Assuming
that
necessary provisions
for
power
switching have been made,
the following
prelim-
inary steps
should be
taken before
the
amplifier
is
tested.
IMPORTANT
WARNING: MINIATURE
TUBES
CAN
BE EASILY
DAMAGED
WHEN
PLUGGING
THEM INTO THEIR SOCKETS. THEREFORE,
USE
EXTREME
CARE
WHEN
INSTALLING
THEM. WE DO NOT GUARANTEE OR
REPLACE
MINIATURE
TUBES
BROKEN DURING
INSTALLATION.
( )
Insert tubes in the sockets as follows:
Socket
VI
-
type
12AU7
Socket
V3
-
type
KT66
Socket
V2
-
type
12AU7
Socket
V4
-
type
KT66
Do
not
install
the
5R4GY
tube
in socket
V5
yet.
(
)
Place tube
shields
over the tubes
in sockets
VI
and
V2.
(
)
Adjust the
balance control
D
so
that it
is
halfway between
the
rotation
stops.
( )
Connect
a
load
of
some
type to the appropriate
speaker
output
terminals. A
4,
8 or
16
fi
resistor
will
do, or the
line
to
the
speaker system.
It
is not
advisable to
operate any
am-
plifier without a load
of
some
type
on the output, although theW-5M will
not
be
damaged
if
so
operated.
(
)
Plug
the
preamplifier into
the power socket
(if
used)
or connect a jumper
switch
between
pins 6
and
7
of
the socket.
Make sure
that the switch is
turned
off
and plug
the power cord
into
a
110 volt
AC
50-60
cycle
outlet.
CAUTION:
DO
NOT CONNECT THIS
INSTRUMENT
TO
A
DC
(DIRECT CURRENT)
LINE.
SERIOUS
DAMAGE TO
THE POWER
TRANSFORMER
WILL
RESULT.
Do
not
attempt
to op-
erate the
amplifier
on
a
25 cycle
source,
for
it
will not operate
and the
transformer
will
be
damaged.
(
)
Turn
the power switch
on and observe
the four vacuum
tubes
that have
been
installed. The
filaments in
the top
center
of the output tubes
should show
a
red glow
and a
similar glow
should
be
evident ineachl2AU7.
If
a
preamplifier is powered
by
the
W-5M
main amplifier,
the
filaments
of the preamp
should also be
lit.
If
the
filaments fail to
light,
check the steps
outlined under
"In
Case
of Difficulty.
"
(
)
Plug
the
5R4GY
rectifier
in
socket
V5
and watch
it carefully. If
the
plates
begin to show
a
red color or a
purple glow appears
inside
the tube
elements, shut
the
amplifier off
immed-
iately and
check
for
trouble as
outlined above.
A
soft blue
glow
can
be
expected,
especially
when the
amplifier is first
turned on
and need
not
be cause
for
concern. This is
caused
by
fluorescence of impurities
in
the
glass
envelope
due
to stray
electron bombardment.
(
)
Balance
the output tubes. This is
accomplished by
connecting a
voltmeter of practically any
type across the Bass-Bal jacks
provided
on
the
chassis
apron.
Start
with
the voltmeter set
on one of the
higher
ranges and
rotate
the
balance control on
the
chassis
top
until the meter
reads
0.
Set
the meter to
the
highest
sensitivity or
the lowest
voltage range and
adjust
the
control
carefully until
the
meter reads
exactly the
same
when
plugged
in and when
discon-
nected.
Zero voltage or
current indicates
that the
current
in
both
output
tubes
is
exactly
identical.
See
notes
on
Page
28.
(
)
If
theHeathkit
WA-P2
or a
similar
preamplifier is used,
drawing
power
from the
main am-
plifier, adjust
the hum balance
control on the
preamplifier
for
minimum
hum, using
a
loud-
speaker connected
to the
amplifier
output as
an
aural
indicator.
A meter
can
be
used
if
desired. In
all
cases,
the
instructions
included with
the preamplifier
in question
should be
observed.
(
)
Mount the
bottom cover
on the chassis
bottom, using
the
#6
sheet metal
screws
furnished
.
See Figure
17. Make
sure the
ventilating holes are
directly under
socket
V3,
V4
and
V5
.
Page
24
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