Simpson 260 series 5M User manual

PANEL METERS
by
MODELS 27, 37, 47, 57
3~" RECTANGULAR
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A
CCU RAC Y: 2$
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MODELS 127, 137, 147,
MODELS 29,39,49,59
157.
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A
CCUR A CY : 2$
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PANEL METE R ••••• OR A DOZEN ••••• LOOK FOR THE FAMI LIAR OR AN GE
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CO •• 5200 W. KIN ZI E ST• • CH I CA GO Itlt. I LL •• ESTEBROOK 9-1121.
-~
OPERATOR'S
MANUAL
VOI.,..oHM-MlLLIAMME'I'ER
MODEL 260
SIMPSON ELECTRIC COMPANY
5200 W. KINZIE ST., CHICAGO 44, ILLINOIS. EStabrook 9.1121
IN CANADA, BACH·SIMPSON, LTD., LON DOH, ONTARIO
Copyright 1955. Simpson El ec tric Co .•
Print ed in U.S.A.

T ABLE OF CONTENTS
SECTION III FUNCTIONING OF PARTS
Schematic Diagram .................. .
D.C. Volcmeter Circuit - 20,000 Ohms Per Volt.
Resistance of Multiplier Resistors ...•....
A.C. Voltmeter Circuit -1000 Ohms Per Volt.
A.C. Rectified by Copper Oxide Rectifier.
A.F. Output Meter ...
Reading A.C. Voltage
Effective Resistance.
2.5 Volt Range ....... .
Volume
Level Meter.
Conversion of Scale.
Output Meter .... .
D.C. Ohmmeter ... .
D.c. Milliammeter and Ammeter.
SECTION IV MAINTENANCE
Do Not Drop Your 260 .......... .
Make
Proper Settings Before Use .. .
Battery Replacement .................. .
Pointer Won't Zero on Rx1 and RxlOO Ranges.
Pointer Won't Zero on Rx10,000 Range.
How to
Replace Batceries.
Parts List .................. .
SECTION V
MODEL 260 SPECIFIC APPLICATIONS
General. .......... .
Measuring Grid
Currents.
F .M. Alignment ..... .
A.V.C. Diode
Circuits.
High Mu Plate Voltage.
20
20
20
21
21
22
22
23
23
23
24
24
24
25
27
27
27
28
28
28
32
34
34
34
34
35
T ABLE OF CONTENTS
Bias of Power Detector ...... .
Model 260
as a Condenser Tester.
Initial Deflection Not Present ...
Positive Jack to Positive Condenser Terminal
Should
Read About. 5 Megohm ..... .
Paper Condensers ............. .
Condensers From .001 Mfd. to 1.0 Mfd.
Descriptive Tables ............ .
SECTION VI SUPPLEMENTARY DATA
RMA Resistor Color Code Chart .....
RMA Mica Capacitor Color Code Chart.
RMA Condenser Marking Code ...
Volts-Decibels Conversion Table.
Capacitive Reactances.
Audio Frequencies.
Radio Frequencies ..
35
35
35
36
36
36
37
38
39
40
41
42
44
44
44
')
4

Fig.
1
Fig.
2
Fig.
3
Fig.
4
Fig.
5
Fig.
6
Fig.
7
Fig.
Sa
Fig.
8b
Fig.
9
Fig. lOa
Fig. lOb
Fig. 11
Fig. 12
Fig. 13
6
LIST OF ILLUSTRATIONS
Simpson Volt-Ohm-Milliammeter Model 260
Simplified D.C. Volcmeter Circuit.
Simplified A.C. Voltmeter Circuit ......
Simplified Output Meter Circuit ........
Ohmmeter Circuit with Selector Switch in
Position Rx 1 .................
Ohmmeter Circuit with Selector Switch in
Position Rx 100 ................
Ohmmeter Circuit with Selector Switch in
Position RxlO,OOO ....... . ...
Simplified Microammeter Circuit ....
Simplified Milliammeter and Ammeter
Circuit. ................. .
Model 260
Schematic Diagram ......
Model 260 Parts Layout - Rear View ..
Model 260 Parts Layout - Rear View of
Front Panel ...............
Model 260 Used as Condenser Tester ....
RMA Resistor Color Code Chart .......
RMA Mica Capacitor Color Code Chart ...
PAGE
2
21
22
23
24
25
25
26
26
29
30
31
37
39
40
f¥oJWW-oJUI
WORLD FAMOUS
As the purchaser of a Simpson 260, you are now the owner
of
the most famous testing instrument in the world. Com-
pact, of unusually high sensitivity (50 microamperes full
scale), the Model 260 has earned its top ranking reputation
as the result of quality construction joined to exceptional
engineering versatility. This engineering superiority is, in
turn, the product of invaluable years of experience with
every single unit comprising the complete assembly.
. In choosing the Simpson 260, you have concurred in
the verdict of over 300 governme nt agencies and
university laboratories which, long before World War
II, and all through it, purchased it. in quantities un-
equalled by any competitive instrument. Ie served
on every batdefront and in every branch of our
armed service s.
MANY FEATURES IN "260"
In no other instrument of its kind do you find features such
as are contained in the Simpson Model 260. Ics trim, scien-
tific appearance -- the 4];i" modernistic instrument, the
heavy bakelite case, the neat bakelite . panel -- gives evi-
dence of inner quality. These hidden features are too nu-
merous to mention here, but your pride in your new instru-
ment will grow as you learn of them. Parts are assembled
and placed in position so they cannot become loose or
detached from their original positions. All the sub-assem-
blies are mounted on specially designed bakelite pane ls,
or on a specially designed sub-panel, made and engineered
expressly for a specific function in the Model 260.
7

