HP 211A Service manual

Model

211A

Table of Contents

List of Illustrations and Tables

TABLE OF CONTENTS

Section Page Section I GENERAL INFORMATION

1.1

.

General Description

1.9

.

Damage in Transit

1.11

.

Power Transformer Conversion

OPERATING INSTRUCTIONS

2.1

.

Controls and Terminals

2 -1 1

.

Instrument Loading

.

2 -1 7

Ringing

2.19

.

External Sync Operation

2.22

.

Pulses

2 .24

.

Balanced Output

THEORY OF OPERATION

.

3 .1

Introduction

3.3

.

Sync Trigger

3.7

.

Multivibrator

3.12

.

Clipper Amplifier

3-1 5

.

Power Amplifier

Number

2 .1

.

Common Impedance Matching Networks

2.2

.

Front Panel Showing Operating Controls

2.3

.

Basic Output Circuit of

2.4

.

Method of Obtaining a Balanced

Output from the

3.1

.

Block Diagram Showing Operating

Controls of

4.1

.

Model

Amplifier and Power Supply

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

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

21

211A

21

1A

Bottom View Showing

.........

..........

.

.......

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.......

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LlST OF ILLUSTRATIONS

.

211A

1A

......

.........

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

......

1-1 1-1 4.1 1-2 4.3 1-2 4.5

2-1 2-1

2 -1 2 -1

2-1 2-3

2-3

3-1 3 -1 3-1 3-1

3-1 3-2

Page Number

2-1 4.2 2 -2 3 -1 4.4

3 -3

3 -0 4.8

4-2 4.11

IV MAINTENANCE

.

4.3

.

4.5

.

4.6

.

4.7

.

4.9

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

4.10

.

Introduction

.

Cabinet Removal

.

Equipment Required

.

4.7

Trouble Localization

.

4.12

Tube Replacement

.

4.15

Adjusting the Power Supply

.

4.20

Frequency Calibration

4.24

.

Adjusting External Sync Sensitivity

4.27

4.41

REPLACEABLE PARTS

5 .1

5.2

Model Test Setup for Frequency Calibration

Test Setup for Sync Sensitivity

75-Ohm

Defects on Positive Portion Model Voltage and Resistance Diagram Multivibrator and Power Supply Output Section Range Switch Detail Attenuator Switch Detail

Sync Sensitivity

.

Waveform Observation and

Measurement

.

Servicing Etched Circuit

Boards

.

Introduction

.

Ordering Information

211A

Output Waveform which has

211A

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........

.........

.....

.......

.........

..........

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

.........

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

........

Top View

Waveforms

..........

......

.........

.....

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

.........

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

page

4-1 4-1 4-1 4-1

4-1

.

Page

4-5 4-6

.

4-6

LlST OF TABLES

Number Page

.

1.1

Specifications

.

4.1

Tube Replacement Chart

4.2

.

Test Equipment Required

4.3

.

Troubleshooting Chart

.

4.4

Calibration Chart

.

5.1

Reference Designation Index

5 .2

.

Replaceable Parts

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

..........

...........

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

........

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

1-1 4-0 4-1 4-3 4-4 5-2 5

-7

Section Figure

I

1-1

Model

211A

Figure

1-1.

Model

2llA

Square

Wave Generator

Model 211A

Paragraphs

Section I

1-1

to 1-5

SECTION

GENERAL INFORMATION

1-1.

GENERAL DESCRIPTION.

1-2. The @ Model 211A Square Wave Generator

precision wide range instrument particularly suited

for use with a fast oscilloscope for video amplifier testing, permitting a rapid examination of amplifier frequency characteristics computer, pulse code, telemetering, and similar applications it offers great convenience as a variable trigger source for switching purposes. In television work it

as

can serve cations it finds use in testinga variety of devices such uators, filters, delay lines and audio systems.

1-3. The Model

puts, one 75-ohm output and one 600-ohm output. The

rise time of the 20 millimicroseconds, which

Frequency Range

Low

a bar generator. In highfrequency appli-

is

valuable as a modulator source. It also

2llAhas been designed with two out-

signal

1

cps to 1 mc, continuous coverage.

