HP 450A Owner's manual

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450A
AMPLIFIER
SERIALS PREFIXED: 010-
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PR I NTED 1/61 I
00001-1 i

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00001·1
OPERATING AND SERVICING MANUAL
MODEL 450A
SERIALS PREFIXED: 010 -
AMPLIFIER
Copyright HEWLETT-PACKARD COMPANY 1961
ISOI PAGE MILL ROAD. PALO ALTO. CALifORNIA. U.S.A.
Printed: JAN 1961

Model 450A
T AILE OF CONTENTS
Table of Contents
List of Illustrations
)Section
Page Section Page
GENERAL INFORMATION 1-1
IV SERVICE INSTRUCTIONS ...
...
· .
4-1
1-1.
Description . . . . 1-1 4-1. Warnings and Cautions ...... 4-1
1-5.
Applicable Literature
1-1
4-4.
Equipment Required for Maintenance 4-1
4-6. Troubleshooting
......
· .
4-2
4-8. Tube Replacement . . . .
....
4-2
II
OPERATING INSTRUCTIONS.
2-1
4-10. Locating Shorts in Power Circuits
4-2
2-1.
Incoming Inspection 2-1
4-12. Testing Power Supply Operation.
4-2
2-4. Ins talla tion
....
2-1 4-15. Measuring Amplifier Stage Gain.
4-3
2-10.
Operating Procedure
2-2 4-17. Amplifier Adjustments. . . . .
4-3
4-19. AdjustingVI and V2 Heater Voltage
4-3
4-21. Adjusting Amplifier Gain
..
· .
4-3
III
THEORY OF OPERATION ......
3-1 4-23. Noiseand Distortion Measurement
4-4
3-1.
Amplifier Circuit Operation . . 3-1
VREPLACEABLE PARTS . 5-1
3-4.
Regulated Power Supply Operation
3-1
5-1. Introduction
..
5-1
3-6.
DC Heater Supply. . . . . .... 3-1
5-3. Ordering Information 5-1
LIST OF ILLUSTRATIONS
)
Number
Page
Number
Page
1-1.
Table of Specifications .
1-0 4-3.
Top View of Model 450A . . 4-6
1-2.
Model 450A Amplifier
1-0
4-4.
Bottom View of Model 450A 4-7
4-1.
Test Setup for Measuring Amplifier
4-5.
Voltages and Resistances on Tube
Gain
..............
4-3
Sockets and Terminal Boards
4-8
4-2.
Test Setup for Measuring Amplifier
Distortion and Noise . . . . . .
4-4
4-6.
Schematic Diagram Model 450A . .
4-9
)
00001-1
iii

Section I
Figures 1-1 and 1-2
GAIN:
FREQUENCY RESPONSE:
STABILITY:
IMPEDANCE:
OUTPUT LEVEL:
DISTORTION:
Model 450A
40 ± 1/8 db (100X), 20 ± 1/8 db (lOX) at 1000 cps.
For 40 db gain (open circuit): 5 cps to 2 megacycles, within ± 1 db;
10 cps to 1 megacycle, within ± 1/2db.
For 20 db gain (open circuit): 2 cps to 1.2 megacycles, within ± 1 db;
5 cps to 1 megacycle, within ± 1/2 db.
±2% with line voltage changes (115/230 volts ± HYfo) and normal
changes in tube characteristics.
Input: 1 megohm shunted by approximately 15 pf.
Output: 150 ohms maximum over full frequency range.
10 volts maximum into 3000 ohms or higher resistive load.
Less than 1% distortion from 2 cps to 100 kc at rated output and load
resistance; less than 2% above 100 kc.
NOISE: For 40 db gain:
For 20 db gain:
Equivalent to 40 microvolts at input terminals.
Equivalent to 250 microvolts at input terminals.
POWER:
DIMENSIONS:
WEIGHT:
ACCESSORIES AVAILABLE:
115/230 volts ± HYfo, 50 to 1000 cps ac, 50 watts.
Cabinet Mount: 8-5/8 in. wide, 5-1/2 in. high, 10-3/4 in. deep.
Rack Mount: 19 in. wide, 5-7/32 in. high, 10-9/16 in. deep.
Cabinet Mount: Net 10 lbs; shipping 14 lbs.
Rack Mount: Net 11 lbs; shipping 24 lbs.
AC-16A Cable Assembly (terminates indual banana plugs 44 in. long).
AC-16B Cable Assembly (dual banana plug to BNC male 45 in. long).
Figure 1-1. Table of Specifications
AMPLIFIER
MODEL ctj) 450A
HEWLETT PACKARD
,AUl Al.TO CAUFOflHIA
•
INPUT
40 DB
;(
GAIN
@
20 DB
POWER
ON
OUTPUT
1-0
Figure 1-2. Model 450A Amplifier
00001-1

Model 450A
SECTION I
GENERAL
INFORMATION
Sections Iand II
Paragraphs 1-1 to 2-7
1-1. DESCRIPTION.
1-2. The Model 450A is a general-purpose, stabi-
lized, fixed-gain amplifier for use with low-level
signals from 2 cps to 2 mc. It provides two calibrated
gain factors, lOX (20 db) and 100X (40 db), selectable
by atoggle switch on the front panel. Each gain factor
is accurate to within ± 1/8 db in the audio frequency
range; frequency response is given in the table of
specifications (figure 1-1). Principal characteristics:
stable gain with smooth attenuation beyond rated fre-
quency range, wide frequency range, low distortion.
