Tektronix 1A2 User manual

INSTRUCTION
MAN OUAL
Tektronix, Inc.
S.W. Millikan Way @ P. O. Box 500 @ Beaverton, Oregon 97005 @ Phone [phone] @ Cables: Tektronix
070-0430-01
tyPE
[A2
PLUG-IN
466

http://manoman.sghill.com
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TYPE
1A2
DUAL-TRACE
PLUG-IN
UNIT
CALIBRATED “~~
7 PREAMP
.
POSITION
POSITION
CH1421N
ADD
ONLY
VAR
VAR
ATTEN
BAL
ATTEN
BAL
} . TRIGGER
SELECTOR
QD)
|
“move
\@)
cn
A©°
cue
ALT
cHoP
“a
VARIABLE
VARIABLE
VOLTS/CM
CH!
votts/
cM
)
5
2
5
:
8
TRIG
OUT
|
(05 /Puito
/ INVERT
puto
20
invert
BRATEO
a
SERIAL
©
CHANNEL
1
CHANNEL
2
AC pc
GND
AC
pc
GND
INPUT 2
PORTLAND,
OREGON,
U.S.A.
y,
TEKTRONIX,
Fig. 1-1. Type 1A2 Dual Trace Plug-In Unit.

SECTION I
CHARACTERISTICS
Introduction
The Type 1A2 Dual-Trace Plug-In Unit contains two identi-
cal fast-rise calibrated preamplifier channels. Either chan-
nel can be used independently, or electronically switched to
produce dual-trace displays. In addition, both channels can
be combined at the output, adding or subtracting according
to the settings of the polarity switches.
Each channel has its own input coupling, attenuator, gain,
polarity and position controls which allows each display to
be adjusted independently for optimum viewing.
There are two modes of dual-trace operation: Chopped
or Alternate. In the chopped mode, an internal multivibra-
tor switches the channels at a free-running rate of about
220 kHz. In the alternate mode, the oscilloscope time-base
generator internally switches the channels at the end of each
sweep during the retrace interval.
The Type 1A2 can be used with any of the Tektronix 530-,
540-,
or 550-series Oscilloscopes. It can also be used with
the 580-series Oscilloscopes in conjunction with the Type 81
or 81A Plug-In Adapter. The Type 1A2 can also be used with
other oscilloscopes and devices through the use of the Type
127, 132, or 133 Plug-In Power Supplies.
CALIBRATED PREAMPLIFIER
Characteristic Performance Requirement
Supplemental Information
Deflection Factor
.05 volts/cm to 20 volts/em in 9 calibrated
steps for each channel
Steps in 1-2-5 sequence
Deflection Accuracy Within =&3% of indicated deflection with
VARIABLE control fully clockwise
With gain correct at .05 V/cm
Variable Deflection Factor
Uncalibrated deflection factor at least 2.5
times the VOLTS/CM switch indication. This
permits continuous (uncalibrated) adjustment
from 0.05 volts/em to at least 50 volts/cm.
Frequency Response (not more
than 3dB down): Type 1A2
with Tektronix oscilloscope;
544, 546, or 547 DC to 50 MHz
581, 581A, 585, 585A DC to 50 MHz with Type 81A Plug-In Adapter
DC to 33 MHz with Type 81 Plug-in Adapt-
er
541, 541A, 543, 543A, 545, | DC to 33 MHz
545A, 545B, or 555
551 DC to 27 MHz
531, 531A, 533, 533A, 535, | DC to 15 MHz
or 535A
536 DC to 11 MHz
Risetime: Type 1A2 with Tek-
tronix oscilloscopes;
544, 546, or 547 7 ns
‘581, 581A, 585, 585A
7 ns with Type 81A Plug-In Adapter
11 ns with Type 81 Plug-in Adapter
541, 541A, 543, 543A, 545. | 11 ns
545A, 545B, or 555
551 13 ns
531, 531A, 533, 533A, 535, | 24 ns
or 535A
536 32 ns
Input RC Characteristics
Typically 1 MQ parallel with approximately
15 pF
Maximum Input Voltage
600 volts combined DC and peak AC; 600
volts peak-to-peak AC
Input Coupling Modes AC or DC, selected by front-panel switch
GND, disconnects
amplifier input
signal and grounds
@i 1-1

Characteristics—Type 1A2
Characteristic
Performance Requirement
Supplemental Information
AC Low-Frequency Response Typically 3 dB down at 2 Hz direct; 0.2 Hz
with 10 probe
Display Modes Channel 1 only
Channel 2 only
Dual-trace, alternate between channels. Dual-
trace, chopped between channels. Added
algebraically
Chopped Repetition Rate 220 kHz 20% rate to show successive 2 us
segments of each trace
Common Mode Rejection Ratio 20:1 for common-mode signals up to 10cm in
amplitude
With optimum GAIN adjustment for both
channels
Polarity Inversion
Signal on either Channel 1 or 2 can be
inverted
Output Trigger? Measured at TRIG OUT connector
Output Trigger Voltage
Approximately 0.5 V/cm or gain of 10 VOLTS/CM at .05
Bandwidth Low-Frequency 3 dB down is about 10 Hz when
output of the amplifier is working into 1 MQ;
High-Frequency 3dB down is amplitude
dependent and shown in the graph of Fig. 1-2
Output Coupling AC
1Applies only to instruments with a serial number of 716 or higher.
MECHANICAL CHARACTERISTICS ACCESSORIES
Characteristic Information . ; . . .
CG i Alumi i hassi Standard accessories supplied with this instrument will be
onstruction Uminumeal’oy Chassis found in the Mechanical Parts List. For optional accessories,
Finish Anodized front panel see the current Tektronix, Inc. catalog.
10
9 4
; x
7 \
6 \
5
\
4
= \
6 N
3
Qo
a
2 \
2 N
=
3
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2 |
6 9 =
o 8 AN
& 47
z AN
F
6
\
\
5
4 \
\
3 \
2
1 2 3 4 5 6 7
Frequency in MHz at 3 dB down
Fig. 1-2. Type 1A2 Trigger output amplitude and High-Frequency Response (3 dB down).

