Tektronix 546 User manual

I IN I S T R L J C T I 0 1 \ 1
MANUAL
Serial Number
Tektronix, Inc.
S.W. Millikan Way • . O. Box 500 • Beaverton, Oregon • hone Ml 4-0161 • Cables: Tektronix
Tektronix International A.G.
Terrassenweg 1A • Zug, Switzerland • H. 042-49192 • Cable: Tekintag, Zug Switzerland • Telex 53.574
364
070-367

WARRANTY
All Tektronix instruments are warranted
against defective materials and workman
ship for one year. Tektronix transformers,
manufactured in our own plant, are w ar
ranted for the life of the instrument.
Any questions with respect to the w ar
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. lease include the
instrument Type and Serial number with all
requests for parts or service.
Specifications and price change priv
ileges reserved.
Copyright © 1964 by Tektronix, Inc.,
Beaverton, Oregon. rinted 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.

CONTENTS
Section 1
W arranty
Characteristics
Section 2 Operating Instructions
Section 3Circuit Description
Section 4 Maintenance
Section 5 Calibration
Section 6arts List and Diagrams
A list of abbreviations and symbols used in this
manual will be found on page 6-1. Change
information, if any, is located at the rear of
the manual.

TYPE 546 OSCILLOSCOPE
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AC - n
TRIGGERING UVEl
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IN UT
TRIGGERING ------------ —
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TRIGG!RING lE Vft
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ASTIGMATISM
j n tin s i t y
TYPE 1A1 DUAL-TRACE RLUG-IN UNIT
_ ___________ -- CAU»*AUD
VAR IA Si I 1 "tAMR
VARIANT
TIME/CM or QUAY TIME Of I At-TIME m uitipuir
MO
VARIABLE
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OSITION
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TCRTROWl TW TIONIX INC. ORTLAND OREGON U.S.A.

SECTION 1
CHARACTERISTICS
Introduction
The Type 546 Oscilloscope is a versatile laboratory instru
ment designed for use with all Tektronix letter-series plug-in
units. The instrument features two identical time-base gen
erators. The two time-base generators can be used singly
or in "delaying" and "delayed" sweep operation for highly
accurate time-differential measurements.
the display in fixed steps of 2X, 5X, and
10X. Sweep-rate accuracy is within 5%.
Trigger Source Internal, internal plug-in, external and line.
Selection
Trigger Coupling Dc, ac and ac low-frequency rejection.
Selection
Vertical Deflection System
The plug-in unit and probe used with the Type 546 deter
mine the overall characteristics of the vertical deflection sys
tem. Refer to Table 1-1 for the characteristics.
S eep Generation
Trigger features and sweep rates of both Type 546 time-
base circuits are identical.
Sweep Rates
(at IX
magnification)
Sweep
Magnification
0.1 /xsecond/cm to 5 seconds/cm in 24
calibrated steps. Displayed sweep-rate ac
curacy is ±2% for both sweeps. An un
calibrated variable control of sweep rate
permits either sweep to be slowed to no
more than 40% of the indicated rate.
Any sweep rate can be increased by hori
zontal expansion of the center portion of
Trigger Signal Internal (ac): Minimum deflection is 2 mm,
rising to 1 cm at about 50 me.
Requirements Internal (dc): Minimum deflection is 5 mm.
Internal (ac low-frequency rejection): Min
imum deflection is 2 mm with signals at
about 2 kc, rising to 1 cm at about 50 me.
External: Frequency ranges are the same
as internal. Minimum amplitude is: 200
mvolts, peak-to-peak, (ac), 200 mvolts,
change in dc level (dc) and, 200 mvolts
peak-to-peak (ac low-frequency reject).
Maximum trigger level range is greater
than ± 2 volts with the TRIGGERING
LEVEL control pushed in and ±20 volts
with the control pulled out.
TABLE 1-1
PLUG-IN CHARACTERISTICS FOR THE
TYPE 546 OSCILLOSCOPE
LUG-IN
UNIT CALIBRATED DEFLECTION FACTOR BAND ASS RISETIME IN UT
CA ACITANCE
Type 1A1** 50 mv/cm to 20 v/cm
5 mv/cm dc to 50 me
dc to 28 me 7 nsec
12.5 nsec 15 pf
Type B 5 mv/cm to 0.02 v/cm
0.05 v/cm to 20 v/cm 2 cps to 12 me
dc to 20 me 30 nsec 18 nsec 47 pf
Type CA** 0.05 v/cm to 20 v/cm dc to 24 me 15 nsec 47 pf
Type D 1 mv/cm to 50 v/cm dc to 300 kc-2 me 0.18 xsec 47 pf
Type E 50 juv/cm to 10 mv/cm 0.06 cps to 20 kc-60 kc 6 ,usec 50 pf
Type G 0.05 v/cm to 20 v/cm dc to 20 me 18 nsec 47 pf
Type H 5 mv/cm to 20 v/cm dc to 15 me 23 nsec 47 pf
Type K 0.05 v/cm to 20 v/cm dc to 30 me 12 nsec 47 pf
Type L 5 mv/cm to 2 v/cm
0.05 v/cm to 20 v/cm 3 cps to 24 me dc to 30 me 15 nsec
12 nsec 20 pf
Type M** 0.02 v/cm to 10 v/cm dc to 20 me 17 nsec 47 pf
Type N* 10 mv/cm dc to 600 me 0.6 nsec 50Q
Input Z
Type O* 0.05 v/cm to 20 v/cm dc to 25 me 14 nsec 47 pf
Type Q* 10 /Astrain/cm to
10,000 /istrain/cm dc to 6 kc 60 jusec Adjustable
Type R* 0.5 ma/cm to 100 ma/cm
Type S* 0.05 v/cm and 0.5 v/cm
Type T Time-Base Generator lug-In Jnit
Type Z* 0.05 v/cm to 25 v/cm dc to 13 me 27 nsec 24 pf
♦Special feature plug-in units— see your Tektronix catalog for more information on any of the plug-in units.
♦♦M ultiple-trace plug-in units.
® l - l

