RCA VoltOhmyst WV-77C User guide

PRICE 0NE DOlLAR
JUNIOR
,
VOLTOHMYST®
Type WV-77C
ELECTRONIC METER
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• SpecifkatioriS~
• Operation
• Applications
'. Maintenance
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~WV_77C i~,~ ~
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12V R ~ fOOQ JOD v At VDtTS - +'
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RADIO CORPORATION 0' AMEN rCA
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TEST AND MEASURING EOUIPMENT ~,ARRISON_N. J.

L
Safety Precautions
The metal case of this instrument is connected to
theground of the internalcircuit. For proper opera-
tion, the ground cable ofthe WV-77C shouldalwaysbe
connected tothe ground of the equipmentunclertest.
The WG-299B DC/AC-OhmsProbeand Cable hasa
shield throughout its lengthwhichis connected tothe
instrumentground and case.Alwayshandle the WG·
2998 by theinsulated probe housing.
An important point to rememberis that thereis
always danger inherentin testing electrical equipment
which operates at hazardousvoltages. Therefore, the
operator should thoroughly familiarize himself with
the equipment under test before workingon it,bearing
in mind thathigh voltages may appear atunexpected
pointsin defectiveequipment.Additional precautions
which experience in the industryhasshownto be
importantare listed below.
l. It is good practice to remove power before can·
necting test leads to high.voltage points. If this is
impractical,be especiallycarefulto avoid accidental
contact with equipment racks and other obj ects which
can provide a ground.Working withone hand in your
pocket and standing on a properlyinsulated floor les-
sens the dangerof shock.
2.Filtercapacitors may storea charge large
enoughtobe hazardous.Therefore, discharge filter
capacitors before attaching test leads.
3. Rememberthatleadswith broken insulation
provide the additional hazard of highvoltagesappear·
ing at exposed points alongtheleads. Check test leads
for frayed or broken insulation before working with
them.
4.To lessen the danger of accidental shock,discon-
nect test leads immediatelyaftertest is completed.
5. Remember thattherisk of severe shock isonly
one of the possible hazards. Even a minorshockcan
placetheoperator in hazard of more serious risks such
as a bad fall orcontactwith asource of high,er voltage.
6. The experienced operatorcontinuously guards
against injury and doesnot work on h.~zardous circuits
unlessanother person is availabk to \assist in case of
accident....... --...
ACCESSORIES
Supplied with WV·77C '""'
..-./ -:::;...~
--'-1.' '
D~/AC-Oh~s Probe.and Cable .. ~ r. Type WG-299B
1 Shp-On . .lhgator Clip..Stock No.210088
I1.5-Volt Battery. . . .......... . .. . Type VS036
IRCA-I2AU7 Tube I Registration Card
IRCA·I2AL5Tube Clip Insulator I Instruction Booklet
Available on Separate 9rder
ForMeasuring AC Voltages at Frequenciesfrom50 Kc t0250 Me:
Crystal-Diode Probe TypeWC.30IA
ForIncreasing DCVoltage Range to 50,000 Volts:
High-Voltage Probe .... Type WG-289
NIultiplier Resistor ...Type WG·206
..
Cables and probe supplied with WV·77C
Devices or arrangem~nt. ~ho""n or tle~cribed herein may ""C patenl~ of RCA or I)ther~. Informationco[]tail]~d
her~in i. furni hed withon' responsibilityby RCA for it~uselint. without prejutliceto RCA'& patent r;~"I~.
© 1956 byRgdio Corporglion of Americg
All Rights Reserved
TMK®, Mgrcg Regi.lrodgTESTAND MEASURING EQUIPMENT
RADIO CORPOHATION OFAMERICA, HARBISON, NEW J£H.SEY
,
Inst'- WV-77C (l) 10-56
Printed in U.S.A.

CONTENTS
Page
SafetyPrecautions_.
General Desci·jptlon ..
Functions of Controlsand Terminals...
Specifications .. .
Operation and Applications...
Accessories . .. ..
Special Applications..
11aintenance.....
Schema tieDiagram
Replacement PartsList
0.1
MILl1WATTS IN 600-0HM RESISTIVE LOAD AT 1000 CPS
10100
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6 7 8 g
10
ACROSS 600-0HM RESISTIVE LOAD AT1000 CPS
67 6 g
100
4 > £, 7:8 g
I (.0
0.775
A.C.VOLTS(RMS) MEASURED
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92CS·7130
Note:For loads otherthan600 ohms, sec lable on page 10
•
Figure 1. Chart forconversion ofrms voltage to dbmvalues.
