HP 711A User manual

HP Archive
This vintage Hewlett Packard document was
preserved and distributed by
www.hparchive.com
Please visit us on the web !
Scanned by on-line curator: Tony Gerbic
** For FREE Distribution Only ***

~
I
~
;I
I
71lA
I
I
~
~
i
~. ;i
I
POWER
SU PPLY
SERIALS PREfiXED: 002-
I
i
~ II
II
I: i
J
~
I
~
!
i!
I
I
~
~
~ ,
~
~
I
OPERATING AND SERVICING MANUAL
~
~
t.
~
I

)
OPERATING AND SERVICING MANUAL
MODEL 711A
POWER SUPPLY
SERIALS PREFIXED: 002-
Copyright HEWLETT-PACKARD COMPANY 1956
275 PAGE
MILL ROAD, PALO ALTO, CALIFORNIA, U. S. A.
711A004 -3/1-60

)
OUTPUT VOLTAGES
DC Regulated High Voltage:
AC Unregulated:
REGULATION
RIPPLE
METERING
Current Meter:
Voltage Meter:
TERMINALS
OVERLOAD PROTECTION
POWER
SIZE
Cabinet Mount
Rack Mount
WEIGHT
Cabinet Mount:
Rack Mount:
SPECIFICATIONS
o to 500 volts (without switching), 100 rna maximum load.
6.3 volts, 6 amps maximum load; 12.6 volts CT, 3 amps maxi-
mum load
For line voltage 115/230 volts ±10%, less than 0.5% change or
1. 0 volt chang~, whichever is greater; from no load to full load,
change of less than 0.5% or 1. 0 volt (whichever is greater).
Less than 1. 0mv
o to 100 rna; 0 to 10 with push-button
o to +500 volts; 0 to +50 volts with push-button
Either positive or negative dc regulated high voltage terminal may
be grounded
AC line fused. Overload relay prevents dc output from greatly
exceeding current rating of output milliammeter thus protecting
instrument from overload conditions including short circuit output.
115/230 volts ±10%, 50/1000 cps. Approximately 145 watts de-
pending on load and line voltage.
7-3/8 in. wide, 11-1/2 in. high, 14-1/4 in. deep.
19 in. wide, 7in. high, 12-7/8 in. deep behind panel.
Net: 20 lbs., shipping: 26 lbs.
Net: 24 lbs., shipping: 35 lbs.

SECTION I
CONTENTS
GENERAL DESCRIPTION
1 - 1
1 - 2
1 - 3
1 - 4
General Description
Inspection ....
Power Cable. . .
230-Volt Operation
1-1
I - 1
1- 2
I - 2
SECTION II
OPERA TING INSTRUCTIONS
2 - 1
2 - 2
2 - 3
Controls and Terminals .
Operating Procedure
Output Options . . . . .
II -1
11-2
II - 3
SECTION ill
CIRCUIT DESCRIPTION
3 - 1
3 - 2
3 - 3
3 - 4
3 - 5
General Description. . . . . .
Input .
Regulation. .........
Setting of Output Voltage Level.
Overload Relay. . . . . . . .
ill -1
ill -2
ill -2
ill -3
ill -5
SECTION IV MAINTENANCE
4 - 1
4 - 2
4 - 3
4 - 4
4 - 5
4 - 6
4 - 7
4 - 8
4 - 9
4 - 10
General .....
Cover Removal
Tube Replacement
Replacement of Electrolytic Capacitors .
Replacement of Variable Resistors. . .
Replacement of Rectifiers. ......
Meter Zero Adjustment . . . . . . . .
Power Transformer Primary Connections.
Trouble Shooting Chart
Trouble Localization . . . . . . . . . .
IV -1
IV -1
IV -1
IV -2
IV -2
IV - 3
IV -3
IV - 3
IV -4
IV - 6
SECTION V
TABLE OF REPLACEABLE PARTS
5 - 1 Table of Replaceable Parts . . . . . . . . . . . . . . . . . . V - 1

Sect. I Page 1
SECTION I
GENERAL DESCRIPTION
,------------------ CAUTION -------------------,
Dangerous voltages are present at the terminals and within this instrument
)
)
1·1 GENERAL DESCRIPTION
The Model 71lA Power Supply is a general-purpose
low-power d-c and a-c voltage supply particularly
suited to powering experimental setups.
By means of the facilities provided by the Model
711A the following voltages are made available at
the output terminals on the control panel:
Unregulated ac:
6.3 volts, 3 amperes maximum load current
(two supplies) or
6.3 volts, 6 amperes maximum load current
(one supply) or
12.6 volts, 3 amperes maximum load current
(one supply, tapped at 6. 3V).
Regulated dc:
oto 500 volts, continuously variable; maxi-
mum output load current, 100 mao
NOTE: Insulation within the Model 711A permits
operating the d-c output voltage as much as 500 volts
from chassis ground so that two Model 71lA power
supplies may be operated in series to obtain 1000
volts d-c output while each instrument chassis re-
mains at ground potential.
The d-c output of the Model 71lA has high stability;
for line voltage variations within rated limits, the
level of the regulated output will vary less than O. 5%
or 1 volt (whichever is greater), and from no load
to full load the level of the output will vary less than
0.5% or 1 volt (whichever is greater). Ripple will
be less than 0.001 volt.
While the internal impedance of the Model 711A will
vary both with the d-c load current and the frequency
of any reflections from the equipment being powered,
the internal impedance of the Model 711A will be
less than 10 ohms with any load current and at any
frequency up to afew megacycles.
The dc output is continuously monitored by two
meters, a voltmeter and a milliammeter. Alow
and high range are provided for each meter so that
low values of voltage and current may be read accu-
rately.
The power supply is protected from input or out-
put overload by (1) afuse in the line-voltage input
circuit and (2) a relay, in the main positive bus,
which operates at overload current to interrupt con-
duction through the regulator.
1·2 INSPECTION
This instrument was thoroughly tested and inspected
before being shipped, and is ready for use when re-
ceived.
After the instrument is unpacked, it should be in-
spected carefully for damage received in transit.
If any shipping damage is foUId, follow the procedure
outlined in the" Claim for Damage in Shipment"
sheet in this instruction manual.