Characteristics — Type 546/RM546
Sweep Delay The Time-Base A sweep can be delayed
by the Main Time Base (B) sweep. De
lay is continuously variable over the
range of 0.1 jusec to 50 sec with the DE
LAY TIME and DELAY-TIME MULTI LIER
controls. Delay time is accurate to ±1%
of indicated delay ± 2 minor divisions of
the DELAY-TIME MULTI LIER at sweep
rates from 50 fxsec to 50 sec. At delay
times shorter than 50 /csec, indicated de
lay accuracy is the same as above plus
approximately 75-100 nsec. The 75-100
nsec represents the fixed inherent delay
of the internal trigger circuitry of the
Type 546. Incremental delay accuracy is
± 2 minor divisions of the DELAY-TIME
MULTI LIER dial at sweep rates from 1
[xsec to 50 sec. Incremental accuracy at
the three fastest sweep rates (.1, .2, and
.5 [xsec) is ± 5 minor divisions. Stated
accuracies apply only when the VARI
ABLE controls are set to CALIB. Delay
jitter is no greater than 1 part in 20,000.
Horizontal Deflection System
The following characteristics apply when the HORIZONTAL
DIS LAY switch is set to the EXT positions.
Deflection Factor 0.1 volt/cm to 20 volt/cm; continuously
adjustable.
Frequency Dc to 400 kc (3-db down frequency).
Response
Input 1 megohm paralleled by approximately
Characteristics 55 pf.
Amplitude Calibrator
Output Voltages 0.2 millivolts to 100 volts, peak-to-peak, in
18 steps. In addition, a 100-volt dc output
is available.
Frequency
Risetime
Output Current
Output
Impedance
Approximately 1-kc square wave.
.2 mv-5 volts; .5 fxsec or faster. 10-100
volts; 1 /xsec or faster.
5 milliampere, 1-kc square wave available
at the front-panel current loop.
50 Cl in 0.2 to 200-millivolt positions. ro
gressively higher output impedances in the
.5- to 50-volt positions up to about 4 kQ
in the 50-volt position. Output impedance
of the 100-volt positions (ac and dc) is
about 420 Cl.
Amplitude eak-to-peak amplitude accuracy is within
Accuracy ±3% of indicated when working into an
impedance of 1 megohm or higher in the
.5 to 100 volt positions. When working
into a 50-ohm load, in the .2 to 200 mvolt
positions, output amplitude is one-half of
the indicated voltage. Nominal accuracy,
in this case, is ±3% —assuming the ex
ternal load impedance is an accurate 50
ohms. Accuracy of the current in the cur
rent loop is ±3% .
Front-Panel Output Signals
+GATE B Approximately a 20-volt, peak-to-peak,
square-wave pulse having the same dura
tion as the B sweep. Minimum load im
pedance is 5 kfi.
DLY'D TRIG Approximately a 10-volt peak-to-peak
pulse with a maximum duration of .5 /xsec
occuring at the end of the delay period.
SWEE A Approximately a 100-volt, peak-to-peak
sawtooth voltage having the same dura
tion as the A sweep. Minimum load im
pedance is lOOkQ.
±GATE A Approximately a 20-volt, peak-to-peak,
square-wave pulse having the same dura
tion as the A sweep. Minimum load im
pedance is 5 kn.
VERT SIG OUT Vertical signal output connector. Output
amplitude is approximately 0.4 volts per
centimeter of deflection on the crt. Rise
time is 20 nsec or faster. Output is ac
coupled.
External Single-
Sweep Reset
Input-Signal
Requirements
Requires a positive going step or pulse of
at least +20 volts with a risetime of 0.5
/xsec or faster.
Cathode Ray Tube
Type T5470-31-2
Unblanking Dc coupled
Accelerating 10 kv
otential
Deflection System Electrostatic
Useable 6 cm high by 10 cm wide
Viewing Area
Construction All glass, 5-inch, flat faced crt
Graticule Internal; adjustable edge lighting. 6 x 10
cm; with vertical and horizontal 1-centi
meter divisions with 2-millimeter markings
on the center-lines. rovision made for
risetime measurement.
Po er Supplies
Line Voltage 115 volts ±10% or 230 volts ±10%
Line Frequency 50-60 and 400 cps*.
ower
Consumption
Overload
rotection
About 510 watts
rimary of power transformer is fused and
a thermal relay is installed that interrupts
power in the event of over-heating.
♦W ith line frequencies of 400 cps, a special fan modification is
required; contact your local Tektronix Field representative.
1-2

Characteristics — Type 546/RM546
Cabinet and Chassis Construction
Cabinet Three piece, blue vinyl covered, textured
aluminum. Front panel is photo etched and
anodized. Cabinet dimensions are 13"
(w) x 24" (I) x 16%" (h).
Chassis
Net weight
Aluminum alloy.
653/4 pounds.
1-3

NOTES

SECTION 2
OPERATING INSTRUCTIONS
FUNCTION OF EXTERNAL CONTROLS
AND CONNECTORS
Time Base A Controls
TRIGGERING
LEVEL
TRIGGERING
MODE
SLO E
COU LING
SOURCE
TIME/CM
VARIABLE
Selects the amplitude point on the trigger
ing signal where sweep triggering occurs.
When the knob is pulled out, greater trig
gering range is offered for triggering on
higher amplitude trigger signals. With ac
coupling, the triggering circuit is most sen
sitive with the TRIGGERING LEVEL control
pushed in and set at 0.
AUTO STABILITY permits normal trigger
ing on signals with repetition rates higher
than about 20 cps. With no trigger signal,
or with a lower repetition rate, the time
base circuit free runs and provides a handy
reference trace. TRIG (triggered) permits
normal triggering on all triggering signals.
No trace occurs when the triggering signal
is removed.
Determines whether the time base is trig
gered on the negative-!—) or posifive-(+)
going slope of the signal.
AC position blocks any dc component of
the triggering signal and allows trigger
ing to take place only on the changing
portion of the signal. With frequencies
below about 30 cps, use the DC posi
tion. AC LF REJ position rejects trigger
signal frequencies below about 1.5 kc
allowing the trigger circuits to respond
to higher frequencies.
DC position permits triggering on both
high- and low- (to dc) frequency signals.
NORM position uses a version of the sig
nal applied to the vertical deflection plates
of the crt as a trigger signal.
LUG IN position applies to the Tektronix
Type 1A1 or a modified Type CA plug-in
unit when it is desired to trigger only on
the Channel 1 signal.
LINE position uses the line frequency sig
nal as a trigger.
EXT position is for external triggering on a
signal applied to the TRIGGER IN UT
connector.
Selects the sweep rate of Time Base A.
rovides an uncalibrated adjustment of
sweep rate. The sweep rate can be slowed
by a factor of at least 2.5X. An UNCALI
BRATED lamp lights to warn when the
VARIABLE control is not in the CALIBRATED
position.
Main Time Base (B) Controls
All controls of the Main Time Base (B) serve the same func
tion as the Time Base A controls with the exception of the
following additional control.
BRIGHTNESS Allows adjustment of the contrast or bright
ness ratio of the B trace compared to the
A trace.
HORIZONTAL
DIS LAY
READY LAM S
SWEE
MAGNIFIER
SINGLE SWEE
DELAY-TIME
MULTI LIER 1-10
The A position allows only Time Base A to
display on the crt.
The B position allows only the Main Time
Base (B) to to display on the crt. B INTENS
BY 'A' is one of the delayed sweep func
tions. In this position, a portion of the
Main Time Base (B) is intensified during
the time that Time Base A (the delayed
sweep) is in operation.
A DLY'D is one of the delayed sweep func
tions. In this position Time Base A is dis
played at the end of each delay period as
determined by the B TIME/CM OR DELAY
TIME and DELAY-TIME MULTI LIER
controls.
EXT XI and X10 positions permit an ex
ternal signal to be applied to the hori
zontal deflection circuit. Sensitivity is con
tinuously variable (with the VAR 10-1
control).
These light when the corresponding time-
base circuit is ready for triggering.
Expands the sweep from the center of the
graticule at any given setting of the TIME/
CM switch by the amount indicated.
ermits single sweep operation in all
modes of horizontal display except EXT.
Works in conjunction with the TIME/CM
OR DELAY TIME control of the Main Time
Base (B). Varies delay from 0.10X to
10.10X the time indicated by the Main
Time Base (B) TIME/CM OR DELAY TIME
switch.
HORIZONTAL
OSITION
VERNIER
AM LITUDE
CALIBRATOR
ositions the display along the horizontal
axis of the crt.
Determines the peak-to-peak voltage at
the CAL OUT connector.
5 mA Current rovides a calibrated source of square-
Strap wave current. The arrow shows direction
of conventional current flow (i.e. positive
to negative).
OWER SWITCH Toggle switch for turning the instrument
on and off.
INTENSITY Controls brightness of the display.
FOCUS Used in conjunction with the INTENSITY
and ASTIGMATISM controls for obtaining
a well-defined display.
2-1

