Allied Radio Knight-Kit 83 Y 140 User manual

@® REGISTERED TRADEMARK OF ALLIED RADIO CORP.—100 NORTH WESTERN AVENUE, CHICAGO 80, ILLINOIS TELEPHONE HAYMARKET 1-6800
copyrighted 1956, by Allied Radio Corp / printed in U.S.A.
20,000 OHMS/VOLT VOM
83 Y 140
ASSEMBLY MANUAL

HOW
TO
BUILD
THE
KNIGHT
VOM
The improved circuit design of the
KNIGHT
VOM
assures
a
sensitive
and
accurate
test
instrument
for
the
radio-
TV
serviceman,
the
laboratory
technician,
or
the
amateur.
You
may
measure
any
AC
or
DC
voltage
found
in
radio
and
electronics
work
up
to
5000
volts.
The
input resistance for DC scales is 20,000
ohms
per
volt.
This
enables
you
to
read
voltages
in
high
impedance
circuits
with-
out
interfering
with
the
circuit.
For
AC
voltage
measurements
it
is
5000
ohms
per
volt.
Direct
currents
may
be
meas-
ured up to 10 amperes.
There are three resistance ranges.
Center scale readings are at 12, 1200,
and 120,000 ohms. All multipliers are
1% precision resistors, which assure ac-
curate measurements for the life of the
instrument.
Check all of the parts against the Parts
List
as
you
unpack
the
VOM
kit.
If
you
are unable to identify some of the parts
by
sight,
locate
them
on
the
pictorial
dia-
grams.
Hardware is listed in the last part of
the
Parts
List.
To
keep
our
kits
at
the
lowest
possible
price,
we
frequently
weigh
hardware, rather than to count it one by
one.
Therefore,
do
not
be
concerned
if
more
nuts
and
machine
screws
for
ex~
ample,
are
supplied
than
are
specified
in
the Parts List.
The only tools you will need are: long-
nose pliers, diagonal cutters, a screw-
driver,
a
small
set-screw
driver,
and
a
soldering iron.
Building your KNIGHT 20,000 ohms per
volt
VOM
will
be
easier
if
you
study
all
of
the
diagrams
and
instructions
before
assembly is started.
The pictorial diagrams show the actual
location of all parts and wiring. The
KNIGHT
VOM
will
work
best
when
all
parts
are
placed
as
shown
in
the
dia-
grams.
The
schematic
diagram
shows
how the parts are connected electrically,
and is useful in understanding how the
instrument works.
These step-by-step instructions were
prepared while actually building the
KNIGHT VOM. They are the best and
fastest way of assembling this unit. May '
we suggest that you check off each step
after you have completed it. Some build-
ers also put a pencil mark on the wiring
views along the leads and parts that they
have just installed.
Both of these methods are good and will
assure speedy and correct wiring.
WIRING AND SOLDERING
The quality of workmanship in test
equipment will often determine whether
an instrument will be an accurate and re-
liable service tool. While these wiring
and soldering hints will be more helpful
to a beginner in electronics, the more ex-
perienced builder may also benefit by re-
viewing them.
Make good mechanical connections at
joints,
clean
metal
to
clean
metal.
Loop
the wires around the switch, other con-
nection terminals, and clamp tight.
Cut the excess lengths of all end leads
of the resistors when they are soldered.
When
a
solder
connection
is
made
close
to one of the precision resistors, hold the
jaws of a pair of long-nose pliers on the
lead between the tip of the soldering iron
and the resistor to conduct the heat away
from the resistor. Arrange the long wire
leads to lay close to the panel.
USE ONLY ROSIN CORE SOLDER. Use
the
rosin
core
solder
supplied
with
the
kit
as KITS WIRED WITH ACID CORE SOL-
DER OR ACID FLUX WILL CORRODE
and WILL NOT WORK FOR LONG. SUCH
KITS ARE NOT ELIGIBLE FOR REPAIR
OR SERVICE.
The soldering iron tip must be well
tinned. First, clean the tip with steel
wool or a fine file until the bright copper

shown
in
Figure
6
and
on
the
label.
The
large
‘‘C’’
battery,
B-1,
fits
into
the
space
shown
by
the
dotted
lines
on
the
label.
The
positive
end
of
this
battery
must
be
toward
the
left.
(
)
Install
the
small
penlite
batteries,
B-2,
B-3,
B-4,
and
B-5,as
shown.
The
positive
end
of
B-2
and
B-4
must
be
toward
the
right.
