Philips PM 3266 - Page 121

126
In
this
condition
(see WRITE
and
FAST
mode
description),
the
output
to the
FGA
is at
+
50 V.
c. When
the
input
to
V2437
is
switched
to
+1
1.2
V
by D2401
(pin
9
to
pin
8)
then
this
transistor
is
blocked.
As
a result,
V2438
conducts
and
brings
V2442
into
conduction.
The
resulting
drop
in the
collector
voltage
of V2242
is
applied
to
the
base
of V2439
and
switches
off
this
transistor.
In
this
condition
(see
STORE
mode
description),
the
output
to the FGA falls
to
0
V.
COLLIMATOR
1
AMPLIFIER
This
amplifier,
V2444,
V2446,
is a
two-transistor
feedback
circuit.
With no
signal
input
the output
on R251
7 to collimator
1
(Cl
)
is
at
-t30
V.
When
an
earth
is
applied
via
D2401
(pin 1
1 to
pin
10)
to input
transistor
V2444,
it
conducts less
and
ihe
increase
in
its
collector
potential
is applied
to the base
of V2446.
As
a
result,
this
transistor
conducts
further.
In
this
condition
(see WRITE
and FAST
mode
description),
collimator
1
potential is
increased
to
-t90
V.
COL LIMA
TOR
3 AMPLIFIER
This
circuit
is
almost
identical
to
the collimator
1 circuit
described.
The
amplifier
comprises
transistors
V2449
and
V2451. The
collimator
3
potential
can be switched
by
an
earth
from D2401
(pin 1
to pin
2)
from
its normal
+
75V
level to
between
+
75V
and
+
100V
(set by
preset
R2404)
(see WRITE
and
FAST
modes).
COLLIMA
TOR
2 AMPLIFIER
This is a
two-stage transistor
amplifier,
V2462, V2448, with
a
preset
gain control R2523
in the base circuit
of
V2448.
The
collimator
2
potential can
be adjusted
between
the values
of
I30
V and
-t90
V. When there
is no input via
diode V2464
then
the base of
V2462
stands at
a
positive
value determined
by the
-t5.6
V line (FAST
and
STORE modes).
In
the WRITE mode,
pulses
are
received
via
V2419 and diode
V2456 which are integrated
by
C2427.
Depending on the
setting
of the PERSISTENCE
control,
the integrated
potential
on the base of
V2462
is
modified, and
,
in
turn modifies
the
output potential to the collimator
2 electrode.