HP 120B Service manual

Table of Contents

TABLE OF CONTENTS

Section Page Section Page

I

GENERAL INFORMATION

1- 1

.

Introduction

1.4

.

Description

1.14 . Cathode Ray Tube Warranty

1.16

.

Options

11

INSTALLATION 2-1

.

2.1 Incoming Inspection 2-

2.7

.

Power Requirements 2-1

2.10 . Installation 2-2

2.13 . Repackaging for Shipment 2-2

.

3.1

3.3

3.5

IV

PRINCIPLES OF OPERATION

4.1

4.9
4- 10

4.16

4.30

4.34

4.41

Introduction

.

Controls and Indicators

.

General Operating Suggestions

.

Overall Block-Diagram Description . 4-1

Circuit Analysis

.

Vertical Amplifier

.

Sweep Generator

:

Horizontal Amplifier

.

Low-Voltage Power Supply

.
.

High-Voltage Power Supply 4-6

.................

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......

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.......

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....

.........

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1-1
1-

1-1

1-2
1-2

3-1
3-1
3-1

4.1

4-2
4-2
4-3
4-4
4-5

V MAINTENANCE

1

1

5.24

5.27 Low-Voltage Power Supply 5-6

5.33 High-Voltage Power Supply 5-6

5.35

5.42 Horizontal Amplifier 5-10

5.48 Sweep Generator 5-11

5.52 Performance Check 5-11

5.67 Diagrams 5-14

VI

REPLACEABLE PARTS

6.1 Introduction 6-1

6.3 Ordering Information 6-1

Introduction 5-1
Test Equipment 5-1
Troubleshooting 5-1

Repair 5-5

Adjustments 5-6

.

.

.
.
.

.

.
.

.

.

...................

.................

...............

...............

System Troubleshooting 5-1
Sectional Troubleshooting
High-Voltage Power Supply

....................

Replacement of Semiconductors
Servicing Etched Circuit Boards
Crt Replacement

...........

................

Adjustments Following Repair

Vertical Amplifier

..........

...........

...........

..................

............

................

..........

Model 120B

......

.....

....

.
.

. .

.....

....

........

-6-1

5-1

5-2
5-2

5-5
5-5
5-5

5-6

5-9

Model 120B

LlST OF ILLUSTRATIONS

Number Title Page Number Title Page

List of Illustrations and Tables

Model 120B Oscilloscope

Primary-Power Connections
Rack Mounting.

Model
Operation Using Internal Horizontal

Operation Using External Horizontal
Operation Using Balanced Vertical
Vertical Deflection Calibration and

Overall Block Diagram 4­Sweep Generator, Block Diagram 4-2
Sweep Generator Waveforms 4-3
Typical Schmitt Trigger 4-3
Low-Voltage Power Supply, Block

High-Voltage Power Supply, Block

120B Oscilloscope, Front View

Sweep or Single Sweep 3-3

......................

Input .3-4

......................

Input .3-5
Balance Adjustment 3-6

Diagram.
Diagram. .4-6

...............

...................

...................

...........

........

;

.

.

.

...........

.............

............

.....

........

...........

.4-5

LlST OF TABLES

1-1
2­2-2

3-2

Top View, Location of Parts and

1

1

Adjustments 5-3

High-Voltage Power Supply, Location

of Parts. 5-4

Vertical Sensitivity

Source
Parts and Adjustments

Right-Side View, Side Panel Removed,

Location of Parts and Adjustments 5-6
Servicing Etched Circuit Boards.
Vertical Amplifier, Schematic

Diagram 5 - 15
Horizontal Amplifier, Schematic

Diagram 5- 17
Sweep Generator, Schematic Diagram
Low-Voltage Power Supply, Schematic

Diagram 5 - 2
High-Voltage Power Supply, Schematic

Diagram 5- 23

Horizontal Display Switch, Schematic

Diagram. 5-25

..................

....................

(A21 and Trigger

(A201) Switches, Location of

...........

...

.....

.....................

.....................

.....................

.....................

....................

5-5

5-7

.

.

5-19

1

Number Title Page

1-1.

Specifications 1-0
Recommended Test Equipment

System Troubleshooting. 5-4
Adjustments Following Tube,

Transistor, and Diode Replacement.
Low-Voltage Power Supply Voltages
Horizontal Sweep-Time Adjustment.
Horizontal Sweep Time 5-14
Reference Designation Index
Replaceable Parts 6- 14
Code List of Manufacturers

..................

.......

...........

..

...
...

............

........

...............

.........

5-

1

5-8
5-9
5-12

6-

2

6-17

Section I

1-

Table

Model 120B

1

Table

1- 1.

Specifications

SWEEP

Sweep Range:

One

p3ec/cm to

calibrated sweeps accurate to within

1,2,5,10.. . sequence, from 5 psec/cm to 200
millisec/cm. Vernier control permits contin­uous adjustment of sweep time between calibra­ted steps, and extends the 200
least 0.5 sec/cm.

Sweep Expand:

X5 sweep expansion may be used on all ranges
and expands fastest sweep to
panded sweep accuracy

Automatic Synchronization:

Internal: from signals 50 cps to 450 kc with
approximately 0.5-cm or more vertical deflec­tion; and from line voltage.

External: from signal 50 cps to 450 kc, 1.5
peak-to-peak.

Trigger Point:

Zero-crossing negative slope of external sync

signals; or zero-crossing positive or negative
slope of vertical deflection signals. Front-panel
control overrides automatic and permits the
trigger point to be set between
Turning control fully counterclockwise restores
automatic operation.

at

least 0.5 sec/cm.

millisec/cm to at

1

is

*lo%.

psec/cm. Ex-

-7 to +7 volts.

Fifteen

*5%, in a

v

VERTICAL AMPLIFIER

Bandwidth: ating potential. Face plate eliminates glare and

DC coupled: dc to 450 kc. AC coupled: 2 cps reduces hazard of implosion. P2, P7, and
to 450 kc. Bandwidth
less of sensitivity setting.

Sensitivity:

10 millivolts/cm to 100 volts/cm. Four cali- divisions. Eliminates parallax error.
brated steps with attenuator accuracy of
10 mv/cm, 100 mv/cm, 1 v/cm, and 10 v/cm.

Vernier permits continuous adjustment of
tivity between steps, and extends 10
to at least 100

Internal Calibrator: 16-3/4

Calibrating signal automatically connected to deep, overall; hardware furnished for quick con­vertical amplifier for standardizing of gain, ac­curacy

Input Impedance

1

Balanced Input:

On 10 mv/cm range only; input impedance
megohms shunted by approximately 25 pf.

