Philips PM 3266 - 3.2.7. X Final amplifier

120
3.2.7. X
Final
amplifier
FROM
X-DEFLECTION
SELECTOR
I
I
T, B MAGN.
X-FINAL
AMPLIFIER
CRT
V1701
V1718
MATS
9
Fig.
3.12.
X Final
amplifier
The
final
X amplifier
consists
of two
identical
amplifier
stages in parallel
(one
for
each deflection
plate).
One
stage
consists
of
transistors
V
1
706,
V
1
707,
V
1
708,
V 1
709,
V 1
722
and V
1 724
and
the
other
consists
of
transistors
V1714,
V1716,
V1717,
V1718,
V1726
and
V1723.
The final
stage is supplied
from
the
+130 V and
—130
V because the X
plates
of the
C.R.T.
are
mechanically
displaced
such
that they
are less
sensitive
than
the
Y
plates.
The amplifier
stages
are controlled via
the transistors
VI
701
and VI
702.
With the X POSITION
potentiometer R2
and V1704 the
bias of transistor V1702
can be varied.
Potentiometer R2
consists
of a tandem potentiometer
R2a/R2b with back-lash,
giving a nice vernier control.
Variation of
the bias
causes the balance of
the amplifier
to be
disturbed, which
results in
a
horizontal trace
shift
on
the screen.
The X amplifier
allows choice
from
X deflection by
the time-base signals or one of
the sources, channel A,
channel
B, line or an
external
signal. The
X deflection
source is selected with the aid of X deflection mode
selector
switch
S2 and the X
deflection source
selector switch
S22.
The
selected X
deflection signal
is
applied via R1703 to
the base of transistor VI
701
.
The X amplifier
offers the possibility
of using either
the nominal gain (XI position
of X MAGN switch
S3), or
the gain
increased
by
a
factor
of
10
(XI
0
position of the X MAGN switch
S3).
When the
front-panel
X
MAGN
switch
S3
is operated for
X10
magnification,
the emitter resistance
of
VI
701
and VI 702 is
shunted by
resistors R1704, R1706
and R1707 via relay K1701,
reducing the value
by a factor
of 10.
Consequently,
the gain
of the stage is increased
by the same factor.
The XI gain
can be
set by potentiometer
R1 709 and the
gain
X10
by potentiometer R1706.
The gain X 10 is
not
operative when EXT
X
DEFL
is selected.
Both outputs
of the X final
amplifier
are
connected
to the X deflection plates of the C.R.T.