SIMPSON BUILDS ITS OWN TEST EQUIPMENT
When you purchase Simpson test equipmenr, you get equip-
menr made almost enrirely within the various planrs of our
Company. Each component pan of the 260 has been de-
signed and completely rooled and manufactured in our own
planrs, with the exception of the resistors and one or two
other functionally less important parts. The Model 260,
like all other Simpson testers, is not an assembly job made
up from
purchased pans such as is true of the majority of
testers offered on the market.
We are by far more self-conrained than any other manufac-
turer of test equipmenr. This is your assurance that the
testers we offer will not quickly become obsolete. Our
tremendous investmenr in expensive production rools is
your safeguard against obsolescence and further assurance
of unvarying quality.
Here at Simpson we do not think of making instrumenrs
merely to sell. We think of making instrumenrs ro serve.
Our inrerest in your Model 260 and in your satisfaction
with it never ceases. That is the reason for this Operator's
Manual. We want you to know how to get the most from
your 260.
The Model 260 is a rugged instrumenr and will withstand a
great deal of abuse. We urge you, however, to treat it with
care as its mechanism is actually more delicate than that
of a watch. If you will keep it clean, free from conrinuous
severe vibration and avoid dropping it, your Model 260 will
give you a lifetime of accurate, dependable service.
OPERATOR'S MANUAL
SIMPSON MODEL 260 YOLT·OHM·MILLIAMMETER
SECTION I
GENERAL DESCRIPTION
The Simpson Volr-Ohm-Milliammeter Model 260 offers the
service dealer a small, compact and complete instrument
with high sensitivity for testing and locating trouble in all
types of circuits. The large four and one-half inch meter
provides a long scale that is easy to read, and the compact
arrangemenr of the conrrols allows the overall size of the
bakelite housing ro be comparatively small for maximum
portability.
Each unit is supplied with an operator's manual and one
set of red and black test leads with insulated clips.
The electrical circuit is designed to give maximum insur-
ance against inaccuracy and damage to the componenr
pans. Highly accurate carbofilm resistors are used ro in-
sure long life and dependability, and these are firmly held
in place in a special bakelite housing designed for this
purpose. The entire assembly is truly rugged and can well
withstand the wear and tear of the service work for which
it is designed.
ACCURACY
Accuracy is 3% D.C. and 5% A.C. of full scale deflection.
8 9

GENERAL DESCRIPTION
MEASUREMENT RANGES
D. C. VOLT AGE
0-2.5 voles
0-10
voles
0-50
voles
0-250 voles 20,000
ohms per vole sensieiviey
o-1000 voles
0-5000 voles
A. C. VOLTAGE
0-2.5 voles
0-10 voles
0-50
voles
1,000 ohms per vole sensieiviey
0-250
voles
0- 1000 voles
0-5000 voles
A. F. OUTPUT VOLTAGE
0-2.5 voles
0-10
voles
0-50
voles
0.1 Mfd. internal series condenser
0-250 volts
0-1000 voles
VOLUME LEVEL IN DECIBELS
-12 co + 3 decibels
o co + 15 decibels
Calibrated for reference level
+14 to +29 decibels
of 500 ohms and .006 Wacts
+28 co +43 decibels
+40 to +55 decibels
10
GENERAL DESCRIPTION
D. C. RESISTANCE
0-2000 ohms (12
ohms cencer)
0-200,000 ohms (1200 ohms
cencer)
0-20 megohms (120,000 ohms
cencer)
CURRENT IN D. C CI RCUITS
100 microamperes
10 milliamperes
100 milliamperes 250 millivoles
500 mi lliamperes
10 amperes
D. C. VOLT AGE MEAS UREME NTS
D. C. vole age is measured by applying ehe unknown volcage
co ehe meeer ehrough suieable ineernal series resiseors.
The meeer has a full scale sensieiviey of 50 microamperes
ae 100 millivolcs wieh an incernal resiseance of 2,000 ohms,
giving ehe inserumenc an overall sensieiviey of 20,000 ohms
per vole.
A. C. VOLTAGE MEASUREMENTS
A. C. voleage measuremencs, including oueput and decibel
readings, are made possible by ehe use of an incernal cop-
per oxide receifier conneceed in series wieh ehe meeer. A
precision wound incernal shunt resiseor is conneceed in
parallel wieh ehe meeer in order co obeain a sensieiviey of
1,000 ohms per vole.
D. C. RESISTANCE MEASUREMENTS
D. C. resiseance measuremencs are made by employing an
ineernal bactery and precision series and shune resistors,
resulcing in accuraee indicaeion of resiseance values.
11