1-3. Typical uses include increasing the sensitivity
of ac test equipment (voltmeters, oscilloscopes,
bridges, etc), obtaining larger signals across lower
impedances in test bench setups and permanent system
installations. An electronically-regulated power
supply and large amounts of degenerative feedback
around the entire amplifier circuit provide very re-
liable and stable operation in case of changing line
voltage, load resistance, or tube characteristics.
1-4. The amplifier is constructed on a single chassis
with removable cover and bottom plate. A leather
carrying handle is provided on the left side of the
cabinet model. The front panel is finished in light
grey enamel; the rest of the cabinet is finished in
dark grey wrinkle paint. Operating controls and ter-
minals consist of toggle-type power and gain switches
and binding post type input and output terminals on
the front panel. Binding posts are spaced 3/4 inch
on-centers to receive dual banana-plug connectors.
The power cable is permanently attached to the rear
of the amplifier and is terminated in a 3-prong,
grounding-type plug. A fuse is provided on the rear
and can be replaced externally.
1-5. APPLICABLE LITERATURE.
1-6. This handbook contains complete operating and
servicing instructions for the 450A Amplifier and
conforms to the format specified in MIL-M-5474C.
)
SECTION II
OPERATING INSTRUCTIONS
)
2-1. INCOMING INSPECTION.
2-2. MECHANICAL. When unpacking the amplifier,
inspect it for any sign of physical damage. If the
cabinet is damaged, remove cover and bottom plate
and inspect chassis parts for further damage. Re-
port all damage to the carrier and keep amplifier
intact for inspection by carrier and insurer. All in-
struments shipped by the Hewlett-Packard Company
are insured against shipping damage. See Warranty
at rear of manual.
2-3. ELECTRICAL. Electrical inspection consists
of testing certain electrical characteristics of the
amplifier to determine that it functions normally after
having been stored or transported. Only one test is
required; full instructions are given in paragraph
4-20 steps athrough f.
2-4. INSTALLATION.
2-5. INPUT CONNECTIONS. The amplifier can be
connected to a signal source through either twisted
pair leads or shielded cable. Keep input leads as
short as possible to avoid excessive capacitive shunt-
ing of the signal source. If necessary, use coaxial
cable to prevent unwanted signal pickup from stray
electric and magnetiC fields. 00 NOT connect the
amplifier input to circuit potentials greater than
00001-1
400 volts unless an externall-j..lfcapacitorhaving suf-
ficient voltage rating is used in series with the input
terminals.
2-6. OUTPUT CONNECTIONS. The amplifier output
can be connected through any convenient lead set or
cable. The low output impedance of 150 ohms permits
shielded cable to be used freely without capacitive
loading in the audio range and permits twisted pair
leads to be used with much less effect from stray
fields. The amplifier is designed to be used with
resistive loads of 3000 ohms or more. Loads below
3000 ohms reduce amplifier gain bandwidth, and maxi-
mum output voltage available. For higher frequencies,
the load must have small capacitive reactance topre-
serve full output signal quality and stability. DO NOT
connect the output terminals to dc potential of more
than +50 or -300 volts, or output capacitor ratings
will be exceeded.
2-7. CONSIDERATION FOR LOW SIGNAL LEVELS.
When amplifying low-level signals it may be necessary
to eliminate an electrical ground loop formed by the
power cable ground lead and signal ground lead between
two instruments. If this electrical path is completed
(typically a combination of the signal groundand power
line ground leads do), line frequency currents flow in
the signal ground lead and develop voltages across the
leads which are in series with the desired signal. To
1-1
2-1

Section II
Paragraphs 2-8 to 2-11
avoid this situation, select one ground path from a
group of instruments connected together, and permit
no other ground path to the power line ground.
Grounding one of the instruments may give less ripple
trouble than grounding any other; or ungrounding all
instruments may give lowest line-frequency modu-
lation of the desired signal.
2-8. POWER CABLE. The plug on the power cable
has a round grounding terminal combined with stand-
ard, 2-prong plug. If the ac outlet will not accommodate
this plug, an adapter must be used. The round pin on
this plug grounds the amplifier chassis. When the
adapter is used, the chassis connection is a pigtail
lead extending from the adapter, which should becon-
nected to agrounded ac outlet mounting box to ground
the chassis.
2-9. POWER LINE VOLTAGE. The amplifier is
shipped from the factory for operation on 11S-volt
2-2
Model4S0A
ac power, unless otherwise specified. The power
transformer can be reconnected for use on 230-volt
power by connecting its dual primary windings in
series as shown on the schematic diagram, note 1.
After such conversion, replace the 0.8-ampere fuse
with an 0.4-ampere slow-blow fuse.
2-10. OPERATING PROCEDURE.
2-11. The only operating precaution to be kept in
mind are the instructions in paragraphs 2-S and 2-6
regarding excessive dc voltages. For operation in
undesirable atmospheric conditions, provide any
physical protection possible to prevent mechanical
damage, and operate amplifier as usual. Do not
obstruct ventilating louvers. The power cord may be
left connected to the power source during periods of
non-operation.