The
positive
end
of
B-3
and
B-5
must
be
toward
the
left.
(_ ) Place the battery retaining strap over
the two screws which come through
the battery board. Use two of the
small nuts to fasten the retaining
strap.
See Figure 7.
ie
Secon
the
Function
switch,
S-1l,
on
e
panel.
The
locking
pin
of
S-1
fits
into
the
small
hole
at
the
base
of
the
meter.
Use
the
other
large
nut
to
fasten
S-1.
Connect
the
other
end
of
the
2
inch
red
lead
from
terminal
50toterminal
2
of
R-24.
Solder
this
connection.
Connect
the
other
end
of
the
4
inch
yellow
lead
from
terminal
10
of
S-1
to
the
terminal
of
Jack
D.
Solder
this
connection.
Aw
Connect
the
other
end
of
the
7
inch
violet
lead
from
terminal
41
of
S-1
to
terminal
4
of
the
battery
clip
board.
Solder
this
connection.
Connect
the
other
end
of
the
3
inch
range
lead
from
terminal
28
of
S-1
to
the
terminal
of
Jack
E.
Solder
this
connection.
Connect
the
other
end
of
the
2
inch
red
lead
from
terminal
32
of
S-1
to
the
terminal
of
Jack
C.
Solder
this
connection.
Connect
the
other
end
of
the
9
inch
white
lead
from
terminal
34
of
S-l
to
terminal
1
of
the
battery
clip
board.
Solder
this
connection.
Connect
the
other
end
of
the
6
inch
blue
lead
from
terminal
38
of
S-1
to
terminal
10
of
the
battery
clip
board.
"
Solder
this
connection.
12
DS
Connect
the
other
end
of
the
5
inch
green
lead
from
terminal
42
of
S-l
to
the
positive
(marked
with
the
plus
sign
on
the
label),
terminal
of
the
meter.
Solder
this
connection.
Dy
check
all
of
the
work.
Every
connec-
tion
should
be
strong
mechanically
and
all
should
now
be
well
soldered.
You
have
finished
wiring
your
KNIGHT
20,000
Ohms
per
Volt
VOM
kit.
Check
the
wiring
very
carefully.
A
few
extra
minutes
spent
in
checking
can
save
hours
of
trouble
shooting.
(
)
Push
the
large
knob
on
the
shaft
of
S-l.
Tighten
the
set
screw
of
the
knob
against
the
flat
on
the
shaft.
(_)
Push
the
small
knob
on
the
shaft
of
R-24.
Tighten
the
set-screw.
HOW
TO
TEST
YOUR
KNIGHT
VOM
Your
KNIGHT
VOM
is
precalibrated
by
the
use
of
R-3,
the
meter
calibrating
re-
sistor
which
has
been
matched
to
the
meter
movement
supplied
in
your
kit,
and
R-8
and
R-9,
the
two
rectifier
calibrating
resistors
which
have
been
matched
to
the
rectifier
supplied
with
your
kit.
Remove
the
1.5
volt
‘‘C’’
battery,
B-1.
It
will
be
used
to
eheck
the
voltage
ranges
of
your
VOM.
Set
the
range
switch
at
2.5
volts
DC.
Insert
the
black
test
lead
into
the
jack
marked
‘‘Com’’.
Insert
the
red
test
lead
into
the
jack
marked ‘‘V-ohm-A’’. e
Zero
the
meter
if
the
indicator
needle
does
not
rest
directly
over
the
zero
on

ES
the
scale.
Use
a
small
screwdriver
to
turn
the
adjustment
screw,
which
is
im-
mediately
above
the
OFF
position
of
the
switch,
until
the
needle
is
in
the
correct
position.
Touch
the
probe
tip
of
the
red
test
lead
to
the
positive
end
of
the
1.5
volt
‘‘c”’
battery,
B-1.
Touch
the
probe
tip
of
the
black
test
lead
to
the
negative
end
of
B-1.
The
meter
should
read
1.5
volts.
Turn
the
range
switch
to
the
10
volt
DC
scale.
On
this
scale
the
meter
should
read
1.5
volts
also,
but
the
deflection
of
the
needle
will
be
smaller.
Turn
the
range
switch
to
the
50
volt
DC
scale.
The
meter
will
read
1.5
volts
on
this
scale,
too,
however,
the
needle
deflection
will
be
very
small.
There
will
not
be
much
deflection
if
you
check
the
250,
1000,
5000
volt
scales
with
the
‘*C’’
battery.
