RCA VoltOhmyst WV-77C Specifications, Operation, Applications, Maintenance

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PRICE 0NE DOlLAR

Type WV-77C

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• SpecifkatioriS~

JUNIOR

VOLTOHMYST®

ELECTRONIC METER

• Operation

• Applications

'. Maintenance

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RADIO CORPORATION

TEST AND MEASURING EOUIPMENT ~ ,"ARRISON_ N.

AMEN-rCA

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Safety Precautions

The metal case of this instrument is connected to

the ground of the internal circuit. For

tion, the ground cable of the WV-77C should always be

connected to the ground of the equipment uncler test.

The WG-299B DC/AC-Ohms Probe and Cable has a

shield throughout its length which is connected to the

instrument ground and case. Always handle the WG·

2998 by the insulated probe housing.

An important point to remember is that there is

always danger inherent in testing electrical equipment

which operates at hazardous voltages. Therefore, the

operator should thoroughly familiarize himself with

the equipment under test before working on it, bearing in mind that high voltages may appear at unexpected points in defective equipment. Additional precautions

which experience in the industry has shown to be important are listed below.

It is good practice to remove power before can·

necting test leads to high.voltage points. impractical, be especially careful to avoid accidental

contact with equipment racks and other obj ects which

proper

opera-

this is

can provide a ground. Working with one hand in your

pocket and standing on a properly insulated floor les-

sens the danger of shock.

2. Filter capacitors may store a charge large

enough to be hazardous. Therefore, discharge filter capacitors before attaching test leads.

3. Remember that leads with broken insulation

provide the additional hazard of high voltages appear·

ing at exposed points along the leads. Check test leads

for frayed or broken insulation before working with them.

4. To lessen the danger of accidental shock, discon-

nect test leads immediately after test is completed.

5. Remember that the risk of severe shock is only

one of the possible hazards. Even a minor shock can

place the operator in hazard of more serious risks such

as a bad fall or contact with a source of high,er voltage.

6. The experienced operator continuously guards

against injury and does not work on h.~zardous circuits

unless another personisavailabk to \assist in case of

accident. ...... --...

ACCESSORIES

Supplied with WV·77C '" "'

D~/AC-Oh~s Probe.and Cable .. ~

1 Shp-On . .lhgator Clip. . Stock No. 210088

I 1.5-Volt Battery. . . . . . . . . . . . . . .. . Type VS036

I RCA-I2AU7 Tube I Registration Card

I RCA·I2AL5 Tube Clip Insulator I Instruction Booklet

..-./

--'-1.'! '

Type WG-299B

Cables and probe supplied with WV·77C

-:::;...~

Available on Separate 9rder

For Measuring AC Voltages at Frequencies from 50 Kc t0250 Me:

Crystal-Diode Probe Type WC.30IA

For Increasing DC Voltage Range to 50,000 Volts:

High-Voltage Probe ... . Type WG-289

NIultiplier Resistor .. . Type WG·206

Devices or arrangem~nt. ~ho""n or tle~cribed herein may ""C patenl~ of her~ini.furni!hed withon' responsibility by

1956 by Rgdio Corporglion of Americg

TMK ®, Mgrcg Regi.lrodg

RCA

for it~ use lint.! without prejutlice to

TEST AND MEASURING EQUIPMENT

RADIO CORPOHATION OF AMERICA, HARBISON, NEW J£H.SEY

or I)ther~. Information co[]tail]~d

RCA'&

patent

r;~"I~.

Inst'- WV-77C

Printed in U.S.A.

(l)

10-56

Safety Precautions _ .

General Desci·jptlon ..

Functions of Controls and Terminals ...

Specifications .. .

Operation and Applications . ..

Accessories . .. ..

Special Applications ..

11aintenance .. . ..