00001-1

Model 450A
SECTION III
THEORY OF OPERATION
Sections III and IV
Paragraphs 3-1 to 4-5
)
3-1. AMPLIFIER CIRCUIT OPERATION.
3-2. The amplifier circuit consists of two stages of
high-gain voltage amplification and a cathode follower
output stage connected as shown in the schematic
diagram. Pentode tubes are used in all three stages
for wide bandwidth with low noise. The triode con-
nected cathode follower presents a relatively low
source impedance at the OUTPUT terminals. De-
generative feedback is carried around the entire
amplifier to stabilize gain. The amount of degen-
erative feedback is adjusted by the GAIN switch to
obtain 20 or 40 db amplification. The resistive feed-
back circuit is shunted by a small adjustable capacitor
for gain compensation at high frequencies. Resistance-
capacitance coupling is used between each stage.
Cathode bias is used at each stage.
3-3. Degenerative feedback is taken from the ampli-
fier output through a resistive divider consisting of
R3 and R6 to the cathode of the first stage VI. The
R3A portion of the divider is shorted by the GAIN
switch Sl to decrease feedback and increase gain to
40 db. Resistor R6 provides fine adjustment of gain
for calibration purposes. Capacitors Cll and Cl2
provide gain compensation at high frequencies.
3-4. REGULATED POWER SUPPLY OPERATION.
3-5. The power supply for the amplifier is electron-
ically regulated to stabilize operation during changes
in line voltage and to minimize line frequency modu-
lation of the output signal. The regulated supply
consists of power transformer TI. rectifier V4.
series regulator tube V5, regulator amplifier V6 and
vOltage reference V7. The series regulator is a
cathode follower whose cathode supplies the regulated
voltage to the load consisting of VI, V2 and V3. The
series regulator serves as an adjustable impedance
controlled by amplified feedback from V6. Ampli-
fier V6 samples the regulated voltage and amplifies
any difference between it and the reference voltage
provided by V7. Voltage comparison is accomplished
by applying the sample voltage to V6 grid and the
referen~e voltage to V6 cathode. If the regulated
voltage tends to rise, V6 amplifies this increase and
applies it to the grid of V5 causing the impedance of
V5 to increase, thus instantly and exactly counter-
acting the original tendency to increase. This grid
control automatically holds the series regulator
cathode voltage constant. The high plate resistance
of the series regulator tube assisted by amplifier
feedback attenuates ripple and stabilizes the output
voltage during changes in line voltage and rectifier
output. The high transconductance of V5. assisted
by the same feedback, stabilizes the cathode voltage
during changes in load current. The sample of the
regulated output is obtained from resistive divider
R24 and R26. Resistor R25 is selected to adjust the
value of the regulated voltage to +210 volts.
3-6. DC HEATER SUPPLY.
3-7. DC vOltage is supplies to the heaters of VI, V2
and V3 to prevent line-frequency modulation of the
output signal through heater-cathode leakage in the
tubes. This voltage is obtained from a 9-volt winding
on the transformer rectified by a full-wave bridge
rectifier CRI. The rectified voltage is filtered by C7.
Resistor R27 provides adjustment of the heater voltage
to accommodate aging changes in rectifier resistance.
SECTION IV
SERVICE INSTRUCTIONS
)
4-1. WARNINGS AND CAUTIONS.
4-2. The amplifier contains a selenium rectifier.
When selenium rectifiers burn out due to overheating,
poisonous fumes are released. Ventilate immediately,
and do not inhale these fumes. Do not handle the
rectifier until it has cooled.
4-3. Do not remove VI or V2 with the amplifier
turned on. These tubes are supplied with unregulated
dc heater voltage. If VI or V2 is removed with the
amplifier operating, the heater voltage on the re-
maining tube will rise sharply and possibly damage it.
00001-1
4-4. EQUIPMENT REQUIRED FOR MAINTENANCE.
4-5. General troubleshooting requires an electronic
multimeter such as the Hewlett-Packard Model 410B.
Other multimeters can be used if they have 20,000
ohm/volt sensitivity or greater. To calibrate the gain
of the amplifier requires an ac signal source and an
accurate ac voltmeter ofthe required frequency range,
such as the Hewlett-Packard Model 650A Oscillator
and 4000 Voltmeter. Other test instruments can be
used if they provide the necessary frequency range
and accuracy. To measure distortion from theampli-
fier requires a signal source producing a signal with
3-1
4-1

Section IV
Paragraphs 4-6 to 4-14
Model 450A
4-12. TESTING POWER SUPPLY OPERATION.
4-13. The amplifier employs an electronically-regu-
lated power supplywith very low line-frequency ripple.
To test operation of the supply, proceed as follows:
circuit, power transformer windings, or in the trans-
former primary circuit. The resistance of each trans-
former winding is as follows:
8 ohms
8 ohms
RESISTANCE
COLOR
Black- Black/yellow
Black/red-Black/green
Brown-Brown 0.14 ohm
Yellow-Yellow 0.06 ohm
Green-White 0.18 ohm
Green-Red 0.12 ohm
Red- Yellow 105 ohms
Yellow-Red 105 ohms
*Fil. #4 part of winding for Fil. #3.