(
)
Install
the
‘‘C’’
battery,
B-1,
on
the
battery
clip
board
again.
(
)
Push
the
handle
mounting
studs
through
the
hole
in
each
end
of
the
handle.
Insert
the
stud
through
the
hole
in
the
meter
case
on
one
side.
Use
a
shakeproof
washer
and
one
of
the
larger
hex
nuts
to
fasten
the
handle.
Insert
the
other
stud
through
the-nole
in
the
other
side
of
the
case.
Use
the
other
shakeproof
washer
and
hex
nut
to
fasten
it.
(-)
Mount
the
meter
panel
on
the
case.
Tuck
in
all
of
the
leads.
(
)
Insert
one
of
the
3/4
inch
small
ma-
chine
screws
in
each
corner
of
the
panel.
Tighten
these
screws
into
the
tapped
holes
in
the
corners
of
the
case.
Set the
range
switch
to
the
250
volt
AC
scale.
Insert
the
probe
tips
into
the
recep-
tacles
of
a
wall
outlet.
Hold
the
insulated
Part
of
the
probe
and
donot
touch
the
tips.
The
meter
should
read
between
110
and
120
volts
depending
upon
the
line
voltage
in
your
area.
You
may
find
that
the
line
voltage
will
vary
at
different
times
of
the
day.
Set
the
range
switch
to
1000
volts
AC.
The
reading
on
the
meter
will
be
between
110
and
120
on
this
scale.
HOW
TO
CHECK
THE
OHMMETER
Insert
the
black
test
lead
into
the
jack
marked
‘‘Com’’,
common,
Insert
the
red
test
lead
into
the
jack
marked
‘‘V-ohms-A’’.
Set
the
range
switch
at
XI
and
touch
the
probe
tips
together.
The
needle
should
swing
all
the
way
over
to
zero.
Adjust
the
OHMS
ADJUST
knob
to
bring
the
needle
directly
above
the
zero
on
the
scale.
.
Set,the
range
switch
at
X100
and
touch
the
‘probe
tips
together.
Again
the
needle
‘should
swing
all
the
way
over
to
zero.
Adjust
the
OHMS
ADJUST
knob
again
so
that
the
needle
zeros
correctly.
Set
the
range
switch
at
X10K
and
touch
the
probe
tips
together.
The
needle
should
Swing
all
the
way
over
to
zero.
Adjust
the
OHMS
ADJUST
knob
until
the
needle
zeros
correctly.
13

SERVICE HINTS
If you have followed all the previous
instructions carefully your KNIGHT
20,000 ohms per volt VOM should operate
properly. If it does not perform properly
under the tests outlined, here are some
helpful hints.
If the DC voltage ranges do not operate
properly, or are inoperative, check all
connections to and the placement of R-19,
45K
ohm;
R-20,
150K
ohm;
R-21,
800K
ohm; R-22, 4M; and R-23, 15M;resistors.
If the AC voltage ranges operate im-
properly, or are inoperative, check all
connections to CR-1, the rectifier, and
all connections to and the placement of
R-4,
3.75M;
R-5,
1M;
R-6,
200K;
R-7, 37.5K; and R-8 and R-9 the recti-
fier calibrating resistors.
If
the
ohmmeter
ranges
do
not
operate
correctly,
or
are
inoperative,
check
all
of
the
connections
to
and
the
placement
of
R-17,
100K
ohm;
R-18,
80
ohm;
and
R-19,
45K
ohm
resistors.
If the milliammeter ranges do not op-
erate properly, or are inoperative, check
the connections to and the placement of
R-11, 25.1 ohm wirewound resistor;
R-12, 2.5 ohm wirewound resistor; R-13,
.225 ohm wirewound resistor; and R-15,
11.0 ohm wirewound resistor.
Should it be necessary to replace R-3,
the meter calibrating resistor, please
include with your order the four numbers
written on the tape on the back of the
meter movement. This determines the
value of R-3.
In the unusual case where it would be
necessary to replace CR-1, the meter
rectifier, or R-8 or R-9, the rectifier
calibrating resistors, please order an-
other rectifier and we will include the
proper value of calibrating resistors with
i.
If
the
meter
still
does
not
function
properly,
have
someone
else
check
your
wiring,
preferably
someone
with
radio
experience.
USING
YOUR
VOM
SPECIFICATIONS
0-2.5,
10,
50,
250,
1000
and
5000
volts
sensitivity
20,000
ohms
per
volt.