·3'

General Description
The JuniorVoltOhmyst-* WV-77C is designed to
measure de voltages from 0.1 volt to 1200 volts, rms
sine-wave voltages from 0.1 voltto1200 volts, and
resistance values from 0.2 ohm to 1000 megohms.
The aevoltmeterof the ~rV-77C featuresan electron
tubeas the half·waverectifier. It is a peak indicating
type -and is calibrated in terms of the rmsvoltage of a
sine wave. The V.rV-77C has highinput impedance on
all de and aevoltage ranges. Only two cables are used
with this instrument for all measurements,providing
easeand flexibility in operation.
The frequency range of the WV-77C,depending on
theimpedance of the voltagesource,is flat to approxi-
mately 3 megacycles. When the auxiliary \VG-301A
Crystal Diode Probeisused,thedc voltageranges are
accurateto within ±10%from50Kc to 250 Kc.
TheWV-77C is equippedwith a singleunit probe,
the WG·299BDC/AC-Ohms Probe andCable_This
probeis provided with abuilt-inswitchwhich permits
quick adaptationto eitherdc-voltage measurements or
ac-voltageand resistance measurements without requir-
inga change of probes and cables_
TheJunior VoltOhmyst-ufilizes :8 p,ush-put{ ampli. r
. "
IJ ~~e debridge circuit which_arordr" excellent
lineariij-_.f response,goodstability, -and very high
input impedance. (See SchematicDiagram, Fig.5.)
When no measurementis beingmade, the cathode cur-
rents through the triodes of V2are equaL When a
measurement is being rnade~ avoltageis applied be-
tween the grid ofV2A andground toprovide a change
in cathode current of this triode unit_Sinceresistor
R20 functions asa cathode-couplingelement,the
change incathode current through this resistor alters
the grid-to-cathode potential ofV2B, a condition which
modifiesthe cathode current ofV2B. When, for ex-
ample, the currentflow through V2Aincreases, the
flow of current throughV2Bdecrea.ses. Themeter
readingisproportional to the differencebetween the
plate currents of the triodes.
AdditlOnal features of the \VV-77C include provi-
sion for zero-center indication, usefulindescriminator
and biasmeasurements; separate'scales for lowac.
,
voltage measurements;acircuit desig,n which allows
measurements of theac component ~-...f a signal when
the de componentis pre~ent dnd vice ,~ersa; a separate
dcprobe with aI-megohm resistor whichminimizes
capacitance-loading effects; and electronicprotection
against meter burn-out.
The \VV-77C JuniorVoltOhmyst is alight-weight
compact,and versatile instrument. -Areliablemeas-
uring device, it will prove extremelyuseful in tele-
vision applicationsas well as in manyindustrial
applications.
*Trade \tark "VoItOlunysl" Reg.U.S. Pal. Off.
-- .../~
,LFunctions of Controls and Terminals
Function selector~Has two functions; turnsthe
poweroff in "OFF"position, andpermits choice of
type ofmeasurement to be made.
Range selector-Permits choice of range for the
desired voltageor resistance measurement.
ZERO ADJcontrol-Used to position the meter
pointer ateither theleft-hand "0" position or tothe
zero·center "-0+" position, when functionselector is
set to "+VOLTS".
OHMS ADJ--control-Used to positionthemeter
pointer atthe extreme right line on the "R" scale when
thefunctionselector is in "OHMS" position.
VOLTS OHMS terminal-Voltages and _resistances
to be measured are applied between this terminaland
theclip of the GROUND cableas described under
"operation" below.
GROUND cable--isdirectly connected to the chassis
of theinstrument.It serves as a common ground for
the ~rV-77C and thechassis of theequipment under
test orassociated testinstruments .
• 4 •

Specifications
Electrical
DC Voltmeter:
Ranges.0 to 3, 12, 60, 300, 1200 volts
Input Resistance (With
WithWG·299B switch set to "DC":
All Ranges. 11 megohms
Accuracy:
WithFunctionSelector.Set on "+VOLTS"
± 3% of full scale
WithFunction Selector Sct on 'I-VOLTS"
± 5% of full scale
AC Voltmeter:
Ranges:
{
0 to 3 volts on
.....()...separate scale
~0 to 12,60, 300,
tAJP 1200 volts
Accuracy. . ....... -e... ± 5%of full scale
InputResistance and Capacitance-Ap.prox.