WINDING
Pri. #1
Pri. #Z
Fil.#l (6.3 v)
Fil.#2 (5 v)
Fil.#3 (9 v)
*Fil.#4 (6.3 v)
H. V. #1
H. V. #2
less than 0.5% distortion and a distortion meter such
as the Hewlett-Packard Model 202C Oscillator and
330B Distortion Analyzer. The frequency range of
the 330B is considered adequate for this application.
Measurement of distortion at higher and lower fre-
quencies requires rejection filters not readily avail-
able. A variable line transformer is required to
produce line voltages from 100 to 130 volts.
4-6. TROUBLESHOOTING.
4-7. The first step in servicing a defective amplifier
is to inspect for any sign of overheating, physical
damage, or wear. The second step is to attempt oper-
ation to see if the fuse blows, pilot lamp lights, and
if the amplifier can be operated without damage.
There are two sets of operational tests: power supply
checks (see paragraphs 4-10, 4-12 and 4-18) and
amplifier checks (see paragraphs 4-15, 4-20 and
4-22). Suspect electron tube failure first, then as-
sociated circuitry. Look for intermittent and margi-
nal malfunctions. These types of failures can some-
times be found while troubleshooting, by physical
shock and by applying low and high line voltages
while making the tests.
4-1. TUBE REPLACEMENT.
4-9. The best way to test atube is to replace it with
anew one, noting any change in amplifier perform-
ance while measuring noise and distortion in the amp-
lifier output. If the replacement tube does not im-
prove performance, return original tube to socket to
avoid complicating the troubleshooting procedure.
Make the test at low and high line voltage to see if
malfunction is marginal. If atube tester is used to
check tubes, consider its indication semi-final if it
shows "good", final if it shows "bad". Tube testers
do not measure second order effects such as exces-
sive change in transconductance, plate current and
grid current with changes in heater voltage, noise,
microphonics, heater-cathode leakage, etc, which
may be important in certain circuits. Remember
that most tube failures occur during the first hundred
hours of operation. After this period tubes age slowly
and should not be replaced prematurely as part of
routine maintenance.
4-10. LOCATING SHORTS IN POWER CIRCUITS.
4-11. Check the amplifier for shorts whenever ap-
plication of line power causes the fuse to burn out, or
whenever operation causes the power transformer or
other part to overheat. Proceed as follows:
a. Replace blown fuse, remove V5 and again attempt
operation. If the amplifier no longer blows fuses,
the trouble is located in the circuits which follow the
regulated power supply; check C8C, C8D, C2 and C4.
b. If amplifier continues to blow fuses with V5 re-
moved, remove V4 also and again attempt operation.
If the amplifier no longer blows fuses, the trouble is
located in the power supply filter; check C8A and C8B.
c. If the amplifier continues to blow fuses with V4
removed, the trouble lies either in the tube filament
a. Connect the amplifier to an adjustable line trans-
former which can supply from 100 to 130 volts.
b. Remove the amplifier bottom plate and connect the
negative leads of the multimeter and ac voltmeter to
the amplifier chassis.
c. Set the line voltage to 115, turn amplifier on and
allow 3-minute warmup.
d. Measure the ac and dc volts at V5 pin 5. The dc
voltage must be about 15 volts less than that measured
in step g; the ac voltage must beabout 1/10 that mea-
sured in step g. Excessive dc voltage drop indicates
excessive current being drawn by the amplifier cir-
cuits or filter capacitors. Insufficient attenuation of
ripple indicates filter capacitors low in capacity.
e. Measure ac and dc voltage at V5 pin 8. The dc
voltage must be between 205 and 215 volts; the ac
voltage must be less than 3 millivolts. The value of
R25 can be selected to obtain exactly +210 volts.
f. Increase the line voltage to 127 volts; the dc volt-
age must remain within 1volt of that read in step d;
the ac voltage must not increase above that in step d.
g. Decrease line voltage to 103 volts; the dc voltage
must remain within 1volt of that read in step d; the
1lC voltage must not increase.
h. With line voltage set to 115 volts, measure the ac
and dc volts at V4 pin 8. The dc voltage must be close
to +390, the ac voltage less than 3 volts.
4-14. Possible trouble symptoms in electronic voltage
regulators include rectifier tube which does not deliver
full voltage to the series regulator tube, which in turn
prevents good regulation at low line voltages. The
same symptom may be observed with aweak series
regulator tube. Another indicationof this same trouble
4-2 00001-1

Model 450A Section
IV
Paragraphs 4-15 to 4-21
)
is increasing line-frequency ripple as the line volt-
age is decreased. Incorrect or unstable voltage level
can be due to incorrect or unstable reference voltage
obtained from V7. High ripple at all line voltages is
an indication of poor electrolytic filters or weak V6.
4-15. MEASURING AMPLIFIER STAGE GAIN.
4-16. The typical amplification factor for each stage
in the amplifier is given below. Gain is meas ured
by applying 0.01 rms volts at 1000 cps to the ampli-
fier INPUT terminals with the amplifier GAIN switch
set to 40 DB. The 4000 Voltmeter is then used to
measure the resultant signal level at the input and
output of each stage, each time dividing the output
by the input voltage.
VI
V2
V3
E. Eout Gain E. Eout Gain E. Eout Gain
In In In
0.01 0.043 4.3 0.43 1.1 25.6 1.1
l.0
0.91
4-17. AMPLIFIER ADJUSTMENTS.