SECTION 2
OPERATING INSTRUCTIONS
FUNCTIONS OF FRONT-PANEL CONTROLS
The functions of all controls, adjustments and connectors
except the MODE and TRIGGER SELECTOR switches are
identical for both channels.
POSITION
PULL TO
INVERT
GAIN
VAR ATTEN
BAL
MODE
VOLTS/CM
VARIABLE
AC-DC-GND
TRIGGER
SELECTOR?
TRIG OUT*
Positions the trace vertically on the CRT.
Only the Channel 1 POSITION controls
position in the ADD mode.
A two-position switch that presents the
display in a normal or inverted polarity
with respect to the applied signal.
A screwdriver adjustment that calibrates
the basic deflection factor of the channel.
A screwdriver adjustment for setting the
amplifier DC levels so the trace does not
shift position under no-signal conditions
as the VARIABLE VOLTS/CM control is
turned.
A five-position switch that sets the mode
of operation as follows:
ALT—Dual-trace alternate mode of opera-
tion (triggered electronic switching between
channels during the beam retrace interval).
CH 1—Selects the use of Channel 1 only.
ADD—Permits adding the outputs of the
two channels algebraically.
CH 2—Selects the use of Channel 2 only.
CHOP—Dual-trace chopped mode of oper-
ation (free-running electronic switching of
channels at about a 220-kHz rate).
Nine-position switch to select the calibrated
vertical-deflection factors.
Provides overlapping variable uncalibrated
attenuation between the calibrated deflec-
tion factors and extends the attenuation
range to about 50V/CM.
Three-position switch to provide either AC-
or DC-coupled input into the amplifier. A
third
position (GND) connects the ampli-
fier input to ground without grounding the
input signal.
Determines whether the Channel 1 or Chan-
nel 2 signal is applied to the Trigger
Amplifier.
Output signal of the Trigger Amplifier.
Permits the use of Channel 1 or 2 as an
external trigger source.
FIRST TIME OPERATION
The following procedure will help you become familiar
with the Type 1A2 operation.
1. Insert the Type 1A2 into the oscilloscope, tighten the
securing rod and turn on the oscilloscope power.
2. Allow about 2 to 3 minutes warm-up time and free run
the oscilloscope sweep at 0.5 sec/cm.
3. Set the applicable Type 1A2 front-panel controls for
both channels as follows:
AC-DC-GND DC
VOLTS/CM .05
VARIABLE CALIBRATED
PULL TO INVERT Pushed in
POSITION Centered
MODE CH 1
TRIGGER SELECTOR? CH 1
4. Position the trace about one centimeter above the grati-
cule centerline with the Channel 1 POSITION control.
5. Place the MODE switch to CH 2 and position the trace
one centimeter below the graticule center line with the
Channel! 2 POSITION control.
6. Place the MODE switch to ALT. Both Channel 1 and
2 traces should be displayed.
7. Set the oscilloscope Time/Cm switch to 50 msec. Note
that for each sweep cycle one channel is displayed and the
other is shut off. Electronic switching from one channel to
the other occurs during the retrace interval.
8. Set the MODE switch to CHOP. Notice that both traces
seem to start simultaneously and continue across the CRT.
9. Set the oscilloscope Time/Cm switch to 5ysec and
adjust the oscilloscope trigger controls to obtain a stable
display. Notice that each trace is composed of many short-
duration bits or segments with visible switching transients
existing between channels (see Fig. 2-1A).
10. To see the chopped-mode switching action clearly,
increase the sweep rate to 1 wsec/cm. Notice that Channels
1 and 2 are alternately on and off at about 2 us intervals.
(See Fig. 2-1B.) Chopping rate is determined by the free-
running multivibrator switching rate and is about 220 kHz.
11. Blank out the switching transients between channels
by setting the CRT Cathode Selector switch (located on the
rear panel of most Tektronix oscilloscopes) to the Dual-Trace
Chopped Blanking position (see Fig. 2-1C).
12. Set the oscilloscope Time/Cm switch to 0.5 msec. Using
coaxial cables, a T connector connected to Channel 1 and
a connector adapter {if needed), apply 0.1 volt from the
oscilloscope Amplitude Calibrator to the Channel 1 and 2
input connectors.
13. Set the trigger controls for +internal (plug-in) trigger-
ing or connect a jumper coaxial cable from the TRIG OUT
connector! to the oscilloscope Trigger Input connector and
1Applies only to instruments with a serial number of 716 or higher.
2-1

Operating Instructions—Type 1A2
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Fig. 2-1. Chopped-mode waveforms: (A) trace broken up into
segments, (B) chopped-mode switching action from channel to
channel, and (C) switching transients blanked out.
set the trigger controls for + external triggering. Both Chan-
nel 1 and 2 should display the calibrator waveform. Each
waveform should be 2 cm in amplitude.
NOTE
If the waveforms are not exactly 2 cm in amplitude,
overlook the inaccuracy until completing this oper-
ating procedure. Subsequent paragraphs describe
how to properly set the gain of the unit.
14. Set the MODE switch to ADD. There should be one
waveform display 4¢cm in amplitude. This is the addition
of the Channel 1 and 2 signals (2cm each), Notice that
only the Channel 1 POSITION control will move the display
vertically.
15. Pull out the Channel 1 PULL TO INVERT switch and
free run the time base. The display should be a straight
2-2
line, indicating the algebraic difference between the two
signals. Since both signals have equal amplitudes and wave-
shape, the difference is zero.
NOTE
If the display is not a straight line, this indicates
that the gains of the channels are not matched.
This may be overlooked until this operating pro-
cedure is completed. Subsequent paragraphs
describe how to properly set the gain of each
channel.
Before the Type 1A2 is used for accurate measurements,
the GAIN and VAR ATTEN BAL for each channel should be
adjusted. These adjustments are described in the following
paragraphs.
Gain Adjustments
The gain adjustments should be checked periodically to
assure correct vertical deflection factors, particularly when
the Type 1A2 is used for the first time or is moved from one
oscilloscope to another. Use the following procedure to
check the gain of each channel:
1. Set the applicable Type 1A2 front-panel controls for
both channels as follows:
AC-DC-GND DC
VOLTS/CM .05
PULL TO INVERT Pushed in
POSITION Centered
VARIABLE CALIBRATED
MODE CH 1
TRIGGER SELECTOR CH 1
2. Set the oscilloscope sweep rate and triggering controls
for a 0.1 msec/cm free-running sweep.
3. Apply a 0.2-volt peak-to-peak signal from the oscillo-
scope calibrator through a coaxial cable to the Channel 1
Input connector.
NOTE
For maximum accuracy use a calibrator signal
source which has an amplitude accuracy of better
than 3%.
4. The resulting display should be exactly 4m in ampli-
tude. If not, set the Channel 1 GAIN for the correct wave-
form amplitude. (Use the Channel 1 POSITION control to
align the display with the graticule markings.}
5. Set the MODE switch to CH 2 and apply the calibrator
signal to the Channel 2 input connector.
6. The display should be exactly 4cm in amplitude. If
not, adjust the Channel 2 GAIN contro! for the proper display
amplitude. Use the Channel 2 POSITION control to align the
display with the graticule markings.
7. Disconnect the calibrator signal.

