Tektronix Type M User manual

IIS IS T R U C T IO IS!
I V 1A I N I U / \ L _
Tektronix, Inc.
S.W . Millikan W ay
™ M
PLUG-IN UNIT
JT /V /// t2
^ ^V-&J-i^ r C tU A i c ( u. s (y i f : <./cn^e. L
P. O . Box 500 • Beaverton, Oregon • Phone Ml 4-0161 • Cables: Tektronix
Tektronix International A .G .
Terrassenweg 1A • Zug, Switzerland • PH .04 2-49192 • Cable: Tekintag, Zug Switzerland • Telex 53.574
070-295

CONTENTS
Warranty
Section 1 Characteristics
Section 2Operating Instructions
Section 3 Circuit Description
Section 4 Maintenance
Section 5Calibration
Section 6 Accessories
Section 7Parts List and Diagrams
Copyright © 1962 by Tektronix, Inc.,
Beaverton, Oregon. Printed in the United
States of America. All rights reserved.
Contents of this publication may not be re
produced in any form without permission
of the copyright owner.

WARRANTY
All Tektronix instruments are warranted
against defective materials and workman
ship for one year. Tektronix transformers,
manufactured in our own plant, are war
ranted for the life of the instrument.
Any questions with respect to the war
ranty mentioned above should be taken up
with your Tektronix Field Engineer.
Tektronix repair and replacement-part
service is geared directly to the field, there
fore all requests for repairs and replace
ment parts should be directed to the Tek
tronix Field Office or Representative in your
area. This procedure will assure you the
fastest possible service. Please include the
instrument Type and Serial number with all
requests for parts or service.
Specifications and price change priv
ileges reserved.

'A " SIG N A L:
, OUT
FOUR-TRACE PREAMP
TYPE M PLUG-IN
VOLTS/CM MODE
. n o r m . ■
DC AC
p o s i t i o n :
V A R . G A IN
GAIN AB4.
1 m&. 4? p
position:
GAIN
NORM.
P OS ITIO N
V A R . GA IN
GAIN
n o r m
P OS ITIO N
CHOPPED
alternate
POSHANO. 0 R650N,
SERIAL
TEKTRONIX, INC
The Type M Plug-In Unit
Type M

C H A R A C T ER IS TIC S
General Information
The Type M Plug-In Unit preamplifier contains four
identical channels that can be used separately or electron
ically switched to produce single- or multi-trace displays.
The unit thus provides a convenient means for viewing one
to four signals, either separately or in combination, reduc
ing cable switching to a minimum. Each amplifier in the
unit has its own attenuator, mode, gain, and position con
trol, which enables the display to be adjusted for optimum
viewing and information.
When using the channels separately (without electronic
switching), the M Unit is useful in all single-trace applica
tions within its frequency and sensitivity capabilities.
During the alternate mode of operation, when the oscillo
scope sweep is set for free-running operation, the sweep
triggers the M Unit and one to four traces can be displayed
alternately. The number of traces depends upon the setting
of the MODE switches. In applications where signals,
related in repetition rate to the sweep, are applied to the
M Unit input connectors, a stable display can be obtained.
In the alternate mode of operation, when the oscillo
scope is set for triggered operation, stationary displays of
four signals unrelated in frequency can be obtained. The
signals internally trigger the sweep which, in turn, triggers
the M Unit to produce alternate displays. Because the
sweeps are identical and time-delay characteristics of the
four channels are equal, accurate time comparisons can
be made between signals.
In the chopped mode of operation, channel switching
occurs at a rate of approximately 1 me divided by the
number of channels in use, making it possible to view from
one to four simultaneous transients. The number of dis
played waveforms depends on the setting of the MODE
switches and the number of inputs used. In four-trace
operation transients of as little as 0.5 millisecond duration
can be well delineated, with approximately 125 elements in
each trace. For many purposes, shorter transients can be
adequately observed.
Amplifier Sensitivity
Nine calibrated steps are provided for each channel:
0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5 and 10 volts/cm. Accuracy
is within 3% of panel reading. Variable controls for each
channel permit continuous adjustment (uncalibrated) from
0.02 to 25 volts/cm.
Amplifier Transient Response and Bandwidth
Your instrument was adjusted at the factory for optimum
transient response. Table 1-1 summarizes the risetime and
approximate bandwidths available when the M Unit is
used in combination with various oscilloscopes.
TABLE 1-1
TRANSIENT RESPONSE AND BANDWIDTH
Oscilloscope - M Unit
Combination
Risetime Bandwidth (at — 3 db points)
MODE switch
in any posi
tion except
OFF
MODE switch in
either DC posi
tion
Mode switch in either
AC position
541, 541 A, 543,
543A, 545, 545A,
555, 581* or 585*
17 nsec dc to 20 me
2 cps to 20 me; 0.2 cps
to 20 me with P6000
Probe or equivalent
551 18 nsec dc to 19 me
2 cps to 19mc; 0.2 cps
to 19 me with P6000
Probe or equivalent
531, 531 A, 533,
533A, 535 or 535A
25 nsec dc to 14 me
2 cps to 14mc; 0.2 cps
to 14 me with P6000
Probe or equivalent
536 35 nsec dc to 10 me
2 cps to 10 me; 0.2 cps
to 10 me with P6000
Probe or equivalent
532 70 nsec dc to 5 me
2 cps to 5 me; 0.2 cps to
5 me with P6000 Probe
or equivalent*
* Type 81 Plug-In Adaptor required for use with Types 581 and 585.

Characteristics— Type M
Operating Modes
Channels A, B, C, or D, separately.
Chopped—Sequential electronic switching of channels at
approximately 1-mc rate.
Alternate— Triggered electronic switching of channels
at the end of each sweep, during retrace intervals.
Front-panel switches, in conjunction with the chopped or
alternate modes of operation, permit viewing any combina
tion up to four channels.
Polarity Inversion
Polarity of any channel selected can be inverted for
comparison of signals 180° out of phase.
Input Coupling
Choice of ac or dc coupling. In the AC positions of the
MODE switch a coupling capacitor is inserted, limiting the
low-frequency response to approximately 2 cycles at 3 db
down.
Input Impedance
1 megohm ± 1 % paralleled by approximately 47 pf.
Maximum Allowable Combined DC and Peak
AC Input
600 volts.
Construction
Aluminum-alloy chassis.
Finish
Photo-etched anodized aluminum front panel.
New Weight
5 pounds, 2 ounces.

