Section
3
Circuit Description
Introduction
The
Tektronix
Type
561A Oscilloscope contains
a
lo
v-
voltage
power
supply
circuit,
a cathode-ray-tube
circuit,
and
a
calibrator.
The
low-voltage
power
supply
circuit
provides
the
regu
lated
and
unregulated
power
used
by
the
instrument
and
the
plug-in units.
The
crt circuit contains
the necessary controls
and
input
facilities
to
present
a
sharp
trace
of
desired
intensity
for dis
playing
a
signal. Two
negative
high-voltage
power
supplies
provide
the
voltages
for
the crt
cathode,
focus
element,
and
control
grid.
Amplitude-calibrated
square
waves
are
produced
by the
calibrator.
LOW-VOLTAGE
POWER
SUPPLY
Power
for
the
Type
561A
Oscilloscope
and
its
plugin
units is supplied
through
the
power
transformer
T601.
The
two
primary windings
of
T601
are
connected
in
paral'el
for
117-volt operation,
or
in
series for 234-volt
operation,
as
shown
on
the
schematic
diagram.
The
low-voltage
power
supply
provides
regulated
outputs
of
—100,
—12.2,
+125,
and
+300
volts,
and
an
unregu
lated
output
of
+420
volts.
Each
circuit
is
a
series-regulator
type,
employing
silicon
diodes
for
rectifiers.
A
series
regu
lator
circuit
uses
a
vacuum
tube
(or transistor,
in
the
cose
of
the
—
12.2-volt
supply)
in
series
with
the
load.
This
tube
controls
the
current
through
the load
to
maintain
a
constant
voltage
drop
across
the
load.
For
example,
if
the
load
increases
(resistance
of
load
decreases)
the
series
tube
allows
more
current
to
flow;
if
the load decreases
it
allo
vs
less
current
to
flow.
—
100-Volt
Supply
Reference
voltage
for
the
—
100-volt supply is
establish
rd
by
the
gas
diode,
V609.
The
constant
voltage
drop
across
V609
establishes
a
fixed
potential
of
about
—85
volts
at the
grid
of
V634B.
Voltage
at
the
grid
of
V634A
is
established
by
the
divider
R616,
R617,
and
R618.
The
difference
in
vclt-
age
between the
two
grids
of
V634
determines
the
plate
current
of
V634A.
Plate
current
of
V634A
determines
the
base
voltage
of
transistor
Q624 which
in
turn
determines
the
grid
voltage
of
the
series tube,
V627. The
series
tube
controls
the
current
through
the
load
to
hold
the
load
vc
It-
age
constant.
R616,
—
100
V
adjustment,
determines
the
percentage
of
the
total
divider
voltage
applied
to
the
gdd
of
V634A
and
thus
controls
the
output
voltage. When
this
control
is
properly
adjusted,
the
output is
exactly
—
100
volts.
Should
the
output
voltage
tend
to
change
because
ol
a
change
in
input
voltage
or
a
change
in
load
current,
the
potential
at
the
grid
of
V634A
will
change
a
proportional
amount.
Any
change
at
the
grid
of
V634A
is
amplified
by
V634A
and
Q624
and
applied
to
the
grid
of
V627.
The re
sulting
grid
change
at
V627
will
cause
the load
current
to
change
in
the
direction
needed
to
bring
the
output
back
to
—
100
volts.
C616
improves
the
response
of
the regulator
to
sudden
changes
in
output
voltage.
+1
25-Volf
Supply
The
—
100-volt
supply
serves
as
a reference
for
the
+125-
volt
supply.
With the
lower
end
of
R651
fixed
at
—
100
volts,
any
change
in
the
+1
25-volt
output
produces
a
pro
portional
change at
the
grid
of
V654.
This change
is
ampli
fied
and
supplied
to
the
grid
of
the
series
regulator
tube,
\667
A.
The
change
at
the
grid
of
V667A
changes
the
load
current
in
the
manner
needed
to
bring
the output voltage
back
to
a
n125 volts.
C650
improves
the
response
of
the
regulator
to
sudden
changes
in
output
voltage.
A
small
sample
of
the
unregulated-bus
ripple
appears
at
the screen
of
V654
through
R657.
The
ripple
at
the
screen
(which
acts
as
an
injector
grid)
produces
a
ripple
at
the
grid
of
V667A which is opposite in
polarity
to
the
ripple
at
the
plate
of
V667A. This
tends
to
cancel
ripple
at
the
output.
This
same
circuit
also
improves
the
regulation
of
the
circuit
in
the
presence
of
line
voltage
variation.
4-300-Volt
Supply
The
+300-volt
supply
functions
in
the
same
manner as
the +125-volt
supply.
To
supply
the
voltage
for
the
+300-
volt
regulator,
rectified
voltage
from
transformer
terminals
21
and 22
is
added
to
the
voltage supplying
the
+1
25-
volt
regulator.
The
+300-volt
supply
provides
an
unregulated output
of
+420
volts
for
the
crt
circuit.
— 12.2-Volt
Supply
Operation
of
the
—
12.2-volt
regulating
circuit
is
essential
ly
the
same
as
that
of
the
other
regulating
circuits,
except
that
transistors
are
used
instead
of
vacuum
tubes.
The
base
of
Q734
is
fixed
near
—12 volts
by
the
voltage divider
R731-R732
between
—
100
volts
and
ground.
Any
variation
of
the
—
12.2-volt
output
at
the
emitter
of
Q734
is
amplified
by
Q734 and
Q744
to
change
the
emitter-collector
current
of Q757
which
is
in
series
with
the
supply
load. F720
protects
the
transistors
in
case
of
an
overload
on
the
—
12.2-volt
supply.
The
collector
of
Q757
is
connected
to
pin
5
of
the Inter
connecting
Socket.
This
provides
a
return
for this
supply
separate
from
the
chassis
and
prevents
large
chassis
currents.
CRT
CIRCUIT
The
crt
circuit
contains
the
cathode-ray tube
and
two
high-voltage
supplies
(one
for
the
crt
cathode
and
focus
element,
the
other
for
the
control
grid).
The
circuit
also
contains
the
necessary
controls
and
signal
input
facilities.
3-1
Содержание 561A
Страница 44: ...0 Wh T801 TERMINALS CONNECTIONS...
Страница 47: ...RIGHT HAND 07 2 7 62 TYPE 561A OSCILLOSCOPE PLUG IN CONNECTORS...
Страница 49: ...MOD 6860 Type 561A Tent S N 7860 Type RM561A Tent S N 5280 Change to Chassis Mtg Connectors BNC 131 279...
Страница 52: ...RT 5O RT5I IOOV IOOV IOOV PLM I I 2 PART PWR SPLV DIAQ...