D-C Voltmeter:
A-C
Voltmeter:
0-2.5,
10,
50,
250,
1000
and
5000
volts
sensitivity
5000
ohms
per
volt.
To 20 megohms in 3 scales with
center
scale
values
of
12,
1200
and 120,000 ohms, respectively.
Ohmmeter:
D-C
Milliammeter:
0-0.1,
10
and
100
milliamperes.
D-C
Ammeter:
0-1,
and
10
amperes,
Accuracy:
Within
+
2%
of
full
scale
on
all
ranges.
Meter:
4-1/2
inches,
50
pa
full
scale.
Batteries:
1
flashlight,
type
C
(1”’
dia.
x
I-
15/16).
4
flashlight,
‘“‘penlite’’
type
(37/64
dia.
x
2”’).
Size:
6-3/4’
high,
5-1/4”’
wide,
3-3/4?
deep, including knob.
14
FUNCTIONS
Type of
Ranges |Measurement
0- 2.5 DIRECT
CURRENT
MA")
Type of
Measurement
DC VOLTS
(‘DC Vv”)
0- 10 0- 10 ma
XI
12 ohms
mid scale
X100 1200 ohms
mid scale
XIOK 120K ohms
RESIST -
DB Range
AC
VOLTS
-30to+
3ddb
(“AC V"’)
0-250 |+10to +43 db
0- 1000 }+22 to +55db
0- 5000 |+30 to +63 db

With your KNIGHT VOM you can perform a very
great variety of measurements. The different measure-
ments are selected (a) by different panel jacks into
which the test leads are inserted and (b) by the posi-
tion of the Function Switch. A number of scales on
the meter allow proper readings for any range of any
function provided. The Function Switch has 18 posi-
tions and 2 decks. This makes it possible to connect
the different components of the instrument so that d-c
and a-c voltages, direct and alternating currents, and
resistances can be measured. The meter has a highly
sensitive 50-ua moving coil permanent magnet move-
ment. A calibrating resistor (R3) assures the highest
degree of accuracy of the dial indications. The meter
serves as the indicator for all measurements. It has
separate scales for a-c voltage, d-c voltage, decibels,
xesistance and current.
Preliminary Adjustments
Before any measurements are made, be sure the
instrument is placed squarely on a bench where the
measurement is to be performed. Always check that
the meter pointer is lined up with the zeros on the
left hand side. If the pointer does not fall in line
with these marks, turn the bakelite screw directly
above the word “‘OFF”’ either left or right until pointer
is positioned correctly.
Another reminder before using the meter for a par-
ticular type of measurement is to make certain that
the operator understands fully how to handle this in-
strument, as well as its capabilities. With this in
mind, the following paragraphs are written, to give an
outline on how to use the KNIGHT VOM to your best
advantage.
How to Measure D-C Voltoges
Coution: Wherever possible, disconnect power
from the equipment under test before connecting
the meter. In cases where it is impossible to do
this, connect the leads separately and use only
one_hand at any one time. Grasp the test prod
well back from the metal tip and make momentary
contact with the circuit under test by letting the
metal tip of the prod touch the point at which the
potential exists. Never touch any part of the
equipment under test with the other hand.
Plug the black test lead into the ““COM’’ jack and
the red test lead into the ““V. , .A”’ jack. First touch
the probe end of the black (negative) test lead to the
negative side of the circuit to be checked. Then,
leaving one hand free, touch the red (positive) test
probe to the positive terminal of the circuit to be
tested.
It is a good practice always to start with the
highest range available, as a protection for your
meter. Then, after first indication, the switch should
be reset to the position in which more accurate read-
ings can be obtained. If possible, make final readings
on a range on which the indication is in the right hand
half of the scale, because meter accuracy is based on
full scale value.
Turn
the
power
on
and
observe
the
meter
deflec-
tion.
(If
the
pointer
deflects
to
the
left
instead
of
to
the
right,
turn
the
power
off
and
switch
the
connections
of
the
red
and
black
test
leads
around.)
The value of the measured voltage can now be
read from the appropriate meter scale, taking into
account the range setting of the Function Switch.
Read on tne meter scale whose extreme right-hand
Rn
marker is labeled with the full-scale value indicated
by the Function Switch or some multiple or submultiple
of it. For d-c voltage readings, use only the black
scales marked “*DC’’.
For the 0-2.5 v d-c range use the 250 v d-c scale.
Divide meter scale reading by 10. Each minor scale
division equals 0.05 v d-c.
For the 0-10 v d-c range use the 10 v d-c scale.