OISI 2
O P E R A T IN G
IN S T R U C T IO N S
FRONT-PANEL CONTROLS AND CONNECTORS
Functions of the channel A front-panel controls, channel A
connectors, ALTERNATE/CHOPPED switch and Securing Rod
are described in Table 2-1. The functions of the front-panel
controls and input connectors for the other channels are the
same as for channel A. Grouping of the front-panel controls
and connectors is shown in Fig. 2-1.
TABLE 2-1
Input Connector
.................. Connector for coupling ac or dc
signals to the channel A ampli
fier.
VOLTS/CM ............................. Nine-position switch to select the
calibrated vertical-deflection fac
tors.
MODE
....................................... Five-position switch to provide a
choice of ac or dc coupling,
operational in-phase (normal) or
out-of-phase (inverted) output, or
to turn the channel “off” .
Fig. 2-1. Front-panel view of the Type M Plug-in Unit showing the
grouping of the controls and connectors for each channel.
GAIN ADJ
............................ Screwdriver-adjust potentiometer
to set the gain of the amplifier
accurately.
VAR. G AIN ............................. Potentiometer to provide continu
ously variable attenuation be
tween the calibrated sensitivities
and to extend the attenuation to
a sensitivity of 25 volts/cm. This
control does not have a mechani
cal stop and is therefore con
tinuously variable. It does, how
ever, have a detent stop for the
CALIB. (calibrated) position.
"A " SIGNAL O U T
............. Output signal from channel A.
Amplitude is 2 volts for each cm
of display on crt. Bandwidth of
the internal channel A Signal
Output Amplifier is 1 me at —3
db with gradual rolloff.
DC BAL
.................................... Screwdriver-adjust potentiometer
to set the dc level so the trace
does not shift position as the
VAR. GAIN control is adjusted.
POSITION
............................... Potentiometer to shift the trace
position vertically.
ALTERNATE/CHOPPED . . Slide switch to select either al
ternate or chopped mode of
operation. When used in con
junction with the MODE switches,
the ALTERNATE/CHOPPED switch
permits viewing any combination
of channels in either mode of
operation.
Securing R o d
.......................... Holds the M Unit securely in the
oscilloscope plug-in compartment.
(The Securing Rod is located at
bottom center on the front panel.)
FIRST TIME OPERATION
Plug the M Unit into a Type 530-, 540-, 550-, or 580-
Series* Tektronix oscilloscope, tighten the Securing Rod,
and turn the power on. Allow the instrument to reach
operating temperature, about 2 to 3 minutes, and free-run
the oscilloscope sweep at 0.5 millisec/cm. Set the front-
panel controls of the M Unit as follows:
* A Type 81 Adaptor required Tor use with Types 581 and 585
Oscilloscopes.
®2-1

Operating Instructions— Type M
VOLTS/CM (All channels) .02
MODE (channel A) DC NORM.
MODE (channels B, C and D) OFF
VAR. GAIN (all channels) CALIB.
POSITION (all channels) Centered
ALTERNATE/CHOPPED ALTERNATE
1. Position the trace to about + 2 cm with the channel A
POSITION control.
2. Set the channel B MODE switch to the DC NORM, posi
tion and position the B trace to about -f 1 cm with the
channel B POSITION control.
3. Set the channel C MODE switch to DC NORM, and posi
tion the C trace to about — 1 cm with the channel C POSI
TION control.
4. Set the channel D MODE switch to DC NORM, and
position the D trace to about —2 cm with the channel D
POSITION control. This makes a total of four traces which
appear on the crt screen. For each sweep cycle one channel
is conducting and the others are cut off. The channels are
switched alternately at the end of each sweep cycle, during
retrace intervals.
5. To observe the alternate trace switching cycle at a
slower rate, decrease the sweep rate to 0.1 sec/cm.
6. To observe the CHOPPED mode of operation set the
ALTERNATE/CHOPPED switch to the CHOPPED position.
7. Set the oscilloscope triggering controls for -plnfemal
triggered-sweep operation. Notice that all four traces seem
to start simultaneously and continue on across the screen.
8. Increase the sweep rate to 10 psec/cm. Adjust the oscillo
scope Triggering Level control to obtain a stable display.
Notice that each trace is composed of several short-
duration elements with switching-transient traces existing
between the channels. [To blank out the switching tran
sients, set the CRT Cathode Selector switch (located at the
rear of most Tektronix oscilloscopes) to the Dual-Trace
Chopped Blanking position.]
All four channels are being switched successively at a
rate of approximately 1 me. Increase the sweep rate to 1
fisec/cm. Observe that each channel conducts for about
1 psec and then is cut off for 3 psec while the three other
channels each conduct for 1 psec. Chopping rate of each
channel is 250 kc (1 me divided by the number of channels
in use). Approximate switching time between channels is
0.1 psec (see Fig. 2-2a).
9. Now set channel B and D MODE switches to OFF.
Notice that the M Unit switches between channels A and C
only. Each channel conducts for about 1 psec and then is
cut off while the other channel conducts for an equal time
(see Fig. 2-2b). Chopping rate for each channel is now
approximately 500 kc.
GENERAL OPERATION
Any of the four amplifier channels can be used inde
pendently by rotating the appropriate MODE switch to
one of the DC or AC positions and connecting the signal
to be observed to the appropriate input. The following
remarks apply equally to each channel.
= 1 /xsec.v
3 /xsec.—
= 0.1 /isec
r -
(a)
= 1 /./„sec. v
—► III:
= 0.1 i'sec.
A Trace ►
-L*
__
\
/xse<
(b)
Fig. 2-2. (a i Chopping rate of each channel is approximately
250 kc, and (b) the chopping rate is about 500 kc. Switching
rate is approximately 1 me. Sweep rate of the oscilloscope is
1 psec/cm.
Signal Connections
The signal(s) to be displayed is applied to the appropri
ate input connector on the front panel of the M Unit. For
best results, following are some precautions you should
observe when making the connections.
1. It is often possible to make signal connections to the
M Unit with short-length, unshielded test leads. This is
particularly true for high-level, low-frequency signals. When
such test leads are used, you must also use a ground con
nection between the M Unit or oscilloscope chassis ground
and the chassis of the equipment under test. Position the
leads away from any stray electric or magnetic field source
to avoid erroneous displays.
2. In many low-frequency applications, however, unshielded
leads are unsatisfactory for making signal connections be
cause of unavoidable pickup resulting from magnetic fields.
Whenever possible, use shielded (coaxial) cables. Be sure
that the ground conductors of the cables are connected to
the chassis of both the oscilloscope and the signal source.
3. In broadband applications, it may be necessary to ter
minate the coaxial cable with a resistor or an attenuator
equal to the characteristic impedance of the cable, to pre
vent resonance effects and ringing. It becomes more neces
sary to terminate the cable properly as the length of the
cable is increased. The termination is generally placed at
the oscilloscope end of the cable, although many sources
require an additional termination at the source end of the
cable as well. (Refer to the Accessories section of this
manual for a listing of available cables, terminating re
sistors, and attenuators.)
4. As nearly as possible, simulate actual operating condi
tions in the equipment under test. For example, the equip-
2-2

Operating Instructions— Type M
merit should work into a load impedance equal to that
which it will see in actual use.
5. Consider the effect of loading upon the equipment under
test due to the input circuit of the M Unit. The input circuit
can be represented by a resistance of 1 megohm (± 1 % )
shunted by a capacitance of approximately 47 picofarads.
With a few feet of shielded cable, the capacitance may
well be 100 picofarads. Where the effects of these re
sistive and capacitive loads are not negligible, you might
want to use a probe in the manner described next.
Use of Probes
An attenuator probe having a standard length cable
(42" long) lessens both capacitive and resistive loading,
but at the same time reduces sensitivity. The attenuation
introduced by the probe permits measurements of signal
voltages in excess of those that can be accommodated by
the M Unit alone. When making amplitude measurements
with an attenuator probe, be sure to multiply the observed
amplitude by the attenuation of the probe (marked on the
probe).
An adjustable probe capacitor compensates for variations
in input capacitance from one plug-in unit to another. To
assure the accuracy of pulse and transient measurements,
this adjustment should be checked frequently.
To make this adjustment, set the oscilloscope calibrator
controls for a calibrator output signal of suitable ampli
tude. Place the MODE switch for the channel in use to
DC NORM. Touch the probe tip to the calibrator-output
connector and adjust the oscilloscope controls to display
several cycles of the waveform. Adjust the probe variable
capacitor for best square-wave response, as shown in the
right-hand picture of Fig. 2-3.
Deflection Factor
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 VAR. G AIN control. Calibrated
deflection factors indicated by the settings of the VOLTS/CM
switch apply only when the VAR. G AIN control is set to
the CALIB. position. Serious errors in display measurements
may result if the setting of this control is unintentionally
moved away from this position.
The range of the VAR. GA IN control is approximately
2.5 to 1 to provide continuously variable (uncalibrated)
vertical-deflection factors between calibrated settings of the
VOLTS/CM switch. The VAR. GAIN control can be manu
ally rotated continuously in either the clockwise or counter
clockwise direction, thus permitting the control to be set
quickly to any desired position. The control has one detent
position (CALIB.), which is the calibrated deflection factor
setting.
Voltage measurements may be made directly from the
oscilloscope screen by noting the calibrated VOLTS/CM
switch setting for the applicable channel and the amount
of vertical deflection on the crt. Multiply the deflection on
the screen by the setting of the VOLTS/CM switch and the
attenuation factor, if any, of the probe.
MODE Switch
The MODE switch has five positions: DC NORM., AC
NORM., OFF, DC INV. and AC INV. To display both the
ac and dc components of an applied signal, set the MODE
switch to one of the DC positions; to display only the ac
component of a signal, set the MODE switch to one of the
AC positions.
In the AC positions of the MODE switch, the dc com
ponent of the signal is blocked by a capacitor in the input
circuit. The lower frequency limit (3-db point) of the M
Unit is about 2 cps (0.2 cps if using a 10X attenuator probe).
Therefore, some low-frequency distortion of signals with
components below this frequency will result if the AC posi
tions are used.
It may be desirable, at times, to invert the displayed
waveform, particularly when using the multi-trace feature
of the M Unit. With the MODE switch you can choose
either a normal or inverted display, and either dc or ac
coupling. In the DC- or AC-NORM. positions the displayed
waveform has the same polarity as the input signal. In
the DC- or AC-INV. positions the displayed waveform is
inverted.
Placing the MODE switch to the OFF position turns the
channel “off", disconnects the input signal, and excludes
the channel from the electronic switching cycle.
Fig. 2-3. Probe compensation waveforms.

