Tektronix 7A12 User manual

1 N
ST
FR
U GTI O N
MAN
VAL . Serial

Number
J~
l
)
V
~ 1 '~Cr
7A 12
DUAL TRACE
AMPLIFIER
Tektronix, Inc . 0
P .
O .
Box 500 " Beaverton,
Oregon97005 " Phone [phone]
"
Cables : Tektronix
070-0977-01

971

WARRANTY
All Tektronix
instruments are warranted
against
defective materials
and workmanship
for one year .
Any questions
with respect to the
warranty,
mentioned above,
should he taken up
with your
Tektronix
Field Engineer or
representative .
All
requests for repairs
and replacement parts
should
he directed to
the Tektronix Field
Office or
representative in your
area . This procedure
will assure
you the fastest
possible service . Please
include the
instrument Type
(or Part Number) and
Serial or
Model Number
with all requests for parts
or service .
Specifications and price change privileges
reserved .
Copyright © 1971 by Tektronix,
Inc
.,
Beaverton,
Oregon . Printed in the United States of
America . All
rights
reserved . Contents of this
publication may not
be reproduced in any form
without permission of the
copyright owner .
U .S .A . and
foreign Tektronix products covered
by U .S .
and foreign patents and/or patents pending .

TABLE OF
CONTENTS
7A12
SECTION 1 SPECIFICATION Page
SECTION
5 CALIBRATION
Page
Introduction 1-1
Introduction
5-1
Electrical Characteristics 1-1
Test Equipment Required
5-1
Environmental Characteristics 1-3
Performance Check
5-3
Physical Characteristics
1-3 Adjustment
5-7
SECTION2 OPERATING INSTRUCTIONS
General 2-1
SECTION 6 ELECTRICAL PARTS LIST
Front Panel Controls and Connectors 2-1
Abbreviations and Symbols
General Operating Information 2-3
Parts Ordering Information
Basic Applications 2-5
Index of Electrical Parts List
SECTION 3 CIRCUIT DESCRIPTION
Introduction 3-1
SECTION 7 DIAGRAMS AND CIRCUIT BOARD
Block Diagram 3-1
ILLUSTRATIONS
Detailed Circuit
Description
3-1
SECTION 4 MAINTENANCE SECTION 8
MECHANICAL PARTS
LIST
Introduction
41
Mechanical Parts List
Information
Preventive Maintenance
41
Index of Mechanical Parts
Illustrations
Troubleshooting 41
Mechanical Parts
List
Corrective Maintenance 44
Accessories

Fig . 1-1 . 7A12
Dual Trace
Amplifier .

Introduction
The 7A12 vertical
amplifier plug-in is
designed for use
with Tektronix
7000-Series Oscilloscopes
. The 7A12 is a
dual-channel,
wide band amplifier
with the upper frequency
limit mainly
determined by
the oscilloscope mainframe
in
which it is
used . For example,
the 7A12 used with
the 7504
oscilloscope
will have an upper
bandwidth limit of
about 75
MHz
. When used with a
7704 oscilloscope, the upper band-
width limit is about 105
MHz . . Internal gain and
compen-
sation circuits are auotmatically
switched to correspond
to
the
setting of the
VOLTS/DIV switch . A
+UP/INV switch
for each channel
allows either channel to
be inverted for
differential
measurements . The 7A12
features a DC offset
circuit with a
DC offset of at least
±500 divisions for
SECTION 1
SPECIFICATION
TABLE 1-1
ELECTRICAL
7A12
viewing low level AC signals in the presence of a
high-level
DC component .
This instrument will meet the electrical
characteristics
listed in Table 1-1 following
complete calibration as given
in Section 5 . The performance
check procedure given in
Section 5 provides a convenient method of checking instru-
ment performance withoutmaking internal adjustments .
The following
electrical characteristics are valid over the
stated
environmental range for instruments calibrated at an
ambient temperature of +20 ° C to +30 ° C, after a five
minute warmup unless otherwise stated .
Characteristic
Performance Requirement Supplemental
Information
Deflection Factor
Calibrated Range 5 mV/div to 5 V/div, 10 pushbuttons
in
a
I, 2, 5 sequence
Deflection Factor
Within
2%
with GAIN adjustment at 10
Accuracy
mV/div
Uncalibrated
Continuously variable ; VAR V/DIV
extends
deflection factor
to at
least 12 .5
V/div
+UP to . INVERT Gain
Ratio
1 :1 within 1%
Frequency Response See Table A
AC (Capacitive)
10 Hz or less without probe, 1 Hz or less
Coupled Input
Lower with P6053
Bandwidth
Frequency
Time Delay Between
Channels
500 ps or less
Channel Isolation At least 3000 :1 or 0 .3 div with 5
div
reference signal at 75
MHz . At least
100 :1 with equal deflection factors at
50
MHz or less