Operating Instructions—Type 1A2
502 coaxial cable
with GR connectors
P6034 or
P6035, Probe
Y
ye _-Y ge
X = GR Type 874
Connectors
Optional Items
‘Select length which will move small reflection (due to
input Z of Type 1A2) out of area of interest.
*Used to reduce reflection by a factor of 4. Doubles
probe attenuation factor.
Used to reduce bulk on front of the Type 1A2.
GR Type 874-K
Coupling Capacitor
017-0028-00
‘50.9
GR
2X
GR-to-BNC
I
type
1A2
Attenuator
Adapter
|
Input
017-0046-00
017-0064-00
Let
yet:
|
‘Short
50
{2
coaxial
50
{2
BNC
I
cable
with
GR
Termination
|
connectors
011-0049-00
I
017-0505-00
|
Fig. 2-2. Using the P6034 or P6035 Probe with the Type 1A2.,
Variable Attenuator Balance Adjustments
If the VAR ATTEN BAL control of a channel is not properly
set, the position of a no-signal free-running trace will shift
vertically as the VARIABLE control is turned. If there is
a trace shift, set the VAR ATTEN BAL adjustment for each
channel as follows:
1. Set the Type 1A2 front-panel controls to the same
positions as in the Gain Adjustments procedure except the
AC-DC-GND switch must be set to GND and the MODE
switch to ALT.
2. Carefully adjust the Channel 1 VAR ATTEN BAL control
to a point where there is no trace shift as the Channel 1
VARIABLE control is turned back and forth through its full
range.
3. Carefully adjust the Channel 2 VAR ATTEN BAL control
to a point where there is no trace shift as the Channel 2
VARIABLE control is turned back and forth through its full
range.
4. Due to interaction between channels, repeat steps 2
and 3 until there is no further interaction.
GENERAL OPERATION
Either of the two channels of the Type 1A2 can be used
independently by setting the MODE switch to CH 1 or CH 2
and connecting the signal to be observed to the appropriate
input. Table 2-1 lists several input systems compatible with
the Type 1A2 input. Fig. 2-2 shows a block diagram of the
input when using the system outlined in Method 7 of Table
2-1. Figure 2-3 shows the X, and R curves for the Type 1A2.
Use of Probes
A conventional passive attenuator probe with a standard
42-inch cable lessens both capacitive and resistive loading,
but at the same time reduces sensitivity. The attenuation
introduced by the probe permits measurement of signal volt-
ages that would overscan the CRT if applied directly to the
Type 1A2. However, in applying high-amplitude signal volt-
ages to either the probe or Type 1A2, do not exceed their
maximum voltage ratings. When making amplitude meas-
urements with an attenuator probe, be sure to multiply the
observed amplitude by the probe attenuation factor.
To assure the accuracy of pulse or high-frequency measure-
ments, check the probe compensation. To make the adjust-
ment, proceed as follows:
1. Set the oscilloscope Amplitude Calibrator for a calibra-
tor output signal of suitable amplitude (at least 2 cm).
2. Place the MODE switch to the appropriate channel set-
ing (CH 1 or CH 2) to be used with the probe.
3. Touch the probe tip to the calibrator output connector
and adjust the oscilloscope controls to display several cycles
of the waveform.
4, Adjust the probe compensation for best square-wave
response as shown in the right-hand picture of Fig. 2-4.
NOTE
If a square-wave source other than the oscilloscope
calibrator is used for compensating the probe, do
not use a repetition rate higher than 5 kHz. At
higher repetition rates, the waveform amplitude
appears to change as the probe is compensated.
Thus, proper compensation is difficult. If the probe
remains improperly compensated, measurements
will be inaccurate.
2-3

Operating Instructions—Type 1A2
1M T
=S
N
100 k x
~
AN
~
N
N
N X
\ \,
N Xe
Ohms 10k x x
aN »
aN
. \
\
1000
— eH
ww
N
N
N
100
:
1 MHz 10 MHz
Frequency in Megacycles Per Second
Fig. 2-3. Type 1A2 nominal input resistance and capacitive reactance vs frequency at any position of the VOLTS/CM switch.
AC-DC-GND Switch
To display both the DC and AC components of an applied
signal, set the AC-DC-GND switch to DC; to display only the
AC component of a signal, set the AC-DC-GND switch to AC.
In the AC position of the switch, the DC component of
the signal is blocked by a capacitor in the input circuit.
The input time constant of the input circuit is about 0.1
second and the low-frequency response of the unit is down 3
dB at about 2Hz. If a 10X attenuator probe is used with
the Type 1A2, the low-frequency response will be extended to
about 0.2 Hz with a 100X probe, low-frequency response ts
about 2 Hz.
Placing the AC-DC-GND switch to the GND position
grounds the input circuit of the Type 1A2 to provide a DC
2-4
zero reference. When the AC-DC-GND switch is set to GND,
the switch internally disconnects but does not ground the
applied signal at the input connector. The GND position of
the switch eliminates the need for externally grounding the
input of the unit or probe tip to establish the ground
reference.
VOLTS/CM Switch and VARIABLE Control
The amount of vertical deflection produced by a signal is
determined by the signal amplitude, the attenuation factor
{if any) of the probe, the setting of the VOLTS/CM switch
and the setting of the VARIABLE control. Calibrated deflec-
tion factors indicated by the settings of the VOLTS/CM switch
apply only when the VARIABLE control is set to the CALI-
BRATED position. Errors in display measurements may result

Operating Instructions—Type 1A2
— SS “S — —— lau Va _—
~/
Incorrect Incorrect
Correct
Fig. 2-4. Probe compensation waveforms using 1-kHz calibrator signals.
if the setting of this control is moved away from the CALI-
BRATED position.
The range of the VARIABLE control is at least 2.5 to 1
to provide continuously variable (uncalibrated) vertical deflec-
tion factors between all calibrated settings of the VOLTS/
CM switch. When the control is turned to its maximum-
counterclockwise position and the VOLTS/CM switch is set
to 20, the VARIABLE control extends the vertical deflection
factor to about 50 volts/cm. By applying the oscilloscope
calibrator voltage or any other calibrated voltage source to
the Type 1A2, any specific deflection factor can be set within
the range of the VARIABLE control.
PULL TO INVERT Switch
The PULL TO INVERT switch may be used to invert the
displayed waveform, particularly when using the dual-trace
feature of the Type 1A2. The PULL TO INVERT switch has
two positions. With the knob pushed in, the displayed wave-
form will have the same polarity as the applied signal; that
is, @ positive-going pulse applied to the Type 1A2 will be
displayed as a positive-going waveform on the CRT. If a
positive voltage is DC coupled to the Type 1A2, the beam will
move up.
With the switch pulled the displayed waveform will be
inverted; that is, a positive-going pulse applied to the Type
1A2 will be inverted or displayed as a negative-going wave-
form on the CRT. If a positive voltage is DC coupled to the
Type 1A2, the beam will move down.
MODE Switch
The MODE switch has five positions: ALT, CH 1, ADD,
CH 2, and CHOP. These positions and their purposes are
described in subsequent paragraphs. Useful triggering inform-
ation is included in the description of the ALT and CHOP
switch positions.
CH 1, CH 2—Single Channel Operation
To display a single signal (single-channel operation), apply
the signal either to the Channel 1 or Channel 2 Input con-
nector and set the MODE switch to the corresponding posi-
tion: CH 1 (Channel 1) or CH 2 (Channel 2).
To display a signal in one channel independently when
the same signal or a different signal is applied to the other
channel, simply select the signal in the channel to be dis-
played by setting the MODE switch to the appropriate CH 1
or CH 2 position.
ALT, CHOP—Dual Trace Operation
To display two signals together (dual-trace operation),
apply one signal to the INPUT 1 connector and apply the
other signal to the INPUT 2 connector.
In general, use the CHOP position (chopped-mode opera-
tion) with sweep rates of 50 usec/cm or slower for displaying
two non-repetitive signals occurring within the sweep-time
interval set by the oscilloscope Time/Cm switch. Non-repeti-
tive signals are those signals which are transient or random.
The CHOP position is also useful for displaying low-frequency
synchronous signals. Synchronous signals are those which
have the same repetition rate or are frequency-related by
whole number multiple.
NOTE
When using chopped-mode operation, be sure to
set the oscilloscope CRT Cathode Selector switch
to the Dual-Trace Chopped Blanking position to
blank out the undesirable chopped-mode switching
transients.
Use the ALT position (alternate-mode operation) when
using sweep rates at about 0.5ms/cm or faster to display
high-frequency synchronous and asynchronous signals. Asyn-
chronous signals are those which do not have the same repeti-
tion rate or are not frequency related to each other by a
whole number multiple. Table 2-2 summarizes the following
discussion for dual-trace operation.
Displaying Two Non-repetitive or Low-Frequency
(Below 2 kHz) Synchronous Signals. To show true time
and phase relationship between two non-repetitive or low-
frequency synchronous signals, use chopped-mode operation.
Transients as short as 0.5ms can be well delineated or
resolved. At 50 us/cm a 0.5 ms duration transient, for exam-
ple, will contain about 200 on segments in the trace. If a
higher sweep rate is used, the number of segments that make
up each of the traces will be less and therefore resolution will
be poorer.
2-5