Operating Instructions— Type AA
ALTERNATE/CHOPPED Switch
For single-trace operation the ALTERNATE/CHOPPED
switch is inoperative and no electronic switching of the
channels occurs. For multi-trace operation the setting of
the ALTERNATE/CHOPPED switch is important. The best
setting to use depends on the repetition rate of the applied
signals and whether or not they are related in time to
each other.
In general, the ALTERNATE position is usually used with
sweep rates above 10/xsec and the chopped position with
lower sweep rates. The ALTERNATE position is useful for
observing unrelated or related signals of high repetition rate
(usually above 100 kc), observing fast transients, and making
phase and time-delay comparison measurements. The
CHOPPED position is most useful for observing related low-
frequency signals and for observing transients having a dura
tion as short as 0.5 millisecond.
When determining the best mode of operation to use in
a particular application, it is also necessary to choose the
best triggering method. In the discussion that follows, trig
gering methods are described in more detail.
Multi-Trace Triggering
Multi-trace triggering is divided into the following order:
(1) External triggering using ALTERNATE and CHOPPED
modes, (2) Internal triggering using ALTERNATE mode, and
(3) Internal triggering using CHOPPED mode.
External triggering using ALTERNATE and CHOPPED
modes. For multi-trace operation, it is usually best to trig
ger the time base with an external triggering signal which
bears a fixed time relationship to the applied signals. A
convenient source for obtaining the external trigger signal
is from the "A " SIGN AL OUT connector. With an external
triggering signal a stable display is more easily obtained
and the true time or phase relationship between input sig
nals can be determined.
To trigger from the channel A signal, simply connect a
test lead between the “ A" SIGNAL O UT connector on the
M Unit and the Trigger Input connector on the oscilloscope.
Then set the oscilloscope triggering controls for external
triggered-sweep operation. To obtain a stable display, the
signals applied to the other channels must be related in
frequency to the channel A signal.
If the trigger signals have components above 10 kc, use
the AC Fast or AC LF Reject triggering mode (if your oscil
loscope has these positions). For lower frequency signals,
use the A C or AC Slow triggering mode.
Internal triggering using ALTERNATE mode. If the time
or phase relationship between signals is not critical, you
can use internal triggering of the time base when the
ALTERNATE/CHOPPED switch is set to ALTERNATE. In
this mode of operation, the signals applied to the indi
vidual channels can be either related or unrelated in fre
quency. The oscilloscope Triggering Level control must be
set at a point where the sweep will trigger on the display
having the lowest amplitude. If the signals have components
above lOkc, use the AC Fast or AC LF Reject triggering
mode (if your oscilloscope has these positions). For lower
frequency signals, use the AC or AC Slow triggering mode.
In the AC Fast or AC LF Reject position, an rc filter is in
serted into the trigger-input circuit of the oscilloscope which
allows it to recover quickly from the dc level changes en
countered with ALTERNATE sweep.
Internal triggering using CHOPPED mode. For multi-trace
CHOPPED mode of operation, internal triggering should not
be used unless the input signals are related to the chopped
switching rate. If the signals are not related to the chopping
rate, the sweep will try to trigger on the switching wave
form rather than on the applied signals and will result in
an unstable display. To obtain stable displays, externally
trigger the sweep from the channel A signal. To do this,
use the "A" SIGN AL OUT connector and set the oscillo
scope controls for external triggered-sweep operation.
DC Balance Adjustments
After the M Unit has been in use for a period of time,
the trace may change position as the VAR. GAIN control
is rotated. This is caused by slight changes in the operating
characteristics of components in the M-Unit amplifier stages
and resultant shift in operating potentials. To correct this
condition in one or all channels proceed as follows:
1. Set the front-panel controls of the channel to be dc-
balanced to these settings:
VOLTS/CM Any position
MODE DC NORM, or AC NORM.
VAR. GAIN CALIB.
POSITION Centered
ALTERNATE/CHOPPED ALTERNATE
2. Set the oscilloscope sweep rate and triggering controls
for a 0.5-millisec/cm free-running sweep.
3. With the POSITION control, position the trace to approx
imate center of the graticule.
4. Set the DC BAL. adjustment to the point where there is
no trace shift on the crt as the VAR. G AIN control
is rotated.
Gain Adjustments
The gain adjustments should be checked periodically to
assure correct vertical deflection factors, particularly when
the M Unit is transferred from one oscilloscope to another.
The following procedure describes a method for setting the
gain of each channel when the M Unit is used with an
oscilloscope having 4 centimeters of vertical scan. If the
vertical scan of your oscilloscope is greater than 4 centi
meters, use 100 millivolts from the oscilloscope calibrator
and set the gain for a vertical deflection of exactly five
centimeters. In other respects the procedure for setting the
gain is the same.
To check the gain of each channel:
2-4

