Eico 221 User manual

INSTRUCTION
MANUAL
FOR
1100 ELECTRONIC
INSTRUMENT CO., Inc.
131-01 39th AVENUE, FLUSHING 54, N. Y.

DC
VOLTMETER-
u
O
k
Diagram

GENERAL DESCRIPTION
The EICO Model 221 Electronic Volt-Ohm Meter is ohigh quality
VTVM that is especially suited for use in television, f-m, and a-m radio ser-
vicing. Featuring arugged and easy reading 41/2" meter, this instrument
provides enti rely electronic measurement of a-c voltage, d-c voltage, decibels
and resistance.
Complete overload protection is provided electronically on all a-c
voltage, d-c voltage, andohmmeter ranges. To eliminate the need for revers-
ing the test leads on d-c voltage measurement (when anegative d-c voltage
is to be measured), positive and negative d~c positions have been provided
on the function switch .Azero centering position on the meter facilitates
discriminator alignment in f-m and a-f-c circuits.
This instrument allows measurement of d-c and a-c voltages up to 1000
volts in five ranges. The d-c voltage range can be extended to 30,000 volts
with the EICO Model HVP-1 High Voltage Probe. Another accessory, the
EICO Model P-75 RF Probe extends the frequency range of the instrument (20 -
200,000 cps) to 200 Me.
The readings on the d-c voltage ranges are accurate within 3% and on
the a-c ranges within 5% of ful l-scale (the multiplier resistors used are accu-
rate within 1%). As the input impedance is 25 megohms on d-c and 3meg-
ohms on a-c voltage ranges, the current drawn by the instrument is negligible,
so there is no problem of error due to circuit loading. Abalanced bridge
circuit maintains constant accuracy despite variations in line voltage.
On the ohmmeter ranges, advantage is taken of the high sensitivity
of the d-c amplifier to provide resistance measurements up to 1000 megohms
using only the 11/2 volt battery. This feature avoids any danger to delicate
apparatus that may be tested with the instrument, since it eliminates the high
voltage normally encountered in high resistance measuring circuits.
The user of the instrument will benefit from direct reading scales,
simple operation, and the dependable quality that results from high grade
components, and careful engineering and testing in the field. It will prove
to be an extremely valuable tool for signal tracing, alignment, for voltage
and resistance measurements in television and radio receivers, and for testing
many types of electrical equipment.
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SPECIFICATIONS
D~C Voltage Ranges:
0to 5, 10 #100, 500, 1000 volts
(to 30 KV with HVP-1 probe)
Input impedance: 25 Meg.
A~C Voltage Ranges:
0to 5, 10, 100, 500, 1000 volts
(Special scale for 0to 5volts)
Input impedance: 3Meg.
Electronic Ohmmeter Ranges:
0to 1000 ohms, 10,000 ohms,
1Meg., 10 Meg., 1000 Meg.
(Measures from 0. 2ohm to 1000 Meg .)
Decibel Ranges: -20 to +55 db
Frequency Range: 20 -200,000 cps
(Up to 200 Me with P-75 probe)
Accuracy: d-c volts, ohms —+3%
a-c volts —i5%
Power Supply: 115v,50-60 cps, 10 w
Ohmmeter Battery: 11/2 vdry cel!
Tubes: 6X5, 6H6, 6SN7
Overall Dimensions: width -6in. ,
height -97/16 in. ,depth -5in.
Weight: 10 pounds
Cabinet: Blue grey wrinkle
lacquer on steel
Panel
•
3color, deep etched
OPERATING INSTRUCTIONS
INl TIAL STEPS
:
Check the mechanical zero adjustment of the meter pointer
when the power is off. If the pointer is off zero, turn the slotted screw direct-
ly beneath the meter face until the pointer is brought to zero.
Plug the line cord into the 60 cycle, 115 volt a-c supply, turn the
power on with the "ON-OFF" switch, and aIlow anormal warm-up time (about
one minute).
