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

Download

Page 1

PRICE 0NE DOlLAR

Type WV-77C

~:..

".-:.

• SpecifkatioriS~

JUNIOR

VOLTOHMYST®

ELECTRONIC METER

• Operation

• Applications

'. Maintenance

ZfRO AUI

~ WV_77C

..;:~s

AOJ~· ~).

i~ ,~ ~

V ~.' \~)'

6QV ~'

12 V R ~ fOOQ

R , 1D~. • • R. 1001( VOLTS.·. VOlTS

JOD

.IZOOV Off .~. 0 liS

~ , 1 NEG H

At VDtTS -

•

~~-

RADIO CORPORATION

TEST AND MEASURING EOUIPMENT ~ ,"ARRISON_ N.

AMEN-rCA

y---

Page 2

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

Page 3

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

~ +3

~ ~

0.1

MILl1WATTS IN 600-0HM RESISTIVE LOAD AT 1000 CPS

10 100

,- ,-

10'

6 7 8

.......

:-_.

•

, ,

92CS·7130

6 7 6

100

-I

0.1

, ,

A.C. VOLTS(RMS) MEASURED

, ,

£,

7:8

(.0

0.775

, ,

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'

Page 4

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

.../~

,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

• 4 •

Page 5

Specifications

Electrical

DC Voltmeter:

Ranges. 0 to 3, 12, 60, 300, 1200 volts

Input Resistance (With

With WG·299B switch set to "DC":

All Ranges.

Accuracy:

With Function Selector. Set on "+VOLTS"

With Function Selector Sct on 'I-VOLTS"

AC Voltmeter:

Ranges:

RMS Values of Sine Waves.

Accuracy. . . . . . . . .

Input Resistance and Capacitance-Ap.prox.

(with WG-299B switch set to "AC") : 0

3, 12, and 60-V Ranges .. " O,,2~ohm shunted by 75

3aO-V

Range

1200-V Range 2 megohms shunted by 50

Frequency Response (with WG-299B switch set to "AC" ) :

For Source Impedance of 100 Ohrrts#. . flat within±1 db

For Source Impedance of 1000 Ohms# ... flat within±1 db

With Crystal-Diode Probe WG-2M.&.... flat within±1 db

..... ().. . separate scale

~ 0to12, 60, 300,

tAJP 1200

-e. ..

megohm shunted

11 megohms

±3%of

±5%of

{

from 30 cps to 3 Me,

from 30 cps to

0.75 Me.

from 50 Kc. to 250 Me.

full scale

0to3

volts on

volts

5% of full scale

by 50

µµf

µµ£

Maximum Input Voltages:

Combined AC Peak Voltage and DC Voltage:

When Instrument is Set up to Measure DC .. 1800 peak volts

When Instrument is Set up to Measure AC:

3-volt. 12-volt, and 60-volt ranges. 400 de volts

300-volt and 1200-volt ranges. 600 de volts·

Ohmmeter:

Ranges, five. 0 to 1000 megohms

Center-Scale Values

10, 1000, 10000 ohms, 1.0 megohm, 10 megohms

Meter Movement:

DC Current for Full·Scale Deflection.

Tube CompleInent:.

Power Supply:

Voltage Rating.

Frequency Rating.

Consumption.

Battery:

1.5-volt cell. RCA Type VS036

. . _ .1 R<ll\-12ALS, 1 RCA-12AU7

105 to 125 volts

5 watts approx.

200 µa

50 to 60 cps

Mechanical

Over-all

Weight.

#The frequency response shown is for only the .~. 12. and 60-volt range~.

AAvailable on separate order.

*Combined AC Peak aud DC Voltages must not exceed 1800 volts.

Dimensions:

I'leight

Width

Depth

The in~tnllnent is accurateatpnwer.line frequencies for all ranges.

8 inches

5% inches

4% inches

4 pounds

Operation and Applications .......

Preliminiry Adjustments:

To prepare tlie ·\VV-77C

connections and adj ustrnents:

1. Connect the WG-299BDC/ AC-Ohms Probe and Cable to the VOLTS OHMS terminal.

2. Plug the power cord into an ac outlet supplying 105-125 volts at 50/60 cycles, and adjust the con·

troIs as indicated below:

a. Turn the function selector to

position, and allow several minutes for the instrument to warm up.

b_ Adjust the ZERO ADJ control to position the

meter pointer at the left-hand "0".

for

use~make the following

VOLTS" .