Operating Instructions—Type 1A2
To make the low frequency or non-repetitive display stable,
use either internal triggering on Channel 1 or 2 {from pin
5 of interconnecting plug—see Block Diagram in Section 10)
or use the TRIG OUT connector as the external trigger source.
lf there is no Plug-In position on the oscilloscope Trigger
Source switch, use the signal available at the TRIG OUT con-
nector of the Type 1A2 by connecting a jumper coaxial
cable from the TRIG OUT connector to the oscilloscope
Trigger Input connector and setting the Triggering Source
switch to Ext.
Type 1A2's below SN716 do not have the Plug-In trigger-
ing capability.
NOTE
Use the oscilloscope Plug-In position of the Trig-
gering Source switch in preference to external
patching to obtain optimum bandwidth capabilities
from the Trigger Output Amplifier.
Do not set the oscilloscope Triggering Source switch to
Norm Int or Int (oscilloscope vertical amplifier trigger take-
off signal) because a stable display is difficult and sometimes
impossible to obtain. During dual-trace chopped-mode oper-
ation the Norm Int or Int trigger source is a composite signal
consisting of the signals applied to both channels super-
imposed on, but not synchronized with, the free-running rate
of the chopped-mode switching signal. The switching signal
has a square waveshape the same as the one shown in
Fig. 2-1B. Its amplitude is dependent on the distance that
the traces are positioned apart and the amount of DC com-
ponent contained in the applied signals; its rate is the chop-
ping rate (about 220 kHz).
Since the internal trigger from the oscilloscope vertical
amplifier is a composite trigger during chopped mode of
operation, and the trigger contains a nonsynchronized chop-
ped-mode switching signal, internal triggering may occur
first on one of the applied signals and then on the chopped-
mode switching signal, or vice versa, resulting in an unstable
display.
TABLE 2-1
Signal Coupling Methods
Source Loading
See Fig. 2-3
Accessories Input R and X,
Method Advantages Limitations Required Curves Precautions
1. Open test un- | Simplicity Limited frequency | BNC to Banana |1 Meg @ and 15 | Stray pickup and
shielded) leads response, subject | Jack adapter (103- | pF at input, plus | spurious — oscilla-
to stray pickup 0003-00}. Two test | test leads tions
leads.
2. Unterminated | Full Sensitivity Limited frequency | Coaxial cable with |} 1 Meg 2 and 15 | High capacitive
coaxial cable response. High ca- | BNC connector(s} pF plus cable ca- | loading
pacitance of cable.
pacitance
3. Terminated co- | Full sensitivity. Presents Ry (typi- | Coaxial cable with | R, plus 15 pF at | Reflection from 15
axial cable. Termi- | Full Type 1A2/Os- | cally 509) load- | BNC connectors R, | Type 1A2 end of | pF at input. DC
nation at Type 1A2 | cilloscope band- | ing at end of co- | termination at Type | coaxial can cause | and AC loading
input. width. Relatively | axial. 1A2 input. (BNC | reflections on test point.
flat resistive load- | May need blocking | 50Q Termination, Power limit of ter-
ing. Long cable j capacitor to pre- | 011-0049-00. mination.
with uniform re- | vent DC loading
sponse. or damage to ter-
mination.
4. Same as 3, with | Less reflection from | Sensitivity is re- | BNC Coaxial at- | R, only DC and AC loaa-
coaxial attenuator | 15 pF at termina- | duced {increased | tenuators ing on test point.
at termination tion Deflection Factor) Power limit of at-
tenuator.
5. Tap into termi- | Permits signal to | 15 pF load at tap | BNC Tee and BNC | 1 Meg © and 15 | Reflections from 15
nated coaxial sys- | go to normal load. | point
connectors on sig- | pF at tap point. pF input
tem. (BNC Tee: | DC or AC coupling nal cables
UG-274/U at Type | without coaxial at-
1A2 input). tenuators.
6. 10X, 10MQ | Reduce resistive | X0.1 sensitivity P6006, P6008 are | P6006?:~7 pF, 10 | Check probe fre-
Probe and capacitive | X0.01 sensitivity 10; P6007, P6009 | MQ quency compensa-
10, 10 MQ loading, nearly full | X0.001 sensitivity | are 100; P6015 is | P6007: Less than 2 | tion. Use square-
Probe Type 1A2/QOscillo- 1000 < pF, 10 MQ wave __ frequency
1000X, 100 MQ | scope bandwidth. P6008:-~7.5 pF, 10 | less than 5kHz,
Probe Mo preferably 1 kHz.
P6009:-2.5 pF, 10
MQ
P6015:
100 MQ.
~~
~ 27 pF,
2P6006 Probe has less
2-6
input capacitance than P6008, but P6008 has
wider bandwidth.
®1

