ok . .
.
Look for
bad
6Y5. Sometimes
test ok
in checker
but change
it
anyway.
(IF
175 kc.)
MAJESTIC
66
Intermittent,
low volume
. . . check
.03
mfd
condenser (Cl
on diagram) in
the
secondary
grid
return
of the an-
tenna coil.
This unit
frequently
opens.
MAJESTIC
66
Low
or
dead Glament
circuit. .
. high
resistance
between
fuse
clips and rivit-
ed lugs.
Solder
each of
the fuse clipo
to their
mounting
lug.
MAJESTIC
66
Fading,
vibrator
refuses
to
function,
pilot
light
still
lights.
.
.
Examine
fuse
holder
for
corrosion.
MAJESTIC
66. Troubles
due
to
wet-
ting
through
cowl ventilators,
\
rater
en-
tering
set through
ribbed
cover
openings
.
. .
Check screen
voltages
by listenirrg
for
clicking
sound
which
should be
heard
when contacting
controt
grid
of
i.f.
tube. If
not heard
check
wire-wourrd
10,000
ohm resistor
in series
with
screens
of
r.f.,
osciltator
and i.f.
tubes
tocated
directly
above
oscillator socket
on
under
side
of set, rivetted
to
chassis
sidewalt.
Look
also
for
electrolysis
on red
lead
going
into
B choke
which
opens up
sol-
dered
joint
inside
choke.
Symptom is
high-vottage
on control-grid
of 89. This
will
cause
slight shock
when
fingers
are
placed
from
grid
to chassis.
Cut
into
first
layer
of choke
insulating
paper
if
repair
is nccessary
and
re-solder
joint.
Wetting also
causes
rectifier
socket
ter-
minals
to arc
to chassis
and carbonize.
rrecessitating
new
socket.
29