Insert the phone plug, PI (on the DC test lead), in the DC jack, Jl,
on the panel. Insert the pin plug, P2 (on the AC-OHMS test lead), in the
AC-OHMS jack, J2, on the panel. Insert the banana plug, P3 (on the COM-
MON test lead), into the COMMON (ground) jack, J3, on the panel. This
is the COMMON lead for all functions.
CAUTION: Never connect the COMMON lead to ahigh voltage point as
this will place the meter chassis and case at ahigh voltage above ground.
When working with high voltages, avoid contact with or close proximity
to high voltage points. If possible, attach the test leads with the power off in
the circuit to be measured. After the leads are attached, turn the power on
and take the reading.
D-C VOLTAGEMEASUREMENT: Set the FUNCTION switch to n+DC" or "-DC
VOLTS", the RANGE switch to desired voltage range, and then use the ZERO
ADJ. potentiometer to bring the meter pointer to zero*. Clip the COMMON
lead to ground or the low side and touch the DC probe to the high side of the
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source to be measured. On the 5V and 500V ranges, read the 0-5 AC-DC
scale (black); on the 10V, 100V, and 1000V ranges, read the 0-10 AC-DC
scale.
A-C VOLTAGE MEASUREMENT: Set the FUNCTION switch to "AC VOLTS" ,
the RANGE switch to the desired voltage range, and then use the ZERO ADJ.
potentiometer to bring the meter pointer to zero*. Clip the COMMON lead
to ground or the low side and touch the AC-OHMS probe to the high side of
the source to be measured. On the 5V range, read the special 5VAC scale
(red); on the 500V range, read the 0~5 AC-DC scale (black); on the IC'V,
100V, and 1000V ranges, read the 0-10 AC-DC scale.
RESISTANCE MEASUREMENT: Set the FUNCTION switch to "OHMS" and
the RANGE switch to the desired ohms range; connect the COMMON lead
to the AC-OHMS lead and then use the ZERO ADJ. tobring the meter pointer
to zero; separate the COMMON lead from the AC-OHMS lead and then use
the OHMS ADJ. potentiometer to set the meter pointer so that it reads exactly
ful l-scale. Clip theCOMMON lead to one terminal of the unknown resistance
and touch or connect the AC-OHMS probe to the other terminal. Read the
OHMS scale on the meter. On theRXl range, read the OHMS scale directly
in ohms; on RX10, RX1000, and RX10,000 ranges, multiply the scale reading
by 10, 1000, and 10,000 respectively and read in ohms; on the RX1MEG
range, read the scale directly in megohms. Note: The small reading noted
on the lowest range is the resistance of the leads.
CAUTION: Never leave the FUNCTION switch set at the OHMS" position
as this will greatly shorten the life of the ohmmeter battery.
DECIBEL MEASUREMENT: The instructions for decibel measurement are the
same as for a-c voltage measurement except that the DB scale is read. To
the reading on the DB scale, add the number of db shown on the meter as
corresponding to the a-c voltage range used. Correction for measuring across
different impedances is included in the APPLICATIONS section under OUT-
PUT METER".
ZERO-CENTER INDICATION: See APPLICATIONS section.
APPLICATIONS
OUTPUT METER: When the RANGE switch is set at 10V and the FUNCTION
switch is set at AC VOLTS, the power level in a500 ohm circuit can be read
directly in decibels on the DB scale, which is calibrated from -20 to +15 DB,
based on areference level of 6.0 milliwatts and 500 ohms. This reference
level is marked "0" decibels, and corresponds to 1.73 vac on the 0-10 volt
scale. To measure higher levels, proceed as instructed in the OPERATING
INSTRUCTIONS section under "DECIBEL MEASUREMENT".
The DB scale on the meter is calibrated across a500 ohm line. If the
DB measurement is being made across an impedance other than 500 ohms, use
*See note on electrostatic pickup in the MAINTENANCE section, page 9.