• 5 •

NOTE: To check this adjustment, notice whether or not the position of the meter pointer changes when the function selector is switched to

"- VOLTS".

the pointer position changes, readjust the mechanical zero control as de- scribed in the Maintenance Section.

c. Turn the function selector to "OHMS" posi-

tion. The pointer should deflect to approxi. ma.tely full scale.

•

d. Rotate the OHMS ADJ control to position the

pointer at the last line on the "R" (ohms)

•

scale.

The instrument is now ready for use.

Page 6

...

Operation and Applications

DC·Voltage Measurements:

CAUTION: See Maximum Input Voltages, under

ELECTRICAL SPECIFICATIONS,

When making dc-voltage measurements, the sliding

switch on the WG-299B probe should be set to "DC".

The WV-77C has five dc-voltage ranges: 0 to 3, 12,

60, 300, and 1200 volts. Although the meter is pro-

tected against burn-out,

a trial measurement at a higher range setting than is

considered necessary, because long-continued or re-

peated overload of the meter movement may eventu-

ally impair the accuracy of indication.

To measure de voltages, proceed as outlined below:

Set the function selector to "- VOLTS",

2. Connect the Ground Cable clip to ground or low side of source voltage.

CAUTION: See first paragraph of "Safety Precau·

tions" on page

3. Set the range selector to a position considerably

higher than the voltage to be measured.

4_ Touch or connect the DC/Direct Probe to the high

side of the source voltage.

5. Reset the range selector to a position which gives

a suitable pointer deflection.

6. Read the dc voltage from the scale corresponding

to the range-selector setting.

Zero~Center Indication:

Zero-center indication is frequently useful because

it allows observation of either positive or negative

dc-voltage excursions without the necessity of resetting

the function selector.

Set the function selector to"+VOLTS".

2. Rotate the ZERO AD] Q9ntrol to position the

pointer at the center

3. Set the range selector to a position at least double

the voltage to be measured.

4. After a test reading has been made, the range

selector may be set to the lowest position which

allows the pointer to remain on the scale.

Resistance Measurements:

When making resistance measurements, the sliding

switch on the WG·299B probe shoul~ be set to "OHMS".

Before resistance measurements are made, the power

should be removed from the equipment under test so

that no voltages are present in the equipment.

required.

H_O+".

is good practice to make

VOLTS" or to

;:;;;====================

1. Set the function selector to "OHMS" position.

2_ Set the range selector to the position nearest to the

value under measurement.

3. Connect the probe tip to the ground clip and adjust

the ZERO ADJ control to position the pointer at

the left-hand "0", if necessary.

4. Disconnect the WG-299B probe from the Ground

Clip. Meter pointer will deflect approximately full

scale.

meter pointer does not deAect to exactly

full scale, use

accurately to the last line on the "R" scale. See

Ohms Adjustment section on page 12 if it is neces-

sary to frequently readjust the

5. Connect the clip of the Ground Cable to one ter-

minal of the resistance to be measured.

6. Touch or connect the probe tip to the other ter-

minal of the, 'resIstance to be measured.

7. Reset the range switch to give a convenient deflec-

tion on the "R" (ohms) scale.

8. Multiply the reading on the "R" scale

tor indicated at the range-selector setting.

CAUTION: Low-current, low-resistance devices,

such as thermocouples and meter movements, may

be damaged unless a range above "R xl" is used

because the \VV-77C applies up to 1.5 volts across

the resistance under measurement when the range

selector is set at "R xl".

In the case of resistance measurements, the WG-299B

probe of the WV-77C is always positive with

respect to the Ground Cable. This facilitates the meas-

urement of leakage resistance in components- such as

electrolytic capacitors where polarity must be observed.

Measurement of Resistance Values Above 1000

Megohms:

The leakage resistance of small mica and paper

capacitors is usually above

cuit shown in Fig. 2 can be used to measure resistance

values above

EXTERNAL

VOLTAGE

SUPPLY

OHMS

1000

ADJ control to adjust setting

OHMS

1000

megohms. The cir~

megohms. An external de voltage

•

RESISTANCE

BEING MEASURED

BLACK LEAO

ADJ controL

the fac~

WG-2998 SET

TO"OC"

Figure 2. Circuit for measurement of resistance values above

1000 megohms .