Common-Mode Rejection: 06. Rear terminals in parallel with front.

Rejection at least 40 db. Common mode signal 10. Provision for single sweep operation.
must not exceed

+2%.

megohm, shunted by approximately 50 pf.

v/cm.

:

is

at least 450 kc regard-

+3 volts peak.

*3%,

sensi-

v/cm step

is

2

Phase Shift:

Vertical and horizontal amplifiers have same
phase characteristics within
verniers are in CAL.

+ZO

to 100 kc when

HORIZONTAL AMPLIFIER

Bandwidth:

DC coupled: dc to 300 kc. AC coupled: 2 cps
to 300 kc. Bandwidth
less of attenuator setting.

Sensitivity:

0.1 volt/cm to 100 volts/cm. Three calibrated

steps, accurate within
and 10 v/cm. Vernier permits continuous ad­justment of sensitivity between steps and
tends 10

Input Impedance

1

megohm nominal, shunted by approximately

100 pf.

Phase Shift:

Horizontal and vertical amplifiers have same
phase characteristics within
verniers are in CAL.

v/cm step to at least 100 v/cm.

:

is

at

least 300 kc regard-

&5%,

0.1 v/cm, 1 v/cm,

k2O to 100 kc when

GENERAL

Cathode Ray Tube:

P31 phosphor, mono-accelerator with internal

graticule normally supplied; 2700-volt acceler-

phosphors also available.

Internal Graticule:

10 cm x 10 cm marked in cm squares. Major

horizontal and vertical axes have 2-mm

Intensity Modulation:

Terminals on front panel. Plus 20 volt pulse

required to blank trace of normal intensity.

Dimensions:

in.

wide, 7-1/2 in. high, 18-3/8

version to 7 in. x 19 in. rack mount.

Weight:

Net: 32 lbs; shipping 45 lbs.

Power:

115 or 230 volts

mately 95 watts.

Options

:

05. External graticule crt with P31 phosphor.

13. Special front panel for rack mounting only.

*lo%,

50 to 1000 cps, approlci-

ex-

PI1

sub-

in.

Model 120B

Paragraphs

Section

1-1

to 1-8

I

SECTION

GENERAL INFORMATION

1-1. INTRODUCTION.

1-2. This manual provides complete instructions on

the installation, operation, theory of operation, and

maintenance of the Hewlett-Packard Model 120B Os-

cilloscope.

1-3. The Hewlett-Packard Company uses a

section, eight-digit serial number (e. g. 000-00000).

If

the serial prefix (first three digits) on your instru-

ment does not agree with the prefix shown on the title

page of this manual, refer to either the separate

I,

change sheet included or Appendix
changes required to adapt this manual
prefixes. The separate change sheet also contains
corrections required for all known errata (errors).
Contact your Hewlett-Packard

if

additionalinformation or clarification is required.

Sales/Service Office

which contain

to

1-4. DESCRIPTION.

1-5. The Model 120B
scope whose bandwidth extends from dc to 450 kc. It
combines the precision characteristics of calibrated

is

a general-purpose oscillo-

two-

the listed

I

horizontal sweeps, calibrated vertical sensitivity,

a

crt that eliminates parallax error; in addition,

and
its construction provides easy circuit accessibility
and quick convertibility from a rack-mounting to a
bench-model configuration. Specifications are listed
in table

1-6. The internal graticule of the Model 120B
the same plane as the phosphor and crt trace; conse­quently, crt parallax error

quicker, and more accurate measurements.

1-7. The Model 120B can be used with either internal

or external sweeps, which can be either internally or
externally synchronized. Because of
tivity and balanced input, the Model 120B can be used
to view complex waveforms and monitor transducer
outputs.

1-8. Computations are avoided and possibilities of

error are reduced by direct-reading calibrated sweeps.

A

between the ranges

1-1.

is

in

is

avoided, allowing easier,

its

high sensi-

single control selects 1 of 15 calibrated sweeps

microseconds/cm and 200

of 5

Figure

1-

1.

Model 120B Oscilloscope

1-1

Section I

Paragraphs 1

-

9 to 1 - 18

Model 120B

milliseconds/cm or determines the calibrated sensi­tivity of the horizontal amplifier. Continuous control

of sweep time and horizontal sensitivity between cali-

brated steps is provided

vernier control extends the 200

sweep time to at least 0.5 seconds/cm, and reduces
the horizontal amplifier sensitivity to at least 100
volts/cm.

1-9. Accurate direct-reading sweeps are obtained
from a feedback type (Miller) integrator, which en-

sures high linearity and stability of the horizontal
sweep. This type of sweep generator is reliable and
relatively independent of vacuum-tube characteristics.

1-

10. Observation and analysis of transients are sim­plifiedby the expanded-sweep control. This X5 sweep
expander may be used on all sweep time settings, and
expands the fastest sweep time to

1-

11.

An automatic trigger capability facilitates es­tablishinga base line on the crt when a synchronizing
signal is not present. The automatic baseline pro­vision can be easily locked-out and an adjustable trig­ger level established.

1-

12. Accurate voltage measurements of waveforms
are quickly made with the Model
calibrator that
mits rapid verification and standardization of vertical
amplifier sensitivity.

1-13. Phase-shift measurements can be made ac­curately over a wide range of input frequencies. Rel­ative phase shift between the vertical and horizontal
amplifiers is less than 2 degrees up to 100 kc.

is

accurate to within *2 percent per-

by

a vernier control; the

milliseconds/cm

1

microsecond/cm.

120B. A built-in

1-14. CATHODE RAY TUBE WARRANTY.

1-15. The cathode ray tube supplied with the Model

120B and replacement crt's purchased from Hewlett­Packard Company are guaranteed against electrical
failurefor one year from the date of sale by Hewlett­Packard. The Cathode Ray Tube Warranty and Claim
sheet is included at the rear of this manual.

1-19. OPTION 06.

connectors in parallel with the front panel input con­nectors.
VERTICAL input terminals on the front panel, and
one connector is
TAL input terminals as shown in figures 5-6 and
Mating connectors and cable clamps are also supplied.
The additional circuitry changes the vertical input
capacitance to approximately
input capacitance to approximately 135 pf.

1-20. OPTION 10.

single sweep operation.
contained in figure 3-2 and a schematic for the added
circuit is shown in figure 5-8.

1-21. OPTION 13. This option provides a plain

7 x 9 x 3/16 inch front panel for rack mounting only.
The panel is suitablefor installing special handles to
match existing equipment in system or console
configuration.