Operating Instructions— Type M
1. Set the M Unit front-panel controls as follows:
VOLTS/CM (all channels) .02
MODE (channel A) DC NORM, or AC NORM.
MODE (channels B, C, and D) OFF
VAR. G AIN (all channels) CALIB.
POSITION (all channels) Centered
ALTERNATE/CHOPPED ALTERNATE
2. Set the oscilloscope sweep rate and triggering controls
for a 0.1-millisec/cm free-running sweep.
3. Apply a 20-millivolt peak-to-peak calibrator signal from
the oscilloscope to all four channels.
2. With the aid of the graticule, measure the vertical dis
tance in centimeters between the two points on the wave
form at which the voltage measurement is desired. Make
sure the appropriate VAR. GA IN control is set to the CALIB.
position.
In measuring signal amplitudes, it is important to remem
ber that the width of the trace may be an appreciable
part of the overall measurement. For this reason, you
should consistently make all measurements from one side
of the trace. This is particularly true when measuring signals
of small amplitude. Notice in Fig. 2-4 that points a and b
correspond to the bottom side of the trace. The measure
ment would be just as accurate if points a and b corres
ponded to the top side or center of the trace.
4. Set the channel A G AIN ADJ. control for a deflection of
exactly one centimeter. (Use the A POSITION control to
align the display with the horizontal graticule lines.)
5. Place the channel A MODE switch to O FF and set the
channel B MODE switch to DC NORM. Repeat step 4
using the channel B GAIN ADJ. and POSITION controls.
6. Follow the procedure described in step 5 to adjust the
gain of channels C and D.
BASIC APPLICATIONS
The following paragraphs describe procedures for mak
ing voltage, phase, and time-delay measurements with the
Type M Plug-In Unit and associated Tektronix oscilloscope.
An application is also included using the Channel A Signal
Output Amplifier as a preamp for observing low-level
signals. No attempt has been made to describe any but
the most basic techniques. Familiarity with the unit will
enable the operator to apply the essence of these tech
niques to a wide variety of applications.
Voltage Measurements
Following are three categories of voltage measurements
that can be obtained with the Type M Unit: (1) peak-to-peak
voltage of a displayed waveform, (2) dc level at some point
on a signal, and (3) voltage comparison measurements.
The specific examples that follow are intended to show
the general procedure. These examples can be modified
to suit any particular application.
Peak-to-peak voltage of a displayed waveform. To
measure the peak-to-peak voltage of a displayed waveform,
the M Unit MODE switch should usually be set to one of
the A C positions. In these positions only the ac components
of the input waveform are displayed on the crt. However,
if the ac component of the input waveform is very low in
frequency, it will be necessary to make voltage measure
ments with the MODE switch in one of the DC positions to
prevent errors. After selecting the MODE switch position
for your particular application, proceed as follows:
1. Display the waveform over as large a portion (vertically)
of the crt as possible by adjusting the appropriate
VOLTS/CM switch.
3. Multiply the vertical distance between the two points by
the setting of the appropriate VOLTS/CM switch and by
the attenuation factor, if any, of the probe. This is the
voltage between the two points of the waveform.
Fig. 2-4. Measuring peak-to-peak voltage.
As an example of this method, assume that using a 10X
probe and a VOLTS/CM switch setting of .02, you measure
a vertical distance of 4 centimeters as shown in the illustra
tion. In this case, 4 centimeters times 0.02 volt/cm results
in 0.08 volt. This voltage times the probe attenuation factor
of 10 results in the true peak-to-peak voltage of 0.8 volt.
DC level at some point on a signal. The method used
to measure the dc level at some point on a signal is virtu
ally the same as the method described for measurement
of peak-to-peak voltage. However, for dc-voltage measure
ments the M Unit MODE switch must be set to the DC
NORM, position. Also, dc voltages are measured with re
spect to some potential (usually ground).
To measure the dc level at some point on a signal with
respect to ground (see Fig. 2-5), proceed as follows:
1. Set the MODE switch of the channel to which the signal
will be applied to the DC NORM, position.
2. Set the corresponding VOLTS/CM switch such that the
expected voltage (at the channel input connector) is approxi
mately one to four times the setting of the switch. Make
sure the VAR. GAIN control is set to the CALIB. position.
3. Set the oscilloscope triggering controls to produce a
free-running trace.

Operating Instructions— Type M
Fig. 2-5. Measuring a voltage with respect to some reference.
4. Touch the oscilloscope probe tip to a ground point, and
with the appropriate POSITION control position the trace
so that it lies along one of the horizontal lines of the grati
cule, such as b in Fig. 2-5. This line will be used as a
ground reference line; its position in any given case will
depend upon the polarity and amplitude of the input signal
or dc level to be measured. Do not adjust the POSITION
control after the reference line has been established.
As an alternative method, you can set the oscilloscope
for automatic triggering and use the trace of an unused
channel as a reference. To do this, ground the probe tip
as described in step 4. Superimpose the trace of an unused
channel on the trace of the channel to which the signal
will be applied. After establishing the reference, do not
move the POSITION controls for these channels.
5. Remove the probe tip from ground and connect it to
the signal. Adjust the triggering controls for a stable dis
play.
6. Measure the distance, in centimeters, from the ground
reference line established in step 4 to the point at which
the dc voltage level is desired, such as between a and b
in Fig. 2-5.
7. Multiply this distance by the setting of the appropriate
VOLTS/CM switch and the attenuation factor, if any, of the
probe. This is the dc level of the point measured.
1. Apply a reference signal of known amplitude to channel
A and, with the corresponding VOLTS/CM switch and
the VAR. GAIN control, adjust the amplitude of the dis
play for an exact number of graticule divisions. Do not
move the VAR. G A IN control after you have obtained 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 sensitivity conversion factor.
Sens. Conv. Factor = Reference signal amplitude in volts
(Deflection in cm) (VOLTS/CM setting)
3. To calculate the true sensitivity at any setting of the
VOLTS/CM switch, multiply the VOLTS/CM switch setting
by the sensitivity conversion factor obtained in step 2.
True Sensitivity = (VOLTS/CM setting) (Sens. Conv. Factor)
True sensitivity values obtained for any setting of the A
VOLTS/CM switch apply only to this one channel, and
only as long as the VAR. G A IN control is not moved from
the position to which it was set in step 1.
As an example, suppose the voltage amplitude of the
reference signal applied to channel A is 30 volts, and the
VOLTS/CM switch setting is 5. The VAR. G A IN control is
adjusted to decrease the amplitude of the display to ex
actly 4 centimeters. With these values substituted in the
formula for Sensitivity Conversion Factor and True Sensitiv
ity, we have,
Sens. Conv. Factor = - = 1.5
(4) (5)
True Sensitivity = (5) (1.5) = 7.5 volts/cm
As proof that the true sensitivity value thus obtained
is correct we can take the product of 7.5 volts/cm and 4
centimeters of deflection. The result is 30 volts, which
checks with the known amplitude of the reference voltage.
To make a comparison measurement, for example, sup
pose that a signal of unknown peak-to-peak amplitude is
applied to channel A in place of the 30-volt reference
signal. Suppose also that a signal to be compared causes
a deflection of 2.7 centimeters at a VOLTS/CM switch set
ting of 2. Then the peak-to-peak amplitude of the signal
can be determined as follows:
As an example, suppose the vertical distance between a
and b is 4 centimeters when a 10X probe is used and the
VOLTS/CM switch is set to .5. Multiply the distance be
tween a and b (4 cm) by the VOLTS/CM setting (.5 volt/
cm) and by the probe attenuation ratio (10). This shows the
peak voltage level of the waveform with respect to ground
to be 20 volts.
P-P Signal Amplitude = (Sens. Conv. Factor) (Deflection
in cm) (VOLTS/CM setting)
Substituting values just given we have
P-P Signal Amplitude = (1.5) (2.7) (2) = 8.1 volts
Phase Measurements
Voltage comparison measurements. For some appli
cations you can establish a set of sensitivity values other
than those selected by the VOLTS/CM switch. This is use
ful for comparing signals with a given reference. The fol
lowing procedure describes how to set sensitivity values
for channel A. The same procedure can be used for the
other channels.
To establish a set of sensitivity values based upon a
specific reference amplitude, proceed as follows:
Phase comparisons of two to four signals of the same
frequency can be made by making use of the multi-trace
feature of the Type M Plug-In Unit. To make phase com
parisons, proceed as follows:
1. Apply the reference signal to channel A; apply the sig
nals to be compared to the other channels.
2. Connect a test lead between the "A ” SIGNAL OUT
connector on the M Unit and the External Trigger input
2-6