GENERAL DESCRIPTION
CURRENT MEASUREMENTS IN D. C. CIRCUITS
Current is measured through the use of preClslOn internal
shunts resulting in accurate indication throughout the
varIOUS rang es.
SECTION II
OPERATION
CAUTION
When making measurements, turn off the power to the
circuit under test, clip the test leads to the desired
points and then turn on the power to take the reading.
T urn off the power before you disconnec t the meter.
ZERO ADJUSTMENT
Before takin g readings, be sure that the pointer is on zero.
If pointer is off zero, adjust by mli!ans of the slotted screw
located in the bakelite case directly below the meter scale
as shown in Figure 1. Use a small screw-driver to turn
this adjustment slowly to the right or left until the pointer
is directly over the zero point on the scale.
STEP-BY-STEP OPERATING INSTRUCTIONS
D. C. VOLTAGE MEASUREMENTS 0-1000 VOLTS
1. Place the "OUTPUT-A.C.-D.C." switch in the "D.C."
pOSitlon.
2.
Rotate the range selector switch to anyone of the vol-
tage positions required. When in doubt of the voltage pre-
sent , always use the highest range as a protection to the
OPERATION
meter. After obtaining the first reading, the switch can be
reset to a lower range, if needed, to obtain a more accurate
reading.
3. Plug the black test lead into the jack marked "COMMON
-" and the red te st lead into the j ac k marked " + ". Clip
the other end of the black lead to the neg ative side of the
circuit to be checked and the other end of the red lead to
the positive side.
4. Turn on the power to the circuit to be tested. If the
pointer deflects to the left of zero, the connections are
incorrect. Turn off the power and reverse the positions of
the test clips.
5. Read the voltage on the black arc marked "D.C." which
is second from the top.
For the 2.5 volt ran g e, use the 0-250 figures and divide
by 100.
For the 10, 50, and 250 volt ranges, read the figures di-
reedy.
For the 1000 volt range , use the 0-10 figures and multiply
by 100.
D. C. VOLTAGE MEASUREMENTS 1 000-5000 VOLTS
CAUTION
Use extreme care when you check high voltage.
Always turn off power before making connections
and do not touch meter or test leads while taking
the reading.
1. Place the "OUTPUT-A.C.-D.C." swiech in the "D.C."
position.
12
13

OPERATION
2. Set the range selector swicch in the 1000 volt posHlOn.
3. Plug the black test lead into the jack marked "COMMON
-" and che red cest lead into the jack marked "D.C. 5000
V."
4. Be sure power is curned off co che circuic co be cesced
and che condensers are discharged; then clip che black
cesc lead co che negacive side and che red cesc lead to che
positive side.
S. Turn on che power.
6. Read che voltage using che 0-50 figures on the black
arc marked "D.C." which is second from the top. Then
multiply che reading by 100. Turn off power before discon-
neccing meter.
A. C. VOLTAGE MEASUREME NTS 0-1 000 VOLTS
1. Place the "OUTPUT-A.C.-D.C." switch in the "A.C."
posHlon.
2. Rocate the range selector switch to any of the five ran-
ges required. When in doubt of the voltage present, always
use the highest range as a proteccion to the meter. After
obtaining che first reading, the switch can be set to a lower
range for a more accurate reading.
3. Plug che black cesc lead into che jack marked "COMMON
. .
-" and che red cest lead inco che jack marked .. +". Clip
che ocher ends of che cesc leads co the cwo sides of the
circuic to be tested. A.C. volcage will read correctly re-
gardless of which way the test leads are connecced.
4. Turn on che power to the circuit co be cested.
14
-
OPERATION
S. For the 2.5 volt range, read che voltage on che red arc
marked "2.5 V.A.C. ONLY" which is second from the
bottom.
For che other ranges use the red arc marked "A.C." which
is third from the borrom.
For che 10, SO and 250 volt ranges, read the figures di-
reccly.
For che 1000 vole range read the 0-10 figures and multiply
by 100.
A. C. VOLTAGE MEASUREMENTS 1000·5000 VOLTS
CAUTION
High voltage is dangerous. Always turn ott power
before you connect or disconnect test leads. Do not
handle mecer or test leads while power is on.
1. Set the "OUTPUT-A.C.-D.C." switch in the "A.C."
posHlon.
2. Rotate the range selector switch to the 1000 V. pOSHlOn.
3. Plug the black test lead into the jack marked "COMMON
-" and che red Cest lead into the jack marked "A.C. 5000
V "
4. Be sure power is turned off in circuic to be tested, and
then clip the cesC leads co che cwo sides of the circuit.
A. C. voltage will read correctly regardless of which way
the leads are connecced.
S. Turn on the power.
15