Impedance Output:

-3.5 volt peak across 75-ohm load -7 volt open circuit, zero level clamped to chassis; rise time less than 0.02

up

to many megacycles. In

from the 75-ohm output

is

sufficiently fast to test

:

pec.

as

is

Table

is

atten-

only

1-1.

the response of video devices out to approximately 20

a

megacycles or toprovide age the signal across the 75-ohm internal impedance volts, or 3.5 volts peak-to-peakinto a 75-ohm external load. This output level may be adjusted with a 60-db step attenuator trol, a particularly desirable arrangement when low output levels are required.

1-4. The second output from the generator provides 55volts peak-to-peak from a source impedance of 600 ohms. The rise time of this signal microsecond with the output level controlled separately from that of the 75 -ohm output. Both outputs are used

simultaneously.

1-5. The frequency range of the instrument,

1

mc,

S~ecifications

Dimensions:

Cabinet Mount: 9-3/4 in. wide, 15-1/4 in. high, Rack Mount:

I

a

high speed triggeringvolt-

of

variable rate. The peak-to-peak amplitude of

in

combination with an amplitude con-

is

less than 0.1

is

covered in six 10/l bands. The frequency

14-5/8 in. deep.

m

11

nmm!BDL

t

1

cps to

is

7

High Impedance Output:

-27 volt peak across 600-ohm load -55 volt open circuit, zero level clamped to chassis; rise time less than 0.1

Relative Phase

180° phase difference between high and lowim-

pedance output

Amplitude Control

Low

Impedance Output - Potentiometer and 60 db attenuator, variable in 20 db steps. High Impedance Output

Frequency Control:

Dial calibrated

switch. Six bands.

Symmetry Control:

Allows exact square-wave balance.

Sync Input

Positive-going pulse or sine wave signal, min. amplitude 5 volts peak.

Power:

ii5/230 volts +looh, 50-60 cps, 225 watts.

psec.

:

signals.

:

-

Potentiometer.

"1

to 10" and decade multiplier

:

Cabinet Mount: Net 26 Rack Mount: Net 25 lbs, shipping

Accessories Available: (Cable Assemblies)

@

AC-16A.

coaxial cable terminatedwith dual banana plugs.

@

AC-16B. Four feet of RG-58C/U calbe terminated by UG-88/U type BNC male connector on the other.

$9

AC-16D. Four feet of RG-58C/U cable terminated on one end by

@

AC-16K. Four feet of RG-58C/U cable terminated by BNC male connectors on each end.

Four feet of RG-58C/U 50-ohm

a

dual banana plug on one end and

lbs,

shipping 38 lbs.

34

lbs.

a

BNC male connector.

a

Section

I

Paragraphs 1-6 to 1-12

dial

is

linearly calibrated from 1 to 10. The six positions on the range switch multiply these calibrations in decade steps.

For purposes of synchronization a

1-6.

is

ger circuit

located ahead of the multivibrator and

set to trigger on a minimum input sync

Schmitt trig-

signal

of 3 volts

is

peak, but a 5-volt peak sine wave or a positive pulse

is

signal

recommended for practical use. The sync trigger provides a fast trigger of uniform rise and amplitude which aids in

obtainingaccurate time switching of the frequency multivibrator, and at the same time isolates the. multivibrator from the input wave-

If

form.

no sync signal is used the multivibrator free-runs at a frequency controlled by the range switch and the frequency control.

Model 211A

frequency or range. This local feedback together with a regulated power supply assures an output essentially free from amplitude variations over the entire frequency range from

1

cps to 1 mc once the

output

controls have been set.

1-9.

DAMAGE

IN

TRANSIT.

1-10. After unpacking the instrument, should any shipping damage be discovered, follow the procedure described in the "Claim for Damage" sheet in this manual.

1-11.

POWER TRANSFORMER CONVERSION.

1-12. Should it be desired to operate the Model 211A from a 210-250 volt source proceed as follows:

The multivibrator employs two type

1-7.