Sect. I Page 2
1.3 POWER CABLE
The three-conductor power cable supplied with this
instrument is terminated in a polarized three-prong
male connector recommended by the National Elec-
trical Manufacturers' Association. The third contact
is an offset round pin added to a standard two-blade
connector which grounds the instrument
chassis when
used with an appropriate receptacle. To use this
connector with a standard two contact receptacle,
an adapter should be used to connect the NEMA con-
nector to the two-contact
system. When the adapter
is used, the third contact is terminated in a short
lead from the adapter which can then be connected
to the outlet mounting box in order to ground the
instrument chassis.
1·4 230·YOLT OPERATION
This instrument is normally shipped from the
factory with the dual 115 volt primary windings
of
the transformer connected in parallel for oper-
ation from a nominal 115 volt source. If oper-
ation from a nominal 230 volt source is desired,
the windings may easily be reconnected in series.
Refer to the schematic drawing for details.
The power fuse must be changed from a1. 6 am-
pere slow-blow fuse to a 0.8 ampere slow-blow
fuse.

)
)
2.1 CONTROLS AND TERMINALS
All controls and terminals except the fuseholder
are mounted on the front panel. The fuseholder is
mounted on the rear plate of the instrument.
Voltmeter -
This sin~le-scale, two-range (0 to 500 volts; 0to
50 volts) voltmeter indicates the voltage level at the
output of the main regulator. With the DC VOLTAGE
switch
at ON, the level of voltage at the DC VOLT-
AGE output terminals is indicated by the voltmeter.
Normally the meter indicates on the 0- to 500-volt
range; with the
50 VOLTS FULL SCALE push-button
switch
depressed, the meter indicates on the 0- to
50-volt range.
Milliammeter -
This single-scale, two-range
(0 to 100 milliamperes;
o to 10 rna) milliammeter indicates the value of the
d-c l.)ad current. Up to 100 rna can flow in the
load circuit without overloading the milliammeter.
Normally the meter indicates on the 0- to 100-ma
range; with the 10 MA FULL SCALE push-button
depressed, the meter indicates on the 0- to 10-ma
range.
50 VOLTS FULL SCALE -
When
operated (depressed), this SPDT push-button
switch opens the high-range series multiplier re-
sistor and inserts the low-range multiplier.
10 MA FULL SCALE -
This push-button switch, which is ccnnected for
DPST operation, controls the proportion of current
diverted by the respective shunts across (1) the
milliammeter and (2) the protective relay in series
with the milliammeter. When the 10 MA FULL
SCALE switch is operated, the protective relay
operates at between 11 and 17 rna to interrupt con-
duction through the regulator and thereby to inter-
rupt the flow of current through the milliammeter.
Sect. II Page 1
SECTION II
OPERATING INSTRUCTIONS
With the switch at normal, the protective relay oper-
ates at between 110 and 170 rna.
D-C VOLTS ADJ.
Acijustment of the regulated d-c voltage to the desired
level is by means of the FINE and COARSE control
mounted unQ'er the D. C. VOLTS ADJ. designation.
The level of voltage obtained at any given setting
of the controls is indicated by the voltmeter, and
the resulting flow of current in the load circuit is
indicated by the milliammeter.
COARSE -
Operation of the COARSE control (1) adjusts the
setting of a I-megohm variable resistor, R11, and
(2) operates two microswitches, SIA and SIB.
a. Variable resistor R11 is part of the voltage
divider in the circuit which controls the level
of the regulated d-c output voltage.
b. The microswitches make connection to various
taps on the power transformer secondary wind-
ing which
furnishes voltage for the main d-c supply
circuit. At the low-voltage position (ccw) of the
COARSE control, the main d-c supply circuit is fed
by
the low-voltage section of the winding. As the
control
is turned cw, the microswitches are actuated
to complete connection to the higher voltage taps.
FINE -
Operation of the FINE control varies the setting of
variable resistor R12. This resistor also is part
of the voltage divider in the circuit which controls
the level of the regulated d-c output voltage.
Indicator Lights -
There are two indicator lights on the ccntrol panel:
AC'VOLTAGE - This red indicator light glows
to indicate that power is applied to the instrument
circuits.