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the correction table below to obtain the number of DB (corresponding to the
actual impedance) that has to be added to or subtracted from the measured
value. This correction is separate from the correction made for the a-c volts
range used.
ACTUAL
IMPEDANCE
4ohms
8ohms
16 ohms
50 ohms
75 ohms
150 ohms
CORRECTION
FACTOR
+21 db
+18 db
+15 db
+10 db
+8.2 db
+5.2 db
ACTUAL
IMPEDANCE
206 ohms
300 ohms
500 ohms
600 ohms
1000 ohms
2000 ohms
CORRECTION
FACTOR
+4db
+2.2 db
0db
-0.8 db
-3db
-6db
RECEIVER ALIGNMENT: To use the DB scale for receiveralignment: 1) con-
nect the AC~OHM5probe and the COMMON lead across the voice coil; 2)
set the FUNCTION switch at AC VOLTS and the RANGE switch at 10V; 3)
feed a400 cycle modulated r-f or i-f signal into the receiver. Keep the re-
ceiver volume control at maximum, and adjust the signal generator output to
produce asmall deflection on the DB scale. As alignment adjustments are
made, thus increasing the sensitivity, the DB scale will show the improvement
directly in decibels. The effective attenuation of wave traps, in decibels,
can be determined by noting the decrease in decibels as the trap is tuned through
resonance.
ZERO-CENTER APPLICATIONS: In some applications, for example in align-
ing the discriminator in f-m or a-f-c circuits, it is convenient to use azero-
center d-c voltmeter, because the d-c output of the discriminator changes
from +to -to +as the secondary of the discriminator transformer is tuned or
as the input frequency is varied above and below resonance.
Zero-center indication can be obtained as follows: 1) set the FUNC-
TION switch at either "+DC" or "-DC VOLTS", 2) set the RANGE switch at
"5V" (higher if necessary); 3) turn the ZERO ADJ. knob to bring the meter
pointer to the special zero mark (”0+) beneath the center of the DB scale; 4)
connect the COMMON lead to the low side of the discriminator load; 5) con-
nect the DC probe to the high side of the discriminator load; 6) refer to the
special center scale zero mark; when the secondary of aconventional discrim-
inator is correctly tuned, the DC output is zero and the meter will indicate
zero.
POWER OUTPUT IN WATTS:Use formula: Watfs =-^utp '
impedance ~
EXAMPLE: The maximum undistorted output voltage across a2ohm load Is 5
volts.
Power Output =-12.5 Watts
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OSCILLATOR STRENGTH: The negative d~c voltage developed Of the oscilla-
tor grid is always directly proportional to the strength of oscillation. This
voltage can be measured very readily at the osci Motor grid while the band
switch is turned to the various bands, and in each of its positions the main
tuning condenser is rotated from minimum capacity. This will give an indica-
tion of the strength of oscillation at all frequencies within the oscillator's
range.
A-V-C VOLTAGE: The automatic volume control voltage developed by the
incoming signal can be measured at anumber of places in the receiver. This
negative voltage first appears across the diode load resistor. It may also be
measured along the a-v-c bus and at the grids of the r-f tubes being controlled.
The d~c voltage measured at the diode load resistor is avery convenient out-
put indication during receiver alignment.
Owing to the high input resistance of this instrument, It is possible to
measure bias (a-v-c) voltage on the grid of r-f and ?-f amplifier tubes without
disrupting the signal.
D~C SUPPLY VOLTAGES: Power supply d~c voltages can be measured at the
rectifier filaments and in the filter circuits. Plate, screen, and cathode d-c
voltages can be measured at the corresponding pins of the tube sockets.
BIAS CELL VOLTAGE- This instrument will accurately measure the voltage of
abias cell. Current drawing voltmeters are not capable of making this meas -
urement and in many cases will damage the cell.
TELEVISION RECEIVER ADJUSTMENTS: This instrument will measure the d-c
voltage developed across the second-detector load resistor In the picture channel
of atelevision receiver. This measurement hmost useful when adjusting an-
tenna orientation as we' 'as when adjusting antenna matching sec Lions.