6CL6 power

pentodes with precision components in the rc timing

networks. Residual variation in tubes

or time con-

stants may be compensated by a symmetry control

which balances the relative plate voltage swing on the

multivibrator tubes.

1-8. Two outputs are taken from the frequency multivibrator to drive a push-pull clipper amplifier consisting of two for four

parallel as the output power stage.

is

used in the power stage to stabilize the system

6CL6's. The clipper serves as the driver

6CL6 power tubes arranged in push-pull

Local feedback

against variations in output level with a change in

a. Remove the two bare wire jumpers from the

terminal strip located beneath the power transformer.

These jumpers connect the Black to the Black-Green lead and the Black-Red to the Black-Yellow lead of

the power transformer primary.

b. Insert a new jumper on the terminal strip which

will connect the Black-Yellow to the Black-Green lead.

c. Change line fuse

F1 to one with a 1.25 ampere slow-blow rating. As shown in the schematic diagram, this alteration changes the primary windings of the power transformer from a parallel to a series

arrangement.

Model 211A

Section

Paragraphs 2-1 to 2-21

I1

SECTION

OPERATING INSTRUCTIONS

2-1. CONTROLS AND TERMINALS.

2-2. ON. Applies line voltage to the instrument. 2-3. RANGE. Switches time constants in the

vibrator circuit to establish various frequency ranges.

FREQUENCY.

to

produce

RANGE switch position.

2-5. OUTPUT AMPLITUDE. The 600 51 control varies the amplitude of the signal at the 600 51 output terminals. The 75 51 controlvaries the signal voltage applied to the 75 51 output attenuator.

51

2-6. 75 jack in 20 db steps below the level set with the OUTPUT AMPLITUDE control.

2-7. SYMMETRY. A balance potentiometer in the multivibrator plate circuit which effectively balances the amplitudes of the signals tothe multivibrator grids and equalizes each square wave half cycle.

2-8. 600 51 OUTPUT. Two three-fourth inch spaced binding posts which serve a sync out connection when 7551 output

ATTEN. This control reduces the output

':lo

Varies

the

frequency change

as

the 600 51 output, or

is

On

in use.

multi-

grid

each

75

as

51

II

2-15. When it second rise time, 75-ohm output cable should be used

(RG-59/U). When it

systems other than 75 ohms, it both ends of the output cable to impedance.

2-16. Physical arrangements for use in matchingthe instrument output to common impedances are shown

in figure 2-1.

OUTPUT

75n

is

desired to realize the 20 millimicro-

is

desired to drive low impedance

is

necessary to match

its

characteristic

75fi (RG-59lU)

*

-

75

n

OUTPUT

t

93 A (RG-62lU)

b

-

2-9. 75 serves connector when the 60051 output

2-10. SYNC SYNC trigger which accepts sine waves or positive

pulse synchronizing

of 5 volts peak.

a

slightly lower frequency

nized frequency. Figure 2-1. Common Impedance

2-11. INSTRUMENT LOADING.

2-12. For low frequency applications involving high impedance devices under test the output from the-211~ may 600-ohm terminal with little effect on the square wave characteristic and the calibration of the 75-ohm attenuator.

2-13. greater attention to impedance matching and line losses in order to preserve attenuator calibration and to prevent deterioration of square wave shape.

2-14. rent pulse with internal impedances. The use of the 75-ohm terminal

permits

the 75-ohm internal impedance, and the 75-ohm ator allows these square waves to tude without destroying their characteristics.

51

OUTPUT. A female type BNC connector

as

the 75 51 output connector, or as a sync out

is

in use.

IN.

A female typeBNC connector to the

signals

FREQUENCY control must be set at

be

taken from either the 75-ohm terminal or the

Low

impedance devices, however, require

The Model 211A produces

a

peak value of

a

fast rise square wave to

with a minimum amplitude

than

the desired synchro-

a

square-wave cur-

100 ma across

be

developed across

attenu-

be

reduced in ampli-

its

75

n

OUTPUT

77:.