OPERATION
OPERATION
6. Read the "oHa6e on the red arc marked "A. c." which
is third from the botCom. Use the 0-50 figures and multiply
by 100. Turn off power before disconnecting meter.
A. F. OUTPUT MEASUREMENTS
1. Place the "OUTPUT-A. C.-D. C. " switch in the "OUT-
PUT" position. When the switch is in this position, an
internal condenser is connected in series for the purpose
of blocking out the D.C. component whenever connections
are made directly to the plate of a tube.
2. Rotate the range selector switch to any of the five ranges
required. When in doubt of the voltage present, always use
the highest range as a protection to the meter. After obtain-
ing the first reading, the switch can be set to a lower range
for a more accurate reading.
3. Plug the black test lead into the jack marked "COMMON
-" and the red test lead into the jack marked It +". Clip
the other ends of the test leads to the output of the circuit
under test.
4. Turn on the power.
5.
For the 2.5 volt range use the red arc marked "2.5
V.A.C. only" which is second from the bottom.
OTHER RANGES ...
For the 10, 50, and 250 volt ranges, read the figures direct-
ly. For the 1000 volt range, use the 0-10 figures and multi-
ply by 100.
For the other ranges, use the red arc marked "A.C." which
is third from the bottom.
REACTANCE OF SERIES CONDENSER
The reactance of the series condenser used when reading
output volts causes a slight error which varies with fre-
quency. This is explained in Section III.
VOLUME LEVEL MEASUREMENTS
1. Set the "OUTPUT-A. C.-D.c." switch in the "A. c."
position.
2. Rotate the range selector switch to any of the five
ranges required.
3. PI ug the test leads into the two jac ks marked "+" and
"COMMON
-" and connect the clips to the two sides of
the circuit to be checked.
4. Turn on the power and read decibels on the black arc
marked "D.B." which is at the bottom of the scale. In
order to obtain decibel readings it is necessary to add
algebraically the scale reading and the number shown at
the setting of the range selector switch. For example, if
the scale indication is -4 D. B. with the switch in the + 12
D. B. position, the true reading will be +8 D. B. because
(-4) + (+ 12) = +8. (For .001 watt -600 ohm reference level
add +7 D.B.)
D. C. RESISTANCE MEASUREMENTS
CAUTION
Before making any resistance measurements in a
radio circuit, be sure the current is turned off so that
no voltage exists. Otherwise the meter may be dam-
aged.
16
17

OPERATION
1. Place the "OUTPUT-A.C.-D.C." switch in the "D.C."
posJtJOn.
2.
Rotate the range selector switch to any of the three
ranges required.
R X 1 for 0-2000 ohms.
R X 100 for 0 - 200,000 ohms.
R X 10,000 for 0- 20 megohms.
3. Plug the test leads into the two jacks marked "+" and
"COMMON -". Short the ends of (he leads and set the
pointer to zero by rotating the "ZERO OHMS" knob.
4. Separate the ends of the test leads and clip them across
the portion of the circuit to be measured.
5. Read ohms on the black arc at (he top of the scale.
For range R X 1, read the figures directly.
For range R X 100, multiply the reading indicated by 100,
or add two zeros.
For range R X 10,000, multiply the reading indicated by
10,000, or add four zeros.
Example: A 2 megohm resistor should be checked on the
R X 10,000 range. The reading on the scale will be 200.
Adding four zeros will give 2~000,000 ohms, or 2 megohms.
CAUTION
Do not leave the range selector switch in a reSlS-
tance measurement position when the meter is not in
use because the test leads may become shorted and
run down the internal battery. It is also possible
OPERATION
that the instrument may be connected across a volt-
age accidentally and thus cause damage to the meter.
CURRENT MEASUREMENTS IN D. C. CIRCUITS
1. Place the "OUTPUT-A.C.-D.C." switch in the "D.C."
posJtlon.
2. Rotate the range selector switch to any of the ranges
required. When in doubt of the current present, always use
the highest range as a protection to the meter. After obtain-
ing the first reading, the switch can be reset to a lower
range if needed.
3. Plug the black test lead into the jack marked "COMMON
-" and the red test lead into the jack marked "+". For
the 10 ampere range use the jacks marked "-10 A." and
"+ 10 A."
4. Break the circuit to be tested and insert the meter in
series by connecting the red test lead to the positive side
and the black test lead to the other side.
5. Turn on the power.
6. Read milliamperes on the black arc which is second from
the top. If the pointer is forced against the stop at the lefe
of
the scale, the connections are incorrect. Turn off the
power and reverse the positions of the test clips.
For 100 microamperes, read the figures 0-10 and multiply
by 10.
For 10 milliamperes, read the figures directly.
For 100 milliamperes, read the figures 0-10 and multiply
by 10.
18
19