Operating Instructions — Type 546/RM546
ASTIGMATISM
TRACE
ROTATION
SCALE ILLUM
Beam osition
Indicators
TRIGGER IN UT
(Time Base A)
HORIZ IN UT
TRIGGER IN UT
(Main Time
Base (B))
+GATE B
Used in conjunction with the INTENSITY
and FOCUS controls for obtaining a well-
defined display.
ermits horizontal alignment of the trace
with respect to the horizontal lines of the
graticule.
Varies illumination of the grid lines on
the internal graticule.
Four neon lamps with accompanying ar
rows indicate the direction when the dis
play is deflected out of the viewing area.
Connector for applying an external trigger
signal to Time Base A when its SOURCE
switch is set to EXT.
Jack for applying external horizontal sig
nal when the HORIZONTAL DIS LAY
switch is set to either XI or XI0 EXT.
Connector for applying an external trigger
signal to the Main Time Base (B) when its
SOURCE switch is set to EXT.
Supplies a 20-30-volt square-wave pulse
when the Main Time Base (B) is operating.
ulse duration is approximately 10.5X the
setting of the TIME/CM OR DELAY TIME
switch when the VARIABLE control is set
to CALIBRATED.
nsec or faster into a load of 1 k paralleled
by lOOpf. Duration of the pulse is the
same as the length of the B sweep. in D
is ground at all times.
+ 100 v
External delayed trigger input.
Amplitude: + 12 v, minimum
Risetime: 50 nsec or faster
ulse W idth: 1 f sec (typical)
Fig. 2-1. Method of coupling an external delayed trigger into the
Type 546.
NORMAL (NON-DELAYED)
SWEEP OPERATION
DLY'D TRIG
SWEE A
I GATE A
VERT SIG OUT
Chopped
Blanking Switch
(rear panel)
External Single
Sweep Reset
EXTERNAL
DELAY IN UT
(rear panel)
Supplies a sharp positive-going trigger
spike of about 10 volts at the end of the
delay period as set by the TIME/CM OR
DELAY TIME switch and the DELAY-TIME
MULTI LIER control.
Supplies the sawtooth voltage of TIME
BASE A. eak amplitude is about +100
volts.
Same as +GATE B except applies to
Time Base A.
Vertical signal output connector. Output
amplitude is approximately 0.4 volt per
centimeter of deflection.
rovides blanking of between-channel
switching transients when using multi-chan
nel plug-in units in the chopped mode.
Allows remote control of resetting in sin
gle-sweep operation. The sweep resets by
the momentary application of +20 volts
or more.
A four-pin connector is provided for an
external delay generator (rather than the
normal internal delay produced by the B
sweep). in A of the connector permits
disabling of the normal internal delayed
trigger and is the feed-in point for the
external delay trigger (see Fig. 2-1). in
B is normally dc open and ac ground
(through a 0.01 /if capacitor). in C sup
plies a B-gate pulse. ulse characteristics
are: +2 volts peak with a risetime of 50
S eep Triggering
roper sweep triggering is essential for a stable presenta
tion of an input signal. For a stable display, the sweep must
be triggered at the same time relative to the displayed
signal. Thus, the sweep must be triggered by the displayed
signal or by some external signal that has a fixed time rela
tionship with the displayed signal. The external trigger signal
must be the same frequency or a lower frequency multiple
of the input signal.
Selecting the Trigger Source
The SOURCE switches select one of a variety of possible
triggering signals. For most applications, the sweep can be
triggered internally from the displayed signal. This occurs
with the SOURCE switch set at NORM.
The LUG IN position is for plug-in units that will supply
a single-channel triggering signal through pin 5 of the inter
connecting plug such as the Tektronix Type 1A1 Dual-Trace
lug-In Unit. This position is useful when operating the plug
in unit in the dual-trace chopped-mode of operation since
the triggering signal is the same as the applied signal and
is free from any between-channel switching transients.
The LINE position of the SOURCE switch connects a line-
frequency signal to the triggering network. Line triggering
is useful whenever the input signal is related in frequency
to the line frequency.
To trigger the time base from an external signal, set the
SOURCE switch to EXT and connect the external trigger sig
nal to the TRIGGER IN UT connector. External triggering is
often used when signal tracing in amplifiers, phase-shift net
works, and wave-shaping circuits. The signal from a single
2-2 @

Operating Instructions — Type 546/RM546
2-3
Fig. 2-2. Effects of the TRIGGERING LEVEL and SLO E controls.

