Tektronix 543B Instruction Manual page 15

Circuit Description — Type 543B /R M 543B
High-Voltage Power Supply.
supply is an oscillator operating at approximately 50 kc with
the transformer providing three high-voltage outputs. The
use of a 50-kc input to the high-voltage transformer permits
the size of the transformer and filter components to be kept
small. A modified Hartely oscillator converts a'c from the
+325-volt unregulated supply to the 50-kc input required
by high-voltage transformer T801. C808 and the primary
of T801 form the oscillator resonant tank circuit. No pro­
visions are mada for precise tuning of the oscillator tank
since the exact frequency of oscillation is not important.
Voltage Regulation. Voltage regulation of the high-volt­
age outputs is accomplished by regulating the amplitude
of oscillations in the Hartley oscillator. The —1700-voh out­
put is referenced to the +350-volt regulated supply through
a voltage divider composed of R841, R842, R843, R845,
R847, R853, and variable resistors R840 and R846. Through
a tap on the voltage divider, the regulator circuit samples
the —1700-volt output of the supply, amplifies any errors
and uses the amplified error voltage to adjust the screen
voltage of Harley oscillator V800. If the —1700-volt output
changes, the change is detected at the grid of V814B. The
detected error is amplified by V814B and V814A. The error
signal at the plate of V814A is direct coupled to the screen
of V800 by making the plate-load resistor of V814A serve
as the screen-dropping resistor for V800. Any change in the
— 1700-volt output thus changes the screen voltcge of V800
and the amplitude of the 50-kc oscillations. R840 provides
a means of controlling the high-voltage output through con­
trolling oscillation amplitude.
Crt Grid Supply. The approximately 1700-volt output of
the high-voltage power supply is the rectified output of one
of the two high-voltage secondaries on T801. To provide
dc-coupled unblanking signals to the crt grid, the crt grid
supply is floating (the dc voltage on the components shift
in accordance with the unblanking signals). The positive
side of the crt grid supply is returned to the —150-volt sup­
ply through the unblanking cathode-follower load resistor
of the sweep generator. The negative side of the crt grid
supply is applied through the INTENSITY control to the
crt grid.
At the fastest sweep rates, the stray capacitance of the
floating crt grid circuit makes it difficult for the crt grid to
rise fast enough to unblank the crt in the required time.
An isolation network consisting of R827, C829, and C830
isolates the capacitive loading. By this arrangement, the fast
leading edge of the unblanking pulse is coupled through
C830 and C829 to the grid of the crt. For short-duration
unblanking pulses, such as those that occur at the fastest
sweep rates, the dc levels on the rectifier and secondary
winding arc not appreciably affected.
pulses, such as those that occur at the slower sweep rates,
charge the stray capacitance in the 1700-volt output through
R827. This pulls up the floating crt grid circuit and holds
the crt grid at the unblanking potential for the duration of
the unblanking pulse.
+ 8300- and — 1700-Volt Outputs. Both the +8300- and
the --1700-volt outputs arc derived from the same secondary
winding on T801. The full secondary voltage of approxi­
mately 2900 volts is applied to a voltage tripler consisting
of rectifiers V832, V842, and V852 and associated capaci­
tors. A tap on the secondary provides the input for half­
3-4
The high-voltage power
Larger unblanking
wave rectifier V862 in the —1700-volt output. The — 1700-
volt supply is referenced to the regulated +350-volf supply
through a voltage divider network. The +8300-volt output
is connected to the crt post-deflection-accelerator anode
via R836 and the -1700-volt output is connected to the
crt cathode, via R857 to provide a total accelerating voltage
of 10,000 volts.
Crt Circuit Controls and Connectors. Optimum size and
shape of the fluorescent spot on the crt is obtained by ad­
justing the front-panel FOCUS and ASTIGMATISM controls.
FOCUS control R846 provides the correct voltage for the
second anode (focus ring) in the crt. Proper voltage for the
third anode is obtained by adjusting ASTIGMATISM control
R864. To obtain optimum spot size and shape, both the
FOCUS and ASTIGMATISM controls are adjusted to provide
the proper electronic lens configuration in the region of
the second and third anodes of the crt. Spot intensity is
adjusted by means of front-panel INTENSITY control R826.
Varying the INTENSITY control changes the voltage on the
crt grid, which in turn varies the beam current.
GEOMETRY control R861 adjusts the isolation shield voltage
in the crt, and is adjusted to minimize " bowing" or " tilting"
of the display. Front-panel TRACE ROTATION control R778
permits minor adjustments in trace orientation. By adjusting
the TRACE ROTATION control, the trace can be made
parallel with the horizontal lines on the graticule.
An input binding post on the rear panel of the Type 543B
provides an input for externally modulating the crt cathode.
The input binding post is normally grounded by a link. If
it is desired to intensify modulate the display from an exter­
nal source, the link is opened, and the modulating signal is
coupled to the crt cathode through C858.
When the Type 543B is used with a multichannel vertical
plug-in preamplifier that
blanking pulses, the blanking pulses are applied to rear-
panel CRT CATHODE SELECTOR switch SW858. With the
vertical plug-in preamplifier operating in the chopped mode
and SW858 set to the CHOPPED BLANKING position a
positive pulse of approximately 20-vo!fs amplitude is applied
through C858 to the cathode of the crt. At normal intensity
levels, this pulse is sufficient to cut off the crt during the
time the amplifier channels in the vertical plug-in preampli­
fiers are being switched.
Vertical Amplifier System
The vertical amplifier system in the Type 543B consists of
an appropriate vertical plug-in preamplifier, a push-pull
cathode-follower input stage, a push-pull hybrid delay-line
driver, a 186H delay line, and a push-pull hybrid output
amplifier. In addition, the trigger-pickoff circuit functions as
a part of the vertical amplifier by providing reverse termina­
tion for the delay line.
Vertical Input Amplifier.
vertical plug-in preamplifier, with a fixed dc level of ap­
proximately +67.5 volts, is applied to the input of the
vertical amplifier through terminals 1 and 3 of the plug-in
connector.
R491 and R498, in series with the grids of the push-pull
cathode-follower stage, as well as T500 are parasitic sup­
pressors. Input cathode followers V494A and V494B are the
two halves of a 6DJ8 twin triode. The cathodes of the
Internal
provides dual-trace chopped
The push-pull output of the
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