Sect. II Page 2
DC VOLTAGE -
The operating circuit of this in-
dicator light is controlled by the DC VOLTAGE
switch, and the light glows red when the switch is
at ON to indicate that voltage is applied to the DC
VOLTAGE
output terminals.
AC VOLTAGE Switch -
This SPST toggle switch is in the primary circuit
of the power transformer. With the AC VOLTAGE
switch
at ON, line voltage is closed to power trans-
former T1.
DC VOLTAGE Switch -
There is no voltage on the DC VOLTAGE output ter-
minals until the DC VOLTAGE switch is at the ON
position. When operated, this DPST toggle switch:
'(1) connects the positive d-c bus to the DC VOLTAGE
output
terminals and (2) closes the circuit to the DC
VOLTAGE indicator light.
Output Terminals -
Both the AC VOLTAGE and DC VOLTAGE output
terminals are of the binding-post type, will accom-
modate either a banana plug or wire, and are so
arranged that any banana plug with 3/4-inch spacing
may be used.
AC VOLTAGE -
There are two pairs of output terminals associated
with the a-c voltage supply. Depending on how the
terminal connections are made (see paragraph 2-3
below), the Model 71lA may be arranged to supply
the following a-c voltages:
6.3 volts at 3 amperes (two circuits), or
6.3 volts at 6 amperes (one circuit), or
12.6 volts at 3 amperes (one circuit, tapped
at 6.3 V).
DC VOLTAGE -
There is one pair of output terminals for the regu-
lated d-c voltage supply: +and -. The binding-post
nuts for the + and - terminals are insulated. Neither
the + nor the - terminal is connected to the chassis
within the instrument so that the d-c supply may be
operated either above or below ground by appropriate
external connedion to ground.
On the same mounting plate with the + and - termi-
nals is a terminal (G) which is ccnnected to the in-
strument chassis. The G terminal is cmnected to
earth ground when the power-cable connector is
plugged into a grounded female connector.
FUSE -
The fuseholder, which is mounted on the rear plate
of the instrument, contains the time-delay cartridge
fuse which protects the input circuit. Before start-
ing to install anew fuse, check that the power cable
is disconnected from the line. Replacement fuses
must be of the slow-blow type: 1. 6-ampere fuse
for 115-volt operation or a O. 8-ampere fuse for
230-volt operation.
2-2 OPERATING PROCEDURE
Be sure the Model 711A is so placed that nothing
can obstruct the ventilating louvers in the sides of
the cabinet. Safe operating temperatures with the
cabinet depend upon free air flow through the louvers.
a. Before operating the instrument for the first
time, see paragraph 4-7, Meter Zero Adjustment.
b. Check that both the
AC VOLTAGE and DC VOLT-
AGE switches are in the off position. After the
Model 71lA has been plugged into a power source of
specified voltage and frequency, turn the AC VOLT-
AGE switch to ON, and allow a two-minute warmup
period.
NOTE: If the Model 711A is to be operated from a
23Q:Volt
source, check (1) that power transformer
T1 is strapped for 230-volt operation (strapping
options are shown on the schematic diagram), and
(2) that fuse F1 is a O. 8-ampere Slo-Blo fuse. See
paragraph 4-8.
With the DC VOLTAGE switch still in the off position,
connect
the load. For connection arrangements for
the various options, see paragraph 2-3, below.
c. Check that the COARSE control is in its maxi-
mum counterclockwise (low-voltage) position.
Turn the DC VOLTAGE switch to ON.
d.
To obtain the desired level of d-c voltage, ad-
just the COARSE and FINE controls. The volt-
meter indicates the level of the d-c voltage being
supplied to the +and -output terminals. If the level
of the d-c supply is below 50 volts, the voltmeter
may be operated on the 50-volt range by depressing
the 50 VOLTS FULL SCALE push-button during the
voltage adjustment procedure.

)2·3
OUTPUT OPTIONS
A-C Options - (Figure 2-1)
The a-c supply may be arranged for anyone of three
options:
Two 6.3-volt, 3-ampere supplies (Figure 2-1A)
One 6. 3-volt, 6-ampere supply, by connecting the
two 6. 3-volt supplies in parallel (Figure 2-1B)
One 12.6-volt, 3-ampere supply, by connecting the
two 6. 3-volt supplies in series (Figure 2-1C)
Sect. IT Page 3
D-C Options -
Among the operating options for which the d-c voltage
supplyterminationsmay be arranged are the following:
oto 500 volts, positive or negative with respect to
chassis ground.
oto 500 volts, neither side grounded. (It is recom-
mended that the instrument chassis be grounded
whenever both d-c terminals are operated at apoten-
tial above or below ground.)
Up to 1000 volts, by connecting two Model 711A IS
in series.
TO
LOAD
6.3V 6.3 V
3A 3A
EJOI
tAl
TO
LOAD
6.3V 6.3 V
3A 3A
(8)
TO
LOAD
'" "" \"
STR_AP-+-+--, ~r ,~,
(C)
)
)
Figure 2-1. Model 71lA Connection Arrangements for A-C Supply Options