Operating Instructions — Type 546/RM546
point in the circuit can be used as the external trigger signal.
With this arrangement, it is possible to observe the shaping
and/or amplification of a signal at various points through
the circuit without resetting the triggering controls for each
new display.
Selecting the Trigger Coupling
Three means of trigger coupling are available with the
COU LING switches. The different coupling positions permit
you to accept or reject certain frequency components of the
triggering signal.
With the COU LING switch set at DC, the time base can
be triggered with all frequency components of the triggering
signal including dc levels.
With the COU LING switch set at AC, the dc component
of the triggering signal is blocked. Also, low-frequency sig
nals below about 30 cps are attenuated.
With the COU LING switch set at AC LF REJ, dc and
low-frequency signals (below about 1.5 kc) are rejected or
attenuated. Using AC LF REJ, the trigger circuit responds
best to the higher frequency components of the triggering
signal.
In general, use AC coupling. However, it will be neces
sary to use DC coupling for very low-frequency signals.
When line frequency hum is mixed with the triggering signal,
it is best to use AC LF REJ coupling so that triggering takes
place only on the signal of interest (if the signal of interest
contains frequency components above about 1.5 kc).
The AC LF REJ coupling position is also useful when trig
gering internally from multi-trace plug-in units operated in
the alternate mode of dual trace (unless the plug-in unit is a
Type 1A1 and the SOURCE switch is set to LUG IN). AC
LF REJ coupling has a faster recovery time when subjected
to the alternate dc levels from the multi-trace plug-in unit.
Selecting the Trigger Slope
The trigger SLO E switch determines whether triggering
occurs on the rising (+ setting) or the falling (— setting)
portion of the triggering signal. When several cycles of a
signal appear in the display, the setting of the SLO E switch
will probably be unimportant. However, if you wish to look
at only a certain portion of a cycle, the SLO E switch will
help you to start the display on the desired slope of the
input signal. Fig. 2-2 illustrates the effect of both the SLO E
and TRIGGERING LEVEL controls.
Selecting the Trigger Mode
The AUTO STABILITY mode is generally more convenient.
With the MODE switch set to AUTO STABILITY, proper trig
gering takes place after setting the TRIGGERING LEVEL
control. When the triggering signal is removed, the time
base circuit automatically free runs and presents a reference
display.
The TRIG position of the MODE switch should be used if
the repetition rate of the trigger signal has a very low repe
tition rate (below about 20 cps).
Setting the Triggering Level
The TRIGGERING LEVEL control determines the amplitude
point on the signal where triggering occurs.
The trigger circuit is most sensitive to ac triggering sig
nals with the TRIGGERING LEVEL control set near zero and
pushed in. Moving the TRIGGERING LEVEL control in the
+ direction causes the trigger circuit to respond at some
higher positive amplitude on the triggering signal. Moving
the TRIGGERING LEVEL control in the — direction causes
the trigger circuit to respond at some higher negative ampli
tude on the triggering signal. Fig. 2-2 illustrates the effect of
the TRIGGERING LEVEL control and the SLO E switch.
The range of the TRIGGERING LEVEL control is extended
10 times when it is pulled out. This permits more satisfactory
triggering on larger amplitude trigger signals.
Selecting the Time/Cm (S eep Rate)
The TIME/CM and SWEE MAGNIFIER switches control
sweep rate of the display. The SWEE MAGNIFIER expands
the displays of both time bases.
The TIME/CM and SWEE MAGNIFIER allow you to view
an applied signal at a wide variety of calibrated sweep
rates. When you make time measurements from the crt, be
sure the VARIABLE control is set to CALIBRATED.
When the SWEE MAGNIFIER is set to XI, the TIME/CM
switch indicates the displayed sweep rate. With SWEE
MAGNIFIER set to X2 (for example), divide the setting of
the TIME/CM switch by 2 to determine the true sweep rate.
For example, assume that the TIME/CM switch is set at
1 mSEC per division and the SWEE MAGNIFIER is set to
X5. In this case, the true sweep rate would be 1 (msec)
divided by 5 (SWEE MAGNIFIER setting); giving a dis
played sweep rate of .2 milliseconds per division. Fig. 2-3
illustrates how to make time measurements from the graticule.
Number of ^ TIME/CM Switch
Centimeters ____________ Setting = Time Duration
SWEE MAGNIFIER Setting
2-4
Fig. 2-3. Illustration of time measurement from the graticule.

Operating Instructions — Type 546/RM546
Single S eep Operation
In applications where the displayed signal is not repetitive
or varies in amplitude, shape, or time, a conventional repeti
tive display may produce a jumbled display. To avoid this,
use the single sweep feature of the Type 546 oscilloscope.
To use single sweep, first make sure the trigger circuit
will trigger on the event you will wish to display. Do this
in the conventional manner with the SINGLE SWEE switch
set at NORMAL.
Depress the SINGLE SWEE to the RESET position and re
lease the switch so it returns to the SINGLE SWEE position.
When this is completed, the next trigger pulse will actuate
the sweep and the instrument will display the event on a
single trace. The READY lamps, near the HORIZONTAL
DIS LAY switch, first light when the sweep is ready to accept
a trigger and then go out after triggering has taken place.
To ready the circuit for another single display, depress the
SINGLE SWEE switch to RESET and release. In single sweep
operation, make sure the MODE switch is set to TRIG.
B TIME/CM or DELAY TIME Switch Setting X DELAY-TIME
MULTI LIER Dial Setting Amount of delay between
the start of the B (delaying)
and the start of the A
(delayed) sweep.
Fig. 2-4. Determining delay time.
NON-TRIGGERED DELAYED SWEEP
Introduction
The following describes various measurements and other
operations that can be performed using delayed sweep; the
accuracy of those measurements; and the operating pro
cedures involved.
Insert a vertical plug-in unit and set the controls and
switches on the instruments as listed in Table 2-1.
Set HORIZONTAL OSITION so the trace begins pre
cisely at the left-hand edge of the graticule. Notice the posi
tion of the intensified segment in the trace.
Now set the B TIME/CM OR DELAY TIME switch to .2
SEC and A TIME/CM to 20 mSEC. The intensified segment
should be at the same position as with the previous sweep
rates.
Connect the SWEE A output to the vertical plug-in unit
input. Notice that the A sweep sawtooth and the intensified
segment in the trace start and end at the same time. This
display shows that TIME BASE A produces one sweep during
the intensified segment of each B sweep. The A TRIGGER
ING LEVEL control has no effect.
The B sweep rate is .2 second per centimeter. The intensi
fied segment begins 5 centimeters after the beginning of
the trace. Hence, the A sweep starts one second after the
B sweep (0.2 second per centimeter times 5 centimeters).
The number of centimeters between the beginning of the
trace and the beginning of the intensified segment is estab
lished by the setting of the DELAY-TIME MULTI LIER con
trol. Therefore, with any dial setting, the time difference
between the beginning of the A and B sweeps is the product
of the B TIME/CM OR DELAY TIME and the DELAY-TIME
MULTI LIER dial setting (see Fig. 2-4).
TABLE 2-1
B MODE
B SOURCE
B COU LING
B SLO E
B TRIGGERING LEVEL
B TIME/CM OR DELAY TIME
A MODE
A SOURCE
A TIME/CM
VARIABLE (A and B)
HORIZONTAL DIS LAY
SWEE MAGNIFIER
DELAY-TIME MULTI LIER
AM LITUDE CALIBRATOR
HORIZONTAL OSITION
INTENSITY
AUTO STABILITY
NORM
AC
0
1 mSEC
AUTO STABILITY
EXT
.1 mSEC
CALIBRATED
B INTENS BY 'A'
OFF (XI)
5.00
10 Volts
Centered
So both intensity
levels in the trace
are easily seen.
Set the applicable controls and switches of the vertical
plug-in unit as follows:
VOLTS/DIV
VARIABLE
AC-DC-GND
OSITION
5
CALIBRATED
DC
Trace Centered
The following procedures show five common applications
of the delayed sweep feature. These applications are more
accurate than the time measurements that are taken directly
from the ert display.
Demonstration 1
Measurement of pulse duration with the pulse triggering
the Main Time Base (B).
2-5

