B+K precision 177/V-95 User manual

@r77lv-ss
YACUUM
TUBE
VOLTMETER
DYNASCAN
COF|PORANCfN

TESTINSTRUMI]NT
SAI.'ETY
WARNING
Normal useof tcst cquipmcnt cxposes
you to a ccrtainamount of dangerfiom elcctrical
shock becausctesting must often be performed where exposedvoltageis present.
An electrical
shock causing 10 milliamps of ourrent to passthrough the heart will stop most human
hcartbeats. Higher voltages pose an even greatcr thrcat becausesuch voltage can more easily
producc a lcthal current. However, voltage as low as 35 volts DC or AC RMS should be
considered dangcrous
and hazardoussince it can produce a lcthal current under ccrtain
conditions. Your normal work habits should include all accepted practices
that will prevcnt
contaot with cxposedhigh voltage,
and that will steer
current away
from your heartin cascof
accidental
contact with ahigh voltage.
You will significantly
reduccthc risk factorif you know
and observethe following safety precautions:
1. Don't cxposehigh voltageneedlessly.Removc housings
and covers only whcn ncccssary.
Turn off cquipmcnt while making tcst connectionsin liigh-voltagc
circuits.Dischargc
high-voltagccapacitorsafter removing power.
2. Use
an insulatedfloor materialor alarge, insulatedfloor mat to stand
on, and
aninsulated
work surfaccon which to placc
cquipment;and make certainsuchsurfaces
arenot damp
or wet. Whereinsulated floor surfaocis not available,wcar hcavy gloves.
3. Use the timc-proven "one hand in the pocket" tcchniqucwhile handling
an instrunrcnt
probc. Be particularly
carcfulto avoidcontactingancarbymctal
objcct that could provide
agoodgroundreturnpath.
4. Always usean isolation transformerto power transformerless
"hot chassis"
equipntcnt,
wherc onc side of thc AC power line is connected directly to the chassis.
This includes
most recent tclevision sctsand audio cquipment. Without an isolation
transformer,the
chassis
of such cquipmcnt may be floating at line voltage(120 VAC, 60 Hz in USA),
dependingupon which way the 2-wire AC power plug is inserted.Not only does this
prescnt
a dangcrousshockhazardif the chassis
istouchcd,
but damage to test
instrumcnts
or the cquipment undcr test may result from connectingthe ground lcad to some
test
instruments
to a "hot" chassis.Thegroundlead
of rnostoscilloscopcs
andmostother tost
instrumcntswith 3-wire power plugsis at earth ground. Thc B & K-PRECISIONModel
TR-l l0 IsolationTransfbrmerissuitablcfor mostapplications.
5. On test instruments or any equipmcnt with a 3-wire AC power plug, usconly a 3-wirc
outlet. This is a safcty fcaturc to kccp tho housing
or othcr cxposedelcmcnts
at oarth
ground.
6. If possiblc, larniliarize
yoursclf with the cquipmcnt bcing tcstcd
and thc location of its
high voltagc points. Ilowcvcr, rcmembcr that high voltagcmay appear
at uncxpcctcd
points
in defcctivccquipmcnt.
7. Also rcmemberthat AC line voltagc is prcscnt on somc
powerinput circuit points
suchas
on-offswitchcs,fuses,
powcr transformcrs,etc.,evenwhentheequipment
isturnedoff.
8. Ncvcr work alone. Someoncshouldbc ncarbyto rcndcr
aidif nccessary.Training on CPR
(cardio-pulmonary
rcsuscitation)firstaid ishighly rcoonrmendcd.

TABLE OF CONTENTS
Page
KeyFeatures......... I
Specifications
lmportant Notes
Advantages of the VTVM
Accessories
D.C. VoltageMeasurements
A.C. VoltageMcasurements
3
R
o
t)
ResistanceMeasurements
Reading the Meter Scale
8
8
I
1t
t2
t4
Using the db Scale
Circuit Descriptiou
Maintenance Suggestions
Warranty Service Instructions

KEY FEATURES
1. Wide vision 6" x 4" meter scale for efiortless reading.
2. Anti-parallax mirror permits maximum scale-reading accuracy.
3. rnput impedance of 11 megohms on all D.c. voltage rzrnges. This is a very
important feature when measuring oscillator grid-bias, AGC/AVC voltage i-i
high impedance circuitry.
4. special 0-.5 volt D.c. range, useful for accurate measurements of critical
circuit parameters in solid state circuitry.
5. Measures D.C. voltage up to 1500volts.
6. Measures A.C. RMS voltage up to 1500
volts.
7. Measures A.C. peak-to-peak, sine and complex voltages up to 4000 volts.
8. Measures resistances up to 1000megohms.
9. Calibrated DB scale.
10. Zero center on meter scale, useful for F.M. discriminator aligmment'
11. "Transit" switch position automatically clemps and protects meter movement.