Schema tie Diagram

Replacement Parts List

Page

2 4

4 5 5

8 9

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MILl1WATTS IN 600-0HM RESISTIVE LOAD AT 1000 CPS

10 100

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10'

6 7 8

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92CS·7130

6 7 6

100

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A.C. VOLTS(RMS) MEASURED

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£,

7:8

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0.775

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ACROSS 600-0HM RESISTIVE LOAD AT 1000 CPS

Note: For loads other than 600 ohms, sec

Figure 1. Chart for conversion of rms voltage to dbm values.

lable

on page 10

·3'

General Description

The Junior VoltOhmyst-* WV-77C is designed to

measure de voltages from 0.1 volt to 1200 volts, rms sine-wave voltages from 0.1 volt to 1200 volts, and

resistance values from 0.2 ohm to 1000 megohms.

The ae voltmeter of the

~rV-77C

features an electron

tube as the half·wave rectifier. It is a peak indicating

type -and is calibrated in terms of the rms voltage of a

sine wave. The V.rV-77C has high input impedance on

all de and ae voltage ranges. Only two cables are used

with this instrument for all measurements, providing

ease and flexibility in operation.

The frequency range of the WV-77C, depending on

the impedance of the voltage source, is flat to approxi-

mately 3 megacycles. When the auxiliary \VG-301A

Crystal Diode Probe is used, the dc voltage ranges are

accurate to within ±10% from 50 Kc to 250 Kc.

The WV-77C is equipped with a single unit probe,

the WG·299B DC/ AC-Ohms Probe and Cable_ This

probe is provided with a built-in switch which permits

quick adaptation to either dc-voltage measurements or

ac-voltage and resistance measurements without requir-

ing a change of probes and cables_

The Junior VoltOhmyst-ufilizes

~~e de bridge circuit which _ arordr" excellent

lineariij-_.f response, good stability, -and very high

input impedance. (See Schematic Diagram, Fig. 5.)

When no measurement is being made, the cathode cur-

p,ush-put{ ampli.

rents through the triodes of V2 are equaL When a

measurement is being rnade~ a voltage is applied be-

tween the grid of V2A and ground to provide a change

in cathode current of this triode unit_ Since resistor

R20 functions as a cathode-coupling element, the

change in cathode current through this resistor alters

the grid-to-cathode potential of V2B, a condition which

modifies the cathode current of V2B. When, for ex-

ample, the current flow through V2A increases, the

flow of current through V2B decrea.ses. The meter

reading is proportional to the difference between the

plate currents of the triodes.

AdditlOnal features of the \VV-77C include provi-

sion for zero-center indication, useful in descriminator

and bias measurements; separate 'scales for low ac.

voltage measurements; a circuit desig,n which allows

measurements of the ac component

the de component is pre~ent dnd vice ,~ersa; a separate

dc probe with a I-megohm resistor which minimizes

capacitance-loading effects; and electronic protection

against meter burn-out.

The \VV-77C Junior VoltOhmyst is a light-weight

compact, and versatile instrument. -A reliable meas-

uring device, it will prove extremely useful in tele-

vision applications as well as in many industrial

applications.

*Trade !\tark "VoItOlunysl" Reg. U. S. Pal. Off.

~-...f

a signal when

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,LFunctions

Function selector~Has two functions; turns the

power off in "OFF" position, and permits choice of

type of measurement to be made.

Range selector-Permits choice of range for the

desired voltage or resistance measurement.

ZERO ADJ control-Used to position the meter

pointer at either the left-hand "0" position or to the

zero·center

set to

OHMS ADJ--control-Used to position the meter

"-0+"

"+VOLTS".

position, when function selector is

of Controls and Terminals

pointer at the extreme right line on the "R" scale when

the function selector is in "OHMS" position.

VOLTS OHMS terminal-Voltages and _resistances

to be measured are applied between this terminal and

the clip of the GROUND cable as described under

"operation" below.

GROUND cable--is directly connected to the chassis

of the instrument. It serves as a common ground for

the

~rV-77C

test or associated test instruments .

and the chassis of the equipment under

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