Sect. III Page 1
)
SECTION III
CIRCUIT DESCRIPTION
].1 GENERAL DESCRIPTION
The Model 711A Power Supply furnishes a regulated
variable d-c voltage (HV supply) and an unregulated
a-c voltage. Regulation of the HV supply is obtained
by
means of a main regulator, which regulates the
voltage supplied to the DC VOLTAGE output termi-
nals, and a seccndary regulator which regulates
the voltage which supplies the reference voltage and
most of the operating potentials for the regulator
circuits. Arrangement of the main components of
the
d-c supply circuit is indicated in block diagram
form in Figure 3-1, and detailed circuitry of the
Model 711A
is shown in the schematic diagram.
ence to the reference voltage bus (which is approx-
imately 200 volts negative with respect to the main
negative bus).
Power from an external source is applied to the
Model 711A
through power transformer T1. Volt-
age for the HV supply is taken from aT1 secondary
winding which is tapped for various output voltages
and, by means of connections through microswitches
'operated by the COARSE control, provides an in-
put which is variable (paragraph 3-4b). Voltage
from the tapped secondary feeds selenium rectifiers
SR2, SR3, and capacitors C2, C3 connected as a
voltage doubler.
On the schematic, voltages shown for the main posi-
tive bus, the HV voltage supply, and the main series
regulator are with reference to the main negative
bus; those shown for the main control tube, cathode
follower,
secondary regulator (V3A and V3B), and
secondary regulator voltage supply are with refer-
From the doubler, the positive bus is brought through
the winding of overload
relay K1 {para. 3-5), the se-
ries regulator, V1 and V2 (para.3-3), the OC VOLT-
AGE switch, and the milliammeter, to the OC VOLT-
AGE +output terminal. The voltmeter is connected
across the main positive and negative busses. With
the output
circuit so arranged, there is continuous
MAIN NE~nVE' BUS
num
NIIL[I
SRl • SR]
C2. C3
~(
NICIIOlTlI£
SUIILI
TI/I50V-265V
/,-1
111
SIIItH!S f- - - ------ - --- - - - --- --- - - - - --
/
/
// .--_----=MA:=:'::..N .:..:POSJ=nVF:.::-::8US=-- -+-_----.
r-~""""
REF. w;lt.TAGC /IUS
Figure 3-1. Model 711A Power Supply Block Diagram

·Sect. III Page 2
indication of the
level of the voltage between the DC
VOLTAGE +and -output terminals and of current
flow through the load. The Model 71lA circuit is dis-
cussed in greater detail in the following paragraphs.
discussion. The cathodes of the control tubes are
maintained at aconstant level by a voltage-reference
tUbe/cathode follower combination, a circuit designed
to accommodate the current through the cathodes of
both control tubes. The regulator
circuits are shown
in
Figure 3-2, a partial schematic.
].2 INPUT
Line voltage is applied to the primary of power
transformer Tl through fuse Fl and AC VOLTAGE
switch S5. To accommodate
operation from either
a 115-volt or a 230-volt source, the primary of
transformer Tl is arranged in two sections. For
operation from a 115-volt source the two sections
are strapped in parallel, and for operation from a
230-volt source, the sections
are strapped in series.
The schematic diagram shows the primary windings
strapped
for 115-volt operation, the standard factory
strapping.
Indicator light I 1 is connected across one of the fil-
ament windings of transformer Tl to give indication
as soon as the transformer is energized.
].] REGULATION
Regulation of the Model 71lA d-c output voltage is
obtained by using two electronic x:egulators which
are designated main and secondary in the following
a. Main Regulator -The control tube of the main
reguIator
compares a sample of the output volt-
age with a reference voltage, and any difference
between the two results in a compensating adjust-
ment in the amount of resistance inserted in series
with the main positive bus.
Pentode
V4B is the control tube and the series regu-
lator is pentodes Vl and V2 connected in parallel.
Aportion of the output voltage, sampled with respect
to the reference voltage bus, is applied to the grid
of control tube V4B, the cathode of which is held
at a constant potential. The plate of V4B is tied to
the grids of the series regulator tubes. With the
circuit so arranged, any rise or drop in the level
of the output voltage will cause achange in the po-
tential on the grid of the control tube, and also will
result in achange (in the reverse direction) in the
potential on the grids of the series regulator tubes.
By means of this circuitry, the series regulator
becomes avariable resistance which is electronically
actuated to increase or decrease as required to
maintain the output voltage at a constant level.
FROM HV
RECTIFIER
MAIN SERIES REG
TO DC OUTPUT
TERMINALS
C4
0'3
03'
V4B
MAIN
CONTROl. TUBE
,
I:::
\ _ .. -+--+----'
026
47K
024
lelK
C7
V3B
SEC
CONTROL TUBE
"
~:: \
'----+--+---~ --- I
V3 A
SEC SERIES REG
.J
FROM SEC
RECTIFIER
02.
144K
027 .......
t-_-.JV'OO""K_+-_---t_ --- \ V4A
) CATHOOE
" FOLLOWER
032
033
V5
VR TUBE
028
'OK
REF. VOLTAGE BUS
Figure 3-2. Model 711A Main and Seccndary Regulator Circuits Partial Schematic