SPECIFICATIONS
DC VOLTMETER. ELEC'TRONIC:
8 Ranges ...0-.5,r.5,5, 15,50,
150,500,
1b00
volts
fulr
scale.
Input Resistance . .11 Megohms (1 I\4egohm
in probe).
Sensitivity .7[ Megohms per-volt on 1.5
volt range.
Circuit ..
..Ralanced
bridge using twin triode.
Accuracy .,1-3% full scale.
AC VOLTMETER. ELEC'TRONIC:
7 Ranges (R.M.S.) .......0-1.5, 5, 15,
50,150,
500,1500volts
full scale.
7 Ranges (Peak-to-peak) ... .. ....0-.4, 14,
40,L40,400,1400,4000
volts.
Frequency Response (5V Range). . -+1 db 40 Hz to 4 MIIz (600 ohms source).
Accuracy ..isTo full scale.
DB Scale ..-6 to +16db, +4 to +26db, f 14
to +36db,
*24 to +46db, *34 to +56db, +44 to
l-66db (0.775 volts into 600 ohm
line on 0-5 volts AC scale - 0db).
OHMMETER, ELECTRONIC:
TRanges ...0-1000 (x1),10,000 (x10),100,000
(x100),
I meg (x1000),
10 meg (x10K), 100 meg
(x100K), 1000 meg (xl meg). 10 ohms
center scale on Rx1.
No battery required for ohmmeter.
METER . . . . .100 p.A movement, plastic case.
Anti-parallax mirror.
MULTIPLIERS ....t% precision
type.
TUBE ......12AU7, twin triode bridge.
POWER REQUIREMENTS lO5-L25 volts 50-60 cycle AC.

OPERATING
WARNINGS
whe
n this
v'rvM isused
to make
measurements
in
equipmcnt
that
contains
high
voltage,thcrc is always a certain amount of danger
fiorn elcctric shock.The
person
using
theVTVM should
be
a
qualified
electronrcs
technician
orothcrwise
traincd andqualifie
d to work in such
conditions.
obscrve
thc ..Test
Instrument
Safety"
recomme
ndations
listeci
on theinside
front cover
of this
manual.
There t:utt
bc a shock h.azurtr.lrom
touchirlgthc (asco.r
tht'vrvrl u,hcrt
trtt,
cotnrt,, .r gr.urttl leutl,J tha ilrcter
iscttnncc,tetl
t. u ltighvortugc
p.irtt. The
chassis
and case
of the VTVM are
isorate
d from carth
ground to pcrrnityou to
"float" the metcr for measuring
voltage
betweenrwo polnts,
'crther of which
ts grouaded' Howevcr,
this rnust
bedone with caution. The
t,rnitrt.n ,r gr.uttd
leutlof the meterist;ottnectatl
tn thc cltassis
utttlcusc
of the VTVM untlshould
nortnulll' bc corre(ted to ugrcturttrecr
pr.tirt
tn the equipmentundertest.
If thc
common read
is conncctcdto a high vortage
point, thc case
of the VTVM rises
to that potential.The metercasc
shoulcl
beiniurated
from ground und it. ..r.
should
not be
touchcd
while
connccted
in this
manner.
obscrve
Cuution.
one of the most com"only encountercd
shock hazards
is testing
of ,,hot
chassis"
transformerless
ac-powercd
equiprnent
(see
item + on tne in'siae
front
covcr
of this manual
for a fu[ explanation
of the
hazard).
If the
common
lead
of the VTVM is conncctedto a "hot" chassis,
the case
of the vrvM wrll also
become"hot." For safety,always
uscan isolated
transformer
betweenthc ac
power line and any "hot chassis"
ccluipment
undertest.
To beon the sate
side,
treat any ac-powcred
equipment as"hot chassis"
unlessyou o." rurait t u, un
isolated
chassis
or earth
grouncl
chassis.
when handling the test probe, touch onry the rnsurated
portion. Nevertouch
theexposed
tip portion.
i
f^ *"*--