TABLE 2-1 (cont)
Operating Instructions—Type 1A2
Source Loading
See Fig. 2-3
Accessories Input R and X,
Method Advantages Limitations Required Curves Precautions
7. 5009 and 5kQ | Reduced capacitive | Resistive loading. | P6034—I10X P6034: 5000, 0.7 | DC and AC load-
Probes. (Must be |loading to about | X0.1 or X0.01 | P6035—100x ing.
terminated in 50Q
at Type 1A2_ in-
put.)
0.7 pF. Bandwidth
that of Type 1A2/
Oscilloscope.
Probe compensa-
tion need not be
adjusted, since ef-
fect is not apparent
sensitivity. May
need blocking ca-
pacitor to prevent
DC loading or
damage to termi-
nation. Limited
low frequency re-
Items in Fig. 2-2
pF
P6035: 5kQ, 0.6
pF
Voltage rating of
probe.
when used with | sponse when AC
the Type 1A2/Os- | coupled: 70 kHz
cilloscope. for P6034: 7 kHz
for P6035.
8. Current trans- | Current xfmr can | RMS current rating: | CT-l: © Coaxial| CT:1 Insertion; 1Q | Not a quick-con-
former. Terminated | be permanent part | CT-1: 0.5 amps adapter and BNC] paralleled by | nect device.
in 50Q at Type | of test circuit. Less | CT-2: 2.5 amps termination. about 5 wH. Up to | CT-1: low fre-
1A2. than 2.2 pF to test | Sensitivity: CT-2: Nothing ex- | 1.5 pF. quency limit about
Upper Bandwidth | circuit chassis. CT-1: 5mV/mA. tra. (Perhaps addi- | CT-2: Insertion; 0.04 | 75 kHz.
that of Type 1A2/ | Measures signal | CT-2: 1 mV/mA. tional coaxial ca-| Q paralleled by | CT-2: low fre-
Oscilloscope. current in transis- ble for either trans- | about 5 wH. Up to | quency limit about
tor circuits: former.) 2.2 pF. 1.2kHz, and is
CT-1: 20 amps 1/5th as sensitive
peak. as the CT-1.
CT-2. 100 amps
peak.
TABLE 2-2
Dual-Trace Operation
Displays show true
Applied Signals (One Type 1A2 Oscilloscope Trigger time relationship
to Channel 1 and MODE Switch | Oscilloscope Triggering Coupling Switch between signals
other to Channel 2) Setting Source Switch Setting Setting Other remarks
(a) Two non-repetitive sig- | CHOP Plug-In? or Ext (connect | AC or AC Slow or AC Yes
nals or two low-frequency
synchronous signals (be-
low 2 kHz). Set the TRIG-
GER SELECTOR switch to
the Channel with the ref-
erence signal applied.
jumper coaxial cable
from TRIG OUT connec-
tor to Trigger Input con-
nector on the oscillo-
scope).
Fast or AC LF Reject
Use sweep rates up to 50
psec/cm. Higher sweep
rates reduce resolution.
(b) Two asynchronous Sig- | ALT Norm Int or !nt* AC or AC Slow for fre- No
nals, any frequency with- quencies below 1 kHz.
in full bandwidth of the AC Fast or AC LF Reject
system. for frequencies above 1
kHz.
(c) Two synchronous sig- | ALT Plug-In? or Ext (connect | AC or Yes
nals. 60 Hz and above. jumper coaxial cable | AC Slow or Set the TRIGGER SELEC-
from TRIG OUT connec- | AC Fast or TOR switch to the Chan-
tor to Trigger Input con- | AC LF Reject nel with the reference
nector on the oscillo- signal applied.
scope).
Norm Int or Int* AC Fast or AC LF Reject No
3Plug-In position is the Trigger Output Amplifier signal available at pin 5 of the Type 1A2 interconnecting plug to the oscilloscope. If your
oscilloscope is not wired to permit use of this trigger source, use the Ext position and the TRIG OUT signal.
4Norm Int or Int switch position is the internal trigger takeoff signal from the oscilloscope vertical amplifier.
In dual-trace operation this
trigger is a composite of the applied signal superimposed on the DC positioning levels of the channels as they are switched.
Displaying Two Asynchronous Signals. To obtain a
stable display of two asynchronous signals which do not
exceed the system bandwidth, use alternate-mode operation
and set the oscilloscope Trigger Source switch to Norm
Int or Int. Set the oscilloscope Trigger Coupling switch to AC
for stable triggering on signals below 1 kHz, set the Trigger
2-7

Operating Instructions—Type 1A2
Coupling switch to AC LF Reject or AC Fast for stable trig-
gering and a bright display of signals above 1 kHz. Since
the oscilloscope vertical amplifier internal trigger is the trig-
ger source, the applied signals will not be displayed in
their true time relationship because triggering occurs on the
applied signal in each channel as it switches on.
To obtain a stable display in this mode of operation, it is
very important to set the oscilloscope Triggering Level con-
trol to a point where the time base can trigger on the signal
in one channel as it turns on, and on the signal in the other
channel when it turns on. In addition, both applied signals
must be of sufficient amplitude to meet the internal trigger
signal amplitude requirements of the oscilloscope.
If one displayed signal has a smaller amplitude than the
other but is of adequate amplitude for internal triggering,
then set the Triggering Level control to a point that will
assure triggering on the smaller amplitude signal. To do this,
set the Triggering Level control near the zero position.
Though it may seem easy to obtain stable triggering on
asynchronous signals, there are certain conditions that may
promote jitter. When using the AC Fast or AC LF Reject
triggering mode, jitter most likely occurs when attempting to
trigger on high-frequency asynchronous signals that are
vertically positioned apart on the CRT with POSITION con-
trols. If jitter occurs, it can be reduced and sometimes elimi-
nated by positioning the displays close together or super-
imposing them. This not only reduces jitter but may also
increase the display brightness.
If you use the AC or AC Slow triggering mode, stable
internal triggering on asynchronous signals above 1 kHz is
more difficult to obtain and the jitter will be greater. If you
are using sweep rates faster than 0.5 ms/cm, the dual-trace
display becomes noticeably brighter as the waveforms are
vertically positioned together and dimmer when they are
positioned apart. These effects are normal and are caused
by the problem of triggering on the alternate-mode com-
posite trigger waveform. The waveform is very similar to
the one described for chopped-mode operation.
The alternate-mode composite trigger consists of the asyn-
chronous signals applied to the Type 1A2 superimposed on
the DC positioning and signal levels of the alternate-mode
switching waveform. The switching waveform portion of the
composite trigger is a low-frequency square wave whose
amplitude is governed by the setting of the POSITION con-
trols and DC components (if any) of the applied signals. By
itself, the switching waveform viewed on a test oscilloscope
resembles the waveshape shown in Fig. 2-1B when the traces
are positioned two centimeters apart. Repetition rate of the
switching waveform is one-half the sweep repetition rate.
When the alternate-mode composite trigger is internally
AC coupled to the oscilloscope trigger input circuit, the
trigger circuit may not respond instantly to the signals super-
imposed on the alternate-mode switching signal. The delay
is caused by the recovery time of the trigger input circuit
as each cycle of the low-frequency switching waveform
couples into the input stage of the trigger circuits. Since AC
coupling is used in all the Trigger Coupling switch positions
(AC, AC Slow, AC Fast, AC LF Reject) recovery time is
dependent on the RC time constant of the trigger input circuit.
In conclusion, trigger circuit recovery time is shorter, hence
the sweep repetition rate can be higher and the display
brighter, if AC Fast or AC LF Reject triggering mode is used.
In either of these triggering modes, a smaller value coupling
capacitor is used in the oscilloscope trigger input circuit as
compared to the value used in the AC or AC Slow triggering
mode. Trigger recovery time can be shortened and triggering
will be more stable if high-frequency waveform displays are
vertically positioned closer together or superimposed rather
than positioned further apart.
Displaying Two Synchronous Signals, 60Hz and
Above. To show true time and phase relationship between
two synchronous signals, 60Hz and above, use alternate
mode operation and trigger externally from one of the
signals. In practice, for displaying signals between 60 Hz and
2kHz you can choose either alternate- or chopped-mode
operation since this is an overlapping area. Set the Trigger
Coupling switch to the desired AC position (AC, AC Slow,
AC Fast or AC LF Reject). Apply the reference signal to the
external trigger input and set the oscilloscope Trigger Source
switch to the Ext position in high-frequency applications.
Set the TRIGGER SELECTOR switch to the channel with the
reference signal and set the oscilloscope Triggering Source
to the Plug-In position. If your oscilloscope does not have
the Plug-In switch position, apply the signal from the TRIG
OUT connector to the oscilloscope Trigger Input connector
and set the Triggering Source switch to Ext.
When externally triggering the oscilloscope, if one of the
signals changes frequency, one of the signals will remain
stationary while the other signal will appear to free run.
This phenomenon is useful for determining zero-beat points
between the two signals.
ADD—Algebraic Addition of Two Signals
In many applications, the desired signal is superimposed
on an undersired signal such as line frequency hum, etc.
Algebraic addition makes it possible in many cases to
improve the ratio of desired to undersired signal. To do
this, connect one input to a source containing both the
desired and undersired signal. Connect the other input to a
source containing only the undersired signal. Place the
MODE switch to the ADD position. Set the PULL TO INVERT
switches to opposite settings (depending upon the polarity of
the desired signal). By carefully adjusting (especially at low
frequencies) the VARIABLE control of one of the channels, the
undersired displayed signal can be reduced by a factor of at
least 20 compared to the amplitude of the desired signal.
In general the input coupling should be the same on both
channels.

