Revox A76 Service Manual

VTVM
Fig.
4.5.-1
Fig.
4.6.-1
4.5.
Alignment of
center
tuning
discriminator
( narrow band
discriminator)
Important:
The centre
tuning
discriminator
FT
601
must be
aligned
immediately
following
the tuning
of
the IF
filters
( any frequency
drift
of
the
test
generator
would lead to
an
erroneous
adjustment).
Test
equipment:
Test
generator,
frequency
10.7
MHz
(
±
20
kHz
)
63
mV
o.c.v.
no
modulation.
IF
matching
network (see
fig.
4.2.-!
)
VTVM without
RF
probe,
range to
read DC
+
8
V
(+ 1
V/
-2
V)
4.5.1.
Tuner:
Power switch
depressed.
4.5.2.
IF matching
network
remains
connected
to
test
point
1
(see
fig. 4.4.2.)
4.5.3.
Connect a
resistor
of
1
Mohm
directly
to
test
point
3
( see
fig.
4.
5.-1
)
and
connect VTVM
to
that
resistor
4.5.4.
Turn slug
of secondary
winding
of
discriminator FT 601
almost
completely up (see
fig.
4.5.-1
)
4.5.5.
Adjust
primary
circuit
by
finding a
maximum
with the
tuning slug
in its
upper position as
described
under
4.4.
The
voltage
reading thus obtained
should be
from
6
to
9
V.
4.5.6.
Adjust slug
of secondary
coil until
obtaining
a
zero indication
on
the centre
tuning meter
(44)
4
.
6
.
Checking the
selectivity
A.
Bandwidth
Test
equipment:
Test
generator,
frequency
10.7
MHz
(
±
20
kHz
)
63
mV
o.c.v. no
modulation
IF matching
network (see
fig. 4.2.-1
)
VTVM with RF
probe,
range to read
1
V
4.6.1.
Tuner:
power
switch
depressed
4.6.2.
IF
matching
network remains connected to test
point
1
(see
fig.
4.4.2.)
4.6.3.
Connect
RF probe
of
VTVM to
test
point
2
(see 4.4.3.
and
fig.
4.4.-2.)
4.6.4.
Adjust output level
of
test generator
to obtain a reading
of
1
V on
the VTVM
4
6.5.
A
ter
the
frequency
of
the test generator by
±
65
kHz; this
must reduce the
VTVM reading to 0.7 V
(—
3
dB)
B.
Static
selectivity
To
measure
the static
selectivity, a
test
generator
is
required
whose
open
circuit output
voltage
can be
attenuated
to less
than
1
/xV.
4.6.6.
Connect
RF
probe
of VTVM to test
point
4
(see
fig.
4.6.-1
)
4.6.7.
Adjust
output
voltage
of test generator
to
its
minimum
( less
than
1
fiV)
and increase
gradually until a
reading
of 1
V
is obtained
on the
VTVM. During this
test, no
limiting
must
occur in
1C
204.
This can be
checked
by
slightly
increasing
11

Revox A76 Specifications

General

Brand	Revox
Model	A76
Category	Tuner
Language	English