)
)
For example, if there is a drop in the level of the
d-c output voltage, the potential on the grid of con-
trol tube V4B becomes more negative by comparison
with
the reference voltage on the V4B cathode, and
conduction in V4B will be cut down. As a result,
the potential on the plate of V4B and on the grids of
series regulator tubes V1 and V2 will rise. As con-
duction through V1 and V2 increases, their plate
resistances drop, with a resulting decrease in the
voltage drop across the series regulator and rise
in the level of the d-c output voltage.
The voltage divider through which the output voltage
is sampled is discussed in paragraph 3-4, below.
Any
ripple in the output voltage is coupled by capa-
citor C4 to the grid of control tube V4B.
The pentode connection for beam power amplifiers
V1 and V2 gives a series regulator which furnishes
high gain at moderate power cost. The separate
screen voltage supply for V1 and V2 is fed by recti-
fier SR1 connected across the 150-volt secondary
winding of transformer Tl.
b. Secondary Regulator - To regulate the low
end of
the 0- to 500-volt range, potentials ap-
plied to the electrodes of the main control tube must
be negative with respect to the main negative bus.
The secondary regulator, fed by the 285-volt secon-
dary winding of transformer T1 and full-wave sele-
nium rectifier SR4, is arranged to provide this supply
of
regulated negative voltage. In conjunction with
the
voltage-reference tUbe/cathode follower combi-
nation (see paragraph c, below), the secondary regu-
lator also provides the reference voltage for the
Model
71lA circuits.
The circuit of the secondary regulator is similar
to 'and functions in the same manner as the main
regulator. Triode V3A is the series regulator and
is in series with the positive side of the secondary
power supply. Pentode V3B is the control tube; its
cathode is held at a constant potential, a portion of
the output voltage
is applied to its grid, and its plate
is tied to the grid of series regulator V3A. The out-
put voltage is sampled with respect to the reference-
voltage bus by a voltage divider which consists of
precision
resistors R24 and R25. The values selected
for R24 and R25 are such that the level of the refer-
ence-voltage bus is established at approximately
200 volts below that of the main negative bus. Any
ripple in the output
is coupled to the grid of V3B by
capacitor C7.
c.
Reference-Voltage Supply for Control Tube
CathOdes -The amount
of current through the
cathodes of control tubes V3B and V4B is greater
than the current capacity of voltage-reference tube
V5.
Therefore a voltage-reference tube/cathode
Sect. ill Page 3
follower combination
is used to maintain the poten-
tial on the cathodes of the control tubes at aconstant
level.
Arrangement of the reference-voltage supply for
the control tube cathodes is indicated in Figure 3-2.
The cathode circuits of the control tubes and the
cathode follower are connected to the reference-
voltage bus through a common resistor, 10,000-
ohm R28, and therefore achange in the amount of
current through the cathode of one tube also will
effect achange in the potential on the cathode of the
other control tube and the cathode follower. How-
ever,
by connecting the grid of cathode follower V4A
to voltage-reference tube V5, the V4A grid is main-
tained at a constant potential, and thus achange in
the V4A cathode potential causes such change in
V4A ccnduction that the mdrop across R28 is main-
tained
at aconstant value.
For example, if the potential on the grid of main
control tube V4B goes negative, conduction in V4B
will be cut down, the
drop across R28 will be less,
and cathode potential will drop. Since the grid of
V4A is held at aconstant potential and the potential
on
its cathode is now more negative, there is less
difference in potential between grid and cathode,
and
V4A conduction will increase. The increase in
current through the V4A cathode will compensate
for the decrease in current through the V4B cath-
ode, the drop across R28 will be returned to proper
value, and potential on the cathode of each control
tube will be maintained at aconstant level regardless
of changes in the amount of current flowing through
the tube.
]·4 SEnlNG OF OUTPUT VOLTAGE LEVEL
a. General -The level of the d-c output voltage
may be
varied from 0 to 500 volts by adjusting
the level of the potential applied to the grid of main
control tube V4B. This adjustment is obtained by
operation of the COARSE and FINE controls.
If the HV supply input were the same for all out-
puts from 0to 500 volts, the excessive power dis-
sipated in the series regulator tubes would shorten
their life. Therefore the design of the Model 711A
includes a variable input for the HV supply.
The required variation in HV input is obtained by
operation of the COARSE control.
The arrangement of (1) the variable input and (2)
the voltage divider through which potential is ap-
plied to the grid of main control tube V4B are dis-
cussed in the follOWing paragraphs.

Sect. ill Page 4
SI A CAM
SIB CAM
J--+--- SI B ACTUATOR
TO + BUS
TO - BUS
150V
205 V
265 V
STOP CW 300
0
START CW 00
'1tr---Rl1
THROUGH VOLTAGE DIVIDER : , TO + BUS
TO CONTROL TUBE V4 B I I
+ 195 V± 20V -----fr;~ ~ +325V ± 20 V
I~\~ V~V
START CW STOP CW
00 300
0
Figure 3-3. Mode1711A Arrangement of Tap Switch Actuators and Cams on COARSE
Control Shaft FINE Control (not shown) at Electrical Center