Read scale directly. Each minor scale division equals
-2v d-c.
For the 0-50 v d-c range use the 50 v d-c scale.
Read scale directly. Each minor scale division equals
Iv de.
For the 0-250 v d-c range use the 250 v d-c scale.
Read scale directly. Each minor division equals 5
v d-c.
For the 0-1000 v d-c range use 10 v d-c scale.
Multiply scale reading by 100. Each minor scale
division equals 20 v d-c.
For the 0-5000 v d-c range use 50 v d-c scale.
Multiply reading by 100. Each minor scale division
equals 100 v d-c.
If d-c voltages in excess of 1000 v but less than
5000 v are to be measured, the red test lead has to
be plugged into the ‘5000 V DC’ jack. If working
with high potentials of this order, make doubly sure
that the Caution paragraph at the beginning of this
section is strictly observed.
How to Measure A-C Voltages
NOTE: Follow same precautions as under
“Caution”? in above section ‘‘How to Measure
D-C Voltages. ’’
Plug the black test lead into the “‘COM’’ jack and
the red test lead into the “‘V, .A’’ jack. Clip the
probe of the black test lead to one terminal of the
potential to be measured and the probe end of the red
test lead should be touched to the other terminal of
the potential.
Always start with the highest “‘AC V’’ range
available, as a protection for your meter. Then after
obtaining the first indication, reset the Function
Switch to the position in which a convenient meter
reading, preferably in the upper half of the scale, is
obtained.
Tum the power on and observe the meter deflec-
tion. The value of the measured voltage can now be
read from the appropriate meter scale taking into
account the range setting as indicated by the Function
Switch.
For the 0-2.5 v ac range use 2.5 v a-c scale.
Read scale directly. Each minor scale division equals
0.05 v ac.
All other a-c voltage scales are chosen and read
in the same way as the d-c scales discussed in the
previous section, except that the red “‘AC’’ scales
are used.
If a-c voltages in excess of 1000 v, but not higher
than 5000 v a-c are to be measured, the red test lead
has to be plugged into the ‘5000 V AC” jack. If
working with high potentials of this order, be doubly
sure that the Caution at beginning of previous section
is strictly observed.
19

A-C voltage measurements can be made at any
frequency from 25 cps through the audio range. At
higher frequencies, shunting capacitance in the rec-
tifier causes readings to become increasingly low.
How to Measure D-C Resistances
Caution: Before making any resistance meas-
ee . 2 .
urements in a circuit, make certain that the power
is turned off. It is also advisable to discharge
any capacitors in the part of the circuits in which
resistance measurements are to be made.
Turn the Function Switch to one of the “‘ 1 ”
positions. Plug the black test lead into the ‘‘COM’’
jack and the red lead into the ““V. ©..A’’ jack. Con-
nect the prod ends of these two test leads together.
Turn the ‘‘ 1. ADJ’’ knob until meter reads full scale
deflection, at which the pointer lines up with zero on
the ohms scale.
Turn Function Switch to such ‘* (L”’ position that
the meter will read somewhere in, or as near as pos-
sible to, the center portion of the scale when the
measurement is made. Recheck if the meter deflects
full scale when the two test lead probes are connected
together.
Connect the test prods respectively to the termi-
nals of the resistance to be measured and observe the
meter reading. After any change of ranges, the
“<0. ADJ’? should be rechecked. The value of the
measured resistance can be determined by multiplying
the ohms scale meter reading by the factor indicated
by the Function Switch knob,
The following paragraph shows the d-c resistance
range covered, and the center-scale reading for each
Function Switch setting.
If the Function Switch is in “‘fl X1” position,
the 0-1 K ohm range is covered; center scale reading
is 12 ohms. Read scale directly. If the Function
Switch is in the “‘{L X100” position, the 100 ohms -
100 K ohms range is covered. Center scale reading is
1200 ohms. Multiply scale yeading by 100. I£ the
Function Switch is in the “0 X10 K’’ position, the
10 K - 10 Meg range is covered. Center scale reading
is 120 K ohms. Multiply scale reading by 10,000.
It always should be kept in mind that in the
measurement of resistance a current is made to flow
through the unknown resistance. Usually this current
is so smal] that it can be neglected. However on the
lowest ohms range (X1) the halfscale reading is 12
ohms. That means a current of 65 milliamperes is
flowing through the unknown reaistor. If lower re-
sistances than 12 ohms are measured, the current
through them may be as high as 130 ma. Therefore it
is good practice to consider the current flow first
when measuring the d-c resistance of a device which
can safely pass only low currents without burning out.