SECTION 3
APPLICATIONS
Introduction
This section of the manual describes procedures and tech-
niques for making basic measurements with the Type 1A2 and
the associated Tektronix oscilloscope.
No attempt has been made to describe specific applica-
tions, since familarity with the unit enables the operator to
apply these techniques to a wide variety of applications.
AC Component Voltage Measurements
To measure the AC component of a waveform, the AC-DC-
GND switch of the channel you intend to use should be set
to the AC position. In this position, only the AC components
of the input signal are displayed on the CRT. (However,
when the AC component of the input signal is very low in
frequency, use the DC position of the switch.)
To make a peak-to-peak voltage measurement of the AC
component of a waveform, perform the following steps
(Channel 1 is used as the example):
1. Set the Channel 1 VOLTS/CM switch so that the volt-
age to be applied to the input connector is no more than
about four to six times the setting.
2. Apply the signal to the INPUT 1 connector, preferably
through a coaxial cable or an attenuator probe.
3. Set the MODE switch to CH 1.
4, Set the triggering controls to obtain a stable display
and set the sweep rate to display several cycles of the wave-
form.
5. Use the Channel 1 POSITION control to vertically
position the waveform to a point on the CRT where the wave-
form amplitude can be easily determined. For example, posi-
tion the waveform so that the negative peaks coincide with
one of the lower graticule lines and one of the positive
peaks lies near the graticule vertical centerline (see Fig 3-1).
6. Measure the vertical deflection in centimeters from
peak to peak on the waveform. Make sure the VARIABLE
control is set to the CALIBRATED position.
NOTE
In measuring signal amplitudes, the width of the
trace may be an appreciable part of the overall
measurement. To make the measurement as accu-
rate as possible, measure from one side of the trace
(particularly when measuring low-amplitude sig-
nals). Notice in Fig. 3-1 that both points (a) and
(b) correspond to the bottom side of the trace.
The measurement would be just as accurate if
points (a) and (b) corresponded to the top side
or center of the trace.
7. Multiply the peak-to-peak distance measured in step
6 by the setting of the Channel 1 VOLTS/CM switch and the
attenuation factor, if any, of the probe.
As an example of this method, assume that the peak-to-
peak vertical deflection is 4.6 cm using 10X probe with the
VOLTS/CM switch set to 0.5. Substituting these values in the
following formula:
Volts Vertical VOLTS/CM Probe
Peak to peak = deflection X switch X_ atten
in cm setting factor
Then:
Volts peak to peak = 46 X 0.5 X 10 = 23 volts
Instantaneous Voltage Measurements
To measure the DC level at a given point on a waveform
proceed as follows:
1. Set the Channel 1 VOLTS/CM switch so that the voltage
to be applied to the input connector is not more than about
six times the switch setting.
“LE
Vertical
Distance
(Cm)
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ra
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Fig. 3-1. Measuring the peak-to-peak voltage of a waveform.
Fig. 3-2. Measuring instantaneous voltage with respect to some
reference.
3-1

Applications—Type 1A2
2. Set the oscilloscope triggering and time-base controls
so that the time base free runs at the desired rate.
3. Set the Channel 1 AC-DC-GND switch to GND and
position the trace (with the Channel 1 POSITION control) to
one of the horizontal graticule lines such as point (b) in Fig.
3-2. This line will be used as a ground (or zero} reference
line. In any case, the reference line chosen will depend upon
the polarity and DC level of the signal to be measured. Do
not move the Channel 1 POSITION control after the refer-
ence line has been established.
4. Set the Channel 1 AC-DC-GND switch to DC.
NOTE
Any shift in the position of the trace when the AC-
DC-GND switch is moved from GND to DC, or vice
versa, indicates grid current in the appropriate
input Nuvistor (V133 or V233). Maximum trace
shift due to grid current is --2mm. If the trace
shifts more than this amount, replace the faulty
Nuvistor.
5. Apply the signal, preferably through a coaxial cable
or an attenuator probe, to the Channel 1 Input connector.
6. Set the triggering controls of the time base for a stable
display.
7. Measure the vertical distance in centimeters from the
ground (zero) reference line established in step 3 to the
point on the waveform that you wish to measure, such as
between (a) and (b) in Fig. 3-2. If the PULL TO INVERT
switch is pushed in and the point on the waveform is above
the reference line, the polarity is indicated to be positive (++).
If the point is below the line, the polarity is negative (—).
If the PULL TO INVERT switch is pulled out, the indicated
polarities will be reversed.
8. Multiply the measured distance by the setting of the
VOLTS/CM switch and the attenuator factor, if any, of the
probe. This is the instantaneous DC level of the point mea-
sured. For example, assume the vertical deflection is 4.2 cm
above the reference line (see Fig. 3-2) using a 10X attenuator
probe with the PULL TO INVERT switch pushed in and the
VOLTS/CM switch set to 2. Substitute these values in the
following formula:
Vertical
Deflection VOLTS/CM Probe
inem and X switch X_— atten
Instantaneous
Voltage (with
respect to qa =
ground reference polarity setting factor
Then:
Instantaneous Voltage
(with respect to a = +42 XK 2 X 10 = +84 volts
ground reference)
9. To re-establish the (zero) reference line without discon-
necting the applied signal, set the AC-DC-GND switch to
GND. To establish a reference other than zero, set the AC-
DC-GND switch to DC, touch the signal probe to the desired
reference voltage and position the free-running sweep along
one of the horizontal graticule lines.
Voltage Comparison Measurements
In some applications you may want to establish a set of
deflection factors other than those indicated by the VOLTS/
3-2
CM switch. This is useful for comparing signals which are
exact multiples of a given voltage amplitude. The following
procedure describes how to determine deflection factors for
Channel 1. The same basic procedure can be used for Chan-
nel 2. To establish a set of deflection factors based upon
some specific reference amplitudes, proceed as follows:
1. Apply a known-amplitude reference signal to the Chan-
nel 1 Input connector and, with the Channel 1 VOLTS/CM
switch and VARIABLE control, adjust the amplitude of the
display for an exact number of graticule divisions. Do not
move the VARIABLE control after obtaining the desired
deflection.
2. Divide the amplitude of the reference signal (in volts
by the product of the deflection in centimeters (established
in step 1) and the VOLTS/CM switch setting. The result is
the Deflection Conversion Factor:
Deflection
Conversion =
Factor
Reference signal amplitude in volts
(Deflection in cm) X (VOLTS/CM switch setting}
3. To calculate the True Deflection Factor at any setting
of the Channel 1 VOLTS/CM switch, multiply the VOLTS/CM
switch setting by the Deflection Conversion Factor obtained
in step 2:
True
Deflection = (VOLTS/CM switch setting} X (Deflection Con-
Factor version Factor)
The True Deflection Factor obtained for any setting of
the Channel 1 VOLTS/CM switch applies to Channel 1 only,
and only if the VARIABLE control is not moved from the posi-
tion to which it was set in step 1.
For example, assume the amplitude of the reference sig-
nal applied to Channel 1 is 30 volts, the VOLTS/CM switch is
set to 5 and the VARIABLE control is adjusted to decrease the
amplitude of the display to exactly 4cm. Then substitute the
preceding values in the Deflection Conversion Factor and
True Deflection Factor formulas:
Deflection 30
Conversion = ————~ = 1.5
Factor (4) x (5)
True
Deflection = (5} X (1.5) = 7.5 volts/cm
Factor
4. To determine the peak-to-peak amplitude of a signal
to be compared, disconnect the reference signal and apply
the signal to Channel 1.
5. Set the Channel 1 VOLTS/CM switch to a setting that
will provide enough deflection so that a measurement can be
made.
6. Measure the vertical distance in centimeters and deter-
mine the amplitude by using the following formula:
. Deflection . VOLTS/CM
Signal = Conversion Deflection X_ switch
Amplitude F in cm :
actor setting
For example, assume the signal to be compared caused a
vertical deflection of 4.5cm at a VOLTS/CM switch setting
of 10 and the VARIABLE VOLTS/CM control was not moved

