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ST4Q
PAGE
10
HUM
BALANCE;
Separate filament windings
and
hum-
ba
la
nee
controls are
provided
for
the
two
channels,
so
that
an
optimum hum
balance
setting
can be found
for
each
channel,
rather
than
a
compromise
setting for
both channels*
Connect
the
phonograph and
leave
it
shut-off
with
the
tone
arm
at
rest.
Set the
SELECTOR
to
the PH.
A
or
PH.
B
position
depending on which
in-
puts
are
used.
Set
the
MODE
switch
at
v/
CH.
1,
BALANCE
at
0,
LEVELat
10,
BASS
1
&
2 at
0,
TREBLE
1
&
2 at
0 (amplifier turned on).
Setall
slide
switches
at "off"
(down).
Adjust the
channel
1
hum-balance
control
(R-77)witha
screw-driver
until
the
hum
heard
from
the
channel
1
speaker
is
at
a
minimum*
Now
set
the
MODE
switch at
v/
CH.
2
and
adjust the
channel
2
hum-balance
control (R-78)
until
the
hum
heard from
the
channel
2
speaker
is
at
a
minimum.
See
Figure 3
for
the locations of
R-77 and
R-78*
GROUNDING;
The
cause
of
phonograph
hum
maybe
a
metal
pick-up
arm
not
grounded
to
the
cable
shield
(trya
good
single
ground connection
to
the
cable
shield
from
turntable frame,
pick-uparm, and
cartridge case),
direct
hum
pick-up by
the
magnetic
cartridge
from
the
record player
motor
(try
using
a
rubber mat
on
the turn-
tableto
Increase the separation of the
pick-up from
the
motor), or
pick-up
from a
power
transformer or other
magnetic
field
in
the vicinity
(try
moving phonograph
away
from suspected
source).
Check
also that the
phono
input
cable
shielding
is
grounded
to
the amplifier chas-
sis
at
one
point only, through the
skirt
of the input
connector
where
it
plugs
into
the amplifier.
Finally,
try
a
good
building ground, such as
a connection from
a cold
water
pipe terminated
under
the
channel
2,
4Q
Impedance
tap (ground)
on
the rear
apron
of the
ampli-
fier.
Do
not
connect such a ground wire
to
other
com-
ponents
in
the system.
If
possible,
let
each
channel
be connected
to
the amplifier
usinga
separate shielded
cable
to
the
amplifier
input.
It
is
also desirable that
the
ground
leads
on both cables
not
be connected
to-
gether
at
any
point
—
not
even
at the cartridge.
How-
ever,
with
some
cartridges,
it
will
not be
possible to
do
this.
In
this
case,
just
disregard
this*
last
Instruction.
SERVICING
GENERAL
Your
amplifier should require
little
service
except
for
normal tube replacement.
We
recommend no
substitu-
tions for
the
tube
types used
in this
amplifier
except
as
stated.
All the tube types
used are
distributed
nation-
ally,
but
replacements can be obtained
directly
from
E1CO
if
desired.
To
facilitate servicing,
remedial
and
trouble-shoot-
ing
procedures
have been
provided
in
the
TROUBLE-
SHOOTING
CHART
that follows.
A
VOLTAGE
AND
RESISTANCE
CHART
Isalso
provided
asan
aid
in
locat-
ing defective
components.
DC
operating voltages are
given both
at
no
signal
and
signal
developing
20
watts
output, as
well
as the
corresponding Ike
signal
volt-
ages.
TROUBLE-SHOOTING
PROCEDURE©
Connect
a
stereo
phono and
a pair of
speakers
to
the
amplifier
as
described
in
INPUT
CONNECTIONS
and
OUTPUTCONNECTiONS.
Do
not
operate
the
ampli-
fier
without speakers
or equivalent loads
connected
exactly
as described.
Set the
SELECTOR
switch
to the
corresponding
phono
position
(PH.
A
or
PH.
B)and
the
MODE
switch
to
STEREO.
Play a
known
high quality
stereo
recording
on
the
phonograph.
If
there
is
no
output
to
the speaker, or
if
the
output
is
low
or
audibly
distorted,
proceed
to
the
checks
for
those
symptoms,
if
there
is
excessive
hum
in
the output, disconnect the
phono
input
cable from the
amplifier
and
short
the
phono
input
jack
to chassis,
if
the
hum
disappears, the trouble
is
not
in
the amplifier but
in
the
phonograph
or
In
the
connection
to
the amplifier.
In
each
case,
check
for
the trouble
in
the amplifier
which
seems
defective.
If
both
amplifiers are defective,
check
the
power
supply.
Excessive
hum
on
other
inputs
may
be checked
in
a
similar
manner. Disconnect
the input
cable
In
question
and
short
the particular input jack to the
chassis.
If
the
hum
disappears, the trouble
Is
external
to
the
amp-
lifier.
Note
that
on
all
inputs, the
braid of the input
cable should connect
to
the amplifier
only through
the
skirt
of the input connector*
The
cause
and
remedies
for
the following
symptoms
are then
based on
the
assump-
tion that
checks
made
In
the
manner
described
above
have
eliminated the
possibility
of the trouble
being
external
to
the amplifier*
If
trouble
Is
no
output or low output,
check
AC
signal
voltages
and
DC
operatingvoltages
starting at
the in-
put,
and work
step-by-step toward the output
in
each
amplifier* Set the
LEVEL
control to
maximum
(10),
the
BALANCE,
BASS
and TREBLE
controls
to their
mid-
points
(0),
the
SELECTOR
switch to
PH.
A
or
PH.
B
and
the
MODE
switch
to
STEREO. Feed
a
1000 cycle
sine-wave
signal
from an audio
signal
generator through
a
precision 100:1 attenuator
to
the
phono
inputs
selec-
ted.
The
attenuator permits obtaining a
level of 0.
003
volt fed
into
MAG.
PHONO
from
an
audio generator
output of
0.3
volts,
which
can
easily
be.
measured on
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