Operating Instructions — Type 546/RM546
Set the controls and switches on the instrument as listed
in Table 2-1 except as follows:
B TIME/CM OR DELAY TIME .1 mSEC
A TIME/CM 1 /xSEC
Apply the AM LITUDE CALIBRATOR signal to the input of
the vertical plug-in unit. If necessary, adjust B TRIGGERING
LEVEL to obtain a stable display. The display should con
sist of nearly one cycle of the square-wave signal.
Set the DELAY-TIME MULTI LIER dial to intensify the fall
ing portion of the square wave. Set the HORIZONTAL
DIS LAY switch to A DLY'D. The display should now be a
horizontally expanded version of the signal observed in the
intensified segment of the previous display. Adjust the
BRIGHTNESS control of the Main Time Base (B) to equalize
the intensity.
Set DELAY-TIME MULTI LIER so the falling 50% point on
the delayed trace exactly crosses the point where the 50%
amplitude level on the rising portion of the intensified dis
play appeared (this point may be hard to see but will be
very near the start of the trace). Multiply the DELAY-TIME
MULTI LIER dial reading (e.g. 5.03) by the B TIME/CM OR
DELAY TIME setting. The product is the time duration of the
square wave positive-going half-cycle.
Accuracy: Accuracy is determined by the combination of
all the following factors:
1. The basic accuracy of time measurements made by
using sweep delay is as stated in Section 1 of this manual.
2. The DELAY ICKOFF and Time Base A generator cir
cuits typically require a net total of about 75 to 100 nano
seconds to respond to the signal event which triggers the
Delayed Sweep (A). This small inherent delay need not be
considered unless it is a significant percentage (delay times
shorter than 50 / secj of the measured time or when meas
uring time differences when using the same sweep delay
range. When necessary, add the net circuit delay time
to the measured time: that is, when measuring the time
from the start of the B sweep.
Summary: The method described in Demonstration 1 pro
vides a time measurement accuracy within 1 % of reading
± 2 minor division of the DELAY-TIME MULTI LIER dial.
By comparing the delay reading to an accurate external
timing standard (such as a Tektronix 180A Time Mark Gen
erator) and applying a correction factor, an accuracy of ± 7
minor divisions of the DELAY-TIME MULTI LIER dial can be
achieved.
Demonstration 2
Measuring time between two pulses, neither of which
triggers Time Base A.
Set the controls and switches on the instrument as listed
in Table 2-1 except as follows:
B TIME/CM OR DELAY TIME .2 mSEC
A TIME/CM 2 mSEC
Apply the AM LITUDE CALIBRATOR signal to the vertical
input. If necessary, adjust the B TRIGGERING LEVEL to
obtain a stable display. The display should consist of about
two cycles of the square wave. Set the DELAY-TIME MUL
TI LIER so the square wave rise located near the center
of the display is intensified.
Set the HORIZONTAL DIS LAY to the A DLY'D position.
The display should now be a horizontally expanded version
of the intensified segment.
Set DELAY-TIME MULTI LIER so the rising 50% amplitude
level of the square wave intersects the vertical centerline of
the graticule. Note the exact setting of the DELAY-TIME
MULTI LIER (e.g. 5.48). Turn the DELAY-TIME MULTI LIER
clockwise until the falling 50% amplitude level of the square
wave intersects the same vertical graticule centerline used
with the previous dial setting. Again note the exact setting
of DELAY-TIME MULTI LIER dial.
Subtract the first dial setting from the second. The product
of the difference times the B TIME/CM OR DELAY TIME
equals the time duration of the square-wave positive-going
half-cycle (between the 50% amplitude points). This meas
urement should indicate a time of about 0.5 millisecond.
Accuracy: Accuracy is determined by the combination of
the following factors:
1. The basic accuracy of the sweep delay, as described
in Demonstration 1.
2. The error added by the sweep-delay system linearity
is ± 2 minor dial divisions of the DELAY-TIME MULTI LIER
dial. Hence, per cent error of measurement decreases as
the numerical dial difference increases.
NOTE
When the separation between dial settings is 100
minor dial divisions or less, the time measurement
can often be made more accurate by direct read
ing from a magnified ert display. See Demonstra
tion 3; Magnification.
3. The accuracy of time measurements made in Demon
stration 2 is independent of the inherent circuit delays pro
viding the B TRIGGERING LEVEL control setting is the same
for each of the two dial readings.
Summary: The method described in Demonstration 2, pro
vides time measurement accuracy as stated in Section 1.
Accuracy will be greatest when the numerical dial differ
ence between the two DELAY-TIME MULTI LIER readings
is greatest.
Demonstration 3
Complex signals contain a number of individual events of
different amplitudes. Since the trigger circuits of the Type
546 respond to signal amplitude, a stable display will nor
mally be obtained only when the sweep is triggered by the
event having the greatest amplitude. The A DLY'D mode
permits the start of the A sweep to be delayed for a selected
time after the signal event having the greatest amplitude.
Any event within the series of events may then be displayed
in magnified form as follows:
2-6

Operating Instructions — Type 546/RM546
Set the controls and switches on the instrument as listed
in Table 2-1. Apply the AM LITUDE CALIBRATOR signal to
the vertical input. If necessary, adjust B TRIGGERING LEVEL
to obtain a stable display. The display should consist of
several cycles of the square wave signal. Set DELAY-TIME
MULTI LIER to intensify one of the positive-going pulses.
Set the HORIZONTAL DIS LAY switch to A DLY'D. The
display should now be the same signal information as the
intensified trace segment, but horizontally expanded (mag
nified) ten times.
Increase the A sweep rate to 1 microsecond per division.
Set DELAY-TIME MULTI LIER to position a square wave rise
on the crt. The display now gives XI000 magnification of
the intensified segment.
Slowly turn the DELAY-TIME MULTI LIER dial. Note that
any portion of the square wave can be brought into view
in magnified form.
The DELAY-TIME MULTI LIER reading corresponds to the
number of centimeters between the beginning of the time
base B trace and the beginning of the time base A (intensi
fied) trace: e.g. 7.00=7 major divisions.
The A DLY'D display will probably exhibit some horizon
tal jitter. The time jitter contributed by the delay system is
less than 5 x 10-5 times the B TIME/CM OR DELAY TIME
setting. Since the sweep rate of the delayed sweep is now
1 microsecond per centimeter, the jitter due to the delay
system is less than one-half centimeter.
Accuracy: The accuracy of time measurements made
from magnified displays depends solely on the B sweep rate
accuracy as listed in Section 1 of this manual.
Demonstration 4
Delayed Trigger
Ordinarily the displayed signal is also used to trigger the
oscilloscope sweep. In some situations, it may be desirable
to reverse this situation. The sweep-related output pulses,
available from the front panel of the Type 546, can be used
as a triggering signal for an external device. The output
signal of the external device can then produce a stable dis
play while the oscilloscope sweep free-runs.
To demonstrate one method of performing this operation,
proceed as follows:
Set the controls and switches on the instrument as listed
in Table 2-1 except as follows:
B SOURCE EXT
DELAY-TIME MULTI LIER 1.00
B TIME/CM OR DELAY TIME 10 /xSEC
A TIME/CM 1 fxSEC
Connect DLY'D TRIG to the vertical input. The display
should consist of a positive-going spike.
The oscilloscope display shows the pulse that is avail
able at the Type 546 at the end of each delay period. In
a practical application, the pulse would not be applied to
the vertical input, but to some external device to be tested.
The pulse would serve as the trigger pulse, or input signal
for the external device and the output of the device will
provide a stable display on the oscilloscope, as though the
oscilloscope were triggered in the normal manner.
Demonstration 5
Pulse Generation
The +GATE A output signal of the Type 546 can be used
as a variable repetition rate, variable duty factor pulse gen
erator. To use the Type 546 in this manner, proceed as
follows:
Set the controls and switches of the instrument as listed in
Table 2-1 except as follows:
DELAY-TIME MULTI LIER About 0.20
Monitor the signal available at the +GATE B connector
on another oscilloscope and establish the desired pulse repe
tition rate by setting the B TIME/CM OR DELAY TIME
switch and VARIABLE B. Establish the desired duty factor
by setting A TIME/CM.
The maximum pulse repetition frequency that can be ob
tained in this manner is about 130 kc. Maximum duty factor
is about 0.9, decreasing to about 0.15 with faster sweep rates.
TRIGGERED DELAYED SWEEP
Complex signals contain a number of individual events at
different amplitudes. Since the trigger circuits in the Type
546 respond to signal amplitude, a stable display will nor
mally be obtained only when the sweep is triggered by the
event having the greatest amplitude.
The following instructions demonstrate that Time Base A
can be triggered by virtually any event within a series of
events, regardless of relative amplitude.
Set the controls and switches on the instrument as listed in
Table 2-1.
Connect the AM LITUDE CALIBRATOR signal to the verti
cal input. You should obtain a square-wave display.
Turn DELAY-TIME MULTI LIER about 2 turns in either direc
tion. Notice that the brightened segment in the display
moves smoothly across the crt.
Set the DELAY-TIME MULTI LIER so the brightened seg
ment begins about in the middle of a pulse top. Now, set
the A MODE to TRIG and the A SOURCE to NORM. Notice
that the brightened segment in the display has shifted to the
next pulse on the right. (If the brightened segment does not
appear, or is unstable, readjust A TRIGGERING LEVEL). Turn
the DELAY-TIME MULTI LIER dial several full turns. The
brightened segment in the display should jump from one
pulse to the next. Set HORIZONTAL DIS LAY to A DLY'D
and notice that the display now begins on the rising portion
of the pulse. With the present display, if you turn the
DELAY-TIME MULTI LIER dial you will see no change in the
display since all of the AM LITUDE CALIBRATOR pulses are
the same shape. However, if the input signal consisted of a
repeating series of several dissimilar pulses, turning the dial
would provide a triggered display of each pulse in the series
(providing A TRIGGERING LEVEL is set for triggering on the
smallest pulse).
2-7