GASSY TUBES: One effect of agassy tube is to reduce rhe normal new.
grid bias, or even make the grid positive. This instrument is idea! for meas-
uring the voltage directly at the control grid of any tube in order to dtvr.Lpe
whether or not this effect is present. Excessive gas will cause the tube L, rise
operating normal iy ,and in an audio amplifier wi I!usual ly cause the volume con
frol to become noisy. This amount or gas will not always produce anoticeable
change in the operation of the radio receiver. Consequently if repeated diffi-
culty is experienced with volume controls becoming noisy, in this type of cir-
cuit, this instrument should be used to check for incorrect bias.
A-C VOLTAGES: The o-c voltmeter wirhin the instrument is extremely useful
in measuring ali a~c voltages encountered in the average radio receiver. The
measurements that can be made include ali voltages from power transformer
secondaries, audio signal voltages at grids and plates of amplifiers, and audio-
voltages developed across the output transformer or voice coil (as an indication
of output during receiver alignment).
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ACCESSORIES
R-F PROBE P-75 (K): An EICO R-F probe (P-75K -kit form, P-75 -factory
wired) for use in measuring voltages up to 50 volts and to 200 Me is available
to extend the uses of the instrument. This probe is simply plugged into the
D-C jack of the instrument and the r-f voltages are read on the regular D-C
sea Ies
.
HIGH VOLTAGE PROBE HVP-1: An EICO High Voltage Probe HVP-1 (factory
wired only) for measuring d-c voltages up to 3CKV is available to extend the
uses of the instrument. The probe may be supplied with amultiplier resistor
of 240 Megohms to give ahigh voltage range of 10,000 volts or witha multi-
plier resistor of 740 Megohms to give ahigh voltage range of 30,000 volts.
CIRCUIT DESCRIPTION
GENERAL: The meter measures either d-c or a-c voltages by making use of
the rectifying and amplifying characteristics of vacuum tubes. The input
impedances are very high (d-c -25 megohms, a-c -3megohms), and the
current used to actuate the indicating meter is not taken from the circuit being
measured. Abridge circuit, used to stabilize the operating voltages of the
tubes, provides constant accuracy despite line variations. When used as an
ohmmeter, the instrument wi II measure resistances between zero and 1000 meg-
ohms. Decibel measurements between -20 and +55 db can be made using
the DB scale.
D-C AMPLIFIER CIRCUIT: (See Figures 1and 3) Abalanced bridge circuit is
used in the d-c amplifier, comprising the twin triode V“2, acommon plate
load resistor R-3, and the balanced cathode load resistors R-10, R-ll, and
R-12. The meter M-l is connected across the two cathodes of V-2. In the
normal condition, areference current flows through V“2B, which has aground-
ed grid. Current flow through V-2A is adjusted by means of the ZERO ADJ.
control R-12 to equal the current flow in V_2B. The meter then reads zero.
OPERATION AS AD-C VOLTMETER: (See Figures 1and 3) The circuit for
operation as ad-c voltmeter is as follows: The unknown voltage is applied
across the connectors J-l and J-3 (ground). The FUNCTION switch S-3
connects the range voltage divider across J-l and ground. Avoltage, depend-
ing on the RANGE switch setting, is then applied to the grid of d-c amplifier
V-2A. This grid voltage unbalances the bridge circuit, and the meter is
deflected in direct proportion to the unbalanced current.
OPERATION AS AN A-C VOLTMETER: (See Figures 1and 3) The circuit for
operationas ana-c voltmeter is as follows: Theunknown a-c voltage is appl-
ied across the connectors at J-2 and J-3 (ground). The FUNCTION switch
applies the voltage to the diode rectifier V“1 .The d-c output voltage of VI
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is then applied to the voltage divider. Ad-c voltage, depending on the
RANGE switch setting, is then applied to the grid of d-c amplifier V-2A.