Operating Instructions— Type M
on the oscilloscope. Set the oscilloscope for external-
triggered sweep operation.
3. Set the MODE switches to AC or DC NORM, depending
on the type of coupling desired.
4. Set the ALTERNATE/CHOPPED switch to the ALTERNATE
or CHOPPED position. In general, the ALTERNATE position
is more suitable for high-frequency signals and the
CHOPPED position is more suitable for low-frequency sig
nals.
5. Set the VOLTS/CM switches for the desired display am
plitude. Carefully center the signals vertically using the
POSITION controls.
6. Set the oscilloscope time-base controls (includes the
Variable Time/Cm control) so that one cycle of the ref
erence signal occupies exactly 9 centimeters horizontally.
Thus, each centimeter represents 40° of one cycle at this
time-base setting (see Fig. 2-6).
Phase Angle = (Channel B, C, or D distance in cm) X (4 0°)
Fig. 2-6. Measurement of phase angles between electrical wave
forms.
7. Measure the horizontal distance, in centimeters, between
corresponding points on the reference waveform and
each of the other waveforms. Note the distance for each
channel and whether it is leading or lagging. To make
each phase comparison measurement easier, switch the non-
applicable waveforms off by setting the appropriate MODE
switches to the OFF position until you need to display them.
8. For each distance measured, multiply the distance by
40° per centimeter to obtain the phase difference com
pared to the reference waveform.
For more precise measurements, you can increase the
vertical sensitivity and the sweep rate established in steps
5 and 6, but do not change the setting of the oscilloscope
Variable Time/Cm control. However, when you increase the
sweep rate, you must consider this in your calculations.
For example, if you increase the sweep rate by a factor
of 5, and then measure the distance between waveforms,
each centimeter will represent 8° (40° -H 5) of a cycle.
By doing this, you can measure phase angles up to 80°
more accurately. When preparing to make the measure
ment, horizontally position the waveforms to points where
the graticule markings aid in determining the exact dis
tance. Fig. 2-7, for example, shows how the phase angle
of channel B waveform can be computed using this method.
Other phase-angle measurements can be determined using
the same basic procedure.
Phase Angle = (Channel B distance in cm) X (8°)
Fig. 2-7. Computing the phase angle when the oscilloscope 5X
magnifier is on. Accurate phase-angle measurements within a
range of 8 0 ° can be made using this method.
Time-Delay Measurements
The calibrated sweeps of Tektronix oscilloscopes cause
any horizontal distance on the screen to represent a definite
known interval of time. Using this feature in combination
with the multi-trace feature of the M Unit, you can measure
the time lapse or delay between events displayed on the
oscilloscope screen. This is done by the following method:
1. Follow the procedure outlined in the first five steps
of "Phase Measurements” .
2. Set the oscilloscope time-base controls for a calibrated
sweep rate which will allow you to accurately measure the
distance between waveforms.
3. Using the graticule, measure the horizontal distance
between the reference waveform and each of the other
waveforms. For most measurements the distance is usually
measured between 50% amplitude points on the rising
portion of the waveforms. To make the measurements be
tween waveforms easier, switch off the waveforms not
being measured.
4. Multiply the distance measured for each channel by the
setting of the oscilloscope Time/Cm control to obtain the
time interval. (Divide the apparent time interval by the
magnification factor if sweep magnification is used.)
T. _ . Time/Cm switch setting X Distance in cm
Time Delay = -------------
- -------------- —— ; ----------------
Sweep magnification
2-7

Operating Instructions— Type M
For example, assume that the Time/Cm switch setting is
2 ,usec, the Magnifier is set for 5X magnification, and you
measure a horizontal distance of 5 centimeters between the
leading edge of the reference waveform and the leading
edge of the waveform displayed on another channel. For
these conditions, 5 centimeters multiplied by 2 microseconds
per centimeter results in an apparent time delay of 10
microseconds. The apparent time delay divided by 5 then
results in an actual time delay of 2 microseconds.
Channel A Signal Output Amplifier
The two-stage transistorized Channel A Signal Output
Amplifier contained in the M Unit is designed primarily for
use as an external trigger source using the channel A input
signal. However, it can be used as a convenient, built-in,
dc preamplifier for channels B, C or D when used within its
capabilities.
As a dc low-level preamplifier, the Channel A Signal
Output Amplifier has a gain of approximately 100 when
referred to the signal amplitude at the channel A input
connector. It has a bandpass of dc to 590 kc at —3 db
when working into an approximate impedance equivalent
to 10 megohms paralleled by 50 pf. This impedance is
equivalent to the following: a patch cord connected be
tween the “ A" SIGNAL OU T connector and the oscilloscope
external trigger input connector (also serves to trigger the
sweep), and a Tektronix P6017 Probe connected with the
cable end to the channel B, C, or D input connector and the
tip to the "A " SIGN AL O UT connector. Beyond 590 kc
the frequency response of the amplifier rolls off gradually.
If the preamplifier is used to drive one of the channels
directly, such as the case of a short patch cord substituted
for the probe, it has to drive a capacitance of 82 pf. The
bandpass of some M Units, when checked using this setup,
was reduced to about 450 kc.
Other characteristics to consider are noise level, dc
drift, and for sufficient signal to drive the oscilloscope
external trigger input connector. The noise level at the
“ A" SIGN AL OUT connector is equivalent to about a 20-
millivolt peak-to-peak input signal. Noise level and dc
drive are tolerable if a sensitivity less than 500 /tvolts/cm
is used. However, reliable triggering cannot be obtained
unless the external trigger amplitude approaches or ex
ceeds the minimum required amplitude of 0.2 volt.
As an example of this application, assume that a 2-
millivolt calibrator signal is applied to the channel A
input connector. This signal is amplified about 100 times
by the Channel A Signal Output Amplifier, producing an
amplitude of 200 millivolts at the "A " SIGN AL OUT con
nector. Then patch cords are connected from the “A ”
SIGNAL OUT connector to both the channel B input
connector and the oscilloscope trigger-input connector, to
apply the 200-millivolt signal to both points. The A VOLTS/
CM switch is set to .02 and the B VOLTS/CM switch to .05.
The B VAR. G A IN control is adjusted so that the waveform
is exactly four centimeters in amplitude. This makes the
calibrated B VOLTS/CM switch settings equivalent to their
indicated value divided by 100. For the .05 setting, in this
example, the sensitivity is 500 juvolts/cm.
If a probe is substituted in place of the patch cord to
the channel B input connector, the calibrated B VOLTS/CM
switch settings are equivalent to their indicated value
divided by 10 or a maximum usable sensitivity of 2 milli-
volts/cm can be obtained.
When the B VOLTS/CM switch is set to .05 and patch
cords are connected as described earlier, the noise ampli
tude equals about 20 millivolts on the 200-millivolt channel-B
waveform. When the B MODE switch is set to one of its
DC positions, you may have trouble positioning the wave
form onto the crt using the B POSITION control unless the
OUTPUT DC LEVEL control (an internal adjustment in the
M Unit) is adjusted to a more exact setting. If this control
needs to be adjusted, refer to step 17 in the Calibration
portion of the manual. If ac coupling is used, exact ad
justment of the OUTPUT DC LEVEL control is not necessary.
2-8