(with WG-299B switch set to"AC"):0
3,12,and 60-V Ranges .. "O,,2~ohm shunted by 75 µµf
3aO-V Range 1 megohm shunted by 50 µµ£
1200-V Range2 megohms shunted by 50 µµ£
Frequency Response (with WG-299B switch set to AC ):
For Source Impedanceof 100 Ohrrts#..flat within ± 1 db
from 30 cps to
3 Me,
,
RMS Values ofSine Waves.
ForSourceImpedance of 1000 Ohms# ...flat within ± 1 db
from 30 cpsto
0.75 Me.
With Crystal-Diode ProbeWG-2M.&.... flat within ± 1db
from 50 Kc.to
250 Me.
Maximum InputVoltages:
CombinedAC Peak Voltage and DC Voltage:
WhenInstrument isSetupto Measure DC ..1800 peak volts
When Instrument is Setup to Measure AC:
3-volt. 12-volt, and 60-volt ranges.400 de volts
300-volt and 1200-volt ranges.600 devolts·
Ohmmeter:
Ranges, five.0to 1000 megohms
Center-Scale Values
10, 1000, 10000 ohms, 1.0 megohm, 10 megohms
Meter Movement:
DC Current for Full·Scale Deflection. 200 µa
Tube CompleInent:.
Power Supply:
VoltageRating.
FrequencyRating.
Consumption.
. . _.1 R<ll\-12ALS,1RCA-12AU7
105 to 125 volts
50 to 60 cps
5 wattsapprox.
Battery:
1.5-volt cell.RCA Type VS036
Mechanical
Over-all
I'leight
Width
Depth
Weight.
Dimensions:
8 inches
5%inches
4% inches
4pounds
#Thefrequency responseshown isforonlythe.~. 12.and60-volt range~.
The in~tnllnent is accurate at pnwer.linefrequencies for all ranges.
AAvailableonseparate order.
*Combined AC Peakaud DC Voltagesmust notexceed 1800 volts.
Operation and Applications .......
<
Preliminiry Adjustments:
To preparetlie ·\VV-77C for use~make the following
connections and adj ustrnents:
1. Connect theWG-299BDC/AC-Ohms Probe and
Cable to the VOLTS OHMS terminal.
2.Plug the power cord into an ac outlet supplying
105-125 voltsat50/60 cycles, and adjust the con·
troIs as indicated below:
a.Turn the function selector to "+ VOLTS" .
position, and allow several minutes forthe
instrument to warmup.
b_Adjust the ZERO ADJ control to positionthe
meter pointer at the left-hand"0".
NOTE: To check this adjustment, notice whether
or not the position of the meter pointer changes
when the functionselector is switched to
"-VOLTS". If the pointer position changes,
readjust the mechanicalzero control as de-
scribed in theMaintenance Section.
c. Turn the function selectorto"OHMS" posi-
tion.The pointershould deflect to approxi.
ma.tely full scale.
d.Rotatethe OHMS ADJ control to position the
pointer atthelast line onthe "R" (ohms)
scale.
Theinstrumentis now ready for use.
•
•
•5•

r-
...
Operation and Applications ;:;;;====================
DC·Voltage Measurements:
CAUTION:See Maximum Input Voltages,under
ELECTRICAL SPECIFICATIONS,
When making dc-voltagemeasurements, the sliding
switch on the WG-299B probe should beset to "DC".
TheWV-77C has five dc-voltage ranges:0 to 3,12,
60, 300, and 1200 volts. Althoughthe meter is pro-
tected against burn-out, it is goodpractice to make
a trial measurement at a higher rangesetting than is
considered necessary,because long-continued or re-
peated overload of the meter movementmay eventu-
ally impair the accuracy of indication.
To measure devoltages,proceed as outlinedbelow:
1. Setthe function selector to "+ VOLTS"or to
"-VOLTS", as required.
2.Connect the Ground Cable clipto ground or low
side of source voltage.
CAUTION: See first paragraph of"Safety Precau·
tions" on page 2.
3.Set the range selector to a position considerably
higher than the voltage to be measured.
4_ Touchorconnect the DC/Direct Probe tothehigh
side of thesource voltage.
5.Reset the rangeselector to a position which gives
a suitable pointer deflection.
6. Read the dc voltage fromthe scale corresponding
to the range-selector setting.
Zero~Center Indication:
Zero-center indication is frequently useful because
itallows observation of either positive ornegative
dc-voltage excursions without the necessity of resetting
the functionselector.
1. Set the function selector to "+ VOLTS".
2. Rotate the ZERO AD] Q9ntrolto position the
pointer at the center H_O+".
3.Setthe range selector to a position at least double
the voltage to be measured.