• 6 •

Page 7

neA

Jilniol' VohOhmyst

WV-77C

source between 20 and 500 volts is utilized to obtain

a measurable pointer deflection. Make circuit connec-

tions as sho'wn in Fig. 2 and proceed as follows:

Set Selector s'witch to

VOLTS" and measure

the voltage at point "B".

2. Measure the voltage at point "A".

3. Compute the unknown resistance from the follow- ing formula:

(Volts at "A")-(Volts at "B")

Rx (megohms) =

(Volts at "B")

EXAMPLE:

An unknown resistance is to be determined with the

circuit of Fig. 2. An external voltage of 500 volts is applied. The ViV·77C measures 2.5 volts at "B", and

500 volts at "A". Then,

(500-2.5)

= ~_ =

2200 megohms (approx,)

AC-Voltage Measurements:

CAUTION: See Maximum Input Voltages, under

"Specifications".

The switch on the

·WG·299B

probe should be set to

"AC" for all ac-voltage measurements.

I, Set the function selector at "AC VOLTS" position.

2. Set the range selector to a position considerably higher than the voltage to be measured.

3, Adjust the ZERO ADJ control if necessary to posi.

tion the meter pointer at the left-hand "0".

will

be necessary to readj ust this control when switch-

5. Reset the range selector for a convenient deflection.

6. Read the ac voltage from the scale corresponding to'

the range-selector setting.

NOTE:

the 2.1-111egohm de input of the WV-77C

loads the test circuit appreciably when making ac

measurements in the presence of dc, a suitable blocking capacitor should be used ahead of the WG-299B probe

to prevent this loading effect. For this purpose, a high-

quality

10\,,'

leakage, paper capacitor of 0.5 ,uf (or

larger) is suggested.

RESISTANCE MEASUREMENTS

(Set

Function switch and

Resistance to Set Range Read from Multiply

be measured Switch to: Scale Reading by

0.2 to 1000~ Rx1 1000 to 10.000n 10,000to100,000n 100,00010100 l\Jeg RxlOOK R 100,000

100 to 1000 Meg

WG-299B

Rxl00 R 100 RxlOOO

Rxl MEG R 1.000,000

switch to

R 1

R 1000

"OHJ\lS")

DC-VOLTAGE MEASUREMENTS

(Set Funclion switch to "-YOLTS" or "+Y01..'I'S" and

Vollage to Set Range

be measured Switch to: Scale

0.05 to 3V 3Y 3 to 12V

12to60V 60V B 1 60to300V SOOV

300to1200Y

set WG·299B switchto"DC")

Read from

12V

1200V

Multiply

Reading by

100 100

JuniOR VOUOHffiVST

5 ,,78 10 15,

.~o

RRDIO CORPORATI

Figure 3. Details of WV-77C scales

567

1.5

ing from the 3-volt range to a higher range and

vice versa.

4. Touch or connect the WG-299B probe to the high side of the source voltage.

·7'

AC (RMS) VOLTAGE MEASUREMENTS

(Set Function switch to "AC VOLTS" and set

Voltage 10 Set Range Read from

be measured S·~-.Iitchto: Scale

0.1 to 3V 3V 3 to 12V 12V

12 to 60V

60to300V 300V

300 to 1200V

WG·299B

switch

60V

1200V

to "AC")

NULL INDICATIONS (DC VOLTS)

(Set

Function switch to

Voltage to

be measured

-1.5 to +1.5V 3V

-6 to +6V

-30to+30V 60V B 1

-150to +lSOV 300V

-600 to +600V

probe

"+ VOLTS"

switch to

Sel Range Read from Multiply

Switch to: Scale

12V

1200V

"DC")

and

set

WG·299B

Multiply

Reading by

1 100

100

Reading by

1 1

100 100

Page 8

ACCESSORIES

Availahle on Separate Order

The WG-301A Crystal-Diode Probe consists of a

germanium rectifier and an RC network housed in a

probe which slips onto the \VG-299B Probe and

Cable. The maximum voltage rating of the instrument with the WG-301A is 20 volts nns, in the presence of de

voltages up to

250

Me. Voltage readings are made on the de scales

in terms of TIns volts for sine waves.