1-22. AMBER FILTER.
supplied with oscilloscopes having an internal graticule
crt with
for improved visual observation of displays such as

single-shot phenomena or very low frequency applica-

tions.

characteristics desired for visualobservations of this

type display.

a. Remove front panel crt bezel.

b. Set filter into bezel, aligning larger rectangular
slots in the edge of filter with metal guide posts of the
bezel casting.

c. Remove oscilloscope top cover for access to

rear of crt.

d. Carefully move crt towardrear of instrument

enough to provide clearance for thickness of installed

filter (about 1/8 inch).

One connector is wired in parallel with the

P7 phosphor.

The filter will improve the long persistency

To install the filter proceed as follows:

This option provides rear panel

wiredin parallel with the HORIZON-

5-

75pf, and the horizontal

Thisoptionprovides circuitry for

Operation procedures are

A special amber filter is

This filter may be installed

7.

1-16. OPTIONS.

1-

17. The Model 120B is available with four options,

as

listed in table
are listedunder MISCELLANEOUS at the end of table
6-1.

1-18. OPTION 05. This optionprovides a crt without

internal graticule.
able illumination

Refer to figure 5- 9 for

CRT's without internal graticule are available with
types P7,
plied with each crt; amber for
type, and green for P31 type.

1-

1.

Replaceable parts for alloptions

An

external graticule with adjust-

is

installed over the face of the crt.

a

schematic of the added circuit.

P11, andP3l phosphor. Afilter

P7 type, blue for PI1

is

also sup-

e. Loosen clamp at socket of crt.

f.

Replace bezel with filter and tighten bezel

screws.

g. Slide crt forward until light mask on front of crt

just lightly touches filter.

h. Tighten clamp just enough to keep crt from turn-

ing.

Do not over-tighten the clamp or tube damage

may result.

i. Check alignment of trace with graticule accord-

ing to theprocedure given in Section V of this manual.

Model 120B

Paragraphs 2-1 to 2-9

Section

I1

SECTION

INSTALLATION

2-1.

INCOMING INSPECTION.

2-2. MECHANICAL INSPECTION. Unpack and in­spect the Model 120B in the presence of the carrier.
Be careful when unpacking the instrument, for all
electron tubes including the cathode ray tube remain
installed during shipment. Save all packing materials
until inspection

be required for reshipment in the event shipping dam-

is

age

age in shipment such as scratched panel, broken
knobs, etc.
check it operationally (see paragraph

claim with the carrier. Refer to the Hewlett-Packard
Warranty sheet at the front of this manual.

2-5. PERFORMANCE CHECK. Paragraph 5-52 con­tains performance check procedures for verifying

operation within listed specifications. The perform­ance check is recommended for inclusion in receiv­ing quality-control inspection. The following proce-

dure

operation.
2-6. INITIAL TURN ON. Energize the 120B as

follows:
power cable.

LISECONDS/CM position.
POSITION controls.

If

adjust position controls as necessary.

adjust HORIZONTAL POSITION to place left end of

sweep on left-end graticule line.

discovered.

2-3. Inspect the instrument for signs of possible dam-

If

2-4.

a. Turn INTENSITY control to OFF and plug in

b.

c. Set HORIZONTAL DISPLAY switch to 0.5
d. Center HORIZONTAL POSITION and VERTICAL
e. Turn 120B on and allow

f

g. Rotate INTENSITY clockwise until trace appears.

h. Adjust FOCUS for thin, -well-defined trace, and

there are any indications of damage, file a

is

offered, however, as a means to check basic

Set SWEEP MAGNIFIER switch to X1 position.

.

Set TRIGGER LEVEL to AUTO.

crt remains blank, press BEAM FINDER and re-

is

complete. These materials may

If

possible, energize the equipment and

2-

5).

two

minutes warmup.

MIL-

II

230

VOLTS AC

115

VOLTS AC

:41

Figure 2-

I

2

3

4

1L

230 VOLT CONNECTION

I

2

3

4

115

VOLT CONNECTION

1.

Primary-Power Connections

T302

T 302

LO-S-529

2-7.

2-8. The Model 120B requires a power source of 115
or 230 volts
can deliver approximately 95 watts. The oscilloscope

is

with a 115-volts power source. To convert the in-

strument for use with a 230-volt source, change the
dual primary windings of transformer T302 from a
parallel combination to a series combination. Figure

2-1 illustrates the connection for 115- and 230-volt
operation. At the time of the change, replace the

1.5-ampere slow-blow line fuse with 1-ampere

blow fuse.

POWER REQUIREMENTS.

?lo%,

single phase, 50 to 1000 cps, which

normally shipped from the factory wired for use

slow-

2-9.

For the protection of operating personnel, the

National Electrical Manufacturers' Assn (NEMA)

recommends that the instrument panel and cabinet
be grounded. This instrument is equipped with a
three-conductor power cable which, when plugged into

an appropriate receptacle, grounds the instrument.

The offset pin on the power cable three-prong con­nector is the ground pin. To preserve the protection
feature when operating the instrument from a

contact outlet, use a three-prong to two-prong adap­ter and connect the green pigtail on the adapter to
ground.

two-

Section

II

Paragraphs 2-10 to 2-14

INSTRUCTIONS
I. REMOVE TILT STAND, FEET, AND

TRIM STRIP.

2.ATTACH FILLER STRIP AND FLANGES
KEEPING LARGENOTCHONFLANGES
TO INSTRUMENT BOTTOM.

Model 120B

FILLER STRIP

RACK MOUNTING

Figure 2-2. Rack Mounting

2-10. INSTALLATION.

2-11. MODULAR CABINET. The Model l2OB Oscil-

is

loscope
ment with the tilt stand, feet andplastic trim

shipped fromthe factory as a bench instru-

inplace.

The top and bottom cabinet covers may be removed,
giving complete accessibility to all components and
adjustments. When used on the bench, other instru-

be

ments may

stacked on the louver-free top surface;
however, sufficient space should be allowed around
the cabinet for adequate circulation of air.

2-12.

RACK

MOUNTING. Prepare the cabinet for
rack mounting as illustrated in figure 2-2. The trim
strip and rack-mounting flanges are in the shipping
container with the instrument. After preparation, lift
instrument into place and secure mounting flanges to
rack with appropriate screws. Allow adequate venti­lation for the instrument in the rack.

2-13. REPACKAGING FOR SHIPMENT.

2-14. The following

packagingan instrument for shipment; however,
have any questions, contact your authorized

Packard sales representative.

list

is

a general guide for re-

Hewlett-

if

you

LO-M-489

a.

If

possible, use original container designed for

the instrument.

b. Wrap instrument

in

heavy paper or plastic before

placing it in shipping container.

c. Use sufficient quantities of packing material
around all sides of the instrument and protect panel
with cardboard strips.

d. Use heavy cardboard carton or wooden box to
house the instrument and use heavy tape or metal
bands to seal the container.

e. Mark packing box with "Fragile", "Delicate In­strument", etc.

