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maintenance
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 EL34
type
is
distributed national
ly
by
the
Amperex
Electronic
Corp-
oration
(230 Duffy
Ave.
,
Hicksville,
L. I.,
N.Y.
)
and
Mullard
Ltd.
(International Electronics
Corp.
,
81
Spring
St.,
N.Y.
12,
N.Y.)
If
necessary,
replacements
at
any
time
can be
obtained
directly
from
EICO.
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 35
watts output
as
well
as
the corresponding lkc
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
turn
the
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
for
these
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
"G"
to
a
cold water
pipe.
Do
notcon-
nectsucha
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
inputsignal
to.38volt.
The
corresponding
grid
and
plate
signal
voltages
for this
input are indicated
on
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
directlyto volt-
age and
resistance
measurements.
When
the defective stage
is
localized,
proceed
to
a
re-
sistance
and
voltage
check
of the
stage,
using the
data
in
the
Voltage and
Resistance
chart.
Disconnect
the
am-
plifierfromthe
power
line
and
discharge capacitors
prior
to
making any
resistance
check
or
removing
the
EL34out-
put
tubes.
Do
not
turn
the amplifier
on with
any
of the
output tubes
removed.
~~
——
-
—
CHECKING A
TYPICAL TUBE
STAGE
1.
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.
If
no
or
lowB+
voltage on
the tube,
check
decoupling
path
for
open
or
defectiveR31,
R32or
R35,
filter
capac-
itors
C15, C16,
C17
or
C19,
for short,
or
defective rec-
tifiers
CR1
or
CR2.
8.
If
wiring
and
circuit
components
including the tube
check O.
K.
and B+
voltage
is
excessive,
check
the
de-
coupling path
for short
or
defective R31,
R32
or R35.
SERVICE
If
trouble
develops
in
your instrument
which
you can
not
remedy
yourself,
write
to
our service department
listing
all
possible
indicationsthatmightbehelpful.
Note num-
ber
appearing
in
red
under
the
word "Manual" on
the
front
cover.
If
there
is
no number,
state
this.
If
desired,
you
may
return
the instrument
to
our factory
where
it
will
be
placed
in
operating condition
for
$8.
00
plus
the
cost
of
parts
replaced
due
to their
being
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, using
sufficient
packing
material
(cotton,
shredded newspaper,
or excelsior),
to
make
the unit
completely immovable
within the container.
The
original
shipping carton
is
sat-
isfactory,
providing the
original
inserts
are
usedor
suffi-
cient
packing
material
is
inserted
to
keep
the instrument
immovable.
Shipby
prepaid
Rai
Iway
Express,
if
possible,
to
Electronic Instrument
Co.
,
Inc.,
33-00
Northern
B
I
vd.
Long
Is
land
City
1,
N.Y.
Return
shipment
will
be
made
by
express collect.
Note
that
a
carrier
cannot be held
liable
for
damages
in
transit
if
packing
IN
HIS
OPINION,
is
insufficient.
TRANSFORMER
TEMPERATURE
The temperature
of the trensformers
used
in
theHF-87
run
at
less
than
195°F
despite the fact
that the
safety
limit
is
ata
much
higher 221°F.
Although 195°F
is
cool
for
a
transformer,
it
is
very
hot
to
the touch.
Transformers
which seem
too hot
when
touched with
the
hand,
are
usually
good aid
are actually not
overheating.
Output
transformers usually run
cooler than
power
transformers.
Some
output
transformers
may
appear
hotter than others
due
to
being
located near hot
components
such
as
output
and
power
tubes
and power
transformers.
4
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