_ The WG-289 High-Voltage Probe in combination

with a multiplier resistor WG-206 extends the de rating

of the

\'\iV-fie

in high-impedance circuits. DC scales are multiplied

by a factor of 100, providing 4 full-scale positions of 300, 1200, 6000, and 30,000 volts. The 1200-volt range

is also useful up to the maximum rating of 50,000 volts on the probe. When the probe is used, the total input

resistance is increased to 1100 megohms, a valuable

250

volts. The frequency range is 50 Kc

to a maximum of 50,000 volLs for usc

Special Applications

feature for making measurement in photo tube circuits,

TV high-voltage power supplies, and olher high-im-

pedance circuits having inherently poor regulation.

Figure 4. Accessory high-voltage probe and multiplier resistor for

use with the WV-77C

The \'\lV-r7C is generally usefulinthe maintenance

and servicing of ac, dc, af, and high-frequency equip-

ment. ""hen used with the '''G-301A Crystal-Diode

Probe, it can he used to measure quencies between 50 Kc and 250 Mc. The special appli-

cations discussed below will serve to illustrate the wide

field of usefulnessofthe WV-77C.

Oscillator Grid-Bias l\ieasurelnent.

tive de voltage developed at the grid of an oscillator

tube is always proportional to the amplitude of oscilla-

tion. The WV-77C has high input impedance and can be used to measure this bias voltage_ Comparative read-

ings should be taken on each band of a multi-band

receiver. The ganged tuning capacitor should be ro-

tated through each band while the bias is measured.

AGe/AVe Voltage Mca8urements.

\VV·77C has a high input resistance, it can be used measure avc or agc voltage at the diode load resistor, along the bias buses, or at the grids of the tubes.

Output Indication.

output indicator for alignment of radio and television

receivers. The \'\iC-299B probe is usually connected

to the load resistor of the second detector in AM and

The WV-77C is a very useful

voltages at fre-

The nega-

Since the

TV receivers. In an FM receiver, the probe is con- nected to the limiter load resistor. The zero-center

feature of the WV-77C is particularly useful in align-

ment of FM discriminators.

Bias-Cell Voltage Measurements.

ages can be accurately measured with the WV -77C.

Detection of Gassy Tubes. tube may be encountered in electronic equipment. The

presence of gas in an output tube or avc-controlled tube

can lead to various circuit disturbances. Measurement of the grid bias in an RC-coupled circuit shows the

presence of a gassy tube as an abnormally negative or

positive value of bias. The same symptom can also be caused by a leaky coupling capacitor.

Insulation-Resistance Measurements.

leakage through the insulating material of capacitors, coils, transformers, cables, and other components, can

be measured with the WV-77C in terms of resistance. Values of leakage resistance above 1000 megohms can be measured with the circuit shown in Fig. 2_

DBM Measurements.

can be used to determine dbm values corresponding to

The chart shown in Fig. 1

Bias-cell volt-

An occasional gassy

Current

·8·

Page 9

;;:=~=================;;;;;=====;;;;

i'dainLenance

rms ae voltage values across a 600-ohm resistive load.

A dbm value is defined as the number of decibels above

or below a reference level of 1 milliwatt measured in a

600-ohm loadaL1000 cycles. Accordingly, 0 dbm in- dicates a power level of 1 milliwatt; 10 dbm, 10 milli-

watts;

dbm, 100 milliwatts; etc.

Because dbm are defined ,\lith respect to a 600-ohm

load, power levels correspond to voltage values. There-

fore, dbm can be measured in terms of rms voltages

across a 600-ohm resistive load. For example, 0.775

rms volt indicates 0 dbm; 7.75

dbm, etc. While these measurements must be made

with a sine waveform to avoid waveform error, any

rms

volts indicate 20

frequency can be used ·which is within the range of the

\XlV-77C. A lOOO-cps signal is used as a reference

because the correlation bet,veen decibels and ear res-

ponse is maximum at that freq~ency.

The chart sholl,'n in Fig. 1 provides rapid conversion

n,lS

volt~ges to corresponding dbm values. Associ-

ated power levels can be read along the top of the chart.

the rms voltage is measured across a resistive load

other than 600 ohms, the following correction factors

must be added algebraically to the dbm values read

from the graph in figure

Resistive

Load

Correction

Factor"><

at 1000 cps

600

500 300 250 150

+ 0.8 + 3.0 + 3.8

+ 6_0

+ 10_8

+ 16_0 + 18.8

+ 22_7

* Add algebraically to the dbm values read from graph

in figure

For resistive loads not listed in the ahove table, use

the following formula for determining the correction

factor:

where R is the load in ohms. When R is greater than

600, the correction factor is negative.