from the setting used in the previous example. Then, sub-
stitute these values and a Deflection Conversion Factor of
1.5 in the Signal Amplitude formula:
Signal
Amplitude = (1.5) X (4.5) & (10) = 67.5 volts
{in volts)
Time-Difference Measurements
The calibrated sweep rate of the oscilloscope and the
dual-trace feature of the Type 1A2 allows measurement of
the time difference between events. Measure time difference
as follows:
1. Set the AC-DC-GND switches to identical settings; either
AC or DC depending on the type of coupling desired.
2. Push in the PULL TO INVERT switches.
3. Place the MODE switch to either CHOP or ALT, as
desired. In general, the CHOP position is more suitable for
low-frequency signals and the ALT position is more suitable
for high-frequency signals.
4. Connect a trigger signal to the oscilloscope Trigger
Input connector. This trigger signal must bear a fixed time
relationship to the signals to be displayed.
5. Set the VOLTS/CM switches so that the expected volt-
ages applied to the input connectors will provide suitable
vertical deflection on the CRT.
6. Apply the signals to the input connectors. Use coaxial
cables or probes having equal delay.
7. Set the oscilloscope Trigger Source switch to externally
trigger on the signal.
8. Set the oscilloscope time-base controls for a calibrated
sweep rate which will allow accurate measurement of the
distance between the two waveforms.
9. Measure the horizontal distance between the points on
the two waveforms.
10. Multiply the distance measured for each channel by
the setting of the oscilloscope Time/Cm switch to obtain the
apparent time interval.
11. To obtain the actual time interval, divide the apparent
time interval by the amount of sweep magnification, if any,
or by 1 if no sweep magnification is used. The formula is as
follows:
Time Delay =
(Time/Cm switch setting) X (Distance in cm)
Sweep Magnification
For example, assume that the Time/Cm switch setting is
2 wsec, the Magnifier is set for 5X magnification, and there
is a horizontal distance of 3 cm (as shown in Fig. 3-3) between
the leading edge of the reference waveform and the leading
edge of the waveform displayed by Channel 2. Then sub-
stitute these values in the preceding formula:
(2 psec) X (38cm) _
Time Delay = nn 1.2 psec
Applications—Type 1A2
Chan. 1 (Reference) Chan. 2 (Lagging)
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Distance j
beg————————— 9¢m (360°) seal
°
Degrees Per Cm = 360" = 40°
9Cm
Fig. 3-3. Measuring phase shift between two sine waves.
Phase Measurements
Phase comparison of two signals of the same frequency can
be made using the dual-trace feature of the Type 1A2. To
make the comparison, proceed as follows:
1. Follow the procedure outlined in the first seven steps
under Time-Difference Measurements.
2. Set the oscilloscope sweep rate to obtain a display of
less than 1 cycle of the waveform.
3. Adjust the VARIABLE control for each channel so the
waveform amplitudes are equal and fill the graticule area
vertically. Reset the VOLTS/CM switches, if necessary, to
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Phase Shift = Horiz. Distance in Cm Times 8°
Fig. 3-4. Computing the phase shift when the oscilloscope sweep
rate is increased 5X.
3-3

Applications—Type 1A2
obtain equal-amplitude waveform displays. (Equal amplitudes
are used to make comparisons easier.)
4. Use the POSITION controls to center the waveforms
vertically; that is, an equal distance each side of the graticule
centerline.
5. Turn the oscilloscope Variable Time/Cm control counter-
clockwise until 1 cycle of the reference signal occupies 9 cm
horizontally. Use the Trigger Slope and Triggering Level
controls to trigger on the reference waveform at any point
you desire. Each cm on the graticule now represents 40° of
1 cycle (see Fig. 3-3).
6. Measure the horizontal distance, in cm, between cor-
responding points on the waveforms. Note the distance and
whether the Channel 2 waveform is leading or lagging (see
Fig. 3-3).
3-4
7. Muitiply the distance by 40°/cm to obtain the amount
of phase difference.
For more precise measurements, increase the previous sweep
rate but do not change the setting of the oscilloscope Vari-
able Time/Cm control. However, you must consider this
increase in your calculations.
For example, if you increase the sweep rate by a factor
of 5, and then measure the distance between waveforms, each
cm will represent 8° (40° + 5) of a cycle. Thus, phase dif-
ference up to 80° can be measured more accurately. When
preparing to make the measurement, horizontally position
the waveforms to points where the graticule markings aid in
determining the exact distance. Fig. 3-4 for example, shows
how the phase difference of the Channel 2 waveform can be
computed using this method.