ADVANTAGES OF THE VTYM
'I'he greatest of the many advantages ofiered by the VTVM is its high input
impedance. This feature makes possible the measurement of voltages in high
impedance circuits such as oscillator grid circuits and AGC networks with a much
higher degree of accuracy. As a simple illustrative example of this, we have
showl in Figure 1A two 500K resistors connected in series across a 100 volt
source of voltage. A simple knowledge of basic fundamentals makes it obvious
here that the voltagc drop across each resistor will be 50 volts. I\4easuring the
voltage acrosseither resistor with a 20K ohm-per-volt non-electronic type instru-
ment on the 0-100 volt scale however, we obtain a reading of only 44 volts. Why
the discrepancy. As shown in Figure 1A the meter (on the 100
volt range) can be
considereda resistor of 2 meg.,which is connected in parallel with the 500K resis-
tor. A simple Ohm's Larv calculation rvill readily shorvthe total resistanceof the
parallel circuit to be 400K, resulting in a redistribution of the voltage drops in
the circuit. Now the first 500K resistor has approximatety 56 volts across it, and
R(rorAL)
(ruerER
rN
PARALLEL
wlrHRz)=ffiffffi;aoo K
\oLTAGEAcRossRzAND
METER=Eoffi
xtQQ=44
voLTs
(APPRox')
FIGURE
IA
I
R=5OO
K
E=51
V
-t-
loo
v
_l_
-T-
loo
v
_.1_ /ruec.oN\
\ANY SCALE/
R(roTlt-)=4goK
E=49V
I
t
R(rorAu
(METER
rNPARALLEL
wrrHnz)=*#Hili$F. .48MEG.=48oK
VoLTAGEAcRoss
R2ANDMETan=#|ft5xloo=4e
voLTs
FIGURE
IB
the other 500K resistor in parallel with the meter has approximately 44 volts across
it. The low resistance meter is loading or changing the impedance of the circuit
when it is connected. When a VTVI\{ is used as shown in Figure 18 we have a
total of 11 megohms connected in parallel with the 500K resistor, and the total
resistance of our parallel network is now approximately 480K, resulting in the
voltage across
the meter and resistor dropping only to 49 volts or a mere 2/6 lowet
than the actual operating voltage. More accurate readings can only be obtained
with a high-impedance instument such as the VTVM.
R:5OO
K
E=56V
--MULrrMetEd-' E_q?rf;.Ll"4ooK
ONIOOVSCALE=2MEG. I
VTVM

Additional aclvantages
of the VTVM in solid state measurements are:
A t/2 volLfull scalesensitivity range which permits the accurate reading of the
fractions of a volt, (which are often applied between baseand emitter of transistor
devices). 'I'he VTVM input impedance is important, so that the connecting of the
meter doesnot causefalse readings due to current injection in the transistor base.
Other advantagesin the high impedance characteristics of the VTVM include the
ability to acculately measure voltages,without upsetting circuit operation, on AGC
lines, high impedance osciilator grid and other grid circuits, insulation resistance
measurements.
ACCESSORIES
(Available on separate order)
*F*ffi
re d-g]', ^€
ifl n. dry
*-t
MODET AV-2A. Increoses DC voltoge ronge up lo
50,000 volrs.
MODET AV-lA. R.F. Probe. lncreoses frequenq
rqnge up to 250 MHz.
The AV-IA RF PROBE enables the operator to make measurements of sine
wave voltages at frequencies up to 250 MHz.'rhis probe employs a crystal diode
which is useclas a half wave rectifier. The half wave rectifier circuit develops a
DC voltage proportional to the peak value of the sine wave input signal. A cali-
brating resistor convertsthis peak reading to the proper reading on the VTVM.
The AV-2A HIGH VOLTAGE MULTIPLIER PROBE has been developed
as an Accessory item (available at your distributor) to extend all DC voltage
rangesof your VTVM by a factor of 100.
The heavy duty plastic handle and safety-type connector insures maximum
operator safety. Two oversizedflashover guards protect the operator's hands from
leakage at the test point on the probe head.
One of the most u:;eful applications of the AV-2 High Voltage Probe is the
measurernent of 2nd anode voltage in TV sets.
The DYNASCAN Models AV-1A and AV-2A Probes can be used with the
following vacuum tube voltmeters:
- B&K Model 177
- B&K Model 375
- B&K Model 175
- Precision Apparatus Model V-95
- Precision Apparatus Model V-75
- Precision Apparatus Model 48
and most other VTVM's with 11 megohms input resistance

