Tektronix 543B, Instruction Manual

Page: 12 / 90

SECTION 3
CIRCUIT DESCRIPTION
Introduction
This section contains the theory of operation of the
various circuits in the Type 543B. A simplified block diagram
analysis is given first to explain the operation of each cir­
cuit in general terms, then the operation of each circuit
is covered in detail.
BLOCK DIAGRAM DESCRIPTION
Low-Voltage Power Supply
The low-voltage power supply produces all operating
voltages for the oscilloscope with the exception of parts
of the c rt circuit. The low-voltage supply provides regulated
— 150, +100, +225, +350 and +500 volts. It also pro­
vides heater voltages and an unreg325-volt out­
put.
Vertical Plug-In Preamplifier
Any Tektronix letter- or 1-series vertical plug-in preampli­
fier can be used with the Type 543B. For a circuit descrip­
tion of the plug-in unit, refer to the plug-in unit instruction
manual.
Vertical Input Amplifier
The vertical input amplifier is a balanced hybrid ampli­
fier that amplifies the output of the plug-in vertical preampli­
fier and applies the amplified vertical signal to the trigger­
pickoff circuit and the vertical output amplifier.
Delay Line
The push-pull output of the vertical input amplifier is
applied through the balanced delay line to the vertical out­
put amplifier. The delay line is a specially braided 186 Ω
line which delays the application of the vertical signal to
the vertical output amplifier for 200 nsec. This provides
time for unblanking the crt and starring the horizontal sweep
before the vertical signal reaches the deflection plates. The
delay aliows the leading edge of a single fast-rising pulse
to be displayed. The delay line requires no adjustment
because of the precision construction.
Vertical Output Amplifier
The vertical output amplifier is a push-pull cascode ampli­
fier that takes the output of the delay line and amplifies
it to a level sufficient to drive the vertical deflection plates
of the crt.
Trigger-Pickoff Circuit
The trigger-pickoff circuit applies a sample of the input
waveform to the trigger circuit of the time base. The trigger
is picked off at the output of the vertical input amplifier.
Time-Base Generator
The time-base generator provides accurate ramp voltages
for the horizontal deflection system, unblanking for the crt,
and a + gate to the front-panel connector. The time-base
generator may be triggered by signals derived from either
interna! or external sources.
Horizontal Amplifier
The input to the horizontal amplifier is selected from the
output of the time-base generator, or the external horizontal
input amplifier. The selected input is split in phase and
amplified to provide push-pull drive to the crt horizontal
deflection plates.
External Horizontal Amplifier
The external horizontal input amplifier provides the
necessary gain to drive the horizontal amplifier from external
signals. An input attenuator and a gain control provide
horizontal deflection factors from 0.1 to about 100 volts/cm.
Crt Power Supply
The crt power supply provides the high voltages for
operating the crt. The power supply is of the rf type, using
a 50-kc Hartley oscillator. Secondary windings on the
oscillator transformer supply voltages to the high-voltage
rectifiers.
Cathode-Ray Tube (Crt)
The cathode-ray tube used in the Type 5438 is a flat­
faced, internal graticule, 5-inch tube with 6 cm of usable
vertical scan area. The tube is designed for low-input
capacitance to the vertical deflection plates and minimum
x-axis center-to-edge defocusing.
Calibrator
The calibrator in the Type 543B is a multivibrator and
cathode follower that provides a square-wave output with
a maximum amplitude of 100 volts ai a nominal 1 kc. A
step attenuator permits switching the output amplitude from
the front panel.
DETAILED CIRCUIT DESCRIPTION
The following description is a detailed discussion of the
operation of each circuit in the Type 543B. While reading
through the description of a particular circuit, refer to the
proper schematic diagram in Section 6.
Low-Voltage Power Supply
The low-voltage power supply in the Type 543B (see
Power Supply schematic diagram) actually consists of five in-
3-1