IN I 3
AMPLIFIERS
Introduction
The M Unit consists of four identical input amplifiers, a
common output amplifier, and a signal-out amplifier for
channel A. Since the input amplifiers are identical, the
following description applies to all. Throughout the circuit-
description discussion, you should refer to the block and
circuit diagrams located near the back of this manual.
Input Coupling
The signal to be displayed is applied to the input cathode
follower V5323 through one section of the MODE switch
(SW5300, IF) and the VOLTS/CM switch (SW5310). In the
DC positions of the MODE switch, input coupling capacitor
C5301 is bypassed with a direct connection. In the AC posi
tions the signal must pass through C5301 so the dc com
ponent of the signal is blocked. In the OFF position the
signal is disconnected.
Input Attenuation
The M Unit requires an input signal of 0.02 volt, peak-
to-peak, to produce one centimeter of calibrated deflection
on the crt. In order to satisfy this condition, and to make
the instrument applicable to a wide range of input voltages,
precision attenuation networks can be switched into the
input circuitry by means of the VOLTS/CM switch SW5310.
The voltage-attenuation ratios of these networks are X21/2,
X5, X10 and X100.
When the VOLTS/CM switch is in the .02 position, the
signal is coupled without attenuation to the Input Cathode
Follower, V5323. For the other settings of the VOLTS/CM
switch, the attenuation networks are switched into the cir
cuit, either singly or in tandem pairs, so that the input
voltage to V5323 is always 0.02 volt for each centimeter of
crt deflection when the VAR. G A IN control R5326 is set
to the CALIB. position.
The attenuators are frequency-compensated voltage
dividers. For low-frequency signals they are resistive
dividers, and the degree of attenuation is proportional to
the ratio of the resistances. This is because the impedance
of the capacitors, at low frequencies, is high and their
effect in the circuit is negligible. As the frequency of the
input signal increases, however, the impedance of the
capacitors decreases and their effect in the circuit becomes
more pronounced.
For high-frequency signals the impedance of the capaci
tors is low, compared to the resistance of the circuit, and
the attenuators become capacitive voltage dividers. For
these frequencies, the degree of attenuation is inversely
proportional to the ratio of the capacitances. A variable
capacitor in each attenuator (for example, C5308C in the
X2V2 attenuator) provides a method for adjusting the capaci
tance ratios equal to the resistance ratios.
The variable capacitor at the input to each attenuator
(for example, C5308B in the X2'/2 attenuator) provides a
means for adjusting the input capacity of the attenuator to
a standard value of 47 picofarads. Similarly, C5317 pro
vides a method of standardizing the input capacity when
the VOLTS/CM switch is in the .02 position. In this manner,
the probe, connected to the input connector, works into the
same input capacity regardless of the setting of the VOLTS/
CM switch. In addition to providing the same input capac
ity, the resistance values in the attenuators are chosen to
provide the same input resistance (1 megohm) for each
setting of the VOLTS/CM switch.
Input Amplifier
The Input Amplifier consists of two stages: Input Cathode
Follower V5323 and the Paraphase Amplifier Q5324/Q5334.
Input Cathode Follower V5323. This stage employs a
Nuvistor which is essentially a subminiature triode. Nuvistor
V5323 presents a high-impedance, low-capacitance load to
the input circuit and isolates the input circuit from the suc
ceeding stages. The cathode of V5323 is long-tailed through
R5323 to the — 150-volt supply. With this configuration
stable gain is obtained, and large input signals can be
handled without distortion.
C5318 and R5318 form a protection circuit in the grid
circuit of V5323. These components prevent excessive grid
current from V5323 in case a positive-going overload signal
is inadvertently applied to the input connector. Positive
going signals passing through V5323 are prevented from
damaging Q5324 by protective diode D5324. Negative
going signals cannot damage Q5324 because current flow
in the transistor is limited to about 3 ma. R5316 and R5319
in the grid circuit of V5323 are parasitic suppressors.
Paraphase Amplifier Q 5324/Q 5 33 4. This stage is a
transistorized, emitter-coupled amplifier. In addition to
amplifying the signal, the stage converts the single-ended
©3-1

Circuit Description— Type M
input signal at the base of Q5324 to a push-pull output
signal between the two collector circuits. Push-pull gain
of the stage is approximately 2.2. Both emitters are long
tailed (through R5325 and R5335) to the + 100-volt supply
for greater stability with respect to transistor parameters and
temperatures.
There are two gain controls located in the common-
emitter circuit of the Paraphase Amplifier. One is the VAR.
GA IN control R5236 and the other is GA IN ADJ. control
R5336, a front-panel screwdriver-adjust potentiometer. Both
controls vary the emitter degeneration and thus affect the
gain of the stage. The GAIN ADJ. is adjusted so that the
amount of crt deflection agrees with the setting of the
VOLTS/CM switch when the VAR. G AIN control is set
to the CALIB. position.
The DC BAL. control R5332, a front-panel adjustment, is
used to adjust the dc level of Q5334 so that its emitter
will be at the same voltage as the emitter of Q5324 when
no input signal is applied to the unit. With the emitters
at the same voltage there will be no current through the
VAR. GAIN control. With this configuration an adjustment
of the>VAR. G A IN control will not affect the dc level in the
collector circuit of the Paraphase Amplifier stage, and will
therefore not affect the positioning of the beam.
Collector loads R5324 and R5334 develop the output
signal of Q5324 and Q5334. The output signal is push-pull
and is applied to a gate consisting of four diodes— D5345,
D5347, D5346 and D5348. During multi-trace operation
a positive-going gating pulse is applied to the junction
of R5345 and R5347. The pulse at this junction causes the
diodes to conduct and the push-pull signal passes from the
Input Amplifier, through the diode gate and MODE switch
contacts, to the Output Amplifier.
If the MODE switch is set to either the AC- or DC-NORM.
position, the signal passes through the diode gate and
MODE switch directly to the Output Amplifier to produce
a normal display on the crt. However, when the MODE
switch is set to either the AC- or DC-INV. position, the
switch reverses the signal-grid connections of V5364 and
V5374 and inverts the displayed waveform. When the
MODE switch is set to the OFF position, the Input Ampli
fier is disconnected from the Output Amplifier and no
signals pass through the diode gate.
When all MODE switches are set to O FF, diodes D5360
and D5370 clamp the grids of V5364 and V5374 near
ground, preventing the grids from moving toward — 150
volts. In addition, the diodes provide a very convenient
method for checking the dc balance of the Output Ampli
fier. With all MODE switches in the OFF position the grids
are essentially connected together.
Vertical Positioning
The POSITION control, connected between R5341 and
R5343, changes the current through collector load resistors
R5324 and R5334. With the control centered, the current
through each load resistor, under no-signal conditions, is
the same. When the control is moved to either end, a
change of 2 ma per side occurs. This current change re
sults in a positioning voltage range of approximately 300
millivolts at the transistor collectors. The voltage range
corresponds to about ± 1 0 centimeters positioning range
at the crt since direct coupling is employed.
Output Amplifier
The Output Amplifier, which is a common amplifier for
all channels, consists of two stages: Push-Pull Amplifier
V5364/V5374 and Output Cathode Follower V5383.
Push-Pull Amplifier V 53 64/V 5374. The Push-Pull Am
plifier stage provides a total gain of about 5 for signals
and dc-positioning voltages that arrive when the diode gate
for the operating channel is gated “on'1 by the switching
pulse from the Ring Counter. The gating pulse itself is not
amplified because it is common mode and cancels out in
the cathode circuit of the stage.
Static current drain in this stage is about 6 ma per side;
1.5 ma is screen current and 4.5 ma is plate current. Static
plate voltage is about 65 volts.
Peaking inductors L5360 and L5370 provide necessary
high-frequency compensation in the grid circuits of the stage.
In the plate circuits variable inductors L5363 and L5373
compensate the stage for high-frequency attenuation caused
by the tube and stray capacity. The m-derived sections of
the variable inductors provide a means for adjusting the
stage for optimum transient response.
A position range network consisting of R5377, R5378 and
R5365 in the cathode circuits of this stage cancel any static
imbalance for centering the traces. With the VERT. POS.
RANGE control, R5378, all traces can be made to coincide
as a group with the vertical system electrical center. Range
of the VERT. POS. RANGE control is about 200 mv at each
grid of V5383, equal to about a 4-centimeter change in
trace position, 8 centimeters push-pull.
Output Cathode Follower V5383. The Output Cathode
Follower stage operates much the same as the Input Cathode
Follower stage. That is, it provides a high-impedance, low-
capacitance load to the Push-Pull Amplifier stage, and a
low-impedance driving source for the capacitance of the
inter-connecting plug and the input of the main vertical
amplifier in the oscilloscope.
Peaking coils L5384 and L5386 form a series-peaking
circuit with the stray capacitance in their respective circuits.
These peaking circuits are damped by the cathode im
pedance of each side of V5383. Due to the fairly large
cathode resistors (9.1 k) employed, the cathode impedance
is approximately equal to the reciprocal of the transconduc
tance of the tube (1 / G m). By varying the current through
the tube, the H.F. PEAKING control can vary the transcon
ductance, thereby varying the effect of the peaking circuits.
Channel A Signal Output Amplifier
The Channel A Signal Output Amplifier Q5344 and Q5354
is a two-stage transistorized auxiliary amplifier for channel
A only. It provides a dc-coupled signal obtained from
channel A for external triggering purposes, particularly
for use during multi-trace operation in the CHOPPED mode.
3-2