SeeOPERATING
WARNINGS
on page
3 concerning connection
of aommon
lead
ofVTVM.
DC VOLTAGE MEASUREMENTS
Io nrerrsur,,DC
r.oltages
with the V'l'VM, connecttlte commonlearl
to the
common B-, or "grouncl" gide of the voltage to be measured. This is the chassis
in most instances although in many transformerless sets, the chassis is isolated
from the electrical circuitry and the common or B- side must be determined
f
rom the schematic diagram. Set the function switch to -DC or tDC as
requirecl, ancl set the range switch to a range greater than the voltage to be
measured,
if known. If not known, set to the highest, (0-1500
volt) range. set
the AC-OHMS, DC switch on the test probe to the DC position, then touch the
pro|e to the voltage point to be measured. If the reading obtained is less than rf
fuli scale (500 volts rvhen on the 0-1500volt range) move the range switch to the
next lower position. (0-500 volt range in this example.) For greatest accuracy,
always select the range which permits you to obtain a reading nearest full scale
deflection without having the pointer go off scale. IJseonly the scales
marked DC-
RMS for reading DC uoltages. Use the 0-5 scale for reading DC voltages between
0 and .5
volts.
You rvill notice that your vTVM has a convenient
center scale
zero position
for special applications such asbalancing FM discriminator circuits. You may use
this center scalezero feature when the range switch is on either the *DC or -DC
position by simply adjusting the ZERO ADJ. control to bring the pointer to the
center scalemarking.
set Function switch to "-DC or *DC" volts position, and switch in tlre
orobe to "DC".
VOLTAGE TO
BE MEASURED SET RANGE
SWITCH TO READ FROM
SCALE MULTIPLY
READING BY
0to.5V
0to 1.5V
1.5
to5V
5to 15V
15to 50V
50
to 150V
150to
500V
500to 1500V
.5V
DC
1.5V
5V
15v
50v
150v
500v
1500v
0to5
0to 1.5
0to5
0to1.5
0to5
0
to1.5
0to5
0
to1.5
.L
I
1
10
10
100
100
1000
AC VOLTAGE MEASUREMENTS
To measure AC voltages
with the VTVM, connect the common leatl to one
side of the voltage to be measured, set the function switch to AC, and the range
switch to a range greater than the voltage to be measured,if known. ff not known,
set to the highest (0-1500
volt) range.set the AC-OHMS, DC switch on the test
probe to the "AC-OHMS" position, then touch the probe to the other side of
ihe voltage to be measured. If the reading obtained is less than % full scale
(500 volts when on the 0-1500 volt range) move the range switch to the next

iower position. (0-500volt range in thi." exampie.) For greatest accuracy, always
selectthe ra-nge
which permits you to obtain a-reading ne"arest
iutl scale deflection
without havingthe pointer go off scaie. It is importani to remember that 1500
volts
is the highest RMS AC voltage that can be measur.ed
with your v.fvM. The
scalesof the meter are calibrated to read both RMS an.l pe,,i-to-peak voltages.
Read the RMS values on the black scalesmarked "DC-RMS" u.rd.
tn" peakito-
peak values on the red scalesmarked "P-p". peak-to-peiik voltages are equal to
2'83 times the RMS values of sine-rvave
voltages and the scalesa'reso calibratecl
that when a voltage of 10 volts RMS for "*u-pl" is applied to the insirument, the
meter pointer will indicate 10 volts on the 0-15 volt scale, and 28.3 volts on the
0-40 P-P red scale. use the scalemarked "l.bv RMS low AC" and ..0-b.0VRMS
low AC" for AC voltagesthat fall within these ranges.
See the charts below, indicating scalesto be usecl.
AC RMS VOLTAGE MEASUREMENTS: set Function switch to ,.AC",
and Switch in the probe to "AC-OHMS".
IiMS VOL'TAGE TO
t]I] MEASURED
0to 1.5V
1.5
to5V
5to 15V
15
to 50V
50to 150V
150
to 500V
500
to 1500V
SET RANGE
SWITCH TO
1.5V
5V
15V
50v
150V
500v
1500v
READ FITOM
SCALI]
1.5
RMS,LOW AC
5RMS, LOW AC
1.5
DC or RMS
5 DC or RMS
1.5
DC or RMS
5 DC or II,MS
1.5
DC or RMS
MULTIPLY
READING BY
1
1
10
10
100
100
1000
AC PEAK-TO-PEAK VOLTAGE MEASUREMENTS: set Function
switch
to "AC", and Switchin the probe
to "AC-OHI\{S,'.
T)EAK-TO-PDAK VOL READINGS IN RED COLOR
TO BE MI'ASURED
0to4V
4 to l4Y
14
to40V
40
to 140V
140
to400V
400
to 1400V
1400
to4200V
SET RANGE
SWITCH TO
4V
14V
40v
140V
400v
1400v
4000v
RI'AD FROM
SCALE
4 P-P,
LOWAC
14
P-P,
LOWAC
40P-P
140
P-P
40
P-P
140
P-P
40
P-P
MULTIPLY
READING BY
I
I
I
1
10
10
100
Note that the "DC or RMS" scales are correct for AC voltages only when
sine-rvavevoltages are being measured. The peak-to-peak scales"i., l" used for
both peak-to-peak of sine and non-sine (complex) ,'oitag". such as are measured
in TV receivers