-

Matching

2-17. 2-18. Most video amplifiers or rlc circuits resonant

below 30 mc are subject to ringingwhen rise pulse or square wave. these cases to reduce this effect by proper matching before assuming faulty operation of the Model

2-19. EXTERNAL SYNC OPERATION.

2-20. With the instrument externally synchronized, the Schmitt trigger will control the switching of the multivibrator only when the period of the multivibrator

is

2-21. To permit the Schmitt-trigger output to fire the multivibrator, set the FREQUENCY control to a value slightly less use. This setting permits the trigger pulse to fire in

RINGING.

slightly greater than that of the external sync signal.

than

a

free-running recovery.

~etworks

hitwith a fast

Care should be taken in

the frequency desired for sync

(RG-581.

SD-M-8

211A.

2-1

Section

Figure 2-2

II

Model 211A

OUTPUT AMPLIT

LD- L-

I9

1.

RANGE. Select range of output frequency 6. 7552ATTEN. Attenuate voltage at 7552out-

desired.

2. FREQUENCY. Select output frequency.

3. OUTPUT AMPLITUDE 60052. Adjust output signal voltage

4.

OUTPUT SIGNAL. Source impedance 600% tube.

5. OUTPUT AMPLITUDE. Adjust output volt-

age at 7552 output jack.

at

60052 output terminals.

put jack in 20 db steps.

7. OUTPUT SIGNAL. Source impedance 7552.

8.

SYMMETRY. Adjust square-wave output

voltage symmetry by viewing on cathode ray

9.

SYNC IN. Apply external nize square-wave output signal.

signal

to synchro-

-

Figure

2-2.

Front Panel Showing Operating Controls

00093

-

3

Model 211A

Section

I1

Paragraphs 2-22 to 2-29

2-22.

PULSES.

2-23. The clipper amplifier and output tubes in the Model 211A operate in a circuit designed for a duty cycle. The balance of this circuit

is

maintained

50%

by the SYMMETRY control which balances the two

as

padding

range of

this

outputs from the multivibrator. Any alteration of circuit attempting to generate pulses, such the SYMMETRY potentiometer to extend

its

control, would overdrive one side of the clipper amplifier and output tubes beyond the 50% duty cycle factor to the eventual damage of the instrument.

2-24.

BALANCED OUTPUT.

2 -25. The 21 1A can be converted to a balanced source

without modifying the instrument in any way. Figure

2-3 shows the basic arrangement of the output circuit. The output tubesthemselves are in push-pull but have unequal loads as

shown A balanced voltage can thus be obtained by equalizing the tube loads. This can be done directly

75n

LEVEL CONTROL

T

OUTPUT

at

the terminals on the panel.

OUTPUT

ATTENuATOR

nn

OUTPUT

figure 2-4. This additional resistance will reduce the source impedance at the lower terminals to about 75 ohms and will also reduce the voltage available from the lower terminals to approximately the same amount available at the upperterminal. At the same time the additional resistance will form a more favorable time constant with the stray capacity

Co at the lower terminals and thus speed up the normally slower rise time at those terminals until

comparable to

that

of the

it

is

75-ohm output. 2-27. Figure 2-4 suggests the use either of two

75-

ohm cables or abalanced 150-ohm cable for connecting

to the load.

In.

either of these cases

it

is

normally unnecessary to terminate the cables, so that they can be connected directly to the load. The arrangement

has

the advantage that

If

impedance.

cables of other impedances are used, they should be terminated ance of the cable. This will involve

it

can be used with any load

inthe characteristic imped-

a

consideration

of the load impedance in some cases.

75n

OUTPUT

BALANCED

TWO

75n

150n

CABLE

0

R

COAXIAL

1

cneLes

-

-------

OUTPUT

Figure 2-3. Basic Output Circuit of 211A.

2-26.

