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i*
b
useful to
understand the process of convection
where-
'
by heat
Is
removed
In
fudging the
suitability
of
a
location.
Air
heated
by
the heat-producing elements
expands
and
rises;
cool
air
Is
drawn
from
beneath
to
take the place of
the
heated
air.
In this
manner, a
stream of
atr
Is
set In
motion
which
continually
removes heat from
the
ampli-
fier.
(In
particular,
we
are
mainly concerned with
the
mafor heat-producing
elements; the
two
6L6GB
output
tubes
and
the
5U4GB
rectifier
tube.)
If
there
Is
any
Im-
pediment
to or constriction of the
air
flow, the
essential
process of
heat removal
will
be
adversely
affected.
Adequate
venttlatlon
will
be
provided
If
the amplifier
Is
Installed In
an open-back
console provided
that the top
of the amplifier
ts
spaced
at
least
two
Inches
below any
shelf
mounted above
It.
If
the cabinet
ts
enclosed
at the
rear,
provide
several large holes or
slots
as
low
down
and
as
high
up
In
the cabinet
back
as possible.
As an
alter-
nate, holes
may
be
provided
In
the
sides,
bottom,
or top
of the cabinet.
The
Important thing
to
remember
Is
that
effective ventilation
requires provision for
cool
atr to
en-
ter
at
the
bottom
and
hot
air to
leave
at the top.
If
the amplifier
ts
not
Installed In
a
console.
It
should
be
situated preferably
on an open
surface,
not
on a
shelf
of
a
bookcase.
An
attractively finished
matching cover
for
the
Model 20
Is
available
which
will
provide a
"finished
11
appearance
as well
as
protection
when
the amplifier
Is
not
Installed
In
a
console.
Four rubber
feet
are
also
pro-
vided
so that the amplifier
will
not
mar
the surface of
furniture
on which
It Is
placed.
b)
EASY ACCESS
TO CONTROLS:
Mount
the amplifier
at
a height
which
will
permit easy
manipulation of
the
controls.
Tuner
controls
should
be
located nearby.
c)
ACCESSIBILITY
TO
PARTS: Tubes
are the
most
fre-
quently replaced
Items
In
electronic
equipment.
If
the
amplifier
ts
Installed
tna
console,
sufficient
space
should
be
alloted
to
reach
and remove any
tube
In
the amplifier.
Furthermore, Input
and
output terminals of the amplifier
should
be
accessible
to
permit easy interchanging of
sys-
tem components
for
comparlsonjand connection
or
discon-
nection of a
portable tape recorder
which
Is
stored
away
when
not
In
use.
If
antennas are
strung
around
the
back
of the consoletn
which
the amplifier
is
Installed,
arrange
them
so
they
will
not
Interfere
with access
to
the amplifier.
d)
ACOUSTICAL
ISOLATION:
If
amplifier
and
speaker
are
installed In
the
same
cabinet
(not
recomemnded),
pro-
vide
sufficient
separation
to
minimize mechanical
speaker
vibration
reaching
theampllfler.
The
minimum
separation
Is
about
one
foot.
1.
CHASSIS
MOUNTING
IN
CONSOLE
a)
Operation, on
contole
front
panel preliminary
to
am-
plifier
mounting—
M
)
Tape
the panel
template provided
to
the
face of the console
so that the
top of the
mounting
surface line
on
the template
Is
level
with
the top of the
amplifier
mounting
shelf.
(2)
Use an awl
or
a
nail to
.
•
4
4
pierce the centers of the five
5/9" diameter
holes
for
the
controls
and
the
two
small holes
for
mounting
the control
plate, to
transfer their locations
'to
the console panel
be-
neath.
(3)
Remove
the panel template.
(4)
Drill
the
holes
for
the
panel
controls
only
(the
two
small holes
which
have been marked
are
for
wood
screws).
b)
Amplifier
mounting
In
console:
(1) Pull
off
the
con-
trol
knobs
(a
second
set
of knobs with
long shanks has
been
provided
for
console
Installation).
(2)
Remove
the
control plate,
which
Is
attached
to
the
chassis
apron
by
two
screws. (These
may
be
discarded since they are
un-
suitable
for
attaching the
control
plat,
to
the console
panel
and two^4
X
3/Bwood
screws
have been
supplied
for
this
purpose.)
(3)
Fasten the control plate
to
the
con-
sole
panel with the
2 ^4
X
3/3
wood
screws.
(4)
If
the
rubber feet
have been
Inserted
In
the
bottom
plate, re-
move
them.
(They
may
be
pried
out with
a
thin
screw-
driver.)
(5)
Place
the unit
on
the
mounting
shelf
and
slide
It
as
far
forward
as possible,
so that the controls
penetrate the panel
holesas
far
as
possible.
(6).
Place
a
long
shank
knob
on each
control, pressing
each knob
toward
the
chants
firmly so that
each
control shaft enters
fully Into
Its
knob.
(7)
Draw
the
chanls
back evenly
and
carefully
until
the
back
rims
of
all
the knobs are
equally
spaced
from the
control
plate
about
1/8".
(B)
With
a
sharp pencil, placed with
Its
point directly against
the
edge
of the lower
surface of the
bottom
plate,
draw
the outline
of
the bottom plate
on
the
chanls
shelf.
(9)
New
remove
the
knobs and
take the
chants
off the shelf.
(10)
Remove
the
8
screws
which
fasten the
bottom
plate
to
the chanls.
(11)
Place the bottom
plate
exactly
In
theoutllnedrawn on
the shelf
(bumps
facing up)
and
marie
the positions
of the
two
holes
on
the
left
side
and
the
two
holes
on
the
right side.
(12)
Remove
the
bottom
plate
and
drill
each
of the
marked
holes
on
the shelf to
a
diameter of 1/4".
(13)
Refasten the
bottom
plate
to
the
chanls, with
the
4 *8
X
3/B
screws
prevlousljiip-
moved,
using the
2
holes at the rear
and
the
2
horns at
the front
of the chanls.
(14)
Replace
the
chassis
on
the
shelf,
positioning
It
exactly
In
the outline previously
drawn, and
restore
the knobs.
This
time
make
sure that
the Indicator
dot
on each knob
agrees with
the control
position.
(15)
From
the
bottom
side
of the
shelf. Insert
a *8
X
1"
screw with
a
1/2"
flat
washer
against the
head
through
each
of the
four
left
and
right side
holes..
These
screws
engage
the
stamped
nut
over
each
hole
on
the
chanls flange
and
when
tightened secure the
chanls
to
the
shelf.
2.
ELECTRICAL
CONNECTIONS
a)
SPEAKER
CONNECTIONS:
To connect
your speaker
to
the amplifier' properly,
you must
know
Its
rated
Im-
pedance.
This
may
be
read
off
the speaker nameplate.
Connectone
speaker lead
to
the terminal
on
the
rear
apron
marked
n
G"and
the otherspeaker lead
to the
nearby
ter-
minal designated
by
the rated speaker
Impedance
(4,
8,
or
16 ohms). Plastic-covered
lamp cord
may
be
used
for
distances
up
to
50
ft.
with
little
power
Ion.
For shorter
distances,
TV
antenna
lead
can be
used,
particularly
If
It Is
desired
to
run the
speaker lead under
a
rug.
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