The display is produced in the following manner:
Time Base A produces one sweep during each B sweep.
The Time Base A sweep will begin at some time after the
start of B sweep. This time is the total of (1) the B TIME/CM
OR DELAY TIME setting multiplied by the DELAY-TIME
MULTI LIER setting, plus (2) the time between the end of
this delay interval and the next event in the signal which
can trigger Time Base B.
The Time Base A sweep will occur only if A is triggered
before the B sweep ends. If B sweep ends while the A sweep
is in progress, A sweep will also terminate. If this occurs,
the A DLY'D display will not be the full width of the
graticule.
EXTERNAL HORIZONTAL DEFLECTION
Operating Instructions — Type 546/RM546
Fig. 2-5. Transformer connections for 108 to 244 volt, 50 to
60 cps and 400 cps operation.
flection with an externally derived signal. This permits use
of the oscilloscope system to plot one function against an
other (e.g. Lissajous figures). However, the system is not
intended for precision phase-angle measurements.
To use an external signal for horizontal deflection, con
nect the signal to the HORIZ IN UT connector. Set HORI
ZONTAL DIS LAY to EXT. The signal is dc coupled to the
deflection amplifier. The MAG switch is inoperative when
the HORIZONTAL DIS LAY switch is set to either external
horizontal position.
Transformer and Fan Connections
See Figs. 2-5 and 2-6 for transformer and fan connec
tions necessary to operate the Type 546 at line voltages
from 108 to 244 volts, 50 to 60 cps and 400 cps.
White with green stripes
White with black stripes
Yellow with brown stripes
For 216 to 244 volt
operation, move fan
lead.
108 to 122 volt operation
Fig. 2-6. Fan connections for 108 to 244 volt, 50 to 60 cps
and 400 cps operation.
2-8 ®

SECTION
CIRCUIT DESCRIPTION
Introduction
This section contains the theory of operation of the various
circuits in the Type 546. A simplified block diagram analysis
is given first to explain the operation of each circuit in general
terms, then the operaton of each circuit is covered in detail.
BLOCK DIAGRAM ANALYSIS
In the following analysis, it is assumed that the oscillo
scope is equipped with a dual-channel vertical plug-in pre
amplifier, and that the horizontal display switch is set in
the A DLY'D BY B position. Fig. 3-1 is a simplified block
diagram showing the Type 546 operating in this mode. The
functions of the various blocks in Fig. 3-1 are explained in
the following paragraphs.
Lo -Voltage Po er Supply. The low-voltage power sup
ply produces all operating voltages for the oscilloscope with
the exception of parts of the crt circuit. The low-voltage sup
ply provides regulated —150, +100, +225, and +350 volts.
It also provides heater voltages and an unregulated +325-
volt output.
Vertical Plug-In Preamplifier. Any Tektronix letter-series
or 1-series vertical plug-in preamplifier can be used with the
Type 546. For a circuit description of the plug-in unit, refer
to the plug-in unit instruction manual.
Vertical Input Amplifier. The vertical input amplifier is a
balanced, hybrid amplifier that amplifies the output of the
plug-in vertical preamplifier and applies the amplified verti
cal signal to the trigger-pickoff circuit and the vertcal output
amplifier.
Delay Line. The push-pull output of the vertical input ampli
fier is applied through the balanced delay line to the vertical
output amplifier. The delay line is a specially braided 186-
ohm line which delays the application of the vertical signal
to the vertical output amplifier for 170 nsec. This provides
time for unblanking the crt and starting the horizontal sweep
before the vertical signal reaches the deflection plates. The
delay allows the leading edge of a single fast-rising pulse to
be displayed. The delay line requires no adjustment because
of the precision construction.
Vertical Output Amplifier. The vertical output amplifier
is a push-pull, three-stage, transistor amplifier that takes the
output of the delay line and amplifies it to a level sufficient
to drive the vertical deflection plates of the crt.
Trigger-Pickoff Circuit. The trigger-pickoff circuit applies
a sample of the input waveform to the trigger circuits of
both time bases. The trigger is picked off at the output of
the vertical input amplifier.
Main Time Base IB) Generator. The Main Time Base (B)
generator provides accurate ramp voltages for the horizontal
deflection system, unblanking for the crt, and a I B gate to
a front-panel connector. The Main Time Base (B) generator
may be triggered by signals derived from either internal or
external sources.
Delay-Pickoff Circuit. The delay-pickoff circuit compares
the ramp-voltage output of the Main Time Base (B) generator
with a variable reference voltage, and assuming identical
characteristics in the two halves of the compartor, generates
a trigger pulse when the two voltages are equal. The trigger
output of the delay-pickoff circuit may be used to arm or
trigger Time Base A, and is also available at a front-panel
connector.
Horizontal Amplifier. The input to the horizontal amplifier
is selected from the outputs of the Main Time Base (B) gen
erator, Time Base A generator, or the external horizontal
input amplifier. The selected input is split in-phase and am
plified to provide push-pull drive to the horizontal deflection
plates of the crt.
External Horizontal Amplifier. The external horizontal in
put amplifier provides the necessary gain to drive the hor
izontal amplifier from external signals. An input attenuator
and a gain control provide horizontal deflection factors from
0.1 to about 10 volts/cm.
Crt Po er Supply. The crt power supply provides the high
voltages for operating the crt. The power supply is of the
rf type, using a 50-kc Hartley oscillator. Secondary windings
on the oscillator transformer supply voltages to the high-
voltage rectifiers.
Cathode Ray Tube (Crt). The cathode-ray tube used in
the Type 546 is a flat-faced, internal graticule, 5-inch tube
with 6 cm of useable vertical scan area. The tube is de
signed for low input capacitance to the vertical deflection
plates and minimum x-axis center-to-edge defocusing.
Calibrator. The calibrator in the Type 546 is a multivibrator
and cathode follower that provides a square-wave output
with a maximum amplitude of 100 volts at a nominal 1 kc.
A step attenuator permits switching the output amplitude from
the front panel. In the 0.2-mvolt to 200-mvolt range, the
output impedance is 50 f>.
Time Base A Generator. The Time Base A generator
closely resembles the Main Time Base (B) generator. The de
scription of functions and the circuit analysis given for the
Time Base (B) generator in most instances apply also to the
Time Base A generator.
CIRCUIT ANALYSIS
The following circuit analysis of the Type 546 describes the
operation of the various circuits in detail. While reading
through the description of a particular circuit, refer to the
circuit diagram being discussed (see Section 6).
Lo -Voltage Po er Supply
The low-voltage power supply in the Type 546 (see ower
Supply schematic) actually consists of four interrelated sup
plies that operate together as a system. This system de
livers filtered and regulated voltages of —150, +100,
+ 225, and +350 volts as well as an unregulated dc volt
age of +325 volts. A common power transformer, T601,
supplies the input power to each of the supplies, as well
as heater power to time-delay relay K600 and the tubes in
®3-1