In

figure 2-4 the upper terminal represents the 75-ohm output and the lower terminals represent the 600-ohm output. To equalize the source impedance at the two outputs, a resistance of 86 ohms can connected across the lower terminals

as

be

shown in

SEE

TEXT-

'

Figure 2-4. Method

Output from the 2

of

Obtaining a Balanced

11A

2-28. The output voltage can be selected most conveniently if the 75

ATTEN. output

is

first set to

S2

zero. The two OUTPUT AMPLITUDE controls will

then have about the same voltage range and each should

as

be set

necessary to obtain one-half of the desired

output voltage. This will occur when both controls are

If

at about the same angular position.

desired, both

line-to-ground voltages can be measured with a volt-

meter or an oscilloscope. 2 -29. Output voltage will be as high as 14 volts

peak-

to-peak, open circuit, and 7 volts peak-to-peak ter-

minated with 75 ohms.

Section

Figure

III

3-1

Model

211A

SYNC

IN

SCHMITT

TRIGGER

(SINE

OR

POS.

-

PULSE)

OSYMMETRY

\

I

,

AMPLITUDE

-

PLATE

COUPLED

Iw

-v

I----

\

CLIPPER

AMPLIFIER

\

-

POWER

AMPLIFIER

0

\

-

ATTENUATOR

\

-

o.20.40,

+600fL

+75n

-

P

\

-

\

-

\

I

-

Figure

3-1.

Block Diagram Showing Operating Controls of

211A

Model 211A

Section

Paragraphs 3-1 to 3- 18

III

SECTION

CIRCUIT DESCRIPTION

3-1.

INT~?ODUCTION.

3-2. Maior circuit elements are shown in the circuit

diagram figure 3-1. Special aspects

block

circuit elements are discussed in subsequent paragraphs to supplement the general discussion in para-

1-1.

graph

3-3.

SYNC TRIGGER.

3-4.

The

sync trigger switcheswith the application on the input grid. The circuit configuration

tional for a Schmitt trigger except the placed in the trigger-output circuit to produce spikes.

Since the Schmitt trigger changes state once on the

positive-going portion the negative-going ~"rtio% two spikes are developed across the and the other negative.

3-5.

grid of one multivibrator tube (V3) cutting off conduction. Conduction then starts in V2. For the sync

trigger to effect a synchronized condition inthe multivibrator, the negative cut-off pulse from the trigger

must

cut-off in a free-running condition. This

lished

(with the FREQUENCY dial) to a value slightlv less

than

3-6. the Schmitt-trigger circuit adjusting the cathode level.

so that the triggering level of the trigger input grid.

3-7.

3-8. The multivibrator (V2 and V3) free-running, plate-coupled multivibrator. The frequency of operation return voltage with R37 (FREQUENCY control) over

3-9. The RANGE switch S2 inserts various rc time constants into the grid return circuit, and these time constants establish the rate of decay for the cut-off side of the multivibrator toward the voltage established

by the FREQUENCY control 3-10. The diode clamp controls the current of the con-

ducting side of the circuit and thus controls the voltage drop across the plate load resistor of the conducting

half.

clamp control cathode follower V5. Since this adjustment determines the startingvoltage level for decay in the section cutting off, the frequency of operation, and the instrument initially at 1000 The function of the clamps

L1, L2 differentiating circuit, one positive

The

reach

that

Output grid bias (effectively,sync sensitivity) in

This voltage

the grid

the

operator setting

of the incoming sync signals.

MULTIVIBRATOR.

is

a

Schmitt

of

a

of

an

is

of

V3

the

is

adjusted with R10, thus

R10

is

3 volts above the level

is

varied by adjusting the grid

R37.

established by adjusting

it

also exercises control over

it

cps on the XlOO range.

is

to stabilize the frequency

trigger

positive going signal

L1 and L2 are

signal and once on

through

the

tube

free-running

normally adjusted

is

a conventional,

is

used to calibrate

is

conven-

CR1

reaches

is

accomp-

R31

these

which

to

the 3-14. At high frequencies, the effective

rate

on the

Ill

of operation against changes in the circuit such as tube aging, line voltage, and filiament fluctuations.

3-11. The output

push-pull drive for the clipper amplifier V6 and V7.