4. After a testreading has beenmade, therange
selector may be set tothelowest position which
allows the pointer to remainon the scale.
Resistance Measurements:
Whenmaking resistance measurements, the sliding
switchon the WG·299B probe shoul~ be set to "OHMS".
Beforeresistance measurements are made,the power
should beremoved from theequipment under testso
that no voltages are present in the equipment.
1. Set the function selector to "OHMS" position.
2_ Set therange selector to the position nearest to the
value under measurement.
3.Connect the probetip to the ground clip and adjust
the ZERO ADJ control to position the pointer at
theleft-hand "0", if necessary.
4. Disconnect the WG-299B probe from the Ground
Clip.Meter pointer willdeflect approximatelyfull
scale. If meterpointer does not deAect to exactly
full scale, use OHMS ADJ control to adjust setting
accuratelyto the last line on the"R"scale. See
Ohms Adjustmentsection on page 12ifit is neces-
saryto frequentlyreadjust the OHMS ADJ controL
5.Connect the clip of the Ground Cable to one ter-
minalof theresistance to be measured.
6.Touchor connect the probe tip to the other ter-
e
minal of the, 'resIstance to bemeasured.
7. Resetthe range switch to give a convenient deflec-
tionon the"R" (ohms) scale.
8. Multiply the reading on the "R" scale by the fac~
tor indicated at the range-selectorsetting.
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 resistanceunder measurementwhen the range
selector is setat "R xl".
In the caseof resistance measurements, the WG-299B
probe of the WV-77C is always positive with
respect tothe Ground Cable. This facilitates the meas-
urement of leakage resistance in components- suchas
electrolytic capacitorswherepolaritymust beobserved.
Measurement of Resistance Values Above 1000
Megohms:
The leakage resistance of small mica and paper
capacitors is usuallyabove 1000 megohms.The cir~
cuitshownin Fig.2 can be used to measure resistance
values above 1000 megohms. An external de voltage
A
•
RX
RESISTANCE
BEING MEASURED
WG-2998 SET
TO"OC"
EXTERNAL
VOLTAGE
SUPPLY
+
I
BLACK LEAO
Figure 2.Circuitfor measurement of resistance values above
1000 megohms .
•6•

neA Jilniol' VohOhmyst WV-77C
source between 20 and 500 volts is utilized toobtain
a measurable pointer deflection. Make circuit connec-
tions assho'wn in Fig. 2 and proceed as follows:
1. Set Selector s'witchto "+ VOLTS" and measure
the voltage at point "B".
2.Measurethevoltage at point"A".
3. Compute the unknownresistance from the follow-
ing formula:
11
Rx (megohms) =(Volts at"A")-(Volts at"B")
(Volts at "B")
EXAMPLE:
An unknown resistance is tobe determined with the
circuit of Fig. 2.An external voltage of 500 voltsis
applied.TheViV·77C measures 2.5volts at "B", and
500 voltsat "A". Then,
11 (500-2.5)
Rx = ~_ = 2200 megohms (approx,)
AC-VoltageMeasurements:
CAUTION:SeeMaximumInput Voltages,under
"Specifications".
The switch on the ·WG·299B probe should be set to
"AC"forall ac-voltage measurements.
I, Set the function selector at"AC VOLTS"position.
2.Setthe range selector to a position considerably
higher than the voltage to bemeasured.
3,Adjust the ZERO ADJ control if necessaryto posi.
tion themeterpointer at the left-hand"0". It will
be necessary to readjustthis control when switch-
JuniOR VOUOHffiVST
5,,78 10 15,
.~o
1.5
30
567
RRDIO CORPORATI
Figure 3.Details of WV-77C scales
ing from the3-volt range to a higher range and
vice versa.
4. Touch or connect the WG-299B probe tothe high
side ofthe sourcevoltage.
5. Reset therange selectorfor a convenient deflection.
6.Read the acvoltage from the scale corresponding to'
the range-selectorsetting.
NOTE: Jj the 2.1-111egohm deinputof theWV-77C
loads the testcircuit appreciably when makingac
measurements in the presence of dc,a suitableblocking
capacitor should be used ahead of the WG-299Bprobe
to preventthis loading effect. For this purpose, a high-
quality 10\,,' leakage, paper capacitor of 0.5 ,uf (or
larger) issuggested.