Note

If

the instrument

is

to be shipped to

Hewlett-Packard Company for ser-

vice or repair, attach to the instru-

ment atag identifyingthe owner, the

instrument's complete serial num­ber, and the service or repair to be
accomplished; in addition, notify
Hewlett-Packard Company or a rep­resentative before shipping the in­strument. In any correspondence,
reference the instrument by model
number and complete serial number.

Model 120B

Section

Paragraphs 3- 1 to 3-16

III

SECTION

OPERATION

3-2. This section contains operating instructions for
the Model 120B Oscilloscope. Included are descrip­tions of the Model 120B controls and indicators, and
operation of the Model
oscilloscope.

3-3.

CONTROLS AND INDICATORS.

Figure 3-1 illustrates the controls and indica-

3-4.
tors along with a short description of the particular
function of each.

3-5, GENERAL OPERATING

SUGGESTIONS.

3-6. The following paragraphs, 3-7 through 3-16,
provide suggestions for expediting and simplifying
operation of the Model

3-7. SYNCHRONIZING THE SWEEP. The horizontal
sweep can be synchronized with the vertical input

signal (INT positions of TRIGGER SOURCE switch),
the ac line frequency (LINE position), or an external
sync signal (EXT position).

3-8. When the TRIGGER LEVEL control

position, a sweep appears on the crt without applica­tion of any type of synchronizing signal; however,
when a synchronizing signal above approximately 50
cps is applied, the sweep automatically synchronizes
with this signal and the sweep
point where the signal crosses the zero axis (average
dc level of synchronization signal).
ing signal below approximately 50 cps
the TRIGGER LEVEL control should be out of AUTO
position.

3-9. Rotating the TRIGGER LEVEL control in a
clockwise direction permits the trigger point to be
set between
going portion of a vertical input signal, depending on
whether the TRIGGER SOURCE switch is in
INT- position, respectively. When the TRIGGER
SOURCE switch
GER LEVEL control in a clockwise direction permits
the trigger point to be set between
negative-going portion of the synchronizing signal.

3-10. The particular type of synchronization best
suited depends on the type of measurement being made
and the type of crt display desired.

3-11.
switch in AC position) removes any dc level present
in the vertical or horizontal input signals. This pre­vents excessive dc levels from deflecting the crt trace
off the face of the crt, often to the point where the
POSITION controls cannot bring the crt trace within
view.

rt2 cm along the positive or negative-

is

in EXT position, rotating the TRIG-

AC/DC COUPLING. Ac coupling (AC - DC

120B as a general-purpose

120B.

is

in AUTO

is

triggered at the
If

a synchroniz-

is

being used,

INT+ or

rt7 volts along the

Ill

CAUTION

When using ac coupling, do not
ceed a dc level input of 600 volts.

3-12. When pulse or square waves having a
cy less than 200 cps are being measured, dc coupling

is recommended (AC-DC switch-in DC position).
3-13. BEAM FINDER OPERATION. The crt trace

may frequently be deflected off the crt face by exces­sive dc input levels or by misadjustment of the verti­cal POSITION and horizontal POSITION controls.

The BEAM FINDER pushbutton is extremely useful
under these conditions. When the BEAM FINDER
depressed, the beam is confined to the face of the

crt, brightened, and defocused to prevent burning of
the crt phosphor.

POSITION controls when the BEAM FINDER
pressed, the trace will remain on the crt face when
the BEAM FINDER

3-14. VERTICAL SENSITIVITY SELECTION. When
the vertical VERNIER control

VERTICAL SENSITIVITY switch provides attenuation

of the vertical input signal in four calibrated steps,

10

mv/cm, 100 mv/cm, 1 v/cm, and 10 v/cm.

tating the vertical VERNIER control in a counter-

clockwise direction permits continuous adjustment of

sensitivity between steps, and extends 10

at

least 100 v/cm. When the VERTICAL SENSITI-

to
VITY switch

is automatically connected to the vertical amplifier.

3

-

15. COMMON-MODE REJECTION. Balanced in­put to the vertical amplifier
the ground jumper across two of the vertical input
terminals and applying a balanced signal input. Bal­anced input
sired to simultaneously amplify the out-of-phase (dif­ferential) signal and attenuate the in-phase (common
mode) signals, such as hum, noise, etc.

3-16. A change in the relative position of the Model

120B Oscilloscope with respect to the earth's mag­netic field could result in the trace becoming mis­aligned. To re-align the trace with the graticule,
adjust SCALE, screwdriver adjustment ,on the front
panel (Figure 3-1).

Figures 3-2 through 3-5 assume
that the FOCUS, POSITION, and IN­TENSITY controls are preset by the
operator for the desired display.

If

in doubt as to the exact function
of a switch listed in figures 3-2
through 3-5, refer to figure 3-1
for a functional description.

If

the crt trace

is

released.

is

in CAL position, a calibrating signal

is

useful in applications where it

Notes

is

is

in CAL position, the

is

obtained by removing

ex-

frequen-

is

centered with the

is

de-

Ro-

v/cm step

is

de-

Section

III

Figure 3-

Model 120B

1

7

-4

0.c

HEWLC

20 19

1.

FOCUS: Controls crt focus.

18

I7 16 15

11.

14

13 12

11

10 9 8

MP-M-

Vertical POSITION: Controls verticalposi­tion of crt display.

2. Horizontal VERNIER: Adjusts sensitivity
between ranges; in CAL position, deflec-

tion

as

indicated

by

selected

VOLTS/CM

position of HORIZONTAL DISPLAY switch.

3. HORIZONTAL DISPLAY: 15 positions se- 13. SWEEP MAGNIFIER:

3

lect sweep speed,

positions select hori-

zontal deflection sensitivity.

4. TRIGGER LEVEL: Determines level of
trigger point on sync signal.

12. BAL: Adjust for no vertical shift with ro­tation of vertical VERNIER.

In

Xl position sweep
time selected by HORIZONTAL DISPLAY.
In

X5position sweep speed

is

5

times faster.

14. EXT. SYNC OR HORIZ: External sync or
horizontal amplifier input.

5. TRIGGER SOURCE: Four positions select
sweep synchronization. 15. Horizontal AC-DC: AC position input

itively coupled into horizontal amplifier.

6.

Vertical VERNIER: Adjusts sensitivity be-

DC position input directly coupled into hor-

tween ranges; in CAL position, deflection izontal amplifier.
as selected by VERTICAL SENSITMTY
switch. 16. Z AXIS: Input for crt intensity modulation

signal.

