Tektronix 7834 User Manual

Theory of Operation--7834
Output
Amplifier
The Output Amplifier stage, consists primarily of integrated
circuit 01745 ; provides final amplification for the vertical
signal to drive the crt vertical deflection plates . Pins 1, 6, 7,
and 12 allow the use of discrete components to
establish
operating characteristic . Resistors
R1741 and R1756 are
selected to accurately set
the gain
of
the differential chan-
nels . Resistors R 1753, R 1754, R 1767, R 1768, and R 1770
set the operating level of U1745 . The series RC networks in
parallel with R1741 and R1756 provide frequency compen-
sation for uniform gain at all frequencies within the band-
width of the instrument . The BEAMFINDER switch changes
the emitter current source for U1745 to provide the beam-
finder function . Normally, the emitter current for 01745 is
supplied from ground . However, when the BEAMFINDER
switch is actuated, the only emitter current source for
U1745 is through R1771 . This limits the dynamic range of
the stage by limiting its current, so the display is compress-
ed vertically within the graticule area . The signal at the
output pins 2 and 8 of U1745 is connected directly to the
vertical deflection plates of the crt . A distributed deflection
plate system is used in the crt for maximum frequency
response and sensitivity . The signal at the output of 01745
is connected to the deflection-plate structure in the crt and
then to termination network LR1780, R1782A, LR1784,
and R 1782B . As the signal passes through the deflection-
plate structure in the crt, its velocity is essentially the same
as the velocity of the electron beam passing between the
vertical deflection plates . This synchronism of the deflection
signal and the electron beam reduces the loss in high-
frequency sensitivity due to electron-transit time through
the deflection-plate structure .
Transistors 01786 and 01785
comprise
a
protection circuit
for U1745, in case the +15 volt supply is shorted to ground .
If this occurs 01786 turns on causing the base of 01785 to
drop below +-35 volts . Thus, the emitter voltage of 01785 is
kept at a safe level for 01745 .
HORIZONTAL
AMPLIFIER
The Horizontal Amplifier circuit amplifies the
push-pull
horizontal deflection
signal from
the
plug-in unit installed
in either horizontal compartment
and connects it to the
horizontal deflection plates of the crt .
Figure 3-44 shows a
detailed block diagram of the
Horizontal Amplifier circuit .
A schematic of this circuit is shown on
diagram
15,
in the
Diagrams section of this manual .
Readout
Positioning
When
readout is displayed,
the X-Axis Readout signal is
applied
to
the Horizontal Amplifier through J1913 . At the
same time, the X-Y Inhibit signal (HI) causes 01814 to
conduct, connecting the center tap of the R .O . Pos (hori-
zontal readout center) adjustment R1815 to ground .
Grounding the center tap allows R1815 to horizontally
position
the
readout display on
the crt .
3- 60
Input
Amplifier
The Input Amplifier stage is a paraphase amplifier
consist-
ing of 01824 and 01924 . Overall gain for the Horizontal
Amplifier is determined by H Gain adjustment R1832
.
Thermal compensation for the
horizontal amplifier is pro-
vided within this stage by thermistor
RT1833 . The emitter
current for this stage is
normally supplied from the +15
Volt Supply through R1932
and 01932 . However, when
the BEAMFINDER
switch is actuated, 01932 is reverse
biased, and emitter
current
to
01824 and 01924 is supplied
only through R1932 . Transistor 01938 is then forward
biased
which causes CR1843 and CR1943 to conduct . The
combination of 01932 turning off and 01938 turning on
reduces the dynamic range of the horizontal system to
keep
the display within the horizontal limits of the graticule,
regardless of
the setting of the positioning controls or
signal
amplitude .
Left and Right Driver Amplifiers
The
Left
and Right Driver Amplifiers each consist of an
operational
amplifier to drive their respective output
ampli-
fier stages . Transistors 01854 and 01858 comprise the
operational amplifier for the Left Driver Amplifier . Transis-
tors 01954 and 01958 comprise the operational amplifier
for the Right Driver Amplifier . The Plate AVE . (average)
adjustment R1935 sets the quiescent operating level of the
driver amplifiers and output amplifiers . To prevent the Left
Output Amplifier from being overdriven, signal limiting
occurs in the Left Driver Amplifier when the collector of
01854 is driven far enough in the negative direction
for
C R 1851 and CR 1852 to become forward biased
.
As CR 1851
and CR1852 conduct, the effective gain of the stage
is
greatly reduced, and in turn the drive to the
Left Driver
Amplifier . Similarly, to prevent the Right
Output Amplifier
from
being overdriven, signal limiting occurs in the Right
Driver stage when the collector of 01954 is driven far
enough in the positive direction for CR1951 and CR1952
to become
forward biased . As CR 1951 and CR 1952 conduct
the gain of the stage is greatly reduced, and in turn, the
drive to the Right Output Amplifier .
Left Output Amplifier
The Left Output Amplifier consists of
a mid-frequency
operational amplifier paralleled by a
high-frequency signal
path . The network of R1861, R1862, C1862, and
C1863
comprise Zi (input impedance), while R1865 and C1865
comprise Zf (feedback impedance) for the mid-frequency
operational amplifier . High-Frequency components of the
horizontal signal are amplified by 01874 and coupled
directly to the common-base output transistor 01884 by
C1878 . The 1 nanosecond linearity, and 1
nanosecond
compensation adjustments determine the gain of
the high-
frequency signal path .
Right Output Amplifier
Basic operation of the Right Output Amplifier
is the same
as just described for the Left Amplifier
.

Tektronix 7834 Specifications

General

Brand	Tektronix
Model	7834
Category	Test Equipment
Language	English