Eico HF-89 - Checking a Typical Tube Stage; Trouble-Shooting Procedures

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
coldwater
pipe.
Do
not con-
nect such
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
inputsignal
toO.
5volt.
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
directly
to
volt-
and
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-
plifier
from
the
power
line
and
discharge
capacitors
prior
to
making
any
resistance
check
or
removing
the
EL34 out-
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
low B+
voltage
on the tube,
check
decoupling
path
for
open or
defective
R45,
R46
or R47,
shorted
or
defective
Cl
7,
Cl
8,
Cl
9,
or
C20.
Also check
rectifiers
CR1,
CR2,
or
CR3
for
defect.
8.
If
wiring
and circuit
components
including
the
tube
check O.
K.
end B+
voltage is
excessive,
check
the
de-
coupling
path for
shorted or
defective
R45,
R46
or R47.
SERVICE
If
trouble
develops in
your
instrument
which
you
can not
remedy
yourself,
write to our
service
department
listing
all
possible
indications
that might be
helpful.
Mention
any
code
numbers in
red under
the
word
"Manual"
on the
front
cover.
If
there is no
code
number,
state this.
If
desired
you
may
return the
instrument
to
ourfactory
where
itwill
be
placedin
operating
condition
for
$9.
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
news-
paper,
orexcelsior),
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 the
Service
Dept.,
Electronic
Instrument
Co.,
33-00
Northern
Blvd.,
Long
Island
City
1,
New
York.
Return
shipment
will be
made
by
express
collect.
Note
that
a carrier
cannot
be
held
liable for
damages
in tran-
sit
if
packing
IN
HIS
OPINION, is
insufficient.
TRANSFORMER
TEMPERATURE
The
normal
operating
temperature
of
the
power
transformers
in
theHF-89
is
less than
195°F
despite
the
fact
that
the
safety
limit
is a much
higher
221°F.
While
195°F is
cool
for the
transformer,
it is
very
hot
to
the
touch.
Transformers
which
seem too
hot
when
touched,
are
usually
good
and
are
actually
not
overheating.