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Tektronix 7613 User Manual

Tektronix 7613
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optimum
focus.
Fig.
3-21
shows
a
detailed
block
diagram
of
the
CRT
Circuit.
A
schematic
of
this
circuit
is
shown
on
diagram
8
at
the
rear
of
this
manual.
Z-Axis
Amplifier
The
Z-Axis
signal
from
the
Logic
circuit
and
the
Z-Axis
signal
from
the
Readout
system
are
connected
to
the
emitter
of
Q1107.
Transistor
Q1107
is
a
common-base
amplifier
to
establish
a
low
input
impedance
for
the
input
signals.
Transistors
01148,
Q1152,
GQ1154,
and
Q1156
form
a
current
driven
operational
amplifier.
The
input
and
output
transistors
are
complementary
to
provide
a
fast
rise-time
and
a
fast
fall-time
response.
The
amplifier
input
is
through
resistor
R1108.
Resistor
R1152
establishes
a
low
current
in
the
series
connected
output
transistors.
Tran-
sistor
01148
supplies
additional
current
through
C1151
for
the
positive
transients,
and
transistor
©1156
supplies
additional
current
through
C1158
for
negative
transients.
Capacitor
C1158
is
adjusted
for
optimum
square-wave
output,
resistors
R1158
and
R1159
along
with
capacitor
C1158
form
the
feedback
network.
Zener
diode
VR1142
provides
the
necessary
change
of
voltage
from
the
collector
of
01107
to
the
base
of
01156.
Auto
Focus
Amplifier
The
voltage
developed
across
R1108
by
the
Z-Axis
amplifier
driving
current
is
inverted
and
amplified
non-
linearly by
Q1110
and
Q1118,
to
conform
to
the
require-
ments
of
the
CRT
focus
electrode.
As
the
base
of
Q1110
is
driven
negative
CR1115
is
forward
biased,
producing
a
knee
in
the
amplifier
response.
The
Level
where
the
knee
occurs
is
determined
by the
adjustment
R1121.
The
operation
of
the
remaining
amplifier
is
identical
te
the
Z-Axis
amplifier.
High-Voltage
Oscillator
Power
for
operation
of
the
high-voltage
supply
is
provided
from
the
+15-Volt
Supply.
At
the
time
of
turn-on,
CR1215
is
reversed
biased
holding
the
collector
of
Q1214
positive.
This
allows
the
starting
base
bias
current
for
the
High-Voltage
Oscillator
to
be
supplied
from
the
+5-Volt
Supply
through
R1214,
Q1214,
and
the
base
feedback
windings
of
11225
while
the
emitter
potential
of
Q1216-01218
is
established
by
the
negative
side
of
the
+15-Volt
Supply.
As
the
output
of
the
high-voltage
supply
increases
to
its
required
output
level,
the
collector
of
Q1214
goes
negative
until
CR
1215
is
forward
biased.
Then
the
collector
level
of
Q1214
is
clamped
about
0.6
volt
more
negative
than
the
negative
side
of
the
+15-Volt
Supply.
This
configuration
provides
a
controlled
starting
current
for
the
High-Voltage
Oscillator
at
turn-on,
and
at
the
same
time
allows
the
High-Voltage
Regulator
stage
to
control
the
Circuit
Description
-7613/R76
13
Service
current
for
the
High-Voltage
Oscillator
after
the
stage
reaches
operating
potentials
to
provide
a
regulated
high-
voltage
output.
Q1216-01218
and
the
associated
circuitry
comprise
an
oscillator
to
drive
high-voltage
transformer
T1225.
When
the
instrument
is
turned
on,
assume
that
Q1216
comes
into
conduction
first.
The
collector
current
of
01216
produces
a
corresponding
current
increase
in
the
base-feedback
winding
of
11225
to
further
increase
the
conductivity
of
Q1216.
At
the
same
time,
the
voltage
developed
across
the
base-feedback
winding
connected
to
Q1216
holds
Q1218
reverse
biased.
As
long
as
the
collector
current
of
Q1216
continues
to
increase,
voltage
is
induced
into
the
base-feedback
windings
of
T1225
which
holds
Q1216
forward
biased
and
Q1218
reverse
biased.
However,
when
the
collector
current
of
Q1216
stabilizes,
the
magnetic
field
built
up
in
T1225
begins
to
collapse.
This
induces
an
opposite
current
into
the
base
windings
which
reverse
biases
Q1216,
but
forward
biases
1218.
When
the
induced
voltage
at
the
base
of
Q1218
exceeds
the
bias
set
by
the
High-Voltage
Regulator,
Q1218
conducts
and
the
amplified
current
at
its
collector
adds
to
the
current
flowing
through
T1225
due
to
the
collapsing
field.
Then,
as
the
current
through
T1225
stabilizes
again,
the
magnetic
field
around
it
once
more
begins
to
collapse.
This reverses
the
conditions
to
start
another
cycle.
The
signal
produced
across
the
primary
of
T1225
is
a
sine
wave
at
a
frequency
of
35
to
45
kilohertz.
The
amplitude
of
the
oscillations
in
the
primary
of
T1225
is
controlled
by
the
High-Voltage
Regulator
to
set
the
total
accelerating
potential
for
the
CRT.
Filter
network
C1222-L1222
decouples
high
peak
operating
current
from
the
+15-Volt
Supply.
High-Voltage
Regulator
A
sample
of
the
secondary
voltage
from
11225
is
connected
to
the
High-Voltage
Regulator
stage
through
divider
R1245A-R1245B.
Q1201
and
Q1206
are
connected
as
an
error
amplifier
to
sense
any
change
in
the
voltage
level
at
the
base
of
Q1201.
The
ground
reference
for
the
emitter
of
Q1201
through
R1202,
establishes
the
reference
level
for
this
stage.
The
output
voltage
is
set
by
the
fixed
values
of
the
components
in
this
circuit.
Regulation
occurs
as
follows:
If
the
output
voltage
at
the
—1475
V
test
point
starts
to
go
positive
(less
negative),
a
sample
of
this
positive-going
change
is
connected
to
the
base
of
Q1201
through
R1245B.
Both
01201
and
Q1206
3-25
7613

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Tektronix 7613 Specifications

General IconGeneral
BrandTektronix
Model7613
CategoryTest Equipment
LanguageEnglish

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