RESISTANCE MEASUREMENTS
(Set Functionswitch and WG-299B switch to "OHJ\lS")
Resistanceto Set RangeRead fromMultiply
be measured Switch to: ScaleReading by
0.2 to 1000~ Rx1 R 1
1000 to 10.000n Rxl00 R100
10,000 to 100,000nRxlOOO R1000
100,00010100 l\JegRxlOOK R 100,000
100 to 1000 Meg Rxl MEGR 1.000,000
DC-VOLTAGE MEASUREMENTS
(SetFunclion switch to "-YOLTS" or "+Y01..'I'S" and
set WG·299Bswitch to "DC")
Vollage to Set Range ReadfromMultiply
be measured Switch to:ScaleReadingby
0.05 to 3V 3Y A 1
3 to 12V 12V C
1
12 to 60V 60V B1
60 to 300V SOOV A
100
300 to 1200Y 1200V C
100
AC (RMS)VOLTAGE MEASUREMENTS
(Set Function switch to "ACVOLTS" andset
WG·299B switch to "AC")
Voltage 10Set Range Read from Multiply
be measured S·~-.Iitchto: Scale Reading by
0.1 to 3V3V 0 1
3 to 12V 12V C 1
12 to 60V 60V B1
60 to 300V 300V A 100
300 to 1200V 1200V C
100
NULLINDICATIONS (DC VOLTS)
(Set Function switch to "+ VOLTS" and set WG·299B
probe switch to "DC")
VoltagetoSel RangeRead fromMultiply
be measured Switch to:ScaleReading by
-1.5 to+1.5V 3V A 1
-6to+6V 12V C
1
-30 to +30V 60V B1
-150to +lSOV 300V A
100
-600 to +600V 1200V C
100
·7'

ACCESSORIES
Availahle on Separate Order
The WG-301A Crystal-Diode Probe consists of a
germanium rectifier and an RCnetworkhoused in a
probe whichslips onto the\VG-299B Probe and
Cable.The maximum voltage rating of the instrument
with the WG-301Ais 20 volts nns, inthe presence of de
voltages up to 250 volts. Thefrequency range is50 Kc
to 250 Me. Voltage readingsare made on the de scales
in terms of TIns voltsfor sine waves.
_TheWG-289 High-Voltage Probe in combination
with amultiplier resistor WG-206 extendsthe derating
of the \ \iV-fie to a maximumof50,000 volLs forusc
in high-impedancecircuits. DCscales are multiplied
by a factor of 100, providing 4 full-scale positionsof
300, 1200,6000,and 30,000 volts. The 1200-volt range
isalso useful uptothemaximumrating of 50,000 volts
on the probe. When theprobeis used,the total input
resistance isincreased to1100 megohms, avaluable
feature for making measurementinphoto tubecircuits,
TV high-voltage powersupplies, and olher high-im-
pedance circuits havinginherently poor regulation.
Figure 4. Accessory high-voltage probe and multiplier resistor for
use with the WV-77C
Special Applications
The\ \lV-r7Cis generallyuseful in the maintenance
and servicing of ac, dc,af, andhigh-frequency equip-
ment. ""hen used withthe'''G-301A Crystal-Diode
Probe, it can he usedto measure rf voltages at fre-
quencies between 50 Kcand 250Mc. The special appli-
cations discussedbelow will serve to illustrate the wide
field of usefulness of the WV-77C.
Oscillator Grid-Bias l\ieasurelnent. The nega-
tive devoltage developed atthe grid of anoscillator
tube is always proportional totheamplitude of oscilla-
tion.The WV-77C has high input impedance andcan
be used to measure this bias voltage_Comparative read-
ings shouldbetaken on eachband 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. Since the
\VV·77C has a high input resistance, itcan beused to
measure avc oragc voltage at the diodeloadresistor,
along thebias buses,or at the grids of the tubes.
Output Indication. The WV-77Cisaveryuseful
outputindicator for alignment of radio and television
receivers.The \ \iC-299B probe is usuallyconnected
totheload resistorofthe second detector in AM and
TV receivers.In an FM receiver,theprobeis con-
nectedtothelimiter load resistor. The zero-center
feature of the WV-77C is particularlyuseful in align-
ment ofFM discriminators.
Bias-Cell Voltage Measurements. Bias-cell volt-
ages canbe accuratelymeasuredwith the WV-77C.
Detection of Gassy Tubes. Anoccasional gassy
tubemaybe encountered in electronic equipment.The
presence of gasin anoutput tubeor avc-controlled tube
can lead to various circuit disturbances. Measurement
of the gridbiasin anRC-coupled circuit shows the
presence of a gassy tube as anabnormallynegative or
positive valueof bias.The samesymptom can also be
caused by a leaky coupling capacitor.