Circuit Description— Type M
The signal is taken from the junction of R5326 and R5327
located in the common-emitter circuit of Q5324 and Q5334.
The R5326-R5327 junction is a convenient low-impedance
point for extracting the signal without affecting the M-Unit
bandwidth or picking up switching transients.
With the VAR. G A IN control set to the CALIB. position,
the signal amplitude at the junction is about 80% of that
at the grid of V5323. At the base of Q5344, the signal am
plitude decreases to about 60% of that at the grid of
V5323. The gain of the Channel A Signal Output Ampli
fier is about 160; Q5344 has a gain of approximately 10
and Q5354 has a gain of about 16. The overall gain of
160 results in an output signal of approximately 2 volts at
the “ A ” SIGNAL O U T connector for each centimeter of
vertical deflection on the crt. Capacitor C5357, located in
the emitter circuit of Q5354, provides high-frequency peak
ing for optimum transient response. Bandwidth of the am
plifier is dc to about 1 me (3 db down), and the rolloff is
long and gradual.
The OUTPUT DC LEVEL control R5354 is the current
source for adjusting and matching the dc level at the "A ”
SIGN AL O UT connector to the level at the channel A input
connector. Normally, when making the adjustment, the A
input connector is grounded and the OUTPUT DC LEVEL
control is adjusted to obtain a voltmeter reading of zero
at the “ A ” SIGN AL O UT connector. This control com
pensates for variations between Nuvistors and the effects
of tube aging. The high gain of the Channel A Signal
Output Amplifier and the relatively wide variation in trans
conductance between Nuvistors makes the control some
what sensitive. Therefore, the control should be adjusted
carefully when matching dc levels. Exact zero volts is
difficult to obtain and a setting within a few hundred milli
volts of zero is adequate for triggering purposes. How
ever, if this amplifier is used as a dc preamplifier, the
control has to be adjusted more carefully for a setting less
than a few hundred millivolts from zero.
SWITCHING CIRCUIT
Ring Counter
The Ring Counter consists of Q6315, Q6325, Q6335 and
Q6345 and associated circuitry. Each transistor controls
one Input Amplifier channel. The Ring Counter is tetra-
stable; that is, each of its four states is stable and a trigger
from the Switching B.O. Q6350 during multi-trace operation
is required to make it switch channels. When triggered,
the Ring Counter performs the task of sequencing and gat
ing the Input Amplifiers.
When only one channel is on (single-trace operation),
Q6350 is inoperative and the Ring Counter remains switched
on or “ locked" on the one channel, keeping it on. When all
channels are turned off (all MODE switches set to OFF), the
Ring Counter is in a quiescent state.
In the following discussion the Ring Counter is described
under four modes of operation. These are: (1) all channels
off, (2) single-trace operation, (3) alternate multi-trace
operation, and (4) chopped multi-trace operation.
(1) All channels off. With all MODE switches set to
the OFF position, the Ring Counter is placed as close as
possible to a quiescent or static condition. All transistors
in the Ring Counter are reverse-biased except the one that
is switched off last. Assume for this discussion that the
channel A MODE switch was set to the OFF position last.
The base voltage for each transistor is determined by a
matrix of three 10.1-k resistors located in each base circuit.
Matrix currents through R6310, R6320, R6330, R6340 and
R6360 hold all bases at about + 6.5 volts. The common
emitter bus is held at about + 6.8 volts by the emitter cur
rent of Q6315 (channel A turned off last). The collector
bus rests at about —7 volts by the current drawn by Q6315
and the matrix circuits.
The voltage at the collector of Q6315 is held at about
+ 3.7 volts by the current through Q6315; the remaining
collectors are held at about — 1.4 volts. With three tran
sistors cut off, the — 1.4 volts at the collectors of these
transistors reverse bias their D5345/D5347 diodes. Chan
nel A diodes D5345 and D5347 are forward biased by the
+ 3.7 volts at the collector of Q6315, but no signals are
passed since the MODE switch is set to OFF.
(2) Single-trace operation. When the channel A
MODE switch is turned on, the voltage at the base of
Q6315 decreases from about +6.5 volts to about +5.9
volts since the base is no longer connected to R6310. Cur
rent through Q6315 increases slightly, causing the collector
voltage to change from + 3.7 volts to about + 4 volts.
The voltage at the other collectors remains at about — 1.4
volts and the common collector bus drops slightly to about
—6.9 volts. The diode gate for channel A, being forward
biased, couples the channel A signal from the Input Am
plifier through the MODE switch to the Output Amplifier.
The diode gates for the other channels remain reverse
biased.
Total collector current for Q6315 is about 9 ma . . . 5 ma
through R6317 and 4 ma through the channel A diode
gate. The total current through R6316 is the sum of the
base and collector current of Q6315.
Matrix currents through R6320, R6330, R6340 and R6360
reverse bias D6360 and forward bias D6352. D6352 sets
the base level of Q6364. Transistor Q6350 is clamped into
cutoff by emitter current through Q6364, thus preventing
the Switching B.O. from operating. This same action also
occurs when all channels are off, assuming that Q6315 is
the conducting transistor.
Resistors R6319, R6329 and R6339 are series-connected
parasitic suppressors. During single-channel operation, they
prevent the conducting transistor in the Ring Counter from
oscillating. This is accomplished by providing ample resist
ance in the feedback path existing from the collector of
the conducting transistor through the MODE switches and
back to the base of the same transistor.
(3) Alternate multi-trace operation. When two or
more MODE switches are turned on, Q6350 is biased so
that it can be triggered. (Biasing of Q6350 is explained in
the subsequent description of the Switching B.O.) In the
ALTERNATE position of the ALTERNATE/CHOPPED switch,
the trigger to drive Q6350 is obtained by applying the
sync trigger from the oscilloscope time-base generator via
3-3

