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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