Circuit Description — Type 546/RM546
VERTICAL
LUG-IN
RE
AM LIFIER
VERTICAL
IN UT
AM LIFIER
DELAY
LINE
VERTICAL
OUT UT
AM LIFIER
TRIGGER
ICKOFF
MAIN
TIME BASE
IB)
DELAY
ICKOFF
TIME
BASE
A
CALIBRATOR
HORIZONTAL
DIS LAY
SWITCH
CRT
OWER
SU LY
HORIZONTAL
AM LIFIER
EXTERNAL
HORIZONTAL
AM LIFIER
LOW
VOLTAGE
OWER
SU LY Blocks
V
To CRT
3-2
Fig. 3-1. Type 546 sim plified block diagram.

Circuit Description — Type 546/RM546
the oscilloscope. Unless otherwise specified, the Type 546
is shipped with T601 wired for 115-volt ac input. A con
nection diagram on the side of the transformer shows alter
nate connections for other input voltages. An optional
AC converter is available to provide 60-cycle power for
the fan motor if it is desired to operate the oscilloscope
on line frequencies above 60 cycles.
The 115-volt ac input power is applied to T601 through
OWER ON switch SW601. Overload protection is provided
by fuse F601. Thermal cutout TK601 in the primary circuit of
T601 is a protective device that opens the transformer pri
mary circuit if the temperature inside the oscilloscope rises
above a safe value. TK601 resets automatically when tem
peratures return to normal; and to shorten the cooling time,
the fan continues to run while TK601 is open (except when
T601 is connected for 210-250-volt operation). Thermal time-
delay relay K600 provides a filament warmup time of ap
proximately 30 seconds before the dc power supplies are
activated. The heater of K600 is rated at 6 volts and is
connected to 6.3 volts on the T601 secondary winding. Dur
ing heater warmup time, contacts 4 and 9 of relay K600
remain open. At the end of heater warmup time, contacts 4
and 9 close and apply power to magnetic relay K601. Con
tacts K601-1 of relay K601 remove the heater power from
K600, but before K600 can open, contacts K601-1 lock the
holding circuit to the coil of K601. K601 now remains ener
gized until the power to the oscilloscope is switched off or
otherwise interrupted. When K601 is energized, contacts
K601-2, K601-3, K601-4, K601-5 and K601-6 are also closed
and thus activate their respective dc supplies.
150-Volt Supply. The —150-volt supply in the Type 546
is the reference voltage source for the other supplies and
must be very stable. The —150-volt supply includes a high-
gain electronic voltage regulator designed to give good
regulation under extreme operating conditions. This regu
lator circuit contains a series regulator, a glow-discharge
tube reference source, an error detector, and an amplifier.
In operation, the input power to the —150-volt supply is
supplied by one secondary winding of T601. The ac output
of the secondary winding is rectified by silicon-diode rectifier
bridge D642 and filtered by capacitor C642A. In series with
the positive side of the supply and ground are series regula
tor tubes V637 and V647, paralleled by shunting resistors
R646 and R647. The output of the —150-volt supply is taken
from the negative side.
Error sensing in the voltage-regulator circuit is accom
plished by comparator tube V624. Current flow through V624
is established by the setting of the tap on R616 in the voltage
divider R615, R616, and R617. The voltage on the grid of
V624A is held at approximately —85 volts by reference tube
V609. Assuming that the output voltage of the —150-volt
supply increases due to increased line voltage or some other
cause, the voltage increase appears on the cathodes of V624
and, through the tap on R616, on the grid of V624B. Due to
the voltage divider, only a part of the voltage increase
appears between the grid and cathode of V624B, but the
full change appears on the grid and cathode of V624A. The
increase is in the negative direction, therefore, V624A in
creases its conduction to maintain the proper bias between
grid and cathode, and this holds both cathodes more or less
fixed while the grid of V624B is pulled negative by the in
creasing negative voltage across the voltage divider. The
increasing negative voltage on the grid of V624B causes a
decrease in current; thus, the plate voltage goes positive.
The positive change in plate voltage is amplified and in
verted to a negative change by amplifier tube V634. The
amplified error signal from V634 is applied to the grids of
series regulator tubes V637 and V647. The negative-going
error signal on the grids of V637 and V647 decreases the
current through the tubes, effectively increasing their resist
ance and the voltage drop across them. The voltage neces
sary to provide the increased drop across the series regulator
tubes and shunt resistors can only be obtained by sub
tracting it from the negative side of the supply, so the un
desired increase in negative voltage is absorbed in the
series regulators and shunt resistors. If the output of the
— 150-volt supply had decreased instead of increased, then
the error voltage applied to the grids of the series regula
tors would have been positive-going. The positive-going
error voltage on the grids of the series regulators would
lower the resistance of the series regulator tubes, and the
voltage drop across them would decrease, leaving more
voltage for the negative side of the supply. Since the out
put voltage of the —150-volt supply depends upon the
relationship of the voltage on the tap of R616 and the
reference voltage from V609, accurate adjustment of the
output voltage is provided by making R616 variable.
Filter capacitor C642A does not remove all the ripple from
the output of the bridge rectifier, thus the series regulator
circuit also helps to reduce this output ripple voltage. Any
ripple between the —150-volt output point and ground
reaches the grid (pin 2) of V624A via capacitor C610. This
input ripple voltage is amplified by V624 acting as a cath
ode-coupled amplifier. The ripple output voltage at the plate
(pin 6) of V624B has the same polarity as the ripple voltage
at the —150-volt output. C628 couples this ripple output
voltage to the grid of V634. The ripple voltage is further
amplified by V634 and applied to the grids of the series
regulator tubes with a polarity that opposes the original
ripple voltage. Ripple in the positive side of the —150-volt
supply is coupled into a degenerative feedback loop through
R637 to the screen of V634.
Some of the components in the —150-volt supply are not
necessary in normal operation but are included to insure
proper operation of the circuit under adverse conditions.
C636 provides for proper operation of the circuit when ex
tremely low temperatures reduce the capacitance of the elec
trolytic filter capacitors. R640 and R641 protect against
large surge currents, and C642B suppresses sudden load
changes that fall outside the bandwidth of the regulator
circuit.
I 100-Volt Supply. The input to the 4100-volt supply is
the output of secondary winding 19-20 of transformer T601
and silicon diode bridge D672. In addition to its other loads,
the +100-volt supply is required to supply current to a series
string of filaments at all times. When the Type 546 is first
turned on, relay K601 contacts are open and all the regu
lated supplies are inoperative. During this time, the series
string filaments are supplied by the unregulated side of the
-(-100-volt supply through relay contact K601-4. By the
time relay K600 activates K601, the series-string filaments
have reached operating temperature. When K601 is acti
vated by K600, relay contacts K601-4 shift the series string
filaments to the regulated output of the 4100-volt supply.
3-3