Circuit Description— Type M
pin 16 of the interconnecting plug to the collecter circuit
of Q6350. The trigger is regenerated by the blocking
oscillator action of Q6350, differentiated by C6352, and
applied to the common-emitter bus in the Ring Counter.
The negative-going regenerated trigger, when applied to
the emitter bus, drives all emitters in the negative direction.
Since only one transistor in the Ring Counter conducts at
any given time, it is the only one affected by the trigger.
If Q6315 is the conducting transistor when the regenerated
trigger is applied to the emitter bus, the collector current
of Q6315 is sharply reduced and the collector voltage goes
quickly negative, producing a fast, negative-going collector
pulse. This pulse is then coupled through "speed-up" capaci
tor C6317 and the channel A MODE switch contacts to the
base of Q6325. The pulse is also coupled through the
matrix resistors to the bases of the other transistors in the
Ring Counter. The pulse applied to the other bases is of
much lower amplitude and is not significant. However, the
larger and faster pulse applied to the base of Q6325 drives
Q6325 into conduction and a 6-volt positive-going gating
pulse is produced at its collector. The gating pulse is ap
plied to channel B diode gate and turns it on for the dura
tion of the gate pulse.
Due to the matrix action, the positive-going gate pulse
at the collector of Q6325 is coupled to the bases of the
other transistors, tending to hold them in cutoff and com
pleting the cutoff of Q6315. As stated previously, in multi
trace operation the trigger from Q6350 is required to make
the transistors switch states. When the transistors in the
Ring Counter switch states, they always switch in sequence,
regardless of the setting of the ALTERNATE/CHOPPED
switch. The important components that make sequential
switching possible are “ speed-up" capacitors C6317, C6327,
C6337 and C6347. It is these capacitors that provide the
means for coupling the pulse from the “on" transistor to the
base of the following transistor in a sequential order. If
a MODE switch is set to OFF, during multi-trace operation,
the transistor controlled by the MODE switch is bypassed
and excluded from the switching cycle.
(4) Chopped multi-trace operation. When the ALTER
NATE/CHOPPED switch is set to the CHOPPED position and
two or more channels are on, the Switching B.O. Q6350
becomes a trigger generator by operating in a free-running
mode at a rate of approximately 1 me. The 1-mc triggers
generated by Q6350 drive the Ring Counter. Operation of
the Ring Counter in this mode is the same as its operation
in the multi-trace alternate mode.
Switching Blocking Oscillator
The Switching Blocking Oscillator (Switching B.O.) Q6350,
during single-trace operation,. is inoperative to allow the
desired channel to remain "locked on". During multi-trace
operation, Q6350 operates in a triggered mode when the
ALTERNATE/CHOPPED switch is set to ALTERNATE, and in
a free-running mode when set to CHOPPED.
The diodes in the Switching B.O. and Chopped Mode
Blanking Amplifier circuitry are important to circuit opera
tion during the various modes of operation. Table 3-1 lists
the bias conditions of the diodes for all modes. This table
may also be used as a troubleshooting aid when it is nec
essary to locate the cause of trouble in these circuits. Since
these circuits are interrelated, description of the Chopped
Mode Blanking Amplifier Q6364 is included where necessary.
TABLE 3-1
Diode Bias Conditions
Single-Trace Operation Multi-Trace Operation
Diode Alternate Chopped Alternate Chopped
D6360 Reverse Reverse Forward Forward
D6352 Forward Forward Reverse Reverse
D6364 Reverse Forward Reverse Forward
D6368 Forward Reverse* Forward Reverse*
* When the M Unit is used with single-beam oscilloscopes or
with the Type 555. When the M Unit is used with another multi
trace unit in a Type 551, D6368 is forward biased when the
other plug-in unit operates in the alternate mode.
(1) Single-trace operation. Assume all channels are
on and that channels B, C, and D are about to be turned
off. When the MODE switch for channel B is set to OFF,
approximately 0.5 ma matrix current flows through R6320
(see Fig. 3-1). When channel C and D MODE switches are
set to OFF, total current flowing from R6320, R6330 and
R6340 is about 1.4 ma. The total current is enough to starve
the current path through D6360. Diode D6360 reverse biases
and unclamps the junction where it is tied to R6360. Re
sistor R6360 is "long-tailed" to the + 225-volt supply so that
the current through it remains the same regardless of the
operating mode.
When D6360 reverse biases, the voltage at the junction
of D6360 and R6360 drops from about 12.9 volts to about
12.2 volts. The voltage decrease causes diode D6352 to
conduct. The drop across D6352 and that across the base-
emitter junction of Q6364 essentially cancel. Q6364 emitter
current flowing through R6354 sets the emitter level for
Q6350. Under these conditions, Q6350 is cutoff and will
not operate, regardless of the setting of the ALTERNATE/
CHOPPED switch. Thus, chopping-rate switching transients,
which might interfere with the usefulness of single-trace
displays, cannot occur, and triggers are not generated.
(2) Multi-trace triggered operation. When the
ALTERNATE/CHOPPED switch is set to ALTERNATE, one
side of the switch connects pin 8 of the interconnecting
plug to ground, which grounds R6368 and the cathode of
the oscilloscope sync amplifier. The sync amplifier dif
ferentiates and amplifies the positive-going sync trigger
generated by the oscilloscope sweep-gating multivibrator at
the end of each sweep cycle. The negative-going sync
trigger produced at the plate of the sync amplifier is ap
plied through pin 16 of the interconnecting plug to the
junction of R6367 and C6364, located in the collector circuit
of Q6364.
The other side of the ALTERNATE/CHOPPED switch dis
connects divider resistors R6365 and R6366 from the emitter
circuit of Q6350. The divider is now connected to the
switch end of R6367 to supply an operating potential for
the oscilloscope sync amplifier. Since the divider is discon
nected from the emitter circuit of Q6350, current through
R6355, R6353, R6354 and Q6364 determines the emitter
level of Q6350.
3-4

Circuit Description— Type M
Fig. 3-1. Simplified diagram of the Switching B.O and Chopped Mode Blanking Amplifier when the ALTERNATE/CHOPPED switch is set
to ALTERNATE. Currents, voltages and waveforms are shown for single-trace operation. (During single-trace operation the Switching B.O.
does not operate, and no triggers are generated. No waveforms are shown for the CHOPPED position because none occur.)
When more than one channel is turned on, matrix currents
to R6360 decrease. Diode D6360 becomes forward biased
and supplies the current path to R6360 (see Fig. 3-2). The
voltage at the junction of D6360 and R6360 rises from
about +12.2 volts to about +12.9 volts and reverse biases
D6352. The clamping action of Q6364 holds Q6350 cutoff.
The sync trigger, applied to the R6367/C6364 junction,
is coupled through C6364, R6364 and C6351 to the col
lector circuit of Q6350. The sync trigger is not applied
to the collector of Q6364, however, because D6364 is re
verse biased. To provide a load and a complete circuit
for Q6364 during alternate operation, the collector of Q6364
ties to R6368 by forward biasing D6368. The switch end
of R6368 connects to ground through the ALTERNATE/
CHOPPED switch.
With the negative-going sync trigger applied to the
collector circuit of Q6350, current flows through T6350
primary and into C6350. The varying magnetic flux in the
primary induces a negative-going voltage at the base of
Q6350 and starts the blocking oscillator action. This action
continues until Q6350 is driven into saturation and collector
current ceases to increase. Toroid T6350 field collapses
3-5

Circuit Description— Type M
* A S S U M E ; T H I S 1 2 .6 V S U P P L Y
I S L X A C T L Y 1 2 . 6 V
Fig. 3-2. Simplified diagram of the Switching B.O. and Chopped Mode
for four-trace alternate operation.
around the secondary, driving the base in a positive direc
tion in excess of that needed to turn off the transistor. The
base and emitter return to their original level and transistor
Q6350 remains cut off until the next sync trigger arrives to
repeat the cycle.
The signal at the emitter of Q6350 is a single regenerated
negative-going pulse that occurs each time the sync trigger
from the oscilloscope is applied to the Q6350 collector
circuit. This regenerating of the sync triggers standardizes
the varying size and shape of the sync triggers originating
from various types of oscilloscopes. The regenerated trigger
becomes a sharp negative-going spike when coupled
Blanking Amplifier. Currents, voltages and waveforms are shown
through C6352 and is easily handled without jitter by the
Ring Counter.
(3) Free-running operation. The Switching B.O. free
runs when two or more channels are on and the ALTER-
NATE/CHOPPED switch is set to CHOPPED. When the
switch is in this position, one side of the switch disconnects
pin 8 of the interconnecting plug from ground, disabling the
oscilloscope sync amplifier.
The other side of the ALTERNATE/CHOPPED switch dis
connects the R6365/R6366 divider from R6367 and connects
it to the emitter circuit of Q6350. Transistor Q6350 base-
3-6