)
b. Tap SWitching Arrangement, HV Supply -
The
Tl secmdary winding which feeds the high-
voltage supply
is tapped for 150, 205, and 265 volts,
and the
taps are brought out to contacts on two snap-
action, cam -actuated, SPDT microswitches, SlA
and SlB. So that SlB will operate before SlA, and
will be held operated during the time SlA is oper-
ated, the periphery of the high side of the SlB cam
is made longer than the periphery of the high side
of the SlA cam. Both cams are mounted on an
extension of the shaft of the COARSE control. Ar-
rangement of the COARSE control shaft, the cams
and switch actuators, the switch contacts, and con-
nections to the tapped winding of T1 are indicated
in Figure 3-3.
Through approximately 105 0of COARSE control
travel, the low side of each cam is toward its re-
spective switch actuator, therefore neither switch
is operated, and the voltage-doubler connection is
to the 150 -volt tap on the transformer secondary
winding. In this condition of the circuit (shown on
the schematic) with both switches at normal, the
level of the voltage doubler output will be approxi-
mately 400 volts.
For the next approximately 90 0of control travel,
the high side of the SlB cam is engaging the SlB
actuator, and operated SlB completes connection
to
the 205-volt tap. In this condition (indicated in
Figure 3-3), with SlB operated and SlA at normal,
the level at the voltage doubler output will be ap-
proximately 560 volts. With the FINE control set
at electrical center, at the point of change-over
from the 150-volt to the 205-volt connection, the
panel voltmeter indication will be approximately
195 volts.
Through the remaining travel of the COARSE con-
trol, the high side of the SlA cam is engaging the SlA
actuator and, with both switches operated, connection
is completed to the 265-volt tap. In this condition of
the supply circuit, the level
at the output of the volt-
age doubler will be apprOXimately 715 volts. With
the FINE control
set at electrical center, at the point
of change-over
from the 205 volt to the 265 volt tap,
the panel
voltmeter indication will be approximately
325
volts.
c. Main Control Tube -The potential on the grid
of main control tube V4B is applied through a
voltage
divider which is connected between the main
positive bus and the reference-voltage bus. The
divider includes four variable resistors, two of which
(R31
and R33) are adjusted at the factory and for
Sect. ill Page 5
the
purposes of this discussion, therefore, may be
considered fixed. Adjustments for the other two
variables (Rll and R12) are brought out to the front
panel as the COARSE and FINE controls. The mag-
nitude of the potential on the control tube grid, there-
fore, varies not only with the level of the voltage on
the main positive bus but also with the amount of
resistance in the variable arm of the voltage divider,
as fixed by the setting of the COARSE control and,
to a lesser extent, of the FINE control.
As explained in paragraph 3-3, the level of the d-c
output voltage is increased or decreased as the po-
tential on the grid of V4B becomes more negative
or more positive with respect to the reference volt-
age on the V4B cathode.
Unless it is necessary to replace control tube V3B
or V4B, and after tube replacement it is not possible
to
get rated output, it is improbable that the setting
of R31 and R33 will require readjustment. Procedure
for adjusting R31 and R33 after tube replacement is
given in paragraph 4-3c, below.
3·5 OVERLOAD RELAY
To protect the milliammeter, the Model 711A cir-
cuit is so arranged that if current flow in the main
positive bus reaches a value that can damage the
meter, ahigh negative voltage will be applied to the
grids of the series regulator tubes. Arrangement
of the circuit which protects the milliammeter is
shown in Figure 3-4, a partial schematic.
Overload relay K1 is equipped with a set of make-
break contacts: the make contact is connected to
the
reference-voltage bus, and the movable member
is tied to the grids of the series regulator tubes;
the break contact is unconnected, the positive bus
is brought through the winding of relay Kl. The oper-
ating circuit of K1 is so designed that until the cur-
rent in its winding reaches such value that the meter
can be damaged, relay K1 remains unoperated. At
meter-overload value(approximately 180 rna), how-
ever, relay K1 operates and, through its make con-
tacts, applies approximately -200 volts to the grids
of V1 and V2. Cut off of the series regulator tubes
opens
(1) the circuit to the meter and (2) the oper-
ating circuit of Kl. With the restoration of K1, the
high negative potential on the grids of V1 and V2 is
removed, and normal conduction through the series
regulator is resumed. As long as overload current
is flowing, however, relay K1 will continue to oper-

Sect. III Page 6
ate intermittently, interrupting conduction through
the
series regulator until the overload condition is
corrected.
Operation of the 10 MA FULL SCALE switch opens
the
approximately 82 ohms(150 ohms and 180 ohms,
in
parallel) arm of the shunt across the winding of
relay K1. This effectively increases the resistance
of the shunt, a greater proportion of current there-
fore will flow through the winding of relay K1, and
K1 operates when current flow in the main positive
bus is between approximately 12 and 18 rna.
OVERLOAD RELAY
r---------
I
R38
180n.
MAIN SERIES REGULATOR
-~+:........;~-~ 7 1-- ...... ---------------.
RI5A
1.2Il.
---7
/
/
I
I
I
I
I
D
C
V
o
L
T
A
G
E
I DC VOLTAGE I
~
Rt5B
2.n.
RI4
Ion
R16-12Il.
V2
VI
L-----+------<lo------ ..... --+-O MA ~-- ...... -----()ll_ro--_{
FROM~
REF. VOLT. +
BUS
FROM CONTROL ~I S4B
TUBE V4B
__ --------------------------I-D-C-V-O-LT-A-GE-I- ~~v ~
-:---------------~ L
T
A
G
E
FROM
6.3V {
AC
SUPPLY
FROM
HV
SUPPLY
VOLTAGE
DOUBLER
5 2 110 MA FULL SCALE I
S4 IDC VOLTAGE I
TPUSH SWITCH
Figure 3-4. Model71lA Arrangement of positive Bus showing Overload Relay, Milliammeter,
and Associated Switches Switch S4 shown Operated Partial Schematic