7. VERTICAL SENSITIVITY: Four positions
select deflection sensitivity. CAL position 17. Horizontal POSITION: Controls horizontal

displays internal calibrator signal.

position of crt display.

85

capac-

8.

CAL: Adjusts calibration of vertical input.

18.

BEAM FINDER: Returns beam to crt face
regardless of horizontal and vertical POSI-

9.

Vertical input terminals. TION settings.

10. Vertical AC-DC: AC position input capaci- 19. INTENSITY
tively coupled into vertical amplifier. DC

power and controls crt intensity.

&

POWER: Applies ac line

position input directly coupled into vertical
amplifier. 20. SCALE: Aligns trace with graticule.

Figure 3-1.

Model 120B Oscilloscope, Front View

01260-1

Model

120B

Section

Figure

Ill

3-2

INTERNAL HORIZONTAL SWEEP:

1.

Set vertical AC-DC to desired type of input A. Set SWEEP switch to normal (N), TRIGGER
coupling.

2.

Set VERTICAL SENSITIVITY to desired vertical
sensitivity.

3.

Set vertical VERNIER to CAL for calibrated Minimum trigger sensitivity

SINGLE SWEEP (OPTION

SOURCE switch to EXT, and remove any external
trigger source.

B.

Adjust TRIGGER LEVEL control fully clockwise.

is

10):

obtained with the

sensitivity. control in this position.

4.

Set HORIZONTAL DISPLAY to desired horizontal

C. To increase trigger sensitivity, rotate TRIGGER
sweep time. Set VERNIER to CAL for calibrated LEVEL control counterclockwise. Maximum
sweep time.

X1

5. Set SWEEP MAGNIFIER to

6.

Set TRIGGERSOURCE to desired type of horizon­tal sweep synchronization.

or X5, as desired.

If

external sync

selected, connect sync signal to EXT. SYNC.

7.

Apply vertical input signal to vertical input

terminals.

8.

Adjust TRIGGER LEVEL for desired synchroni-

zation.

I

Figure

3-2.

Operation Using Internal'Horizontal Sweep or Single Sweep

is

sensitivity will be obtained just prior to the point

where the oscilloscope sweeps intermittently.

D. Set SWEEP switch to single (S). The instrument

is

now in the "armed" state and will sweep once

when triggered.

E. To rearm the sweep circuit, set SWEEP switch

from S to N and then back to S. External triggering
should not be applied during this operation to
vent the single sweep from occurring immediately

is

when the switch

returned to the S position.

pre-

Section

III

Figure 3-3

SWEEP

MAGNIFIER

Model

120B

1.

Set vertical AC-DC to desired type of input

6.

Apply external horizontal sweep to hori-

coupling. zontal input terminals.

2.

Set VERTICAL SENSITIVITY to desired ver-

7.

Apply vertical input signal to vertical input

tical sensitivity. terminals.

Set vertical VERNIER to

3.

CALfor calibrated

sensitivity. Note

4.

Set HORIZONTAL DISPLAY to desired
VOLTS/CM. Set VERNIER to CAL for cal­ibrated sensitivity.

5.

Set horizontal AC-DC to desired type of

Relative phase shift of hori­zontal and vertical amplifiers

is

the same

+2"

to

100

kc only

when both VERNIER controls

coupling. are set to CAL.

Figure 3-3. Operation Using External Horizontal Input

3

-4

Model 120B

SWEEP

MAGNIFIER

Section

111

Figure 3-4

Remove grounding strap from vertical in-

Set vertical AC-DC to desired type of input

1.

7.

coupling. put terminals.

2. Set VERTICAL
VOLTS/CM. (Input not balanced in any terminals;
other position of VERTICAL SENSITMTY nect

switch.

Set vertical VERNIER to CAL for calibrated

3.

)

sensitivity.
Set HORIZONTAL DISPLAY to desired hor- The common-mode input sig-

4.

izontal sweep speed.

SENSITIVITY to 10 MILLI-

8.

Connect vertical signal to vertical input

if

ac coupling

0. 1-uf 600-volt capacitor in series

with center vertical input terminal.

Note

nal voltage, either positive or
negative, must not exceed 3

5. Set SWEEP MAGNIFIER to
desired.

6. Set TRIGGER SOURCE to desired type of

X1 or X5, as volts minus the peak amplitude

of the differential input signal.

9.

Adjust TRIGGER LEVEL for desired syn-

horizontal sweep synchronization. chronization.

is

desired, con-

LO-U-.92

Figure 3-4. Operation Using Balanced Vertical Input

3-5

Section

Figure 3-5

III

Model 120B

SWEEP MAGNIFIER

CALIBRATION ADJUSTMENTS:

1.

Set vertical VERNIER to CAL.

2. Set VERTICAL SENSITIVITY to CAL.

Adjust CAL for exactly

3.

flection.

6

cm of vertical de-

While rotating vertical VERNIER back and

7.

forth, adjust BAL for no shift of spot.

BALANCE ADJUSTMENTS:

4.

Set VERTICAL SENSITIVITY to 10
VOLTS/CM.

Set vertical AC-DC to DC.

5.

6.

Short vertical input terminals.

LD-Y-490

MILLI-

Figure 3

-

5.

Vertical Deflection Calibration and Balance Adjustment

01260-1

Model 120B

Section

IV

Paragraphs 4-1 to 4-8

SECTION

PRINCIPLES OF OPERATION

4-1.

OVERALL BLOCK-DIAGRAM

DESCRIPTION.

is

4-2. The oscilloscope
functional circuit groups:
sweep generator, the horizontal amplifier, the low­voltage power supply, and the high-voltage power

ply (see figure 4-1).

4-3. The vertical input signal is applied to the ver­tical amplifier through a frequency -compensated
tenuator. The vertical amplifier converts the vertical
input to two 180-degree-out-of -phase signals and ap­plies the amplified signals to the crt as the vertical
deflection; in addition, the vertical amplifier applies
the signals to the TRIGGER SOURCE switch, when
they are used

as

the INT+ and INT- sync signals.

4-41 The horizontal or sync input signal
the HORIZONTAL DISPLAY switch. Depending on the
setting of this switch, the signal is applied to either
the TRIGGER SOURCE switch (to be used as the ex­ternal sync signal) or to the horizontal amplifier (to
be used as the external horizontal input signal).