Circuit Description — Type 546/RM546
The reference voltage source is the regulated output of the
—150-volt supply. V664A is the error amplifier, V664B com
pensates for V664A grid-cathode contact bias changes caused
by changing line voltage, and V667 is the series regulator
tube. The error-feedback circuit is through R650 and R651,
the junction of which is connected to the grid of V664A. The
top end of R650 is connected to the regulated +100-volt
output, and the lower end of R651 is connected to the out
put of the regulated —150-volt supply to obtain reference
voltage. With normal line voltages and loads, the voltage
at the junction of R650 and R651 is about —1.7 volts with
reference to ground; this is the operating bias of V664A.
If the load current, output voltage, or the input voltage
changes (including changes due to ripple), the output of the
regulated +100-volt supply starts to change also, but any
change appears across R650 and R651 and is applied to the
grid of V664A as a change in operating bias. Assuming that
the output of the regulated +100-volt supply tries to de
crease, the reduced voltage at the top end of R650 permits
the voltage at the junction of R650 and R651 to go more
negative than the normal —1.7 volt level at that point. The
increase in negative bias on the grid of V664 reduces the
flow of plate current through V664A, the voltage drop
across plate load resistor R663 decreases, and the plate
voltage of V664 and the grid bias of V677 go more positive.
As the grid of V677 goes more positive, the resistance that
V677 offers to the flow of current is decreased and the out
put voltage rises, compensating for the drop in output volt
age which initiated regulating action. Of course, the regu
lator circuit can never completely compensate for a change
in output voltage, for there must be an error input for the
circuit to operate, but any error in output is reduced by a
factor equal to the loop gain of the regulator circuit.
The screen grid of V664 is used as a signal grid for inject
ing a sample of any ripple or transient voltages present in
the unregulated side of the +100-volt supply into the regu
lator circuit. The regulator circuit thereby becomes a dynamic
filter for ripple reduction. The ripple signal is applied to the
screen of V664A, amplified and inverted in phase by V664A,
then applied to the grid of V667. By the time the amplified
and inverted ripple gets to the grid of V667, it is of proper
amplitude and phase to cancel out the ripple appearing at
the plate of V677.
To keep the proper load on the +100-volt supply when
the vertical plug-in preamplifier is removed, a plug-in sens
ing switch is built into the main frame of the Type 546 at the
top rear of the plug-in compartment. When the plug-in unit
is removed, the sensing switch connects a resistive load in
place of the series-filament string. When it is desired to
operate the plug-in unit outside the Type 546 by means of
a test harness, the sensing switch must be manually operated.
To manually operate the switch, pull the plastic plunger out
ward to the stop position.
Unregulated +325-Volt Supply. The unregulated +325-
volt supply voltage source differs somewhat from the voltage
sources for the —150- and +100-volt supplies. A center-
tapped secondary (13-14-15) on T601 and silicon diodes D702
and D732 form a center-tapped bridge rectifier circuit with
the negative side connected to the positive unregulated side
of the voltage source for the +100-volt supply. The unregu
lated +325-volt output is taken from the transformer center-
tap (14) connection.
The unregulated output of the voltage source for the +100-
volt supply is approximately +180 volts. The unregulated
output of the center-tapped bridge circuit is approximately
+290 volts; this, added to the unregulated +180 volts pro
vides the +470 volts. However, for the unregulated +325-
volt output, the connection is made at the center tap (+145
volts) of the bridge (the midpoint of the +290 volts). Adding
the +180 and +145 volts provides the desired output of
-f325 volts.
+ 225-Volt Supply. The voltage source for the regulated
-)-225-volt supply is the unregulated +325-vo!t supply
described in the preceding paragraphs. The regulator cir
cuit is similar to the regulator circuit found in the —150-
volt supply; the main difference being that instead of using a
glow discharge tube as a reference voltage source, the ref
erence voltage is from the -150-volt supply. The error sig
nal is picked off the junction of precision resistors R680 and
R681. The upper end of R680 is connected to the +225-volt
output, and the lower end of R681 is connected to the regu
lated —150-volt supply. The voltage at the junction between
R680 and R681 is approximately —0.9 volt which is applied
through R682 and R683 to the grid of V684B. The cathodes
of V684 are long-tailed to the —150-volt supply through
resistor R685. The grid of V684A is grounded. The error
signal is fed from the grid of V684B through the common-
cathode circuit to the A side of the tube. Notice that this
comparator is somewhat different from the comparator used
in the —150-volt supply; the output is taken from the A
side. The error signal is amplified by V684 and fed, un
changed in phase, to the voltage divider in the grid of
V694. V694 also amplifies and inverts the error signal and
applies it, out of phase with any change in the +225-volf
output, to the grid of series regulator tube V707.
Here again, the screen of the error amplifier tube is act
ing as an injection grid for ripple reduction. A sample of
the unregulated supply ripple is applied to the screen of
V694. V694 amplifies the ripple, inverts it in phase, and
applies it to the grid of series regulator tube V708. The re
sult is that the same ripple appears simultaneously on the
grid and plate of V707, but 180° out of phase; thus the ripple
cancels out.
4 350-Volt Supply. The input to the +350-volt supply is
the full voltage output of the center-tapped bridge (see de
scription of +325-volt supply) added to the unregulated side
of the + 100-volt supply. The operation of the regulator cir
cuit is very similar to the operation of the +100-volt regu
lator except for different component values and no grid
cathode contact-bias compensating diode.
Crt Circuit
The crt circuit (see Crt schematic) includes the crt, the high-
voltage power supply, and the controls necessary to focus
and orient the display. The crt (Tektronix Type T5470-31-2)
is an aluminized, 5-inch, flat-faced, glass crt with a helical
post-accelerator and electrostatic focus and deflection. The
crt circuit provides connections for externally modulating
the crt cathode. The high-voltage power supply is com
posed of a dc-to-50 kc power converter, a voltage-regulator
circuit, and three high-voltage outputs. Front-panel controls
in the crt circuit adjust the trace rotation (screwdriver ad
justment), intensity, focus, and astigmatism. Internal controls
adjust the geometry and high-voltage output level.
3-4