)
4-1 GENERAL
The Model 71lA Power Supply is designed conserva-
tively for long component life, and it is probable
that tube replacement will correct a majority of the
difficulties which may develop. Tube replacement
instructions are given in paragraph 4-3.
The maintenance data provided in this section as-
sumes that maintenance personnel are familiar with
the operating procedures and circuit theory given
in
Sections II and ill, respectively.
As aguide in tracing the cause of substandard oper-
ation, a troubleshooting chart is provided in para-
graph 4-9. The chart indicates causes and remedies
for certain specific troubles. Where the cause of
the trouble is of a more obscure nature than the
possibilities covered by the chart, the instrument
should be tested to localize the failure to the section
in trouble. General data on localization procedures
is given in paragraph 4-10.-
After locating the source and eliminating the cause
o(trouble, the instrument should be tested and ad-
justed. Rated performance specifications are given
at the front of this instruction book.
4-2 COVER REMOVAL
On both cabinet and rack models, the cover is fastened
to the
chassis at the rear with two screws. To re-
move the cover, remove the screws, and slide the
cover to the rear and off the instrument.
NOTE: When replacing the cover, pull the power
cable through the opening in the rear of the cover.
Be sure the cable is free of the cover along the entire
length of the cable so that it cannot get caught be-
tween chassis and cover as the cover is slid onto
the instrument.
Sect. IV Page 1
SECTION IV
MAINTENANCE
4-3 TUBE REPLACEMENT
a. General -Any tube in the Model 711A may
be
replaced by atube which has corresponding
standard RETMA characteristics. In general,
neither checks or adjustments are required when
tubes are replaced except in the case of the main
and secondary control tubes, V3B and V4B.
b. Replacement of
V3 and V4 - After replacement
of either of these tubes, check the low end and
the high end of the d-c output-voltage range and, if
required, adjust R31 and/or R33 to bring the out-
put within rated limits.
c. Low-End and High-End Adjustments -The ad-
justments for R31 and R33 are brought out to
the upper side of the deck, and are identified in
Figure 4-2.
Check low end of range:
1) Turn FINE and COARSE control maximum ccw.
2) Note voltmeter indication; if not zero volts, ad-
just variable resistor R31 to obtain zero volts.
Check high end of range:
1) Turn FINE and COARSE control maximum cw.
2) Note voltmeter indication; if not 500 vol~s, ad-
just variable resistor R33 to obtain 500 volts.
Check low end of range again:
1) If zero volts not obtained, adjust R31 to obtain
zero volts, and then check high end of range and
adjust R33 to obtain 500 volts.
2) The settings of R31 and R33 are interdependent.
Continue to
adjust for zero and 500 volts until they
are obtained simultaneously.

Sect. IV Page 2
4-4 REPLACEMENT OF ELECTROLYTIC CAPACITORS
The electrolytic capacitors in this instrument are
high quality units which have a useful life of from
five to ten years. Do not replace these capacitors
unless they are proved defective by accurate tests.
4-5 REPLACEMENT OF VARIABLE RESISTORS
1. VARIABLE RESISTOR Rll -
Connections to
variable resistor Rll are indicated
in
Figure 4-5 and location on the chassis in Figure
4-3.
To remove the old Rll and install the new, the in-
strument should be so placed that the bottom is upper-
most. For convenience of maintenance personnel, all
instructions in the following are with respect to the
instrument in this upsidedown position~ Front and
rear are with respect to the control panel. Cams
are identified in Figure 4-3.
a. Removal -The cams which actuate the micro-
switches are mounted on an extension of the shaft
of variable resistor Rll, one (SIB) immediately in
front of the switch mounting plate, the other imme-
diately behind the mounting plate. The shaft of Rll
and the· extension are connected by means of a
flexible mechanical coupler. To remove Rll, it
will be necessary to reposition the SIB cam and to
disconnect the coupler from the Rll shaft. The pro-
cedure follows.
1) Unsolder the three leads connected to two Rll
terminals.
2) Disconnect the coupler from the Rll shaft. With
No.6 allen wrench, loosen the two setscrews which
fasten the front collar on the coupler to the shaft
of resistor Rl1.
3) Reposition the SIB cam. With No.8 allen wrench,
loosen the two setscrews which fasten the cam to
the shaft. Slide the cam toward the control panel.
4) Slide the shaft extension toward the rear of the
instrument.
5) Remove COARSE control knob:
A. With
No.8 allen wrench, loosen the two set-
screws, and remove the knob.
B. With
1/2" socket wrench, remove hex nut and
flat washer on front of control panel, and two
lockwashers on rear.
6) Remove Rll from chassis.
b. Installation - 1) Install assembly in reverse-
of-removal order. NOTE: Do not fasten SIB
cam to shaft at this time-.--
2) Solder leads to Rll terminals. Connections are
shown in Figure 4-5.
c. Adjustments -
1) Coarse positioning of cams:
A. With
No.8 allen wrench, loosen setscrews on
SIA (blue) cam immediately to rear of switch
mounting
plate.
B. Turn COARSE control max ccw. Position each
cam with low side of cam toward switch
actuator
so that neither switch is operated.
C. Turn COARSE control max cw. See that high
side of each cam is engaging respective switch
actuator so that both switches are operated.
D. Tighten setscrews sufficiently to hold cams in
position on shaft.
2) Set FINE control at electrical center, COARSE
control max ccw.
3) Turn on instrument, and allow two - minute
warm-up.
4) Fine positioning of SIB (black) cam:
A. Turn COARSE control until panel voltmeter
indicates 195V.
B.
Loosen setscrews and so position SIB (black)
cam that (1) as COARSE control is turned cw,
switch SIB operates as voltmeter indication is be-
tween 195V and approximately 200V; (2) as COARSE
control is turned ccw, switch SIB releases as volt-
meter indication is between 190V and approximately
195V.
C. Lock
setscrews.
5) Fine positioning of SIA (blue) cam:
A.
Turn COARSE control until panel vo. 'meter in-
dicates 325V.
B. Loosen
setscrews and so position SIA cam that
(1) as COARSE control is turned cw, switch SIA
operates as voltmeter indication is between 325 and
approximately
330V; (2) as COARSE control is turned
ccw, switch SIA releases as voltmeter indication is
between 320 and approximately 325V.
C. Lock
setscrews. Recheck high and low voltage
limits (see paragraph 4-3c).