Insulation-Resistance Measurements. Current
leakage through theinsulating material of capacitors,
coils, transformers, cables, and other components,can
be measuredwith the WV-77C interms of resistance.
Values of leakage resistance above 1000 megohms can
bemeasured with the circuitshown in Fig.2_
DBM Measurements. The chart shown in Fig. 1
can be used to determinedbm values corresponding to
·8·

;;:=~=================;;;;;=====;;;; i'dainLenance
rms ae voltagevalues across a 600-ohm resistive load.
A dbm valueis defined asthe number ofdecibels above
orbelow a referencelevel of 1 milliwatt measuredin a
600-ohm load aL 1000 cycles. Accordingly, 0dbm in-
dicates a powerlevel of 1 milliwatt; 10 dbm, 10 milli-
watts; 20 dbm,100 milliwatts;etc.
I
Because dbm are defined ,\lith respect to a 600-ohm
load,power levelscorrespond 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 rms volts indicate 20
dbm, etc. While thesemeasurements must be made
with a sine waveform to avoidwaveformerror,any
frequency can be used ·which is within the rangeof the
\XlV-77C. AlOOO-cps signalis used asa reference
because the correlation bet,veen decibels andear res-
ponseismaximum at that freq~ency.
The chart sholl,'nin Fig. 1 provides rapidconversion
of n,lS volt~ges to corresponding dbm values. Associ-
ated power levelscan be read along the topof the chart.
If the rms voltage is measured across aresistive load
other than 600 ohms,thefollowing correctionfactors
must be added algebraicallytothe dbm values read
from the graphin figure 1.
ResistiveCorrection
LoadFactor"><
at1000 cps
600 0
500 +0.8
300 +3.0
250 +3.8
150 +6_0
50 +10_8
15+16_0
8+18.8
+22_7
*Addalgebraicallyto the dbm values read fromgraph
in figure 1.
For resistive loads not listed in theahovetable, use
the following formula for determining the correction
factor:
Correction Factor = 10log 6~O
where R is the loadin ohms.When R is greater than
600,the correction factor is negative.
Maintenance
General
The WV·i7C ismanufactured and tested understrict engi·
neeringsupervision.l-Iowever,afterlong continued use the
instrumentmayrequire tubereplacement, orother attention.
Case opens into two sectionsbyremoving fOllr screws:two
holding the strap, oneat theback, and one at the bottom of
the case.
The performance of the Junior VoltOhmyst isdependent
upon the qualityand tolerances ofits circuit components. If
itbecomes necessary to replace a componentpart, thestock
number can be found in theReplaeemcnt PartsList, page 11.
Only RCAreplacement parts,or partswhich have equivalent
specifications, should be used.
Zero Settingof Pointer
Mechanical Adjustment
The pointer should rest at "0" whenthepower is off. If the
pointer should cometo rest at adeflected position when the
Selectorswitchis turned to "OFF", adjust the pointer posi·
tionmechanically,as follows:
1. Unscrew themeter·adjustmentscrew plug.
Z. Insert a scriber or similar tool to engage thezero·adjust-
mentlever,and move the leverlaterallyas required to bring
the pointer to "0"
Caution: Extreme care must be takento prevent insertionof
thetoolto a depth which will injure thepointerspring. The
meterwarranty does not coversuch damage.
3.Replacethemeter·adjustmentscrew plug.
If the difficulty remains, vigorously wipe the outside surface
of the meter·case window with a clean, soft, dry cloth. 1£ the
pointer moves away from its initial pGsitionand remainsat
another off·zeroposition forseveral minutes, the anti·static
coating on the insidesurface of the windowis nolongereircc-
live. Requests foranti·static solution shouldbe addressed to
RadioCorporation of America, OrderService, Building 60,
Camden,New Jersey. A I·ounce bottle with instructions for
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 thefronthalf of the plastic
metercaseis coated withan anti·staticsolution to eliminate
static effects on the action of the pointer. If maintenance neces·
sitates remo\'al of thisCase part, take care to avoid rubbingor
scratchingthe inside surface,
Electrical Balance Check
1. Set the function selectorto"+VOLTS".
2. By rotating the ZERO ADJ control, it should bepossible
to set themeIer pointer at either zero or 65% offull deflection
on anyran. e.
3.Set thefunction selector to "-VOLTS".
4.By rotatingthe Z;ERO ADJcontrol, it should bepossible
to set themeIer pointerat eitherzero or 150/0 offull·scale
deflectionon anyrange.