Correction Factor

10 log 6~O

Maintenance

General

The WV·i7C is manufactured and tested under strict engi·

neering supervision. l-Iowever, after long continued use the

instrument may require tube replacement, or other attention.

Case opens into two sections by removing fOllr screws: two holding the strap, one at the back, and one at the bottom of the case.

The performance of the Junior VoltOhmyst is dependent upon the quality and tolerances of its circuit components.

it becomes necessary to replaceacomponent part, the stock

number can be found in the Replaeemcnt Parts List, page

Only RCA replacement parts, or parts which have equivalent

specifications, shouldbeused.

Zero Setting of Pointer

Mechanical Adjustment

The pointer should rest at "0" when the power is off.Ifthe pointer should come to rest at a deflected position when the Selector switch is turned to "OFF", adjust the pointer posi· tion mechanically, as follows:

Unscrew the meter·adjustment screw plug.

Insert a scriber or similar tool to engage the zero·adjust-

ment lever, and move the lever laterally as required to bring

the pointer to "0"

Caution: Extreme care must be taken to prevent insertion of

the tool to a depth which

meter warranty does not cover such damage.

3. Replace the meter·adjustment screw plug.

the difficulty remains, vigorously wipe the outside surface

of the meter·case window with a clean, soft, dry cloth.1£the

will

injure the pointer spring. The

11.

pointer moves away from its initial pGsition and remains at

another off·zero position for several minutes, the anti·static

coating on the inside surface of the window is no longer eircc-

live. Requests for anti·static solution should be addressed to

Radio Corporation of America, Order Service, Building 60,

Camden, New Jersey.

lise will be sent free to VoltOhmyst Meters users whose war·

ranties are on file at the Camden RCA office.

Caution: The inside surface of the front half of the plastic

meter case is coated with an anti·static solution to eliminate

static effects on the action of the pointer.Ifmaintenance neces·

sitates remo\'al of this Case part, take care to avoid rubbing or

scratching the inside surface,

Electrical Balance Check

Set the function selector to "+VOLTS".

2. By rotating the ZERO ADJ control, it should be possible

to set the meIer pointer at either zero or 65% of full deflection

on any ran!.!e.

3. Set the function selector to "- VOLTS".

4. By rotating the Z;ERO ADJ control,itshould be possible

to set the meIer pointer at either zero or 150/0 of full·scale

deflection on any range.

I·ounce bottle with instructions for

(Contillued on page 12)

• 9 •

Page 10

[leA

Juuior VoltOlllUYlill

WV·77C

>~r

N "'-"

U I

<~.

.,..

~~~3

v '" '"

o '

•

~['

<",0

~>-

5~~

a: ~ -~

-,,"~

-r

~~~

~-J

:<Iv '"

• <

f-~~~~_@--'

I -~ ,---

I -

[

L -'

0 0 N

i~-

a:; ~

---./VV\

~ii5

> >

0;)1013 $0

a:!")wa::.n

~uV)w

01«::E0l...J I

~~J:~o/!~ I

'-'o0a.. u I

;;

....:~ N

INn_

VIc)

W I

-i~

~~(

•

> >

~g

~),:~'?i6

I, _

~l'--h

\A)L

~ ~

=y,?

wu1

rl-Q

I--

-'"

gzo

<~~

~Ow

-;nVl3

"'"

~w~

a:v

I<O

~---d

-Na:

~If)W

~>-

","

ou=> >->-0

~~::!:

w => ",w,

,,-

r«

a:,

,,;

<II

1::

<6 ",w", w>-,

=>°I ~20

~wn

w\[!

v· -

z"''''

<t:~~

>->-"

<:208

"'",w w", ,

W 11

...J...Jo,j

~Zw

<=>,

,;.

oJ;

.,;

•

;

• 10 •

Page 11

Replacement Parts List

JUNIOR VOlTOHMYST

Type WV-77C

When ordering replacement parts, include seriol number and code numbe, of Instrumenl.

Part. should b. ordered through a local RCAtub. and porf.

distributor.

