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RCA BA-13A - Page 8

RCA BA-13A
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5
Figure
3
—
Rear
View
of
Type
BA-1
3
A
Program
Amplifier.
CIRCUIT
MODIFICATIONS
Gain
Controls
In
applications
where
extreme
quietness
or
ex
tended
periods
of
operation
without
servicing
are
prime
considerations
the
dual
continuous-type
attenuator
or
gain
control
furnished
in
MI-11223-A
Hum
Adjustment
A
hum-adjustment
potentiometer
marked
HUM
is
located
on
top
of
the
chassis,
in
front
of
the
output
transformer
and
in
line
with
the
meter
switch,
see
figure
3.
A
screwdriver
slot
is
provided
in
the
potentiometer
shaft,
which
is
accessible
from
the
top
of
the
chassis,
for
adjusting
the
hum
level
to
a
minimum.
plug
J-2,
figures
3
and
8).
To
insure
a
low
hum
level
the
a-c
supply
circuit
should
be
shielded
and
the
shield
grounded.
Metering
The
four-position
rotary
switch
mounted
on
the
front
panel
of
the
amplifier
chassis
(right
side)
is
designed
to
be
used
in
conjunction
with
the
Type
BI-1A
(MI-4388-B
or
MI-4388-C)
or
the
Type
BI-2A
(MI-1
1275
or
MI-1127
5-
A)
Metering
Panel
to
conveniently
check
the
operation
of
the
individual
tubes.
The
numbers
on
the
METER
dial
plate
indicate
the
tube
which
is
being
checked.
Circuit
arrangement
is
such
that,
with
the
tubes
operating
normally,
the
meter
will
read
approximately
1
volt.
When
a
Type
BI
metering
panel
is
not
avail
able
any
suitable
voltmeter
having
an
internal
resistance
of
20,000
ohms-per-volt
or
greater
can
be
used.
Connect
the
positive
terminal
of
the
meter
to
terminal
number
8
and
the
negative
terminal
of
the
meter
to
terminal
number
10
on
the
input
receptacle
(for
input
plug
J-l,
figures
3
and
8).

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