(Contillued on page 12)
• 9 •

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Replacement Parts List
JUNIOR VOlTOHMYST
TypeWV-77C
When ordering replacement parts, include seriolnumber and code numbe,of Instrumenl.
Part. should b. ordered through a local RCAtub. and porf. distributor.
Symbol
No,
Stock
No.
Description
CI
C2
C3
C4
Rl
R2
R3
R4
R5
R6
R7
R8
R9
RIO
Rll
R 12
R 13
R 14
R 15,16
R17
R 18
R 19, 20
R 21
R22
Capacitors
Paper tubular, 0.33 µf, ± 10%,400
volts. 93848
Papertubular, 0.1 µf, ± 20%,200
.volts.73784
Dry electrolytic, 10 µf,- 10%, +
100%,250 volts. 93849
Papef tubular,0.01 µf, ± 20%,400
volts.. 73561
Stock
No_
It 27
Symbol
No.
Description
H 23
213743
502133
522010
512210
502310
502610
93839
Resistors
Carbon filmtype,S meg., ± 1 %, Yz
watt.. . 5588]
Carbon film type, 3.75 meg., ± 1 %,
Yz watt.. 93840
Carbon film type, 1 meg., ± 1 %, Yz
watt. 55658
Carbon filmtype, 0.2 meg., ± 1%,
Yz watt. 56733
Carbon film type, 37,500 ohms, ±
1 %, Yz watt... 93841
Carbon film type, 12,500 ohms, ±
1%, Yz watt. . 93842
Carbon film type, 0.8 meg., ± 1%,
Yz watt. 93843
Carbon film type, 1.36 meg., ± 1%,
Yz watt. 96259
Carbonfilm type, 250,000 ohms, ±
1%, Yz watt.. 56728
Carbon film type, 678,000 ohms, ±
1%, Yz watt. 93845
Carbon film type, 361,000 ohms, ±
1 %, Yz watt. . 96258
Fixedcomposition, 1 meg., ± 5%,
Yz watt. 502510
Fixedcomposition, 15,000 ohms, ±
5%, Yz watt. 502315
Fixed composition, 12,000 ohms, ±
5%, Yz watt.. 502312
Fixed composition, 1500 ohms, ±
5%, Yzwatt. 5022L5
Fixed composition, 47,000 ohms, ±
5%, Yz watt,.502347
Fixedcomposition, 130 ohms, ±
5%, Yz watt. . 33571
Fixed composition, 68,000 ohms, ±
5%, Yz watt. 502368
Fixed composition, 470 ohms, ±
5%, Yz watt. 502147
Variable carbon, 12,500 ohms, ±
20%, 74 watt.213744
R 24
R 25
R 26
11 28
R 29
R 30
J
ML
PI
SI
82
TI
• 11 •
WG~299B Dcl AC~Ohms Probe
and Cable
Bushing,tip: for fl'Ont housing. 212161
Connector: internal, brass for cable. 210190~A
Connector,cable: female, ,viLb set
screw. 203574·
Shell: front end,blue...' .210195
Shell:middle section, with shield,
bushing,andinsulator. 212159
Shell:rearsection, blue 210202-A
Spring, coil: forfront end. 210197
Spring,switch:with insulator. 212162
Tip, probe: withswitchslide and
I-meg. resistor. 212160
Washer, tip: 212163
Variable carbon, 75000hrns, ± 20%,
Yz watt. ,
Variahlecarbon, 15,000 ohms, ±
20%, }4 watt.
Fixed composition, 330 o.hms, ± 5%,
Yz watt.
Fixed composition, 10 ohms, ± 5%,
2'\'atts.
Fixedcomposition, 1000 ohms, ±
5%, 1 watt.
Fixed composition, 10,000 ohms, ±
5%, Yz watt.
Same as R12
Fixed composition, 10 meg., ± 5%,
Yz watt.
Miscellaneous
Connector, cable, chassis receptacle.
IVleter,dc, 0~200 µ amp. (blue)...
Cord, power, withplug.
Switch, "Selector", 2 section, 5 posi~
tion, 6 circuit.
Switch, "Range", 2 sectjon, 5 posi-
tion, 4 circuit.
Transformer,power; primary, 117
volts, 50/60 cps.
Case, meter(plastic)blue .. '.
Clip,alligator:for ground cable.
Clip, alligator:"slip-on" type.
Handle, carrying.
Insulator: for alligator clip,
Knob, cpntrol.
Socket,tube, 7 pin.
Socket,tube, 9 pin.
Stud, carrying-handle.