In

4-5.

addition tothe internal and external sync sig-

nals, the TRIGGER SOURCE switch receives 6.3 volts

ac from the low-voltage power supply; this provides

a

sync-signal repetition rate equal to the line-

for
voltage frequency.

comprised of five major

the vertical

amplifier,

sup-

is

applied to

the

at-

IV

4-6. The sync signal selected by the TRIGGER
SOURCE switch is-applied to the sweep generator,

wherein the sync signal initiates the horizontal sweep

signal and the unblanking gate. The sweep generator
applies the sweep signal to the horizontal amplifier,
and the resultant amplified sweep
crt as the horizontal deflection signal. The unblank-

is

ing gate

If

an external horizontal sweep is being applied

applied to the high-voltage power supply.

place of the sweep from the sweep generator, the ex-

ternal sweep

is

amplified by the horizontal amplifier

and applied to the crt.

4-7. The low-voltage power supply receives
volts, single-phase power from the line andgenerates

the following output voltages: 6.3 volts ac, a regu-

lated +19 volts dc, +99 volts dc,
volts dc,

+300 volts dc, and an unregulated +420 volts
dc. These voltages are distributed, as required, to
the high-voltage power supply, the vertical amplifier,
the horizontal amplifier, and the sweep generator.

4-8. The high-voltage power supply generates the

high voltages for the

crt. The unblanking gate and

Z-axis signals applied to the high-voltage power .sup­ply effectively alter the value of the power-supply
voltages to allow unblanking and modulation of the crt

intensity.

is

applied to the

in

115/230-

+I00 volts dc, -150

VERTICAL DEFLECTION

VERTICAL

GENERATOR HORIZONTAL SWEEP

(

I OF 3 SECTIONS

115/230 VOLTS
60 CPS 6 3 VOLTS AC
l PHASE

)

LOW

POWER

SUPPLY D-C VOLTAGE AND SWEEP

Figure 4-1. Overall Block Diagram

-

-+

HIGH VOLTAGE

POWER FOCUS VOLTAGE

SUPPLY

INTENSITY VOLTAGE

\

*

>TO CRT

b

+

1

CIRCUIT

80-"-266

4-1

Section IV
Paragraphs 4-9 to 4-15

Model

120B

4-9.

CIRCUIT ANALYSIS.

4-10.

VERTICAL AMPLIFIER.

4-11. For ac coupling, capacitor C1

is

placed in
series with the signal path by means of the AC-DC
switch. (See figure 5-6.
applied to VERTICAL SENSITIVITY switch
the switch

is

in the CAL position, the input of the am-

)

The input signal

is

then

S2. When

plifier is directly connected to the output of the cali­brator (V4, V5, and associated circuit parts). When

is

the VERTICAL SENSITIVITY switch

in other posi­tions, precision frequency-adjusted attenuators are
inserted. These attenuators give a ten-to-one atten­uation between adjacent positions. The input signal

is

then applied to the control grid of amplifier VIA.
4-12. Balanced input to differential amplifier V1B

is

obtained by removing the ground jumper across re­sistor

R1 (ground strap on front panel) and applying a
balanced signal input. Balanced input is useful in ap­plications where it

is

desired to simultaneously am­plify the out-of-phase (differential) signal and atten­uate the in-phase (common mode) signals, such as
hum, noise, etc. This rejection

is

an inherent prop­erty of differential amplifiers. The common-mode
signals are attenuated by 40 db
differential input

is

amplified.

(100:1), whereas any

4-13. The vertical amplifier consists of three sets
of balanced differential amplifiers

(Vl, V2, and V3)

in cascade. The three stages are neutralized by

plate-to-grid cross neutralization. The first stage,

V1, has balance and gain adjustments. The balance
adjustment (BAL)

is

potentiometer R16 in the cathode

circuit, which adjusts the current distribution be-

tween the two triodes. Potentiometers
control) and

R20 (CAL) adjust the resistance between

R21 (VERNIER

the plates and therefore determine the gain of the am­plifier. The VERTICAL VERNIER control provides

a

ten-to-one variation in gain between ranges of the
VERTICAL SENSITIVITY switch. The second differ­ential amplifier,

V2, has potentiometer R32 (vertical

POSITION control) between its cathodes. This po­tentiometer controls the current distribution between
the two triodes and thus determines the vertical posi­tion of the crt display. The third differential
fler, V3,

is

the output stage. Synchronization signals

ampli-

are taken from the plates of V3 for application to the
TRIGGER SOURCE switch. Since the horizontal
sweep circuits trigger only on the negative slope of
the signal, provision is made to take the proper syn­chronizing signal from either plate of V3.

4-14. One section of the BEAM FINDER switch is in

the cathode circuit of V3.

When pressed, the switch

increases the common cathode resistance and so re-

duces the gain of the stage that no amount of unbalance
ahead of V3 can deflect the sweep off the crt.

4-15. The calibrator circuit consists of neon lamps
V4,

V5, and associated circuit parts. When VERT-

ICAL SENSITIVITY switch

S2 is placed in the CAL

position, V4 ionizes and capacitor C14 begins charg-

ing. As the voltage across capacitor C14 rises, the

voltage at the junction of V4 and R52 rises propor­tionally. When the voltage at this junction reaches
the firing potential of
ducting potential of V5

V5, V5 ionizes. Since the con-

is

less the firing potential, the
voltage at the junction of V4 and V5 drops, and V4 de­ionizes. C14 discharges through

R53, and the poten-

tial across V4 increases. When the potential across

FROM

ITRIGGER

SOURCE

SW

SYNC

I

-+

9

[TRIGGER LEVEL

I

I

I

TRIGGER

GENERATOR

v201

-

Figure

I

-

NETWORK

4-2.

TRIGGER

v202

STOP

A

HOLD-

OFF

CATHODE

FOLLOWER

V203B

Sweep Generator,

i

Block

SWITCH DIODE

CLAMP

V203A

A

-

Diagram

GATE-OUT

CATHODE

FOLLOWER

V204

-v

n

'

I V205A

I

I

I

I

:--

ISWEEP

MAGNIFIER]

*

-

UNBLANKING
GATE TO
HIGH-VOLTAGE
POWER SUPPLY

SAWTOOTH

*

INTEGRATOR

+

SAWTOOTH

CATHODE

FOLLOWER

V205B

-

A

TO
HORIZONTAL

AMPLIFIER

83-U-267

01260-1

Model 120B

Section

IV

Paragraphs 4-16 to 4-22

GRlD OF

V201A

PLATE OF
V201B

JUNCTION

OF C207

C208

AND

PLATE OF
V202B

GRID OF
V203B
(SEE NOTE)

GRlD

OF

V202A

-1

'

-

I

I

I

I

I

I

I

I

I

I

I

I

I

I
I

I

I

I

1

I

I

I

I

I

I

I

I

I

LENGTH

OF

SAWTOOTH

TIME CONSTANT

ON RC
SELECTEDBY

HORIZONTAL

SWITCH

DISPLAY^

DEPENDS

LD-S-

530

the negative-going output

is

applied to switch diode

CR201.