3-12.

3-13. Clipper amplifier tubes V6 and V7 alternately conduct drivers for the output tubes.

clipper

fier stage through a broadband inter stage network con-

sisting

the R57, R58, sensitive

of

ages

normal plate load resistors

are reduced to preserve fast rise time of the square

waves.

C21 through C23 to ~22 through

this path the high

and R58, since these are small compared to the nor-

mal

3-15.

3-16. The power amplifier consists of four type 6CL6

tubes arranged in push-pull parallel with a constant

resistance network in the cathode circuit, R65, R66,

R67, and L8. This network compensates for the effects of heater-cathode capacitance on the leading and trailingedges of square wave output duringtube switching. The output tubes, like the clipper amplifier stage, alternately conduct and cut-off. The compensating network introduces a reactive transient into the cir-

cuit with a sign opposite to that produced by the tube elements during switching.

3-17. Each side of the power amplifier furnishes a

separate output to the output stage of the instrument. The low impedance output passes through a 75-ohm potentiometer (OUTPUT AMPLITUDE control) to 75-ohm three-section pi-filter. The 600-ohm output passes through a 600-ohm potentiometer (OUTPUT AMPLITUDE control) to the output terminals. The 600a OUTPUT AMPLITUDE control ometer and consists of two 1200-ohm sections lel to accommodate heat dissipation requirements.

3-18. Since the power supply

to the chassis and the output

square wave

ground terminal. Thus the negative portion of the

source wave

portion

CLIPPER AMPLIFIER.

and cut-off in opposition, and serve as the

amplifier

of

C19,

associated

C21

to

the output tubes. ~h~ ,-.lipper amplifier

for

low

The

plate loads whichtheyparallel at highfrequencies.

POWER AMPLIFIER.

is

at ground potential.

from

the rnultivibrator furnishes

The outputs from the

are

dc-coupled to the power ampli-

and

R52,

C20

and

R53,

togetherwith

plate

load

and

C22.

maintain

resistors

This

a

including ~55, R56,

network

voltage on the grids

is

frequency

output

frequencies

high

frequency

B+

C-3

to

B+

frequency

is

actually negative with respect tothe

is

below ground potential and the positive

are

developed

(R56, R50, R51, ~54).

path

is

at

chassis ground, and by C20,

at

chassis ground.

plate loads become R55

is

negativewith respect

is

direct coupled, the

across

plate

defined

is

a dual potenti-

by

~h~~~~h

inparal-

volt-

the

loads

C19,

a

Section IV Table 4-1

-

TUBE

TYPE

Table 4-1. Tube Replacement Chart

FUNCTION

ADJUSTMENT REQUIRED

Model 211A

V1

V2 V3 V4 V5

V6 V7 V8 V9 V10 V11

V12 V13 V14 Vl5

6BQ7 6CL6

6CL6 6AL5 6 C4

6CL6* 6CL6* 6CL6* 6CL6* 6CL6* 6CL6*

5V3

6AS7GA

6BH6 Control Tube

1

5651

*Type 6197 tubes may

Schmitt trigger 1/2 Multivibrator

Multivibrator

1/2 Diode Clamp Clamp Control Cathode Follower

7552 Output Clipper Amplifier 60052 Output Clipper Amplifier 7552 Output Tube 7552 Output Tube 60052 Output Tube 60052 Output Tube

Full-Wave Rectifier Series Regulator

1

Reference Tube

be

used in place of type 6CL6 if desired

Adjust SYNC SENSITIVITY, paragraph 4-24 Recalibrate FREQUENCY dial, para. 4-20

dial, dial, dial,

para. 4-20 para. 4-20 para. 4-20

Recalibrate FREQUENCY Recalibrate FREQUENCY Recalibrate FREQUENCY

No adjustment No adjustment No adjustment No adjustment No adjustment No adjustment

Check power supply output (paragraph 4-15) Check power supply output (paragraph 4-15) Check power supply output (paragraph 4-15) Check power supply output (paragraph 4-15)