The remaining portion of a-c voltmeter operation is the same as the d-c volt-
meter operations. The a-c circuit is also used for decibel measurements but
the readings are made on the DB scale.
OPERATION AS AN OHMMETER: (See Figures land 3) The circuit for opera-
tion as an ohmmeter is as follows: The unknown resistance is connected across
connectors J-2 and J-3. The FUNCTION switch connects the range voltage
divider and battery B-l across J-2 and ground. Avoltage, depending on the
RANGE switch setting, is then applied to the gridof the d-c amplifier V-2A.
The remaining portion of the ohmmeter circuit follows the same pattern as the
d-c voltmeter circuit.
POWER SUPPLY: (See Figures 1and 3) The operating potential for the d-c
amplifier V-2A is obtained from the full wave rectifier V~3. The B+ output
of the rectifier is suitably filtered by R-l ,R-2, and C-2. Filament voltages
for all tubes are obtained from the 6.3 volt winding of the power transformer
T-l
.
Fig. 2-Top View of Chassis -Location of calibrating pots.
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MAINTENANCE
I. CALIBRATION: After construction of the instrument is completed, it is
necessary to carry out the calibration procedure described below.
If achange occurs in the accuracy of the instrument aftera long period
of use, it is probably due to aging of the components. The accuracy of the
instrument may readily be restored by repeating this calibration procedure.
Recalibration wil Ialso be necessary ,whenever parts (tubes ,etc .) are replaced.
A. INITl AL STEPS: Follow the procedure described in "INITIAL STEPS"
in the OPERATING INSTRUCTIONS section. In addition, check to see that
the isolation resistor, R—31 , is properly connected within the D-C test probe.
B. D~C VOLTMETER CALIBRATION; (See Fig. 2) To calibrate the d-c
voltage ranges, use two flashlight batteries connected in series. The terminal
voltage will be 3. 10 volts when fresh batteries are used. Set the FUNCTION
switch to "-DC" and the RANGE switch to "5V". Short the D-C (red) probe
to the COMMON lead (ground) and turn the ZERO ADJ. control until the
meter pointer is at zero (ignore any change after the test leads are disconnected).
Connect the batteries between the D-C test leads with the COMMON (ground)
lead touching the positive side of the batteries. Adjust the "-DC" calibration
potentiometer R-29 until a3. 10 volt reading is obtained on the meter (3.10
on the 0to 5D-C scale). To calibrate the "+DC nvoltage ranges, repeat the
above steps with the FUNCTION switch set at "+DC" and the positive end of
the cells connected to the D-C probe. Adjust the "+DC" calibration potentio-
meter R~27.
NOTE: The electrostatic pickup which appears on the lowa-c and d-c voltage
ranges, when either the AC“OHMS or DC probe is held or touched is normal
in asensitive vacuum tube voltmeter, due to the extreme sensitivity of the
instrument. However, if the AC'OHMS or DC probe (depending upon the
function) is shorted to the COMMON (ground) lead when the zero adjustment
is made, the zero obtained will result in correct meter readings and no error
will be introduced because of electrostatic pickup.
C. A-C VOLTMETER CALIBRATION: (See Fig. 2) To calibrate the a-c
voltage ranges, set the FUNCTION switch at "AC" and the RANGE switch at
"1000V". Short the AC”OHMS (black) test lead to the COMMON lead
(ground) and turn the ZERO ADJ. control until the meter pointer is at zero.
Turn the RANGE switch to the "5V" position and adjust the A“C shift balance
potentiometer, R-5, until the meter pointer returns to zero. Then turn the
RANGE switch to the "500V" position; the meter pointer should move very
little, usually not at all. Connect the COMMON and AC-OHMS test leads
to the 115 volt A-C supplyand adjust theA-C calibration potentiometer, R30,
unti Ithe meter reads 115 volts .Cal ibration with the 115vol tA~C supply wi 1
1
result in the instrument being accurate within 5%. If greater accuracy is
desired, the instrument should be cal ibrated against aknown ,standard A-C
voltage.
-9“