Revox A76 Service Manual

420.
Checking of automatic mono-stereo
changeover
(level-dependent)
Test
equipment:
Test
generator frequency 94
MHz o.c.v.
variable
from
2
to
20
juV,
modulated
with stereo
modulate
,
deviation 40
kHz,
modulating
f
equency 1
kHz
(
L
=
R
),
pilot
carrier
9 %
(deviation
6.75
kHz).
4.20.1.
Tune
:
Power switch
depr essed
Buttons STEREO
AUTOMATIC
(47)
and MUTING
ON
(
49
)
depressed, set dial
pointer to 94
MHz
mark; fine tune
to
obtain zero indication on the
CENTRE
TUN
NG
meter
(
44
).
4. 20.
2
.
Reduce
generator
output level
gradually
from
20
/zV
o.c.v.
while observing the STEREO
(45)
indicator
light, and also
monitoring
the
audio output.
Check generator level
at
which the
STEREO
indicator light
goes off and
the
audio
output
disappears.
The circui
s
work satisfactorily when
swi ching occurs while
lowering
the
generator
level
down th ough
15
/uV
o.c.v.
4. 20.
3
.
Depress button TRIGGER
LEVEL
VAR
(48)
and raise send
level to 100
'
V
o.c.v. Slowly
rotate the
TRIGGER LEVEL
(
39
)
control until reception
again
returns to mono,
or until
the
audio
ou put ceases.
The
automatic changeover
circuit
works satisfactorily when
triggering occurs at position 5
of the control.
4
,
21 .
Checking
range of
output
potmeters
Test
equipment:
Test
generator,
frequency
94
MHz,
2
mV o c.v.,
modulated
w th stereo-
modulator,
40
kHz deviat’on,
modulating
fre-
q
*ency 1 kHz
(
L
=
R
),
p
lot
carrier
9
%
(
6.75
kHz
de-
viation).
15
kHz low-pass
filter
(see
fig
4.2
-3).
4.21.1.
Tuner:
Power
sw
tch
depressed
Button
STEREO
AUTOMATIC
(
47
)
depressed, set
dial
pointer to
94
MHz
mark; fine tune to
obtain zero
indication
on
CENTRE TUNING
mete
(44).
4
21.2.
Connect
15
kHz low-pass
f
Iter between
tuner output
(
56,
channel
I
or channel
II respectively) and
distortion
analyzer
or
audio millivoltmeter.
4.21.3.
Calibrate
distort
on analyzer (
or millivoltmeter
)
to
obtain
reference deflection.
4.21.4.
Turn output-potmeters
(
56
)
of
channel
I and
channel
II
fully counter
clock wise
and
measure output
level.
Both
controls
are
functioning
properly
when
att nuating the
signal
by 26
dB.
18

Revox A76 Specifications

General

Brand	Revox
Model	A76
Category	Tuner
Language	English