For all other cases no damage will result as long as
the ohmmeter current does not exceed the current
rating of the unknown resistance.
How to Measure Direct Current
Never connect the test leads across any source of
voltage directly when the VOM is used as a current
meter, otherwise the meter will be damaged. Instead,
always connect the meter in series with the load.
Plug the black test lead into the “‘COM”’ jack and the
red lead into the “V. 1. .A’’ jack.
Tum the Function Switch to any “MA” or “A’’
position appropriate. It is good practice to start with
highest range and then reset switch to obtain a con-
venient reading.
16
li currents in the order of 1 to 10 amperes are to
be measured, the red lead has to be plugged into the
“10 A”? jack. Open the circuit in which the current
is to be measured. Connect the black test lead probe
to the negative side of the circuit break, and the red
test lead probe to the positive side.
Connect the circuit under test to its power source.
The resulting meter deflection is in a direct proportion
to the unknown current. To find the magnitude of the
current, the meter reading has to be multiplied by the
factor indicated by the Function Switch. The listing
below gives the different ranges covered, the scale on
which the meter reading is done, and the multiplication
factor of each current range.
For 0-0.1 ma range use the ‘‘DC 10” scale.
Divide meter scale reading by 100. Each minor scale
division equals 0.002 ma.
For 0-10 ma range use the ““DC 10” scale. Read
meter scale directly. Each minor scale division
equals 0.2 ma.
For the 0-100 ma range use the ‘DC 10” scale.
Multiply meter scale reading by 10. Each minor scale
division equals 2 ma.
For the 0-1 a range use the “‘DC 10’ scale.
Divide meter scale reading by 10. Each minor scale
division equals 0.02 a.
For the 0-10 a range use “‘DC 10”? scale. Read
scale directly. Each minor scale division equals
0.2 a.
If the meter pointer is deflected to the left of the
scale, the test probes are connected in wrong polarity.
Turn off the power, reverse the meter lead connec-
tions, and turn on the power again.
How to Use the VOM as an Output Meter
Sometimes it is necessary to measure an a-c
voltage which is superimposed on a d-c voltage.
Correct measurement of the a-c component in such a
case is possible by use of the OUTPUT circuit of the
VOM, in which a d-c blocking capacitor is employed
to keep direct current from the meter, which then
indicates only the a-c voltage.
To measure voltages of this nature, plug the black
test lead into the ‘‘COM’’ jack and the red test lead
into the “OUTPUT” jack. Then proceed as indicated
under ‘‘How to Measure A-C Voltages’’. Since the
5000 v a-c range would require a change in the red
lead connection, the blocking capacitor, necessary
for output measurement would not be connected in the
meter circuit, therefore this a-c range can not be used
for output measurements, unless d-c is kept out by an
external capacitor or isolating transformer.
When a-c voltages are measured with the output
meter, the impedance of the d-c blocking capacitor
will have an effect on the accuracy of the meter
reading. The error which occurs varies with the
frequency of the applied voltage, and becomes negli-
gible on the 50 v scale and higher. The actual voltage
will then be higher than the measured value. The
higher the frequency the smaller this error will become.
How to Measure Output Voltages in DB (Decibels)
A-C output voltages are often measured in units
called decibels, which are used to indicate power
levels in amplifiers or general telephone work. The
DB scale (bottom meter scale) is based on the voltage
developed across a 500-ohm line when 0.006 watts
are dissipated. This voltage is a reference taken as
0 db. Such a voltage deflects the pointer to 1.73 v

ac on the 2.5 v a-c range. Therefore, a direct meter
reading
in
terms
of
decibels
can
be
made
only
when
the meter is connected across a 500-ohm resistive
load.
Otherwise
only
relative
db
measurements
can
be obtained. However, in a large number of cases
relative measurements are appropriate, since reference
conditions
are
defined
by
other
factors
and
only
rela-
tive
variations
are
important.
Frequency
response
to
3-db “fall-off? points is an example.
The
following
is
the
procedure
to
obtain
a
db
meter
indication.
Plug
the
red
test
lead
into
the
“OUTPUT”
jack,
to
block
any
d-c
voltage
present
in
circuits
tested.
The
impedance
of
the
capacitor
can
be
disregarded
for
most
applications.
However,
when
no
d-c
voltage
is
present,
the
“V..0..A’’
jack
might
be
used
just
as
well.