4-18. The amplifier contains three adjustable com-
ponents which are used to obtain specified amplifier
performance with the normal variations in replace-
ment tubes and parts values. Resistor R27 adjusts
the dc heater voltage applied to VI and V2. Resistor
R6 adjusts amplifier gain at middle frequencies. Ca-
pacitor C 11 adjusts amplifier gain at high frequencies.
Instructions for making each adjustment are given
in the following paragraphs.
4-19. ADJUSTING V1 & V2 HEATER VOLTAGE.
4-20. The heater of VI and V2 are supplied with dc
power to reduce line-frequency ripple in the ampli-
fier output. The power is obtained from a full-wave
selenium rectifier bridge through an adjustable series
resistor, R27. Resistor R27 permits resetting the
heater voltage as the rectifier ages and its internal
resistance increases. The adjustment must be made
at six-month intervals and when the rectifier is re-
placed. To adjust R27 proceed as follows:
a. Remove amplifier bottom plate; connect ampli-
fier to power source, turn on and allow 3-minute
warmup.
b. Measure the dc voltage from the positive termi-
nal of C7 to chassis. This voltage must be 6.3 volts
when the line voltage is 115 volts.
c. If necessary, adjust R27 to obtain 6.3 volts. After
a 24-hour run-in, recheck voltage to see that it has
settled.
d. Measure the ac voltage across C7. If it is greater
than 150 millivolts, check the capacity of C7.
e. The adjustment is completed; replace amplifier
bottom plate and return amplifier to normal service.
4-21. ADJUSTING AMPLIFIER GAIN.
4-22. Amplifier gain at low and middle frequencies
for both the 20 and 40 db positions of the GAIN switch
is set by a potentiometer on top of the amplifier
chassis. The adjustment per-mitt;' setting the gain of
either range exactly, or diViding any small error
equally between the two ranges. Amplifier gain at
high frequencies for both the 20 and 40 db settings is
set by a trimmer capacitor on the bottom of the ampli-
fier chassis. This adjustment penn its setting the
gain of either range at some selected high frequency
to equal the low-frequency gain, or pennits .dividing
any small error between the ranges, and frequencies.
Both adjustments are required after replacement or
aging of VI, V2, V3, R3 or C12. To adjust the gain
of the amplifier proceed as follows:
a. Connect amplifier and test equipment as shown
in figure 4-1 using the 400D Voltmeter to alternately
measure the input and output signal voltage levels
from the amplifier.
VOLTMETER
4000
@
@
o
00
o
o
o
AMPLIFIER
450A
OUTPUT /';. /' INPUT
/'/'/'
-
--------- ...,.",/
- - - - ~- CONNECT LEADS HERE TO
MEASURE AMPLIFIER
OUTPUT.
CONNECT
LEADS HERE TO
MEASURE AMPLIFIER INPUT.
o
USE OPEN WIRE LEADS LESS THE
ONElI) FOOT IN LENGTH FOR
MEASURING IAND 2MC GAIN.
Figure 4-1. Test Setup for Measuring Amplifier Gain
ADJUSTABLE LINE
TRANSFORMER
o
TO
POWER
SOURCE
~------------~O-U~T~PU""~~ ::: -
--
--
--~
o
HEWLETT- PACKARD
MODEL 650A
OR EQUIVALENT
FOR MEASURING 10 CPS -2MCS GAIN
)
00001-1
4-3

Section IV
Paragraphs 4-22 to 4-23
b. Set the oscillator output to any convenient fre-
quency between 100 and 10,000 cps and the output
voltage to exactly -20 db as read on the 4000 Volt-
meter connected to the oscillator output.
c. Set the amplifier to 40 DB and measure the open-
circuit output signal level with the 4000 Voltmeter.
d. If necessary adjust R6 to obtain a reading of ex-
actly +20 db on the voltmeter. Vary line voltage
between 104 and 127 volts to be sure gain remains
within specifications.
e. Set the amplifier to 20 DB and increase the oscil-
lator output voltage to 0db as read on the 4000 Volt-
meter connected to the amplifier input.
f. Measure the open-circuit output level from the
amplifier which must be within 1/4 db of the reading
obtained in step d.
g. Adjust R6 so that the difference between the 20
and 40 db gains is divided equally about +20 db on the
voltmeter scale. The gaib tolerance is ± 1/8 db on
each range. If the gain difference is greater than
the specified tolerance, R3 in the amplifier or the
voltage range switch in the voltmeter is inaccurate,
or VI or V2 may be defective.
h. Repeat steps band c using an oscillator frequency
of 2 mc.
i. If necessary adjust Cll to obtain an output voltage
within ±1db of +20 db. Vary line voltage from 104
to 127 volts to be sure gain remains within specifi-
cations.
j. Set the amplifier to 20 DB, set the oscillator fre-
quency to 1 mc and increase the oscillator output
voltage to 0db as read on the 400D Voltmeter con-
nected to the amplifier input.
AUDIO OSCILLATOR
205AG
AMPLIFIER
450A
TO
POWER
SOURCE -
ADJUSTABLE LINE
TRANSFORMER
Mode14S0A
k. Measure the open-circuit output voltage from
the amplifier. If necessary refine the adjustment
of Cll so the output level is within ± 1/2 db of +20 db
on the voltmeter.
m. Recheck the 40 db gain at 2 mc. If a satisfactory
compromise cannot be reached for these high fre-
quency gain measurements, the value of C12 may
require adjustment. Increasing C12 increases the
gain of the amplifier at high frequency.
n. In the same manner, amplifier gain at low fre-
quency may be checked using a voltmeter such as
the Model 403A. If the low-frequency gain is below
that specified, check the coupling capacitors and
tubes.
p. The gain adjustment is completed; replace ampli-
fier cover and return amplifier to normal service.