.Ihis vTVM is a highly sensitive electronic AC voltmeter, and since the humarr
body and Iong unshielded test leads pick up AC voltage radiations when near any
sourcesof such radiation such as power lines, the meter may indicate this pickup,
antl consequently reduce the accuracy of the voltage lLeasurement. Therefore for
utmost accuracy when measuring low voltages in high impedance circuits the
user should avoid holding the test probe in his hand. A good practice is to use
an alligator clip or wire hook of some kind on the end of the probe tip to clip
to the voltage point, so that the hands may be removed entirely from the probe
while reading the test voltage.
RESISTANCE MEASUREMENTS
To measure resistance
with the VTVM, set the function switch to the "OHMS"
position, and the range switch to a position that will result in the meter pointer
reading as near to midscale as possible. set the AC-oHMS DC switch on the test
probe to the "AC-OHMS" position, then attach the common alligator clip to the
probe tip and set the meter pointer to ZERO on the ohms scale by rotating the
iZERO" control. Then disconnect the alligator clip from the probe tip and use
the .,OHMS ADJ." control to set the pointer to exactly full scale, marked "co"
(infinity). Connect the common test lead alligator clip to one side of the resistance
to be measured, and the probe tip to the other side. Read the resistance on the
ohms scale, and multiply the proper factor for the range being used.
Set Function Switch to "OHMS" position, and Switch in the probe to "AC-
OHMS''.
RESIS'TANCII TO
BE MENSUNIiD SE'f RANGD
SWITCH TO MULTIPLY
RDADING BY
.2to 1000 O
1000
to 10000 O
10000
to 100000
O
100000Oto1Meg
1Meg
to 10Meg
10Megto 100Meg
100Meg
to 1000Meg
Rx1
Rx10
Rx100
R x 1000
Rx10K
Rx100K
RxlMeg
1
10
100
1000
10,000
100,000
1,000,000
READING THE NTETERSCALE
The needleshould be set to mechanical zero when the instrument is turned oll.
This is accomplished (if necessary) by using the screwdriver adjustment to zer<-r
set the pointer.
The voltagemarkings on the RANGE switch indicate the corresponcling
lull
scale reading on the corresponcling meter scale.
The low voltage AC scales,
0-1.5
RMS, 0-5 RMS' and 4 P-P, 14 P-P are sel
apart from the other AC voltage scales and separately calibrated to give more
accurate readings. The diode rectifiers within the instrument inherently have a
portion -rf their characteristics in a non-linear region. when rectifying low AC
voltages,those non-linearities become
prominent in the metering circuit and would
lead [o inaccuracies if the meter scalewere not properly calibrated to account for
them and to make suitable correction.

This does not apply to the DC scales, since in measuring DC, no rectifiers are
used.
The colored Range Switch positions and their corresponding scales on the meter
face are colored just to remind you that they indicate peak-to-peak AC voltage
measurements,
RMS is an abbreviation oI "Root Mean Square" which is a term relating to a
sinewave of voltage and its e{Iective or heating value, relating it to an equivalent
DC (direct current) voltage. P-P is an abbreviation of "Peak-to-peak", or the
total of the positive-going and negative-going voltages relative to a zero voltage
axrc.
When we are measuring a sinewave of voltage, there is a fixed mathematical
relationship between RMS. Peak. and Peak-to-Peak:
Peak is 1.41times RMS.
Peak-to-Peak is 2 times peak.
Peak-to-Peakis 2.83
times RMS.
RMS is .707 times peak.
RMS is .353
times peak-to-peali.
This relationship is valid, only when we are dealing with a sine-wave voltage.
Since there are almost an infinite number of rvaveforms other than sinewave it is
impossible within the scopeof this manual to make any statement of relationship
between RMS and peak-to-peak when dealing with other than sinewaves; each
such complex waveform would have to be analyzed aird a proper relationship
established.
USING THE DECIBEL (Db) SCALE
'l.he human ear responds in a logarithmic manner to variations in sound
intensity and not linearly-that is when the amount of sound is doubled, the ear
responds to it so that we senseonly a slight increase in loudness rather than a
doubled increase.A unit of loudnessmeasure basedon logarithms called the "bel"
was adopted. The bel corresponds very nearly to the human ear responsevrrria-
tions. Normally, loudness signal levels are given in tenths of a bel, or decibels,
because
this unit represents the smallest variation in sound intensity the ear can
detect. Manufacturers use a variety of signal levels as a standard for zero db. The
Db scale uses.001watt (1 milliwatt) into a 600 ohm line as zero db. This corre-
sponds to O.775
volt AC on the 0-5 volt scale.
The decibel represents a voltage ratio, and it may be used without specifying
the reference level. For example, a responsecurve may be plotted for an amplifier
by injecting a signal of variable frequency and constant amplitude, with the VTVM
connected to the output. Adjust the signal input at some reference frequency,
such as 400 cycles, for a convenient indication on the VTVM. (Zero db for exam-
ple.) As the input frequency is varied, the output variation may be obsetr',1 in
db above and below the reference freouencv level.