Tbe
black
test
lead
is
plugged
into
the
“COM”?
jack.
Rotate
the
range
switch
to
a
high
‘‘AC
V’
range
and
work
down
to
one
which
is
correct
for
the
voltage
to
be
measured.
Connect
the
test
prods
to
the
point
of
the
circuit
where
the
measurement
is
to
be
made.
The
meter
pointer
will
indicate
some
reading
in
db.
If
tbe
measurement
is
made
across
a
500-ohm
impedance,
a
reading
in
absolute
db
(with
respect
to
6
mw)
is
obtained.
The
final
db
indication
is
determined
by
the
value
indicated
on
the
db
meter
scale
plus
the
addition
of
a
constant,
depending
on
the
range
setting.
The
table
at
the
lower
right
corner
of
the
meter
face
will
give
these
constants.
How to Measure Alternating Current
ge RE Ee
The ac voltage ranges may also be used to
measure alternating current at power line frequencies
by simply inserting a known resistor (of low resistance
and sufficient wattage to carry unknown alternating
current) and measuring the voltage across it. The
formula:
I (Amperes) = Sega
is used to find the alternating current flowing in this
circuit.
How
to
Measure
Operating
Voltages_in
Electronic
Equipment
Operating
voltages
are
usually
measured
between
a
given
terminal
and
a
reference
point.
Usually
ground
(chassis)
is
this
reference
point.
Reference
voltage
data
appear
in
service
literature
in
several
different
forms.
However,
in
all
cases
the
conditions
for
these
measurements
should
be
observed,
otherwise
measurements
are
not
valid.
When
the
meter
is
connected
in
d-c
circuits,
polarity
should
always
be
observed.
The
black
lead,
connected
to
“‘COM’?
should
always
be
at
the
low
voltage
points.
Incorrect
meter
connection
will
not
produce
a usable
meter
reading.
Since
d-c
operating
voltage
checks
will
help
to
track
down
circuit
breakdowns,
a
few
examples
of
tube
electrode
voltages,
which
actually
indicate
if
the
circuit
is
functioning
correctly,
will
be
shown.
Cathode voltages are most often bias voltages,
and indicate whether a tube is operating over tbe
proper portion of its characteristic.
Screen grid voltage measurements can give in-
dications of the functioning of the associated circuits.
Very low voltages at these points may indicate a
leaky bypass capacitor. Abnormally high voltages
might mean a faulty dropping resistor.
Plate voltage measurements can show an open
plate load resistor or transformer by the complete
absence of potential. Low plate voltage indicates
higher conduction than a high plate potential. If tbe
value of the plate load resistor has a higher resistance
than the meter impedance, the meter reading will not
read the actual existing voltage, but a value which
is somewhat lower. The suggestions given under
“How to Measure D-C Voltages’’ should be followed
in such cases,
In grid circuits, the grid leak resistors have
usually a rather high resistance. The d-c voltages
are also of low magnitude making it rather difficult
to use a fairly high d-c voltage range to maintain a
high meter resistance.
Consequently the resulting readings are not a
very reliable indication. In clipper, power amplifier,
and oscillator circuits, grid voltage can be measured
with a 20,000 ohms per volt meter, with a minimum
error occurring since the grid leak resistance values
are not very high and will not be affected by the
meter resistance.
In
oscillators
with
grid
leak
bias,
the
grid
voltage
is
proportional
to
the
amplitude
of
the
oscillations.
Therefore
variations
of
this
voltage
when
tuning
the
oscillator
indicate
unequal
output
at
different
fre-
quencies,
D-C voltages in ave or age circuits give important
clues
of
the
operation
of
the
receiver
either
when
the
signal
is
or
is
not
received.
During
alignment
a
specified
voltage
has
to
be
applied
to
such
systems,
which can be checked by a VOM connected to that
line. Also overloading, witb resulting stage blocking,
can
be
checked
by
voltage
measurement
of
the
avec
and age systems.
The d-c voltmeter can also be used as an align-
ment indicator. For this purpose, connect the meter
across
the
plate
load
resistor
of
the
detector
and
set
Function Switch until a deflection of the meter pointer
results.
Tben
proceed
with
the
regular
alignment
using the meter as a peak or dip indicator.
The
operation
of
a-c
circuits
in
electronic
equip-
ment
can
also
be
checked
by
tracing
the
voltages
applied
to
the
different
circuits.
The
frequency
range
of
the
VOM
permits
only
the
check
of
voltages
up
to
the
low
audio
frequencies.