4-23. NOISE AND DISTORTION MEASUREMENT.
4-24. Distortion in the amplifier output is measured
by applying a pure sine-wave signal to the amplifier
input and measuring the harmonics of this signal in
the amplifier output after rejecting the fundamental
frequency. The Model 330B Distortion Analyzer is
an electronic ac voltmeter preceded by an electronic
frequency-rejection filter which is adjustable from
20 cps to 20,000 cps. After the fundamental frequency
is rejected by the filter, the total level of all re-
maining signals is measured by the voltmeter. This
level consists of random noise, line-frequency ripple,
and all harmonics of the applied signal frequency in-
cluding those in the applied signal. To measure dis-
tortion and noise, proceed as follows:
a. Connect the test equipment as shown in figure 4-2,
turn on and allow a ten-minute warmup of all instru-
ments.
DISTORTION ANALYZER
3308
~~~
G~~@~~=
3000
l'zWATT
COMPOSITION
RESISTOR
4-4
Figure 4-2. Test Setup for Measuring Amplifier Distortion and Noise
00001-1

Model 450A Section
IV
b. Set the front-panel controls on the amplifier as
follows:
d. Set the front-panel controls on the distortion ana-
lyzer as follows:
e. After a lO-minute warmup connect the amplifier
INPUT terminals to the METER INPUT terminals on
the analyzer, and adjust the AMPLITUDE CONTROL
on the oscillator to obtain exactly 0.1 volt on the
analyzer.
c. Set the front-panel controls on the oscillator as
follows:
FREQUENCY dial - - - - - - - - - - - - 20
FREQUENCY range - - - - - - - - Xl
OUTPUT ATTENUATOR (upper) - - 30
OUTPUT ATTENUATOR (lower) 5
AMPLITUDE - - - - 0
IMPEDANCE ~O
POWER ON
LOAD - - - - OFF
f. Set the analyzer function switch to SET LEVEL;
meter range switch to 100% (10 VOLT) and connect
the analyzer AF INPUT terminals to the amplifier
OUTPUT terminals. Adjust the analyzer INPUT sen-
sitivity control to obtain afull scale reading on the
0-1 scale on the analyzer meter.
g. Set the analyzer function selector to DISTORTION
and tune FREQUENCY dial for adip. Reduce setting
of the meter range switch as necessary and tune
analyzer FREQUENCY and BALANCE controls for a
minimum reading. The final reading in distortion
must be less than 1%. If it is higher than this, mea-
sure the distortion in the oscillator output alone which
should be less than 0.5%.
i. Disconnect oscillator from amplifier INPUT termi-
nals, and short the input terminals together with
a wire jumper.
h. Repeat above procedure using an oscillator fre-
quency of 20,000 cps. Again, distortion must be
below 1%.
j. Set the analyzer function switch to SET LEVEL
and set the INPUT sensitivity control to MAX; set
the meter range switch to the 0.03 range. The actual
voltage input is now only 0.1 that indicated on the
meter scale. The input voltage must not exceed
4 millivolts.
k. Set the amplifier GAIN switch to 20 DB. The
analyzer voltmeter should indicate less than 2.5 milli-
volts using the same XlO factor used in step j.
ON
- - 40 DB
MIN
- - Xl
20
- METER
.10 VOLT
AF
- - - - - ON
POWER switch
GAIN switch - -
INPUT SENSITIVITY- - - - - -
FREQUENCY range - - - - -
FREQUENCY dial- -
Function switch - - - -
Meter Range switch - -
AF-RF selector
Power switch - - - -
)
)
)
4-5

Section IV
Figure 4-3
V7
V6 FI
V5
V4
Model 450A
CRI
VI
R6
II
C2
CII
C4
4-6
Figure 4-3. Top View of Model 450A
00001-1

)
)
)
Model 450A
V4 PI R21
R3C
V5
FI V6
V7
R3B
R3A
Section IV
Figure 4-4
R6
R2
VI
r-----CI
00001-1
Figure 4-4. Bottom View of Model 450A
4-7

~
8-
~
•
(Jl
~
"Ijtn
.....
(l)
~
8.
~
g
.....
,<
(Jl
RO
NOTES
UNLESS OTHERWISE NOTED,
VOLTAGES ARE
DC,
MEASURED
TO
GROUND
BY
A
VTVM
WITH
100
MEGOHM
I~OUT
IMPED-
ANCE.
LINE VOLTAGE SET
TO
115
VOLTS,
60
CPS
INPUT TERMINALS SHORTED.
GAIN
SET
TO
40
DB.
o
o
NC
2nd
AMPLIfiER
V2
5654
1st
AMPLifiER
VI
5654
71<
o
180
70V
lOOK
1
MEG
220
R8
I
0
101<~
I0
147
1001<
5001< II
188V
600K
'''5
V
'"
lL'"
82K
147
V
70K
195
V
3901<~
LOOI<
ex:>
-
ex;
C?-
O
0
00
II1
MEG
215V
lOOK
II
471<
195V
II
1001<
2200
R82
l80V
i2'Oi<
Figure
4-5.