Symbol

No,

C I

RIO

Rll

R 15, 16

R17

19, 20

R 21

R 22

Description

Capacitors

Paper tubular, 0.33

volts. 93848

Paper tubular, 0.1

.volts. 73784

Dry electrolytic, 10

100%,250

Papef tubular, 0.01

volts.. 73561

Carbon film type,S meg.,±1

watt.. .

Carbon film type, 3.75 meg.,±1

watt..

Carbon film type, 1 meg.,±1

watt.

Carbon film type, 0.2 meg.,±1%,

watt.

Carbon film type, 37,500

Carbon

Carbon film type,

Carbon film type, 361,000 ohms,

Fixed composition,1meg.,

Fixed composition,

5%,

Variable carbon,

20%,

watt.. .

film

1 %,Yzwatt. .

film

watt.

watt. 96259

1%,

watt. .

1%,

watt.

watt. .

watt.

5%,

watt.

5%,

watt..

5%,

Yzwatt.

5%,

watt,. 502347

5%,

watt. .

5%,

watt.

watt. 213744

volts.

Resistors

type,

0.8

1.36

250,000

678,000

12,500

µf,±10%, 400

µf,±20%, 200

µf, -

10%,

µf,

20%, 400

ohms,

12,500

ohms,

meg.,±1%,

ohms,

5%,

15,000

ohms,

12,000

ohms,

1500

ohms,

47,000

ohms,

130

ohms,

68,000

ohms,

470

ohms,

Stock

No_

93849

5588]

93840

55658

56733

93841

93842

93843

56728

93845

96258

502510

502315

502312

5022L5

33571

502368

502147

H 23

R 24

R 26

S I

T I

Symbol

No.

29 30

Description

Variable carbon,

watt. ,

Variahle carbon,

20%,

Fixed composition,

Same as

Fixed

Connector, cable, chassis receptacle.

IVleter, dc, Cord, power, with plug.

Switch, "Selector",2section,5posi~

Switch, "Range",2sectjon,5posi-

Transformer, power; primary,

Case, meter (plastic) blue .. '. Clip, alligator: for ground cable. Clip, alligator: "slip-on" type.

Handle, carrying.

Insulator: for alligator clip, Knob, cpntrol.

Socket, tube,7pin.

Socket, tube,9pin.

Stud, carrying-handle.

Bushing, tip: for fl'Ont housing. 212161

Connector: internal, brass for cable. Connector, cable: female, ,viLb set

Shell: front end, blue.. .' . 210195

Shell: middle section, with shield,

Shell: rear section, blue

Spring, coil: for front end.

Spring, switch: with insulator.

Tip, probe: with switch slide and

Washer, tip: 212163

watt.

2'\'atts.

5%, 1

5%,

R 12

composition,

watt.

tion,6circuit.

tion,4circuit.

volts,

50/60

WG~299B

screw. 203574·

bushing, and insulator. 212159

I-meg. resistor.

75000hrns,

15,000

watt.

330

o.hms,±5%,

ohms,±5%,

watt.

Miscellaneous

0~200µamp. (blue) ...

10,000

cps.

Dcl

AC~Ohms Probe

and Cable

1000

meg.,±5%,

ohms,

20%,

117

Stock

No.

93839

213743

502133

522010

512210

502310

502610

962;;7

213484

70392

21:3514

213513

9:1835

2D48S

;~5262

210088

44091

204717

59543

204825

204900

93854

210190~A

210202-A

210197 212162

212160

• 11 •

Page 12

S.Ifsteps 2 and 4 above cannot be accomplished, the two

triode units of the 12AU7 tuhes are not in close enough bal.

ance for this application and the tube should be replaced.

DC Zero Check

L Set functioll selector to "-VOLTS".

2. Set range selector on "3V".

3. Rotate the ZERO ADJ control until the meter pointer is

at zero.

4. Turn range switch to "1200V".

5.Ifthe meter pointer deviates from zero by more than one

division 011 the 0 to 12 metcr scale, replace thc 12AU7 (see

section on Tu be Replacement).

AC Zero

on "+VOLTS".

the 60V meter scale.

the 12AL5. Thc use of a 12ALS which results ill a meter read- ing outside of ,his 7-13 volt range

of the instrument but adjustment of the ZERO ADJ control.

