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TROUBLE-SHOOTING PROCEDURES
Your
amplifier should require
little
service
except
For
normal tube replacement*
We
recommend
no
substitutions
for
the
tube types used
in this
amplifier.
The
EL84,
and
EZ81
types are distributed nationally
by
the
Amperex
Electronic
Corporation (230 Duffy
Aye*,
Hicksville,
L.
U,
N.
Y* JandMullard
Ltd.
(International Electronics
Corp,
81 Spring
St*
,
N.Y*
12,
N.Y.) Thel2DW7type
is
made
by
several
U.
S*
manufacturers
and
is
available
nationally*
If
necessary,
replacements
at
any
time
can be obtained
directly
from
E1CO.
To
facilitate servicing,
remedial
and
trouble-shooting
procedures
have been
provided
in
the
TROUBLE-SHOOT-
ING CHART
that follows.
A VOLTAGE
AND
RESIST-
ANCE
CHART
is
also
provided
as
an
aid
in
locating
de-
fective
components and
to
permit
a
careful,
stage-by-
stage
check
of the amplifier.
DC
operating voltages are
given both
at
no
signal
and
at
a
signal
developing
14
watts output
as
well
as
the corresponding
1
kc
signal
volt-
ages.
To
isolate
the source of unusual
hum
or noise
in
your
sys-
tem,
first
turnoff the
AC
power and
then
unplug
the audio
cable connecting
to
the amplifier input*
Then
turnthe
AC
power on
again and note whether
hum
or noise has
de-
creased*
if
it
has,
the
fault
is
in
the preamplifier or
associated
equipment and
measures should be taken
to
correct
it
as
described
in
the service notes forthese
units.
If it
is
desired
to
provide a
good
building
ground
for
your
entire system, run
a
lead from
under
either
speaker
con-
nection terminal
11
G
M
to
a cold
water
pipe.
Do
notcon-
nectsuch a ground wire
to
other
components
in
the system*
If
the trouble
is
no
output
or
low output
and
the amplifier
is
suspected,
check
AC
signal
voltages
starting at the in-
put
and work
step-by-step toward
the output,
using
a
sine-wave audio
signal
generator
and
a
VTVM.
Set the
Input signal
to
1
volt.
The
corresponding
grid
and
plate
signal
voltages
forthis input
are
indicatedon
the
voltage
chart.
Repeat
For
the
second
channel.
This
procedure
should
suffice to
localize the defective stage.
If
the trouble
is
an
excessively
distorted
output,
try
tube
replacement,
signal tracing,
or
proceed
directly
to
voltage
and
resistance
measurements*
When
the
defective stage
is
localized,
proceed
to
a re-
sistance
and voltage check
of the stage, using the
data
tn
the
Voltage
and
Resistance
chart.
Disconnect
the
amplifier
from
the
power
line
and
discharge
capacitors*
prior to
making any
resistance
checker removing
the
EL84
output
tubes.
Do
not turnthe amplifier
on with any
of
the
output
tubes
removed*
CHECKING
A
TYPICAL TUBE
STAGE
],
Check
tube*
2.
Check
plate
and cathode
resistors,
3.
Check
coupling
capacitors
for
leakage
or
short.
4*
For output
stage,
check dc
resistance of transformer
windings.
5.
Check
for
open
grid leak
resistor*
6.
Check
cathode
by-pass capacitors
for short,
7.
IFno or
low B+ voltage on
the tube,
check decoupling
path
for
open
or defective
R27orR28, and
filter
capaci-
tor,
Cl
5,
for short,
8.
If
wiring
and
circuit
components
Including the tube
check
O.
K.
and
frt-
voltage
is
excessive,
check
the
de-
coupling path
for
short
or defective
R27
or R28*
SERVICE
If
trouble
develops
in
your
instrument
which
you can
not
remedy
yourself,
write
to
our
service
department
listing
cl!
possible indications
thatmlght be
helpful*
If
desired
you
may
return the
instrument
to
our factory
where
if
will
be placed
in
operating condition
for
$7-50
plus
the
cost
of
parts
replaced due
to
theirbeing
damaged
in
the course
of construction.
NOTE:
Before returning
this
unit,
be
sure
all
parts
are securely
mounted.
Attach a
tag
to
the
Instrument,
giving your
home
address
and
the trouble
with
the
unit*
Pack very
carefully
in
a rugged
container, us-
ing sufficient
packing
material
(cotton,
shredded
news-
paper,
or excelsior),
to
make
the unit
completely
immov-
able within the container*
The
original
shipping carton
is
satisfactory,
providing the
original
inserts
are
used
or
sufficient
packing
material inserted
to
keep
the
instru-
ment immovable-
Ship
by
prepaid
Railway
Express,
if
possible,
to
Electronic Instrument
Co.
,
Inc.
,
33-00 North-
ern
Blvd,,
Long
Island
City
1,
New
York.
Return ship-
ment
wi
11
be
made
by
express collect,
Notethata
carrier
cannot be held
liable
for
damages
in
transit
if
packing
IN HIS
OPINION,
is
insufficient.
4
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