Voltages and
Resistances
on Tube Sockets and
Terminal
Boards
lOOK
215V
3.6
V
o
o
NC
NC
NC
390
V
----ex;
147V
70K
j-
-
_.
NC
,'-
NC
J£..Y
100
K
REGULATOR
CONTROL
V6
6AY6
NC
00
147
V
lOOK
80V
RECTifiER
V4
LINE
V.
5Y3GT
I=
375
VAC
i"5OO
390V
00
NC NC
'
•
I
00
8
8
....
I
....

"--
---./
"'"
en
o
:>
~
8-
(ll
-
@]
RI9
56K
10UTPUTI
C6
20UF
!).
R29
150
RI8
10K
3RD
AMPL
V3
5654
~
RI7
IMEG
C4C
10UF
CII
@
1.5/7
(FREQ.
RESPONSE
AOJUST)
C5
.22UF
RI5
15
K
!).
C4a
10UF
RI4
47K
D
.C4A
-,'
10UF
2ND
AMPL
V2
5654
~r-
RI2
200
RII
~
RI3
I
MEG
S
220
C2c
10UF
C3
.22
UF
®j+
R6
2500
(GAIN AOJ)
R9
10K
RIO
2200
R8
47K
D
+.1.
C2A
-TIOUF
R3A
1625
R3a
150
CI2
390
(NOTE
3)
OIGAINI
20
OB
RI
I
MEG
SI
40
OB
1ST
AMPL
VI
5654
~
..
CI
.22UF
IINPUTI
o---l~
1"\
R2
I
@]
220
§
.-
I
.-
C8C°..l:
C80..l:
20UF
~
20UF
'T_
R26
82K
+210 V(REGULATEO)
R23
~
R24
10K
~
33K
R25
(NOTE 4)
RI6
1500
R28
680
REGULATOR
AMPL
V6
6AV6
~DC8a
:r-
20UF
R21
500
V2
C8A!).I+
20UF
+390V
+6.3
V
!).
RECTIFIER
V4
5Y3GT
2 3
325
V
RMS
325V
RMS
~
6.3)
RMS
~
V5
=?
V6
TI
BLACK-
GREEN
BLACK
BLACK-
YELLOW
BLACK-REO
115V
115V
~
":"
IFUSEI
§]
FI S2
RO
"'"
I
'0
.......
"'"
I
.-
o
NOTE
I.
FOR
OPERATION
ON
230
VOLT
LINES,
REMOVE
115
VOLT
JUMPERS
AND
AOO
230
VOLT
JUMPER.
NOTE
2. UNLESS OTHERWISE INOICATEO, RESISTANCE
IS
IN
OHMS, CAPACITY IN UUF.
NOTE
3.
ELECTRICAL VALUE SELECTEO
FOR
BEST HIGH
FREQUENCY RESPONSE.
NOTE
4. ELECTRICAL
VALUE
SELECTED
FOR
t210V
~5V
REGULATEO
Bt.
Figure
4-6.
Schematic
Diagram
Model 450A
~C/)
oq(ll
c:
()
~
g.
"",=:I
1-
0-<

Model 450A
SECTION V
REPLACEABLE
PARTS
Section V
Paragraphs 5-1 to 5-7
5-1. INTRODUCTION.
5-2. This section contains information for ordering
replacement parts for the Model 450A Amplifier.
5-3. ORDERING INFORMATION.
5-4. To order a replacement part, address order
or inquiry either to your local Hewlett-Packard rep-
resentative or to
CUSTOMER SERVICE
Hewlett-Packard Company
395
Page Mill Road
Palo Alto, California
5-5. Specify the following information on the part:
a. Model and serial number of instrument.
b. Hewlett-Packard stock number.
c. Circuit reference designator.
d. Description.
5-6. Parts not listed in table 5-1 can be ordered
by giving a complete description of part including its
function and location in the circuit.
5-7. Recommended spare parts for complete main-
tenance during one year of isolated service are listed
in the <IRS" column of the parts list.
Circuit
Description
Mfr. •
~
TQ RS
Ref.
Stock No.
C1 Capacitor: fixed, paper,
56289 0160-0018 1 1
.22 J.Lf ±10%, 400 vdcw, 1250C
)C2ABC
Capacitor: fixed, electrolytic,
00656 0180-0016 21
3
sections, 10 J.Lf/sect., 450 vdcw
C3 Capacitor:
fixed, paper,
56289 0160-0017 21
.22 J.Lf ±20%, 400 vdcw
C4ABC
Same as C2
C5 Same
as C3
C6
Capacitor:
fixed, electrolytic,
56289 0180-0011 11
20 J.Lf, 450 vdcw
C7
Capacitor: fixed, electrolytic,
56289 0180-0028 11
2
sections, 1500 J.Lf/sect., 15 vdcw
C8ABCD
Capacitor:
fixed, electrolytic,
56289 0180-0025 11
4
sections, 20 J.Lf/sect., 450 vdcw
C9,10 Not assigned
Cll
Capacitor:
variable, ceramic,
72982 0130-0003 1 1
1. 5-7 pf, 500 vdcw
C12
Capacitor:
fixed, mica,
00853 0140-0016 11
390 pf ±
5%, 500 vdcw
•
Refer to " List of Manufacturers" .RS
Recommended spares for one year
TQ
Total Quantity used in the instrument.
isolated service for one instrument.