SECTION 4
CIRCUIT DESCRIPTION
Introduction
The Type 1A2 contains two channel input amplifiers, a
common output amplifier, a switching circuit for dual-trace
operation and a trigger output amplifier. (Instruments with
serial number below 715 do not have a trigger output
amplifier.)
Channel Input Amplifiers
The applied signal from the INPUT connector passes
through the AC-DC-GND switch to the attenuation network.
The AC position of the AC-DC-GND switch AC couples the
signal to the amplifier; the DC position directly couples the
signal to the amplifier and the GND position opens the cir-
cuit to the input signal and grounds the input of the amplifier.
The deflection factor of the plug-in unit is changed with
attenuators (VOLTS/CM switch) connected in the input cir-
cuit. Each attenuator is frequency compensated for equal
attenuation of low and high frequencies. The input capaci-
tance of each attenuator is standardized so that input capaci-
tance is the same regardless of the settings of the VOLTS/CM
switch.
From the attenuator network, the incoming signal passes
to the grid of the input Nuvistor V133 (or V233 in Channel 2).
The Nuvistor is connected as a cathode follower and has a
voltage gain of about 0.9. The neon bulb B118, between the
grid and cathode of the Nuvistor, keeps the grid-to-cathode
voltage within safe limits while the tube is warming up.
D134 (D234 in Channel 2) protects against excessive plate cur-
rent in the event of a large positive voltage swing on the
grid of the tube. D397 prevents current varitions in the
supply due to positioning controls in common mode operation.
C397 prevents the plate voltage following the grid signal at
frequencies above 50 kHz. Diodes D137 and D138 protect the
transistor stage by limiting the output voltage swing of the
Nuvistor. !n instruments with serial numbers below 715, D397
and C397 are not present; D134 is connected to the +100-V
supply.
The
remaining stage of the Channel Input Amplifier is an
emitter coupled paraphase amplifier. This stage converts the
single-ended input signal to push-pull. Gain of the stage is
controlled by R142 and R161 in the common emitter circuit.
These variable resistors vary emitter degeneration. Maximum
gain occurs with minimum resistance between the two emit-
ters. The VAR ATTEN BAL control sets the level on the base
of the undriven transistor so that no current flows between
emitters under no-signal conditions. This insures that there
is no ground reference shift of the trace when the VARIABLE
control is turned.
Resistors R140 and R160, in the collector circuits of Q143
and Q163, provide thermal stability by forcing the transistors
to operate in a balanced power mode. This means that dis-
sipation of the transistors remains balanced with varying
signals.
The PULL TO INVERT switches reverse the displayed pol-
arity of the signal. With the switches pushed in, a positive
voltage change at the INPUT connector deflects the electron
beam of the oscilloscope upward. With the switches pulled
out, a positive voltage change at the INPUT connector
deflects the electron beam downward.
The POSITION controls vary the current on each side of
the push-pull circuit for positioning control. In the ADD
position of the MODE switch, note that the Channel 2 POSI-
TION control is out of the circuit and only the Channel 1
POSITION control can position the display.
Fig. 4-1 shows a simplified schematic diagram of the rela-
tionship of the last stage of each Channel Amplifier to the
diode gates and the first stage of the Output Amplifier.
Diode Gates
The state of the diode gates determine which Channel
Input Amplifier signal passes through to the Output Ampli-
fier. The diode gates are controlled by the switching circuit.
In the ADD position of the MODE switch, both diode gates
allow both Channel Input Amplifier signals to pass on to the
Output Amplifier. In all other positions of the MODE switch,
the diode gates are never on at the same time.
The diode gates permit the signal current to pass when
D301-D304 (D306-D309 in Channel 2) are forward biased and
D302-D303 (D307-D308 in Channel 2} are back biased. The
diode gates block the signal when the diodes are in the
opposite state. For simplicity, the schematic of Fig. 4-1 rep-
resents the diode gates as switches.
Output Amplifier
The first stage of the Output Amplifier is a hybrid push-
pull cascode amplifier. The Channel Input Amplifiers cur-
rent-drive the emitters of Q354 and Q364. Toroids, T301 and
T310, are parasitic oscillation suppressors. The voltage swing
on the emitters is relatively small, due to the low input
impedance.
The cathodes of V364 are current-driven by Q354 and
Q364. V364 elevates the DC level of the stage to the correct
voltage necessary for the vertical amplifier of the oscilloscope.
The OUTPUT DC LEVEL adjustment is provided so that this
voltage level can be accurately set.
The final stage of the Output Amplifier is an emitter fol-
lower circuit. The emitter follower stage isolates the pre-
ceding stage from the vertical amplifier of the oscilloscope.
The high-frequency compensation network consisting of C377-
R377 and C379-R379 standardizes the response of the
instrument.
Switching Circuit
The switching circuit consists of a bistable multivibrator
(Q315-Q325) and a trigger circuit (Q340). Both circuits are
arranged in various configurations by the MODE switch
SW350A. The operation of the switching circuit and_ its
4-1

Circuit Description—Type 1A2
To To
Q383 Q373
base base
R. +12 RL
V3648B —— — AN— — — — V364A
+10v
—— -—
Q364 , q Q354
Chan 1 = Chan 2
diode gate diode gate
| Seine
/,
To
Qais
/t
To
Q325
‘\\
. ti . :
i in muti 413 / in multi \413¥
/
Q143
VAR ATTEN VAR ATTEN
BAL BAL
CHANNEL 1 CHANNEL 2
A A
Sig in from Sig in from
V133 cathode V233 cathode
—150v —150v
Fig. 4-1. Simplified schematic to illustrate the relationship of the Channel Input Amplifiers to the diode gates and the Output Amplifier.
Resistances of R. and Ri determine overall gain of the plug-in unit.
effect on the diode gates at the different settings of the MODE
switch is described in the following paragraphs. See the
schematic diagrams at the rear of this manual for the appro-
priate waveforms and voltages.
ALT. In the ALT position of the MODE switch, the switch-
ing circuit must switch to the opposite channel at the end of
each sweep of a time-base circuit. The command pulse
(called the Alt Trace Sync Pulse) for this purpose arrives at
the base of Q340 from pin 8 of the interconnecting plug
through diode D332. In this mode, Q340 is connected as a
triggered Blocking-Oscillator. The output trigger pulse is trans-
former-coupled to the steering diodes D317-D327 of the
bistable multivibrator (Q315-Q325). Depending on the state
of the multivibrator, one of the steering diodes is forward
biased by the trigger pulse. This steering diode passes the
trigger signal to the appropriate side of the multivibrator and
causes it to switch to the opposite state. The change of state
of the multivibrator reverses the condition of both diode
4-2
gates. Note that when Q325 conducts, diodes D307-D308
are forward biased, D306-D309 are back biased, and the
Channel 2 diode gate does not permit the signal to pass to
the Output Amplifier. When Q315 conducts, diodes D302-
D303 are forward biased, D301-D304 are back biased, and
the Channel 1 signal is then blocked from the Output
Amplifier.
When the plug-in unit is used with an oscilloscope that
has alternate sweep switching, an Alternate Sweep Slave
Pulse is coupled into pin 7 of the interconnecting plug. The
slave pulse insures that the multivibrator (Q315-Q325) turns on
Channel 1 during the Time Base A sweep of the oscilloscope.
This, in turn, allows the Channel 1 signal to be displayed on
the Time Base A sweep of the oscilloscope and the Channel
2 signal to be displayed on the Main Time Base (B) sweep.
See Fig. 4-2 for the relationship of the slaving pulse to the
oscilloscope sweep voltages. Note that this capability occurs
only in the ALT setting of the MODE switch.
@2