CONVERSION CHART IIOR RMS-P-T-P and DB (Decibel) SCALES.
FTJNC'I'ION SWII'CII S]''|'T'ING TO NC VOLTS
RMS
F'ULL SCALE, VOLTS PEAK TO PEAK
FULL SCALE, VOLTS
DB TO BE ADDED
TO THE DB
SCALE READING
nuJ au
directly
10
20
30
40
50
1.5
b
15
50
150
500
1500
4
1A
40
t40
400
1400
4000
When usiag other than a 600 O load, a correction must be applied, to obtain
true db values. The chart below indicates some typically used loads, and the cor'
rection which must be applied. A generalizedequation for finding the correction is:
db correction = 10 los'o600
R
Where R is the load in ohms. If R is greater than 600 ohms, the factor becomes
negative, and must be subtracted from the db reading. If R is less than 600 obmg,
the correction is added to the db reading.
LOAD, OHMS ADD TO (+) OR
BTRACT FROM (-)
DB READING
9600
4800
2400
1200
600
500
300
250
150
50
15
8
3.2
-15
-t2
-4
-3
0
+0.8
+3
+3.8
to
+10.8
+16
+18.8
+22.7
10

CIRCUIT DESCRIPTION
The 100 microampere meter movement is connected in the plate circuit of a
L2AU7 twin triode in a balanced bridge arrangement. The zero adjust control
sets up a balance between the two triodes so that with zero voltage applied to
the first grid, the potentials on each plate are equal. There will be no voltage
drop or difference in potential across the meter, and consequently the meter will
read zero. with a r,oltage applied to the first grid, the balanced condition is
upset causing a difference in the potentials on the two plates and consequently
across the meter. The meter will then indicate. The relationship between the
test voltage applied to the first grid and the current through the meter is linear
and therefore the meter is calibrated with a linear scale. one of the advantages
of a vacuum tube voltmeter circuit is the voltages to be measured are applied to
the tube and not directly to the meter. since the amount of current a vacuum
tube can draw is limited, the meter movement is electronically protected.
The maximum test voltage which is applied directly to the L2AIJ7 is approx_
imately 1.5 volts. A voltage divider network having a total resistance of l0
megohms reduces voltages higher than 1.5 volts. An additional isolating resist-
ance of 1 megohm, located in the test probe, is used in the DC position, making
it possible to take measurements in circuits with R-F components with a min-
imum disturbance.
AC measurements: D3 and D4 are used to rectify the test voltages providing
a DC voltage proportional to the applied AC. The DC voltages is then applied
through the voltage divider network to the input grid of the L2ALJ7balanced
bridge circuit causing the meter to indicate. The AC voltage scales
are calibrated
to read both RMS and Peal<-to-Peak
'alues. The 0-1.5vand 0-5.0V RMS low AC
scales have been especially calibrated to improve the accuracy of the meter on
these low ranges. stray pickup reduces the accuracy of any highly sensitive
vrvM on the lower AC ranges. with this special scale you have improved
accuracy that many other instruments do not have. In the 0-1.5,0-50,and 0-1b0
volt ranges, the full AC voltage being measured is applied to the diode rectifier.
A voltage divider network reduces the voltage on the 0-500, and 0-1500 voltage
ranges to limit the voltage applied to the diode to a safe level. when the instru-
ment is used properly, it is not possible to apply more than 150 volts to the
diode. when measuring any unknown voltage, always make it a habit to start
on the highest range, and then switch down to a more appropriate range.
For measuring resistances,
a 1.5 volt DC supply is connected through a series
of multiplier resistances
and the external resistance to be measured. This forma
a voltage divider circuit consisting of the l.s volt supply in series with one or
more multiplier resistors and the resistance under test. The voltage across the
unknown resistor is then proportional to its resistance This voltage is supplied
to the input grid of the 12AU7 balanced bridge circuit which produces an ohm-
meter scale reading proportional to the unknown resistance.
rn the "off" position the meter movement is automatically shorted to preven,t
damage in transit.
II

MAINTENANCE SUGGESTIONS
Your VTVM is capable of continuous daily service requirements over a period
of several yeara. In order for the user to fully realize these capabilities, the snme
degree of care in operation and maintenance should be accorded your instrument
that would be given any fine piece of equipment.
SERVICE
WARNINGS
c The following instructionsarefor useby qualifiedpersonnel
only.
To avoid clectric shock, do not perform servicingother than
containedin the operatinginstructionsunlcss
you arequalified
to
doso.
a A shock hazard
is present whcn the caseisremoved
andthe unit is
operating.Line voltagc
(120VAC) may be present
on the input
power cord, on-off switch, power transformer, etc. any time the
unit isconnected
to acpower.even if the switchisoff.
Disconnect
the testleadsfrom external
devicesandfrom the mcter
beforeservicins.
This B&K-PRL.CISION Model 177VTVM is equipped with aJusetl ohms
protection circuit. A I amp pigtail fuse is connected internally between the
comnlon test lead and chassis
ground.The fuse
may blow if the meteris connected
to the 120VAC power line or other high AC voltages
while on the ohmsfunctions.
lf the ohms protection fuseis open, all functions of the vrvM areaffected since
thc fuse is in series
with the common test 1ead.
Test for open fuseby measuring
continuity between the commr.tn
test leadand the vrvM chassis
usinga separate
ohm-meter. Replace
with 1A 3AG fast blow on1y.
The fuse
connects
directlv from
the common jack to the VTVM chassis.
Should failure of the meter movement coil be suspected,the continuity may be
checkedwith another ohmmeter if you first connect a 10K OHM limiting resistor
in series with the ohmmeter test leads. Remember: - NEVER test meter coil
continuity directly with another ohmmeter without using a Iimiting resistance.
Do not attempt self-repair of the meter movement. This will automaticaily void
our standard warranty on the VTVM.
The plastic meter cover may through repeated polishing or cleaning accumulate
chargesof static electricity. This will causeerratic pointer deflection whether the
instrument is on or o{I. These static chargesmay easily be removed by using one
of the commercially available anti-static solutions, or a solution of any good liquid
dish washing detergent and wz:ter. Dip a clean, soft cloth in the solution and wipe
the surface of the meter cover. The cover need not be removed for this operation.
Faulty operation of your VTVM may be causedby open or shorted test leads.
Check the continuity and resistanceperiodically.
Another frequent source of trouble arises from accidental improper usage of
the VTVM, resulting
in failure of oneor more precision resistorsin the multiplier
strings. Symptoms of this difficulty may be slow, upscale drifting of the pointer,
inability to obtain proper- zelo adjust action, ancl of course incorrect voltage or
resistance readings. Keep in mir-rdthat patience and the exercise of proper pre-
cautionary measuresin the use of your instrument are of the utmost importance in
keeping troubles of this type at a minimum.
L2