Specification-7A12
TABLE 1-1 (cont)
Characteristic
Performance
Requirement Supplemental
Information
Maximum Input
Voltage
DC Direct
Couple
5 mV/div &
350 V, DC or DC + Peak AC at 1 kHz or
10
mV/div less
20 mV/div to
500 V, DC or DC
+
Peak AC at 1 kHz or
5 V/div
less
AC (Capacitive)
Coupled Input
5 mV/div &
350 V, DC or DC
+ Peak AC
at
1 kHz or
10 mV/div
less
20 mV/div to
5 V/div
500 V, DC or DC + Peak AC
Input R and C
Resistance 1 Megohm ±2%
Capacitance Approximately 24 .0 pF
R and C
Product Within ±1% between all deflection factors
Recommended X10 Probe P6053, 6ft
Maximum Input Gate
0 .4 nA at 0 to +35 ° C2 nA at +35 ° C to
Current
+50 ° C
IDENTIFY
Trace deflects up 0 .2 div to 0 .4 div
Display Noise
250
pV
at
5 mV/div . 0 .1 div or less at
(Tangentially Measured)
other deflection factors
Chopped Mode
(when
installed
in vertical
compartment
. Mainframe
dependent .)
Repetition Rate
500kHz within 20%
Channel Time Segment
0 .8 ps to 1 .2 ps
DC Drift
Drift With
Ambient
100 pV/ ° C or 0 .01 div/ ° C
whichever is
Temperature
(Line
greater
Voltage
Constant)
DC OFFSET Range
At least +1000 div to -1000
- div at 5 mV/div
At
least +500 div to -500
div from
10 mV/div to 5 V/div
Common Mode Rejection
Ratio
At least 10 :1 at 40 MHz or less

scope .
TABLE
A
7A12 AND MAINFRAME
FREQUENCY RESPONSE (five division reference)
With 7900
Series

With 7700 Series

With 7500 Series

With 7400
Series
120
MHz

105 MHz

I

75 MHz

I

55 MHz
TABLE
1-2

TABLE 1-3
ENVIRONMENTAL

PHYSICAL
Specification-7A12
Refer

to

the

Specification

for the

associated

oscillo-

Size

Fits all 7000-Series Plug-in
Compartments
Weight

I

2 .8 Ibs (1 .3 kg)

General
SECTION
2
OPERATING
INSTRUCTIONS
To effectively use the
7A12, the operation and
capa-
bilities of the instrument
must be know . This
section de-
scribes front-panel
control functions, general
information
on signal input
connections, and other subjects that
pertain
to various measurement
applications .
Installation
The 7A12 is calibrated
and ready for use as received .
It
can be installed in
any compartment of
Tektronix 7000-
Series Oscilloscopes,
but is intended
for principal use in
vertical plug-in
compartments . To install,
align the upper
and lower
rails of the 7A12 with the
oscilloscope tracks and
insert it .
The front panel will be
flush with the front of the
oscilloscope when the 7A12 is fully
inserted, and the latch
at the
bottom-left corner of the
7A12 will be in place
against the
front panel .
To remove
the 7A12, pull on the latch (which is
in-
scribed with the
unit indentification "7A12") and the
7A12 will unlatch .
Continue pulling on the latch to slide
the 7A12 out of the
oscilloscope .
FRONT PANEL CONTROLS
AND CONNECTORS
The following descriptions apply to the controls and
connectors of
both Input Amplifier channels when appli-
cable . See
Fig . 2-1 .
Input
Connector