For
example,
transformers
in
power
supplies
may
be
checked
by
connecting
the
meter
across
the
dif
ferent
windings
and
comparing
the
measured
voltages
to
those
given
as
references,
17

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SYMBOL
NO DESCRIPTION PART NO.
C-1 Capacitor, paper, .1 MFD
600V 247014
Note: When ordering resistors give com-
plete description and part number,
R-1 Resistor, 60 megohm, + 1%
precision a 366005
R-2 Resistor, 20 megohm, + 1%
precision ¥ 362005
R-3 Resistor, meter calibrating
(packed with the meter)
R-4 Resistor, 3.75 megohm, + 1%
precision 343754
R-5 Resistor, 1 megohm, + 1%
precision - 341004
R-6 Resistor, 200K ohm, + 1%
precision 342003
R-7 Resistor, 37.5K ohm, + 1%
precision ina 343752
R-8 Resistor, rectifier calibrating
(smaller value)
R-9 Resistor, rectifier calibrating
(larger value)
R-10 Resistor, SK ohm, + 1%
precision 345001
R-11 Shunt, wirewound on blue form,
25.1 ohm, + 1% 412517
R-12 Shunt, wirewound on yellow form,
2.5 ohm, + 1% 410257
R-13 Shunt, wirewound on red form,
.225 ohm, + 1% 412259
R-14 Resistor, 1150 ohm, + 1%
precision 7 341151
R-15 Shunt, wirewound on green form,
11.0 ohm, + 1% 410110
R-16 Resistor, 18K ohm, + 1%
precision a 341802
R-17 Resistor, 100K ohm, + 1%
precision a 341003
R-18 Resistor, 80 ohm, + 1%
precision — 340800
R-19 Resistor, 45K ohm, + 1%
precision = 344502
R-20 Resistor, 150K ohm, + 1%
precision — 341503
R-21 Resistor, 800K ohm, + 1%
precision _ 348003
R-22 Resistor, 4 megohm, + 1%
precision mg 344004
R-23 Resistor, 15 megohm,
+ 1% precision 351505
R-24 Potentiometer, OHMS
ADJUST, 30K ohm 390116
R-25 Shunt, 10 ampere, 4.3’ #14
Advance Wire, .025 ohm 334001
CR-1 Rectifier, copper oxide 621002
M-1 Meter, 50microampere move-
ment mountedinfront panel 040002
SYMBOL
NO. DESCRIPTION PART NO.
S-1 Switch, FUNCTION, 2-deck
18-position rotary 432302
B-1 Battery, 1.5 V ‘‘C’”’ 450011
B-2,
3,4,5 Battery, 1.5 V penlite 450013
Quantity Description Part No.
1 ea. Board, battery clip 534005
lea, Case 701004
2 ea. End leads for R-25 470022
1 ea, Handle 920005
6 ea. Inserts, jack 532006
1 ea, Knob, large 761301
1 ea. Knob, small 761001
1 ea. Label, paper, showing polarity
of batteries and meter 750040
1 ea, Manual 750041
4 ea. Nuts, 4-36 hex 570230
2 ea. Nuts, 10-32 hex 570540
3 ea. Nuts, 3/8’’ hex 570840
6 ea. Screws, 4-36 x 3/4’’ BH 560237
2 ea. Screws, 4-36 x 3/8’’ BH 560234
24’ Solder, rosin core 930001
2 ea. Spacer, 1/8”’ 940002
6” Spaghetti, small 812001
4" Spaghetti, large 812003
1 ea. Strap, battery retaining 470050
2 ea. Stud, handle 470025
1 set Test leads (red & black) 040001
2 ea. Washer, lock, #10 582500
1 ea, Washer, lock, 3/8"’ 582700
1 ea, Wire, #20 bare, 9’’ length 806000
5 ea. Wire, red, 2’’ length 801002
3 ea. Wire, orange, 3’’ length 801003
1 ea. Wire, yellow, 4’’ length 801004
2 ea, Wire, green, 5’’ length 801005
lea. Wire, blue, 6’’ length 801006
1 ea. Wire, violet, 7’’ length 801007
1 ea. Wire, white, 9’’ length 801009
TOOLS YOU MAY NEED
Stock No. Description Price*
46N852 Soldering pencil $4.73
46N449 Long-nose pliers 1.76
46N431 Diagonal cutting pliers 1.55
45N796_ 6°’ screwdriver 72
43N831 Set-screwdriver .27
*All Prices subject to change
without notice.
19