OPERATION
For 500 milliamperes, read the figures 0-50 and multiply
by 10.
For 10 amperes, read the figures 0-10 directly.
CAUTION
For current measurements, the meter must always be
connected in series with the circuit. Never connect
the meter across a voltage source when the range
selector switch is set for current measurement be-
cause this may damage the meter. Always observe
polarity.
SECTION III
FUNCTIONI NG OF PARTS
SCHEMATIC DIAGRAM ...
The complete schematic diagram of the Simpson Volt-Ohm-
Milliammeter Model 260 is shown in Figure 9. The simpli-
fied sections are descr ibed in the followi ng paragra phs.
D. C. VOLTMETER CIRCUIT - 20,000 OHMS PER VOLT
FIGURE 2
Figure 2 shows the circuit used when the "OUTPUT -A.C.-
D.C." switch is in the "D.C." position and the range se-
lector switch is in anyone of the five voltage positions.
RESISTANCE OF MULTIPLIER RESISTORS
The total resistance of the bank of multiplier resistors and
the meter is 100 megohms, or 100,000,000 ohms , from the
"5000 V." jack to the "COMMON -" jack. Ohms law will
20
FUNCTIONING
OF PARTS
show that when a 5000 volt potential is applied between
these cwo jacks, a current of 50 microamperes will flow
through the circuit, causing a full scale deflection of the
meter.
Dividing the number of ohms, 100,000,000, by the
number of volts, 5000, g ives 20,000 ohms-per-volt which
is the instrument sensitivity.
15MO
."0
lSOKft
48KQ
V
eOMn
50"" .
20000
'0'01
METER
2 . 5\1
IOOOV .
r
NEG·
5000 v o.c
PaS
FIGURE 2 . SIMPLIFIED D.C. VOLTMETER CIRCUIT
A.C. VOLTMETER CIRCUIT - 1000 OHMS PER VOLT
FIGURE 3
Figure 3 shows the circuit used when the "OUTPUT-A.C.-
D.C." switch is in the "A.C." position and the range
selector switch is in anyone of the five voltage positions.
A.C. RECTIFIED BY COPPER OXIDE RECTIFIER
In this circuit the A.C. is rectified by a copper oxide rectI-
fier in order to supply the microammeter with direct current.
The other half of the cycle passes around the meter and
through the rectifier in the opposite direction as shown by
the arrows in Figure 3. The shunt resistor R-24 and the
series resistor R-23 are precision wound and calibrated
21

FUNCTIONING OF PAR IS FUNCTIONING OF PARTS
with the rectifier with which they are used. The resulting
sensitivity is 1000 ohms per volt.
750Kn
R2.3
'OV
RECTIFIER
~
2S0V.
2·5V.
IOOOV.
4Mn.
'I It
+
5000 V,A , C,
POS .
NEG .
FIGURE 3. SIMPLIFIED A.C. VOLTMETER CIRCUIT
A. F. OUTPUT METER
FIGURE 4
Figure 4 shows the circuit used when the "OUTPUT-A.C.-
D. c." switch is in the "OUTPUT" position and the range
selector switch is in anyone of the five voltage positions.
This is the same as the A.C. voltmeter except that the
5000 V. range is omitted, and a 0.1 mfd. condenser is
placed in series with the "+" jack to block the D.C. com-
ponent when connection is made direct to the plate of a
tube.
READING A. C. VOLTAGE
When reading A.C. voltage with the output meter, the imped-
ance of the blocking condenser, which is in series with
the vohage multipliers, must be taken into consideration.
22
This impedance will cause considerable error at 60 cycles,
but the percent of error will decrease with an increase in
frequency.
EFFECTIVE RESISTANCE
J
The actual effective resistance is equal to VXc'+R' where
Xc
is the capacitive reactance of the 0.1 mfd. condenser
~
and R is the multiplier resistance.
. .. 2. 5 VOLT RANGE
F or the 2.5 volt range R = 2500 ohms and Xc at 60 cycle s =
26,500 ohms. Therefore y26,500
2
+2500
2
"" 26,618 ohms,
10V.
250V .
,ooov. _~ 2.5V.
X©'MF
OUTPUT
FIGURE 4. SIMPLIFIED OUTPUT METER CIRCUIT
VOLUME LEVEL METER
f
The decibel is a unit of measurement used in P.A. and
,
telephone work. Two reference levels are commonly used;
they are .001 watt in 600 ohms for telephone service and
.006 waH in 500 ohms for P. A. service. The former estab-
lishes the zero reference level at 0.7746 volt, and the lat-
ter at 1.732 volts. The Model 260 DB scale is based on
the .006 wart-500 ohm level with zero DB at 1.732 volts.
which is the actual effective resistance in the circuit.
750Kn 20QKn .40Kn
75000
Ra3
RECTIFIER ~~:R
~
lit
NEG ·
23