962;;7
213484
70392
21:3514
213513
9:1835
2D48S
;~5262
210088
44091
204717
59543
204825
204900
93854

Beforeinstalling a12AU7, the tube may beaged asfollows:
connect theplates together and apply115volts dc. Operate
the grids and cathodes with no voltage applied,and operate
the heatersat 6.3 volts. The tube should be operated in this
manner fora minimumof12 hoursbefore it isinstalledin
the instrument. TheWV·77C then can be recalibrated.
An alternate, and usually satisfactory,aging procedurecon-
sists of operatingthenew tubein theWV-77Cfor approxi-
mately36 hours,afterwhich time theinstrument may be
recalibrated. If thisprocedure isunsatisfactory,the first aging
procedure should befollowed.
If itbecomes necessary to replace the 12AL5, the tube can
be aged foraminimumperiod of 36 hours by operating it in
the \VV-77C. After this period of time,the instrument may
berecaliurated according totheprocedureoutlinedunder"AC
Calibration Check".
Battery Testing and Replacement
Caution:Donot allowexhausted cellsto remain inside the
case of theWV-77C. Chemicals from deteriorated cellsmay
damage the instrument.
Thebattery shouldbe testedto insure accuracy ofresistance
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 theprobetip and ground clip for about
ten seconds.
5. Open the short-circuitand immediately observethe scale
indication. An appreciable deviation from full-scale indication
revealsweak cellswhich should bereplaced.
Ohms Adjustment
In orderto obtain exactlyfull-scaledeflection of themeter
whenswitchingtherange selector from a low range position
tothe R x 1MEC position, it may be necessary to readjust
the OHMS ADJ control. The necessityfor thisreadjustment
can beminimized bychecking the bauery and installing a
12AU7tubewith a low value of grid current. Refer toTube
Replacement section.
RCA Repair Service
S. If steps 2 and 4 above cannotbe accomplished, thetwo
triode units of the12AU7tuhesare not in close enough bal.
ance for thisapplication and thetube should be replaced.
DC Zero Check
L Set functioll selector to "-VOLTS".
2.Set range selector on "3V".
3.Rotatethe ZERO ADJ control untilthemeter pointeris
at zero.
4. Turn range switch to "1200V".
5. If themeterpointer deviates from zero by more than one
division 011 the 0 to 12 metcrscale, replace thc12AU7(see
section onTu beReplacement).
AC Zero Check
J. Set the range selectoron"3V"and thefunctionselector
on "+VOLTS".
2.RotateZERO ADJcontrol until meter reads10 voltson
the60V meterscale.
3.Turn the function selector to "AC VOLTS".
4. If themeter does not read between7and 13volts,replace
the12AL5. Thcuse of a 12ALS which results ill a meterread-
ingoutside of ,his 7-13 volt range will not impairthe accura~y
of theinstrument but will, however,require morefrequent
adjustment of theZERO ADJcontrol.
Calibration
1. Settherange selectorto ;'60V" andthe functionselector
to "+VOLTS"_
2. Setthc meter pointer to zero byusingthe ZEROADJ
controL
3. Set the slidingswitch on the probeto "DC".
4.Connect the GroundCable to the negativeterminal alld
theprobe tip to thepositive terminal ofa sourceofDC
Voltage that has beenadjustedtoexactly 57 volts.
Note:The accuracyof calibratioll cannot cxceed theaccuracy
of the voltage standardswhich areused.
5.Adjust the ';DC CAL" control (R-23)insidethe case for
a meter readingofexactly 57 volts.
6.Remove theleads at the source of voltage.
7.Set the function selector to "-VOLTS".
8.Connect theGround Cable to the pOSiLi\'eterminal and the
probetip to the negative tenJlinal of the dc-voltage source
adjustedto exactly 57volts.The WV-77C should read57 volts
within±3%.
9. If the WV-77C cannot be calibrated according tothe
foregoingsteps the12AU7amplifier tube maynot beproperly
balanced for this application.
Tube Replaceillent
All tubes supplied originally withtheWV-77C have been
thoroughly aged by operating them for several hoursbefore
illstallatiOri in theinstrument. This preliminaryconditioning
of a new tube helps to insurestability anddependable per-
formance.
RCA maintains a complete repair service for the adjustment,
calibration, and maintenanceof RCA t~st equipment. If it
becomes necessary to service this equipment, thereport forms
enclosed in this bookletshould be filled out as described. It is
important that:
1. Test equipmentbe packed carefully,
2. A full description of the trouble be included in the report.
3.All probesand cablesbe included with theinstrument.
Attentionto these details will help prevent damage intransit
and delay in repairs .
. 12 •

I