Check

Set the range selector on "3V" and the function selector

2. Rotate ZERO ADJ control until meter reads 10 volts on

3. Turn the function selector to "AC VOLTS".

4.Ifthe meter does not read between 7 and 13 volts, replace

will

will,

however, require more frequent

not impair the accura~y

Calibration

1. Set the range selector to ;'60V" and the function selector

"+VOLTS"_

2. Set thc meter pointer to zero by using the ZERO ADJ

controL

3. Set the sliding switch on the probe to "DC".

4. Connect the Ground Cable to the negative terminal alld

the probe tip to the positive terminal of a source of DC Voltage that has been adjusted to exactly 57 volts.

Note: The accuracy of calibratioll cannot cxceed the accuracy

of the voltage standards which are used.

5. Adjust the ';DC CAL" control (R-23) inside the case for

a meter reading of exactly 57 volts.

6. Remove the leads at the source of voltage.

7. Set the function selector to "-VOLTS".

8. Connect the Ground Cable to the pOSiLi\'e terminal and the probe tip to the negative tenJlinal of the dc-voltage source adjusted to exactly 57 volts. The WV-77C should read 57 volts within ±3%.

9.Ifthe WV-77C cannot be calibrated according to the

foregoing steps the 12A U7 amplifier tube may not be properly

balanced for this application.

Tube Replaceillent

All tubes supplied originally with the WV-77C have been

thoroughly aged by operating them for several hours before illstallatiOri in the instrument. This preliminary conditioning

of a new tube helps to insure stability and dependable per- formance.

Before installing a 12AU7, the tube may be aged as follows:

connect the plates together and apply 115 volts dc. Operate

the grids and cathodes with no voltage applied, and operate the heaters at 6.3 volts. The tube should be operated in this manner for a minimum of 12 hours before it is installed in the instrument. The WV·77C then can be recalibrated.

An alternate, and usually satisfactory, aging procedure con- sists of operating the new tube in the WV-77C for approxi-

mately 36 hours, after which time the instrument may be recalibrated. procedure should be followed.

be aged for a minimum period of 36 hours by operating it in

the \VV-77C. After this period of time, the instrument may

be recaliurated according to the procedure outlined under "AC Calibration Check".

this procedure is unsatisfactory, the first aging

it becomes necessary to replace the 12AL5, the tube can

Battery Testing and Replacement

Caution: Do not allow exhausted cells to remain inside the

case of the WV-77C. Chemicals from deteriorated cells may

damage the instrument.

The battery should be tested to insure accu racy of resistance

measurements. To test battery, proceed as follows:

L Set .Function selector to "OHl\.lS".

2. Set Range selector to "R x 1" scale.

3. Rotate OH2VIS ADJ control to bring pointer to full scale.

4. Short·circuit the probe tip and ground clip for about

ten seconds.

5. Open the short-circuit and immediately observe the scale

indication. An appreciable deviation from full-scale indication

reveals weak cells which should be replaced.

Ohms Adjustment

In order to obtain exactly full-scale deflection of the meter

when switching the range selector from a low range position

to the R x 1MEC position, it may be necessary to readjust the OHMS ADJ control. The necessity for this readjustment

can be minimized by checking the bauery and installing a

12AU7 tube with a low value of grid current. Refer to Tube

Replacement section.

RCA Repair Service

RCA maintains a complete repair service for the adjustment,

calibration, and maintenance of RCA t~st equipment.

becomes necessary to service this equipment, the report forms

enclosed in this booklet should be filled out as described.

important that:

Test equipment be packed carefully,

2. A full description of the trouble be included in the report.

3. All probes and cables be included with the instrument.

Attention to these details will help prevent damage in transit

and delay in repairs .

. 12 •

Page 13

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

PRICE 0NE DOlLAR

Type WV-77C

JUNIOR

VOLTOHMYST®

ELECTRONIC METER

V ~.' \~)'

y---

Safety Precautions

ACCESSORIES

--'-1.'! '

CONTENTS

General Description

Specifications

Operation and Applications .......

ACCESSORIES

Special Applications

Maintenance

f-~~~~_@--'

~g

I, _

~l'--h

=y,?

• 10 •

Replacement Parts List

Type WV-77C

R 21

R 22

213743

502133

522010

512210

• 11 •

DC Zero Check

Calibration

Tube Replaceillent

Battery Testing and Replacement

Ohms Adjustment

RCA Repair Service

. 12 •