FUNCTIONING OF PARTS
CONVERSION OF SCALE
This scale may be convened to the .001 watt - 600 ohm
level by adding +7 DB to the scale indication.
OUTPUT METER
The output meter is more commonly used in radio serVIce
work for comparative readings but if desired, A.e. voles can
be converted into decibels by means of a conversion chart.
Refer co Section VI - Supplementary Data.
D. C. OHMMETER
Figures 5, 6 and 7 show
range selector switch is
R x 10,000 respectively.
the
in
ohmmeter circu
positions R xl,
its
R when x 100,
the
and
t----;.~
11.51) 11360.
2'8500
RXI
pos.
NEG.
FIGURE 5, OHMMETER CIRCUIT WITH SELECTOR
!:iwITCH IN POSITION RXI
The selector switch throws · in the proper series and shunt
resiSlors and batteries for each range so that when the
test leads are shorted, the meter will read ' full scale.
24
FUNCTIONING OF PARTS
.-----11 49 .5 n------"
11.~a.
113810
216500
~'"
R X 100
pos.
NEG
FIGURE 6, OHMMETER CIRCUIT WITH SELECTOR
SWITCH IN POSITION R X 100
,-- - -22,999.5 .. ------ -- ---,
11 . 50
1138<> 2 1
,850<>
l'SV 117,700<>
"'ii:i
-
ce . OV .
@ R"'IO.OOO
P OS .
NE G·
FIGURE 7, OHMMETER CIRCUIT WITH SELECTOR
SWITCH IN POSITION RXIO,OOO
D. C. MILLIAMMETER AND AMMETER
FIGURE 80 '
Figure Sa shows the circuit used when the "OUTPUT-
A.e.-D.e." switch is in the "D.e." position and the range
switch is in the 100 microampere position. This circuit is
equi valent to two equal resistors in paralleL The 3000 ohm
25

FUNCTIONING OF PARTS
;U.5n.
<Z.n.
.475"
.025n
pos. NEG.
FIGURE SA. SIMPLIFIED MICROAMMETER CIRCUIT
resistor and 2000 ohm meter form one 5000 ohm leg, and the
five resistors between to +" and "COMMON -" form the
other. As a resulc, when a current of 100 microamperes is
flowing through the circuit, 50 microamperes flow through
the shunt resistors and 50 microamperes flow through the
meter, causing full scale deflection.
30006
22.SA .025n.
SOOMA
a
POS . +10"
FIGURE 8B. SIMPLIFIED MILLIAMMETER AND
AMMETER CIRCUIT
FUNCTIONING OF PARTS
FIGURE 8b
Figure 8b shows the circuit used when the "OUTPUT-
A.e.-D.e." switch is in the "D.e." position and the range
switch is in the 10 M. A., 100 M. A. or 500 M. A. position. Ie
can be seen that the resistance of the shunt resistors be-
comes lower as the higher current positions are used,
thereby permicting a larger amount of current to flow through
them. The amount of current flowing through the meter re-
mains at 50 microamperes for full scale deflection. The
volcage drop appearing across the various ranges is 250
milli volt s.
SECTION IV
MAINTENANCE
DO NOT DROP YOUR 260
The Simpson Volc-Ohm-Milliammeter Model 260 is a very
rugged instrument designed to take the wear and tear of
every day serVIce work. Nevercneless, care should be taken
that the instrument is not dropped or subjected to exces-
sively rough treatment.
MAKE PROPER SETTI NGS BEFORE USE
Al ways be sure of the character of the circuit to be tested,
and see that the selectors are properly set before making
connections. When in doubt of the amount of voltage or
current present, always use the highest range first.
BATTERY REPLACEMENT
Five bacteries are mounted inside of the case to provide
26
27

MAINTENANCE
currenr for rhe resisrance measuring ranges.
These are:
One
Burgess No.2 Uni-cel. ........ . .... 1.5 V.
or
Eveready No. 950 ............ . .... 1.5 V.
or Ray-o-vac No.2 ..... . 1.5 V.
or
equivalent
Four Burgess No. ZUni-eel
1.5 v.
or Eveready No. 915 .
1.5 V.
or
Ray-o-vac No. 7R ....
1.5 V.
or equivalent
POINTER WON'T ZERO ON RXl AND RX100 RANGES.
When ir is no longer possible co bring rhe pointer co zero on
rhe
Rxl and RxlOO ranges wirh rhe resr leads shorted and
roraring rhe
"ZERO OHMS" knob, rhe single large 1.5 V.
barrery should be replaced.
POINTER WON'T ZERO ON RXl 0,000 RANGE
When ir is no longer possible ro bring rhe pointer co zero on
rhe
RxlO,OOO range wirh rhe resr leads shorted and roraring
rhe
"ZERO OHMS" knob, rhe four small 1. 5 V. barreries
should be replaced.
HOW TO REPLACE BATTERIES
To replace rhe barreries, remove rhe insrrument from rhe
case. This is done by removing rhe four screws from rhe
borrom of rhe
case. Slide our rhe bakelire barrery rerainers
and slip rhe barceries from between rhe spring clips holding
rhem in
place. Inserr rhe new batteries, being careful rpar
rhe
polariry corresponds co rhe markings on the bakelire
case.
MAINTENANCE
D
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:t 0 :t
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28