Provides signal connection to
the
channel
.
AC-GND-DC-

Four position pushbutton switch
DC &
OFFSET

selects signal input coupling
mode .
AC-The
AC component of the
signal is coupled to the amplifier
input while the DC component
is blocked .
DC-Both AC and
DC components
of the signal
are coupled to the
amplifier input .
POSITION
IDENTIFY
VOLTS/D I V
Pushbuttons
VAR V/DIV
+UP/INV
Pushbuttons
7A12
GND-Grounds the
amplifier input
while maintaining the same load
for the input signal . Provides a
charge path for the AC coupling
capacitor to precharge the
input
circuit before
switching the
input to AC .
DC
&
OFFSET-Direct couples the
signal to the amplifier and pro-
vides DC offset of at least ± 500
divisions (± 1000 divisions at 5
mV/Div) .
Controls
vertical position of the
trace
.
Deflects trace up about 0 .3 div for
trace identification . Also replaces
readout with the word
"IDENTIFY" when used with
oscilloscopes equipped with a read-
out system .
Volts per major
graticule division .
Selects calibrated deflection factors
from 5 mV/Div to 5 V/Div ; 10
steps in a 1-2-5 sequence .
Provides continuously
variable un-
calibrated deflection factor
settings
between calibrated steps . Extends
deflection factor range to at least
12 .5 volts/division .
Provides
means of inverting the
display .
+UP-A positive-going signal at the
input deflects the CRT display
upward
.
INV-A positive-going
signal at the
input deflects the
CRT
display
downward .

Operating Instructions-7A12
2
.
2
nld rwmDe
x0n cx
Fig . 2-1 .Front-Panel Controls
=uConnectors .

OFFSET
TRIGGER
SOURCE
Pushbuttons
Variable
control permits on-screen
display
of small signal variations
superimposed
upon relatively large
DC
levels .
DISPLAY MODE

Pushbutton

selection

of

the
Pushbuttons

following modes of operation :
CH 1-A single trace display of the
signal applied to Channel
1 input
connector .
ALT-A dual trace
display of the
signals
applied to both channels .
The channels are alternately dis-
played and switching occurs at
the
end of each sweep .
ADD-Algebraically adds the signals
applied to the CH 1 and CH 2 input
connectors and the algebraic sum is
displayed
on the CRT .
CHOP-A dual trace display
of the
signal applied to both
channels . The
two channels time-share the
sweep
at a rate determined by the
main-
frame . An output signal is provided
for trace blanking during the
channel switching interval .
Selects source of trigger signal . The
trigger signals
provide internal trig-
gering
for the oscilloscope time-
base .
CH 1-Internal
triggering signal ob-
tained
from signal applied to
Channel 1
Input connector .
Mode-(Center
pushbutton) in-
ternal trigger
automatically follows
DISPLAY MODE
selection . In
ADD or CHOP
display modes, the
trigger signal
is the algebraic sum of
CH 1 and CH
2 trigger .
CH 2-Internal trigger
signal ob-
tained from signal
applied to
Channel 2 Input connector .
Operating Instructions-7A12
GENERAL OPERATINGINFORMATION
Introduction
For single trace operation,
either of the two identical
amplifier channels can
be used independently by setting the
DISPLAY MODE and
TRIGGER SOURCE switches to CH
1 or CH 2 and
connecting the signal to be observed to the
appropriate
input . In the discussions to follow, single-trace
operation using CH 1 applies equally to CH 2 .
Signal Connections
In
general probes offer the most convenient means of
connecting a
signal to the input of the 7A12 . A X10 atten-
uator
probe offers a high input impedance and allows the
circuit under test to perform very close to operating con-
ditions . The Tektronix P6053 6 foot probe, with its
readout-coding ring, is designed specifically for use with the
Tektronix 7A series vertical amplifiers . The readout coding
ring on the probe connects to a circuit in the 7A12 which
automatically corrects the readout displayed on the CRT to
the actual deflection factor at the tip of the probe . The
Tektronix P6053 3 .5 foot probe is not recommended be-
cause it may compromise the aberration limits of this am-
plifier .
Vertical GainAdjustment
To check the gain of either
channel, set the VOLTS/D IV
switch to 10 mV and connect a 40
mV,
1
kHz signal from
the
oscilloscope calibrator to the Input connector of the
channel being checked .
The vertical deflection should be
exactly four
divisions . If not, adjust the front-panel GAIN
for
exactly
four divisions of deflection . Both channels
should be checked
and adjusted, if necessary, before
making measurements .
If the gain of the two
channels must be closely
matched (as in
differential measurements using the
ADD MODE), use
the adjustment procedure in
Section 5 .
Input Coupling
NOTE
The
Channel 1 and Channel 2 Input Coupling switches
allow a choice of
input coupling methods . The type of
display
desired and the applied signal will determine the
coupling to use .
The DC coupling position can be used
for
most appli-
cations . It must be used to display AC signals below about
30 hertz (10 hertz with a X10 probe) and squarewaves
with
low frequency components, as these signals will be atten-
uated in the AC position .
2- 3