4-19. Switch diode CR201 normally clamps the input
to sawtooth integrator
age, preventing sawtooth integrator
erating a sawtooth waveform. When the
going step signal from the start-stop trigger
to the switch diode, however, the diode

V205A to a low negative volt-

V205A from gen-

negative-

is

applied

is

reverse
biased and allows the sawtooth integrator to generate
a sawtooth waveform.

4-20. The sawtooth output of

V205B

applied to the horizontal amplifier to serve

is

simultaneously

as

the

horizontal sweep signal and the hold-off cathode fol-

V203B. The output of the hold-off cathode fol-

lower
lower

is

applied to the input of the start-stop trigger

terininate the sweep. The values of R and C selected

to
by the HORIZONTAL DISPLAY switch determines the

slope of the
Clamp V204 ensures that the sawtooth always

sweepand therefore the time of the sweep.

starts

at the same level. Figure 4-3 shows the relative
timing of the sweep generator waveforms.

4-21. TRIGGER GENERATOR V201. (See figure

5-8.)

SOURCE switch
resistor

is

control
form of bi-stable multivibrator, and

The sync signal selected by the TRIGGER

is

applied through capacitor C202 and

R201 to the input control grid of V201, which

a Schmitt trigger circuit when the TRIGGER LEVEL

is

not in AUTO. The Schmitt trigger

is

used to obtain

is

pulses with rapid rise and fall times.
4-22. Figure 4-4 illustrates a simplified Schmitt

If

trigger and typical input and output waveforms.

is

itially the input voltage (figure 4-4)

+

DC

such that V1

in-

is

a

Figure 4-3. Sweep Generator Waveforms

V4 reaches the firing potential, V4 fires and the volt-

4

b

(w

OUTWT

age at the junction of V4 and V5 drops, deionizing V5.
C14 starts charging again, and the cycle repeats. A

is

60-mv square wave

this signal

is

applied through the SENSITIVITY switch

developed across R54, and

I

INPUT

v2

v

to the vertical amplifier.

4-16.

SWEEP GENERATOR.

4-17. BLOCK-DIAGRAM DESCRIPTION. (See figure

4-2.) The sync signal from the TRIGGER SOURCE

is

switch

applied to trigger generator V201. The trig-

-

-

-

-

-

ger generator produces a rectangular wave with a
repetition frequency equal to that of the input sync
signal. This rectangular wave is applied to a differ-

it

entiating network which converts

to positive and
negative spikes that are coincident with the leading
and trailing edges of the rectangular wave. These
spikes are then applied to the input of start-stop trig­ger V202.

4-18. The negative spike switches the start-stop
trigger, which produces two step outputs. The posi-

is

tive-going output

applied through V204 to the high-

-

ob

-

-

a

I

b

LO 5-53!

voltage power supply as the crt unblanking gate, and Figure 4-4. Typical Schmitt Trigger

Section IV

Paragraphs 4-23 to 4-32

Model 120B

cutoff, V2 conducts. As the input voltage becomes
more positive, it eventually reaches a predetermined
level (a) at which the circuit changes state; that

V1 conducts and V2
goes negative, the common cathode potential decreases
and the grid of V2 becomes positive. When the input

reaches a second predetermined level
and the circuit switches back to
output of the circuit
or negative depending upon the slope of the input

signal.

4-23. The input voltage levels at which a Schmitt
trigger circuit switches are called the hysteresis
limits. Note that the circuit (figure 4-4) does not
switch unless the input crosses both limits.

4-24. Trigger generator V201 has some additional

features: the TRIGGER LEVEL control adjusts the
bias on

input trigger must reach to change state; in addition,

when the TRIGGER LEVEL control

limit, switch S202
shunt across resistor R207 and capacitors C205 and
C206, and the trigger generator becomes an astable
multivibrator. This provides triggers to the
start trigger even though no sync is applied to the

trigger generator. When a sync signal above approxi-

mately 50 cps

erator then synchronizes with the sync signal. The

step output of the trigger generator

plate of

4-25. DIFFERENTIATING NETWORK. (See figure
5-8.) The differentiating network
series combination of capacitor

and resistor R210. The r-c time constant of this net­work
the trigger generator output pulses; consequently, the

signal developed across inductor L201 and resistor

R210 consists of short negative and positive spikes
that are coincident with the leading and trailing edges
of the trigger generator output pulses. These spikes
are coupled through capacitor C208 to the control grid
of

4-26. START-STOPTRIGGER
AND SWITCH DIODE CR201. -(See figure 5-8. ) The
start-stop trigger is a Schmitt trigger circuit. A

typical Schmitt trigger

V202 is triggered by a negative spike pulse from the
differentiating network. One output step waveform is
taken from the plate of
plies to switch diode

V203A. The waveform applied to V203A cuts off

V203A, and thus disables the clamping action of this
tube. The waveform applied to switch diode

reverse-biases the diode, and thus it ceases conduc­tion. Another step output

V202A and applied through cathode follower V204 to
the high-voltage power supply; this serves as the crt
unblanking gate.

4-27. SAWTOOTH GENERATOR

TOOTH CATHODE FOLLOWER

V2OlA and thus determines the level which the

V201B andapplied to a differentiating network.

is

extremely small compared with the width of

V202A, one half of the start-stop trigger.

is

cutoff.

is

a voltage step, either positive

is

placed in AUTO. This opens the

is

applied, however, the trigger gen-

is

V202B and simultaneously ap-

CR201 and the grid of clamp

If

the input voltage then

(b),

V2 conducts

its

initial state. The

is

at its extreme

is

taken from the

is

composed of the

C207, inductor L201,

V202, CLAMP V203A,

described in paragraph 4-22.

is

taken from the plate of

V205A AND SAW-

V205B. (See figure

is,

stop-

CR201

5-8.) Sawtooth generator
tegrator which produces a linear sawtooth waveform.
When switch diode
tegrating capacitor charges through the integrating

resistance, producing a negative-going potential at
the control-grid of
the plate of

cathode follower

completing the negative feedback required by this

Miller type integrator.

4-28. The sawtooth signal at the cathode of
also applied to SWEEP MAGNIFIER switch S102.
When ,9102
to the horizontal amplifier has
times greater than that applied when S102
position; hence, the angle of slope is increased five
times and the sweep time
by the HORIZONTAL DISPLAY switch.