,.. --------_ ... ---- ...... -- ... ----., ... --- --- - -------- - -- -------.
• • I I
: _ ""'2. + i;: .... + ;, I:l
I g I,' - gw II
: ri r
.. _~~:~-:.-----i;.;,~:===:::::::~~B~~~:_-_-_-~=~=:_-_-_-_1-, -:~~I-----:----:-- " "
+ ',-,' ~10 0
RI
'- ,-,-
Rlt0 RI70 0
Rlo
0
R6
81
RI90 0
RI2
B4
0
R3
R70
o 0
Ritl R8 0=::0
~ @n R23 @ RI04 B.t3
~
C!) 0 ~ o=::lJ 0 0 C!) L~_ ..
R2.4
R RII0
"0
FIGURE lOA. MODEL 260 PARTS LAYOUT
REAR VIEW
30
MAINTENANCE
o
10+
85
MAINTENANCE
METER
@ @
@ @
R21
o
FIGURE 108 MODEL 260 PARTS LAYOUT
REAR VIEW OF FRONT PANEL
31

MAINTENANCE MAINTENANCE
PARTS LIST
Copper oxide receifier
RecL
0-008585
Series resiseor Cali braced R23
Part No.
Descripeion
Reference
Symbol 1-111722 Shune
resiseor
cogeeher
10000 ohm poeenciomeeer R24
R25
1-113372
1-113373
1-113369
1-113367
1-113371
1-113370
1-113309
1-113363
1-113364
1-113368
1138 ohm
resiscor
110 ohm resiscor
21850 ohm resiscor
117700 ohm resiseor
4975 ohm
resiscor
7500 ohm resiscor
40000 ohm resiscor
800000 ohm resiscor
375000 ohm resiscor (2 Required)
48000 ohm resiscor
R1
R2
R3
R4
R5
R6
R7
R8
R9
RIO
1-113733
1-113266
1-111891
1-111728
1-111802
1-111798
3-262871
1-113641
1-113642
0-008375
0.1 MFD. 400 V. condenser
Range seleceor swiech
Ouepuc-AC-DC swiech
Jack, pin eype
Dry
cell 1. 5 vole (4 Required)
Dry
cell 1.5 vole
Range seleccor knob
Zero ohms knob
Ouepuc-AC-DC knob
Tese lead sec
C1
Sl
S2
J 1-6
Bl-4
B5
1-113287 3000 ohm
resiscor (2 Required)
R11
Part No. Part No.
1-113366 150000 ohm
resiscor
R12
Black Brown
1-113365 200000 ohm
resiscor
R13 15-302260 Meeer wieh
panel 15-302109
1-113362 4 megohm
resiscor
R14 3-320068
Bakeliee Case
3-320078
1-113361 7.5 megohm
resiscor (2 Required)
R15 1-113283
Carrying Handle
1-113830
0-008070 11.5 ohm
resiscor (bobbin) R16 0-005572 Meeer
Cover wieh Glass
0.005586
0-008285
0-008133
0-008060
0-113353
.475 ohm resiscor (bobbin)
22.5 ohm
resiscor (bobbin)
2 ohm
resiseor (bobbin)
80 megohm
resiscor
R17
R18
R19
R20
*3-260180
*3-262871
Range Seleccor Knob
Zero Ohms and Ouepue AC-DC
Knob
*3-260185
*3-260186
1-113352 2 megohm
resiscor (2 Re,quired) R21
*For all Models bearing Serial No. 60,000 or above.
0-008033 .025 ohm shunc
assembly 10 amp. 250 Noee -
When ordering parts, specify serial number appearing on
MV-DC
R22 ehe bo[[om of ehe fronc
panel of ehe Model 260.
32 33

SECTION V
MODEL 260 SPECIFIC APPLICATIONS
GENERAL
The high SenSHlVlty of the Volt-Ohm-Milliammeter Model
260 not
only makes it suitable for all of the applications of
a low
sensitivity meter but also makes it adaptable to many
special uses. The following applications are only a few of
the many for which you will find the Model 260 a superior
Instrument.
MEASURING GRID CURRENTS
The Model 260, with its 100 microampere scale is so sensi-
tive that it is possible to measure the grid currents of many
tubes. A readable val ue as low as 1 microampere can be
obtained.
F.M. ALIGNMENT
By opening the load re sistor circuit of the limi ter in a F. M.
recei ver and inserting the Model 260 as a microammeter in
series, a reading may be obtained for I.F. alignment pur-
poses. Adjust the circuit for maximum indication. Manufac-
turers' alignment instructions should be .:onsulted for
exact procedure.
A.V.C. DIODE CIRCUITS
An ordinary low sensitivity meter cannot be used across an
A. V.c. network because of the low resistance which alters
the constants of the circuits. The Model 260, however,
requires so little current that sufficient indication can be
obtained to determine if the A. v.c. circuit is functioning.
SPECIFIC APPLlCA nONS
HIGH Mu PLATE VOLTAGE
High Mu tubes require a high resistance plate resistor. For
this reason a low resistance meter will not give a satis-
factory reading. Due to the high resistance and low current
consumption of the Model 260, it will give a much more
accurate indication.
BIAS OF POWER DETECTOR
A power detector uses a high resistance cathode resistor. A
high
sensitivity meter such as the Model 260 is essential
co obtain a reading of the bias voltage on such a tube.
MODEL 260 AS A CONDENSER TESTER
USE RXl 0, 000 RANGE
Condensers can be roughly tested for shorts and leakage
with the Model 260, using the RxlO,OOO range. A shorted
condenser will cause a large deflection of the pointer of
the ohmmeter and a condenser with high leakage will show
a partial deflection of the pointer.
INITIAL DEFLECTION NOT PRESENT
Any condenser, other than electrolytic types, will normally
cause a slight deflection of the pointer until the condenser
becomes charged, when the pointer will return to zero. If
the initial deflection is not present, it probably indicates
an open lead. The resistance of a good paper condenser
should be above 50 megohms per microfarad, and that of
mica condensers above 100 megohms per microfarad. This
resistance varies inversely according co the size of the
34
35