IN ALL CASES WHERE F:\UL'r'y opIrRAl'ION orr .r.Htr rNS.r.RU-
MBN.I' IS SUSI'EC'I'ED, TI,IE S]]RVIT]I] DEPAN,I'NIEN.I OIT DYNASCAN
CORI'. SHOUI,D ITIRST BE CONSUI,'1'EI]. SHOULD THE SERVICtr DE-
PARTN,IENT ITECON{I,IFJND
ITETURN OF TI]E INSTRUMEN'I,TO THB
FACTORY, TI.IE COXIPLI''|E INSI'RI]NIENT SHOULD BE CATTEFULLY
PACKEI] IN .,\ WF]I,L P.\DDED, S|RONG CORRUGATED SHIPPIi{G
CAR'I'ON AND ADDRI'SSDI) 1'O DYNASCAN'S StrRVICE DEPARTN,fENT.
IMI'oR'rAN'r NorE: 'I'he original packing of the u'it is admir'blv suitcd
for this purpose.
IMPoRTANT: If at an1'
timc this meter is to be rcturnecr
to the factory for
repair, a CONIpLBTtr description
of suspected
faulty opera_
tion, as notecl by the operator, MUST n""ornpo.ry the instru-
mcnt. The more detailssubmitted to the Service
Department
of Dvnascan Corp_,
the more quickly and efficienilv the in-
strument c:rnbe repaircd and returned.It is very important
that this descriptionof suspectecl
faulty operation be given
in un.su:rily exar't
detail due to the ra"i tttnt in nrany cases,
fa'lty operationcan be traced to difficurties
in other items of
test cquipment ancr/orimproper analysis
of results
obtained.
ANY WRITTEN INQUIRIES TO THE FACTORY REGARDING YOUR
METER MUST INCLUDE COMPLETE SERIAL NUMBER OF YOUR
INSTRUMENT. IF YOU NEGLECT TO INCLUDE THE SERIAL NUM-
BER' IT WILL BE NECESSARY FOR THE FACTORY TO REQUEST
THE NT]MBER IN ORDER TO ANALYZE YOUR PROBLEM.
Your meter is a reiatively critical and delicate instrument. Do not attempt any
major repairs before consulting the Service Departmcnt of Dynascan Corrroration.
13

WARRANTY
SERVICE
INSTRUCTIONS
1. Refer to the MAINTENANCE
section
of your B&K-Precision
instruction
manualforadjustments that
maybe
applicable.
2. If the above-mentioned
procedures
do not correctthe problemyou are
experiencing
with your unit,pack
it securely
(preferably
in the
original
carton
or double-packed).Enclose
a letterdescribingtheproblem
andinclude
your
name
and
address.
Deliver
to, orship PREPAID(UPS
preferred)
to the nearest
B& K-Precision
authorizedservice
agency
(see
listenclosed
withunit).
lf your list of authorizedB& K-Precision
service
agencies
has
beenmisplaced,
contact
your localdistributorfor thename
of your
nearestservice
agency,orwrite
to:
ServiceDepartment
B& K-PrecisionProduct
Group
DYNASCAN
CORPORATION
6460West
CortlandStreet
Chicago,Illinois 60635
I4