)
Figure 5-1. Replaceable Parts (Sheet 1of 4)
00001-1
5-1

Section VModel 450A
Circuit
Description
Mfr. •
~
TQ
RS
Ref.
Stock No.
CR1
Rectifier, metallic
84970 1882-0002 11
DS1
Lamp, incandescent: 6.3V,
.15 amp,
24455 2140-0012 11
2
pin base, GE #12
F1
Fuse, cartridge: 0.8 amp,
75915 2110-0020 110
slow-blow, 115V operation
Fuse, cartridge: 0.4 amp,
75915 2110-0019
slow-blow, 230Voperation
P1
Power Cable
70903 8120-0050 11
R1
Resistor:
fixed, composition,
01121 0690-1051 31
1
megohm ±10%, 1 W
R2
Resistor:
fixed, composition,
01121 0687-2211 21
220
ohms
±10%, 1/2 W
R3
Resistor:
fixed, wirewound, 28480 45A-26A 1 1
1625, 150,
17,600 ohms
R4,5
Not assigned
R6
Resistor:
variable, composition,
71590 2100-0067 1 1
2500
ohms
± 20%, 1/2 W
R7 Not
assigned
R8
Resistor:
fixed, composition,
01121 0690-4731 2 1
47,000 ohms
±10%, 1 W
R9
Resistor:
fixed, composition,
01121 0690-1031 1 1
10,000 ohms
±10%, 1 W
R10
Resistor:
fixed, composition,
01121 0690-2221 1 1
2200
ohms ±10%, 1 W
R11
Same as R1
R12
Same as R2
R13
Resistor:
fixed, composition,
01121 0690-2211 1 1
220
ohms ±10%, 1 W
R14
Same as R8
R15
Resistor:
fixed, compos ition, 01121 0693-1531 1 1
15,000 ohms
±10%, 2 W
R16
Resistor:
fixed, composition,
01121 0690-1521 1 1
1500
ohms ±10%, 1 W
•
Refer to "List of Manufacturers".
TQ Total Quantity used in the instrument.
RS Recommended spares for one year
isolated service for one instrument.
5-2
Figure 5-1. Replaceable Parts (Sheet 2 of 4)
00001-1

Model 450A Section V
Circuit
Description Mfr. *
<Fp
TQ
RS
Ref. Stock No.
R17
Same as R1
R18
Resistor:
fixed, composition,
01121 0693-1031 21
10,000 ohms ±10%, 2 W
R19
Resistor:
fixed, composition,
01121 0690-5631 1 1
56,000 ohms ±10%, 1 W
R20 Not
assigned
R21
Resistor:
fixed, wirewound, 35434 0816-0003 1 1
500
ohms ±10%, 10 W
R22
Resistor:
fixed, composition,
01121 0690-5641 1 1
560,000 ohms ± 10%, 1 W
R23
Same as R18
R24
Resistor: fixed, composition,
01121 0690-3331 1 1
33,000 ohms
±10%, 1 W
R25
Resistor:
Optimum value selected at
factory.
R26
Resistor: fixed, composition,
01121 0690-8231 1 1
82,000 ohms
±10%, 1 W
R27
Resistor:
variable, wirewound, 28480
M-77 1 1
)
linear taper, 10 ohms
R28 Resistor:
fixed, composition,
01121 0687-6811 1 1
680
ohms ±10%, 1/2 W
R29
Resistor:
fixed, composition,
01121 0690-1511 11
150
ohms
±10%, 1 W
Sl,2
Switch, toggle
04009 3101-0001 21
T1
Transformer, power
28480 9100-0016 11
.
V1, 2, 3
Tube,
electron:
5654 86684 1923-0001 33
V4
Tube, electron:
5Y3GT 86684 1930-0010 1 1
V5 Tube,
electron: 6AU5GT 33173 1923-0020 11
V6
Tube,
electron: 6AV6 82219 1939-0001 1 1
V7 Tube,
electron: OA2 97966 1940-0004 1 1
)*
Refer to II List of Manufacturers"
TQ Total Quantity used in the instrument.
RS Recommended spares for one year
isolated service for one instrument.
Figure 5-1. Replaceable Parts (Sheet 3of 4)
00001-1 5-3

Section VModel 450A
Circuit
Description
Mfr. •
~
TQ
RS
Ref. Stock No.
MISCELLANEOUS
Binding
Post Assembly: black
28480 AC-10C 2 1
Binding
Post Assembly: red
28480 AC-10D 2 1
Holder, fuse
75915 1400-0007 11
Insulator,
binding post
28480 AC-54A 2 0
Insulator,
binding post
(single) 28480 AC-54D 2 0
Lamp holder for DS1
72765 1450-0022 1 0
Jewel for lampholder
72765 1450-0020 10
Shield, tube:
1-3/8
11
long 71785 1220-0011 3 0
•
Refer to II List of Manufacturers".
TQ Total Quantity used in the instrument.
RS Recommended spares for one year
isolated service for one instrument.
5-4
Figure 5-1. Replaceable Parts (Sheet 4of 4)
00001-1