4-29. The sawtooth signal at the cathode of
applied to the control grid of V202A. When the slope
of the signalreaches the upper hysteresis limit of the
start-stop trigger, the trigger changes state; hence,
the unblanking gate output of
The switch diode
respectively, halting the charging of the integrating
capacitor and terminating the sawtooth waveform.
The hold-off capacitor in the cathode of
during the rising slope of the signal output of the
off cathode follower but does not immediately dis­charge when the sawtooth input to the hold-off cathode
follower terminates. This prevents the start-stop
trigger from again being triggered by a negative spike
until the sweep circuits have fully recovered. A dif­ferent value of hold-off capacity
setting of the HORIZONTAL DISPLAY switch.

4-30.

4-31. The grid of VlOlA (figure 5-7) receives either
the sweep output from the horizontal sweep circuits
or from an external sweep source, depending on the
setting of the HORIZONTAL DISPLAY switch. When
external sweep is being used (EXT SENSITIVITY posi­tions), any one of three horizontal sweep sensitivities
can be selected:
VOLTS/CM. The AC-DC switch allows selection of
direct coupling, or ac coupling through capacitor
C101.

4-32. The horizontal amplifier consists of two dif­ferential amplifiers
the HORIZONTAL DISPLAY switch
EXT SENSITIVITY positions, the resistance between
the cathodes of amplifier VlOl consists of the hori­zontal VERNIER control
horizontal gain control
R107 is between the cathodes. The horizontal POSI­TION control (potentiometer
of VlOl controls the horizontal position of the crt
trace. The second stage

plate-to-grid cross neutralization. The output of the

horizontal amplifier
and applied directly to the horizontal deflection plates
of the crt.

V205A

is

HORIZONTAL AMPLIFIER.

CR201 ceases conduction, the in-

V205A. The amplified signal at

is

V205B to the integrating capacitor,

in the X5 position, the sawtooth applied

CR20l and clamp V204 again conduct,

.1

VOLTS/CM, 1 VOLTS/CM, or 10

(V101 and V102) in cascade. When

is

V205A is a Miller in-

coupled back through sawtooth

V205B

a

peak amplitude five

is

in the X1

is

one-fifth of that selected

V203B

V203A is terminated.

V203B charges

is

selected for each

is

set to one of the

(R275B) in series with the

(R104); otherwise, resistor

R109) between the plates

(V102)

taken from the plates of V102

is

neutralized by

is

is

hold-

Model 120B

Section

Paragraphs 4-33 to 4-40

IV

+I9 VOLT DC

AC

b

REGULATED

POWER SUPPLY

-

115/230 VOLTS

60

CPS

IPHASE

4-33.

the cathode circuit of

increases the common cathode resistance and so re­duces the gain of the stage that no amount of unbalance

ahead of V102 can deflect the sweep off the crt.

4-34.

4-3 5. BLOCK-DIAGRAM DESCRIPTION. (See figure

4-5.) The
plied through switch S301 to transformer
transformer applies 6.3 volts ac to the vertical am­plifier, horizontal amplifier, sweep generator, and
high-voltage power supply for use as filament voltage;
the transformer also applies appropriate ac voltages
to the following: the

supply; the
power supply; and the -150-volt dc regulated power

supply.

4-36. The regulated power supplies deliver their dc
outputs to the following circuits:
applied

'I9, + loo,

vertical amplifier, the horizontal amplifier, the hor-

izontal sweep circuits, and the high-voltage power

supply; in addition, the -150-volt supply applies
ative

supplies for use as a control voltage.

One section of the BEAM FINDER switch

LOW-VOLTAGE POWER SUPPLY.

to

voltage to the +19-. +99-. +loo-. and +300-volt

S301

--

I

I
I

115/230-volt, single-phase power is ap-

+300-, +loo-, and +99-volt dc regulated

the horizontal and vertical amplifiers; and

+300,

TRANSFORMER

T302

Yigure 4-5. Low-Voltage Power Supply, Block Diagram

V102. When pressed, the switch

+19-volt d-c regulated power

and

-

-

-

b

T302. The

+

19 volts dc is

are

'

to

aneg-

+420,*300,+
AND199 VOLTS

OC REGULATED
POWER SUPPLY

-150-VOLT DC

POWER SUPPLY

is

the

T

100

t

REGULATED

in

tor C325A. The resulting dc voltage
further by tubes

4-38. The circuit functions as follows: when power

is

justed properly) the cathode of V310 becomes fixed at

-65 volts and the grid assumes a slightly more nega­tive value.
change were to occur, tending to lower the supply
voltage, V310 grid potential would tend to change by
half the amount, since the grid
divider between -150 volts and ground. The result

is

raising

bias on

resistance, decreasing the voltage drop across this
element which tends to return the supply voltage
its original value.

4-39.
POWER

operates in almost exactly the same manner as the

-

150-volt supply except that it uses the - 150-volt sup-

ply

CR302, V307, and V308
ulator, and amplifier, respectively. The
+99-volt supply is further regulated by V308B, ref­erenced to the +300-volt supply.

+

19

VOLTS DC

TO AMPLIFIERS
VI,V2 AND VlOl

2)

+99VOLTS DC
+300 VOLTS DC
+I00 VOLTS DC
+420VOLTS DC UNREG

TO AMPLIFIERS,

6.3 VOLTS AC AND HIGH-VOLTAGE

-150 VOLTS DC

V309, V310, and V311.

applied (assuming the - 150-volt supply has been ad-

If

a line voltage surge or load current

increased bias for V310, lowering its current,

its

plate voltage, which, in turn, lowers the

V309. This bias change in V309 lowers its

+300-. +loo- AND +99-VOLT DC REGULATED

as

SUPPLY.

its

voltage

The +300-volt supply (figure 5-9)

reference.

are

the rectifier,

SWEEP CIRCUITS,
POWER SUPPLY

is

is

tied to a voltage

In

this

supply,

BD-M-268

regulated and

,to

CR301,

series

reg-

+loo- and

4-37. -150-VOLT DC REGULATED POWER SUP- (See figure 5-9.

PLY. The -150-volt supply (figure 5-91 in the 120B

is

used as a reference supply for the +300-, +loo-, CR304 and capacitor C328 for rectifier and filter.

and

+99-volt supplies; therefore, any change in the

-150 volt supply is reflected as a change inthese sup­ply voltages. The ac voltage from T302
and partially filtered by rectifier

CR303 and capaci-

is

rectified

4-40.
ments of vertical amplifiersvland V2) uses rectifier

Transistor

tial across Zener diode CR302 for its voltage refer­ence. The current in transistor
value of the dc voltage across the filaments.

+19-VOLT DC REGULATED POWER SUPPLY.

)

The +19-volt supply (for the

Q301

is

a

series regulator using the poten-

Q301 determines the

fila-