LIMITED
ONE.YEAR
WARRANTY
DYNASCAN coRPoRATIoN warrants to the original purchaser that its B & K-
PRECISION product, and the component parts thereof, wlti be free from defects in
workmanship and materialsfor a period ofone year from the dateofpurchase.
DYNASCAN will, without charge, repair or replace, at its option, defective product or
mmponent parts upon delivery to an authorizcd B & K-PRECISION service
contractor or the
factory servicc
department, accompanied
by proof of thc date of purchase
in the fbrm of a sales
receipt.
To obtain warranty coverage,
this product must be registered
by completing and mailing the
enclosed warranty registration card to DYNASCAN, B & K-PRECISIoN, plo. nox 35bgo,
Chicago,Illinois 60635 within five (5 days)from the date of purchase.
Exclusions: This warranfy does not apply in the event of misuse or abuseof the product or
as a result of unauthorized alterations or repairs. It is void if the serial number is altered,
defaced or removed.
DYNASCAN shall not be liable for any consequential
damages,
including w.ithout limitation
damagesresulting from loss of use. Some states do not all,ow timitation of incidentzrl or
cnnsequential
damages,
sothe above
limitation or exclusion may not apply to you.
This warranty givesyou specific rights and you may alsohave
other rights which vary from
statcto state.
Iior your convenience we suggest
you contact your B & K-pR.EclsloN distributor, who
may be authorized to make repairs or can refer you to the nearest servicecontractor. If
warranty service
cannot be obtained locally, please
send
the unit to B & K-PRECISION Service
Department, 2815 west lrving Park Road, chicago, Illinois 60618, properly packaged
to avoid
damage
in shipment.
r_ --

trlYNASCAN
CORPORATION
5460
WestCortland
Street
Chicago,
Illinois 60635
I
I
rl
I
l
480.086-9-001H
@
1979ODYNASCAN CORP.
PRINTEDIN U.S.A.

SCHE'\AATIC
SYMBOT
c-1
c-2
c-3
c-4
c-5
c-6
MODEL L77IV95 PARTSLIST
B& K otvtstol
DYNASCAN CORPORATION
4a8-O66-9-OO2E
CAPACITORS
DESCRIPTION
900olrm
r/2wittt
17.6deposited
carbon
resistor
......
gli olrrn
l,!
watt 192,tleposited
carbon
resistor
......
9()I{ ohm l': u'att 192,depositedcarbon resistor ' ' .' . .
10Mfd. @ 175volt electrolytic . .. .021-003-9-007
.02
Mfd. 400volt 207o
tubular .. .. .026-'{01-?-203
.02IUfd. 1600volt 207o tubular .. ..026'162'7'2A3
.02Mfd. discceramic .....020-501-7-203
1500Pfd. dual ceramic
disc
GMV . '035-501-0-152
1600
Mfd. @ 10volt electrolytic .. '022-001-9'013
RESISTORS
- CO]TTROT,S
50K ohm 20Tolinear
taper pot. (twist prong) '....008-060 9-00:l
10K ohm 2O%
linear taperpot. (twist prong) .....008-060-9-002
100K ohm 20To
linear taper pot. . . .008-001-9-030
10K olrm
2\Tolinear
taper
pot. ... '008-001-9-0:9
900K ohm I watt I7o depositedcarbon resistor . .. .002-001-3-904
ll04K ohm \/2watt l/a deposited
carbon
resistor ...004-076-9-001
140K ohm 12 vratt 1/o depositedcarbon resistor . . .002-102-3-14
I
12.7
ohm lwattLTo resistor .......004-074-9-001
1]0
olrm r/2watt 1.o/odeposited
carbon
resistor ......002-102-3-900
DYNASCAN
PART No.
......002-102-391:11
.. .. .002-702-3'9(t2
.....002-102-3-f,03
R-2,R-4
Ii-3
It.-5
t{,-t)
tt-7
R_B
R-9
ti- 19
It-20
R-21
r) 40
It 2il
17-24
It-25
R-26
P.-27
R-28
R-29
R-30
R-31
R-32
R-33
R-34
90{)Kohm r,/2watt
19lodepositcd
carbon
resistor ...002-102-3-904
9 nrcgohm 12 watt 1% dcposited carbon resistor .. .002-102-3'905
10K ohm /z watt 17odeposited
carbonresistor ... .002-102-3-103
20K ohm 1/zwaIt1% deposited
carb<;nresistor ....002-102-3-203
?0K ohm 12watt 1% deposited
carbon
resistor ... '002-102-3-703
200K ohm 1/2
watt 1/6 depositedcarbon resistor .. '002-102-3-204
700K ohm Yzwatt 17odepositedcarbon resistor .. '002-102-3-704
2 megohm 12 watt 1% deposited carbon resistor ' ' .002-L02-3-2Os
7 megohm L/2
watt 1% depositedcarbon resistor .. .002-102-3-705
1megohm Yzwatt 17odepositedcarbon resistor ' . .002-102-3-105
36 ohm 2 watt 1Voresistor, metal fiIm . . . . .004-075-9-001
cofrrPoslTE
499-02r-9-00rc
3-74