SPECIFIC APPLICATIONS
condenser, and is so high that it wi 11 not register on the
ohmmeter.
POSITIVE JACK TO POSITIVE CONDENSER TERMINAL
When testing electrolytic condensers with the ohmmeter,
the positive jack should be connected to the positive termi-
nal of the condenser. Otherwi se the reading will be too
high because of the high leakage in the reverse polarity.
After connecting the test leads to the condenser, allow
sufficient time for the pointer to reach its maximum resist-
ance reading.
.SHOULD READ ABOUT .5 MEGOHM
In general, a high grade, high voltage electrolytic conden-
ser should read about .5 megohm or above, and a low volt-
age electrolytic by-pass condenser should read above .1
megohm. A more accurate test is to apply the rated polariz-
ing D.C. voltage to the condenser with a milliammeter in
series. It should read about 0.1 mao per mfd., the maximum
for a
useful unit being about 0.5 mao per mfd. New electro-
lytics that have been idle for considerable time may show
high leakage but after "ageing" at their rated voltages for
a few
minutes will return to normal.
PAPER CONDENSERS
A rough test of the comparative ca paci ty of paper con-
densers can be made wi th the Model 260 by connecting it
as shown in Figure 11. The larger the unknown condenser
being tested, the smaller its reactance and therefore the
higher the reading will be on the A. C. voltmeter.
SPECIFIC APPLICATIONS
CONDENSERS FROM .001 MFD. TO 1.0 MFD.
The chart shows the approximate readings that will be
obtained when testing condensers from .001 mfd. to 1.0 mfd.
CAUTION
Before connecting an unknown condenser for test,
place the range selector switch of the Model 260 in
the 250 V. position. Connect the condenser and if it
is shorted, the meter will read line voltage. This
would damage the meter if it were in the 10 V. posi-
tion. Do not try to tes t electrolytic condensers in
this manner because only D.C. can be applied to
them.
"V A C POSITION
r'r MOO,u.o
CONNECT
Q.Q
,UNKNOWN
tf "-- CONDENSER
o ,
115 v. A.C
c
60'"
;;;
N
PQS.2.
01-1 MF"
IOV RANGE
POS.3.
PQS I 0
.1-1.0 MF.
001-.01 MF
IOV RANGE
IQv RANGE
FIGURE 11. MODEL 260 USED AS CONDENSER TESTER
(SEE PAGE 38 FOR DESCRIPTIVE TABLES)
36
37

SPECIFIC APPLICA nONS
SPECIFIC APPLICA nONS
.1
............. . .... 10 V.A.C .................. 1
UNKNOWN
APPROXIMATE .2
.................. " " .................. 2
CONDENSER METER READING .3
.................. " " ................... 3
MFD. RANGE A.C. VOLTS
.4
................. ... " " .................... 4
.5
.................. " " .................. 5
Pos.3
.001. ................. 10 V.A.C....... . ........... .6
.6
" " .................. 6
Figure 11
.002 .................. " " 1.1 .7 " "
.................. 7
.003 .................. " " 1.5
.B
" "
.................. B
.004
.................. " " 1.9
.9
" "
.................. 9
.005
.................. " "
.................. 2.5
Pos. 1 1.0 " "
................. 10
.006 .................. " "
.................. 3.0
Figure 11
.007 .................. " "
.................. 3.6
.OOB .................. " "
.... .. ............ 4.0
.009 ... . .............. " "
.................. 4.4
SECTION VI
.01 .................. " "
.................. 4.B
SUPPLEMENTARY DATA
RMA RESISTOR COLOR CODE CHART
.01 .... . ............. 10 V.A.C ................... 1
.02 .................. " " .................. 2
.03
.................. " " .................. 3
.04 .................. " " .................. 4
.05
..................
" "
.................. 5
Pos.2
.06 ..................
" " .
................. 6
Figure 11
.07 ..................
" "
.. ................ 7
.OB ..................
" "
.. ................ B
LOLOR INDICATES FIRST NUMBERI---'---...J
.09 ..................
" "
.. ................ 9
NEW SYSTEM OLD SYSTEM
1
..................
" "
................. .10
FIGURE 12 . RMA RESISTOR COLOR CODE CHART
39
3B