)
)
2. VARIABLE RESISTOR R14 -
Variable
resistor
R14, which
is
part
of
the
shunt
network
across
milliammeter
M2,
is
mounted on
resistor
board
RB2.
Connections
to
R14
are
in-
dicated
in
Figure
4-4,
and the
location
of RB2 on
the
chassis
is
shown in
Figure
4-2.
To adjust R14
after
replacement, the use of a
stand-
ard
milliammeter
is
required.
The
following
ad-
justment
procedure
is
recommended.
a.
Connect
a
standard
milliammeter
and aload,
in
series,
across
the IX:
VOLTAGE
+
and -
out-
put
terminals.
b. Adjust
the
COARSE
control
to obtain a
reading
of 80 rna on
the
reference
milliammeter.
c.
If
the
Model 711A
milliammeter
does
not
in-
dicate
80
rna,
adjust
R14 to bring the 71lA
mil-
liammeter
pointer
right
on 80.
4.6
REPLACEMENT
OF
RECTIFIERS
a. Connections
to
the
rectifiers
are
shown
in
Fig-
ure
4-5
and
their
locations
on
the
chassis
in
Figure
4-3.
b.
After
replacement
of any
rectifier,
voltage
at
the
output
of
the
associated
filter
should
be
measured.
If
the
output
is
not
within
the
limits
specified
in
subparagraph
c,
the
replacement
rec-
tifier
does
not
meet
specifications
and
should
be
replaced.
c.
Measurements
should
be
made
with a
20,000
ohms-per-volt
or
better
voltmeter,
aline input
of exactly 115
(or
230)
volts, and no load connected
to the output
terminals.
SRI: connect voltmeter to
capacitor
C1
terminals
1
aIXi
2;
meter
indication should
be
200V
±10%.
SR2-
SR3:
connect voltmeter
to
terminal
1.of
capacitorC3
and to
terminal
2of capacitor C2.
1)
With
COARSE
control
at
max ccw,
meter
indication should
be
400V
±
10%.
2)
With
COARSE
control
at
max cw,
meter
in-
dication should be
715V
±
10%.
SR4:
connect voltmeter to
capacitor
C6
terminals
1
and
2;
meter
iJrlication should
be
350V
±10%.
Sect.
IV
Page
3
4·7
METER
ZERO
ADJUSTMENT
When the
voltmeter
is
received
from
the
factory,
the
position
of
the
voltmeter
and
milliammeter
pointers
should
be
checked,
and if
the
respective
pointer does not indicate exactly on
zero,
the
pointer
should
be
reset
to
zero.
The
adjustment
should be
made
before
the
voltmeter
is
connected to a
power
source.
The
adjust
screw
is
in
the
meter
frame
at
a
mid-
point
immediately
below
the
meter
face.
The
ad-
justment
is
made
properly
only when
pointer
adjust
travel
is
in the opposite
direction
to
the
turn
of the
adjust
screw. Though the adjust
screw
may
be
turned
in
either
direction, a
practical
procedure
is
to
turn
the
screw
in aclockwise
direction
until the
pointer
starts
to swing back toward
zero.
Then,
still
turning
the screw clockwise, bring the pointer
(now
traveling
counterclockwise) back to
zero.
NOTE:
For
accurate
positioning of the
pointer,
the
resetting must be done with power disconnected
from
the
instrument
circuits.
If
during
the
life
of the
voltmeter
it
is
necessary
to
reposition
the
pointer,
wait
at
least
fifteen
minutes
after
disconnecting the
power
before
resetting
the
pointer
on
zero.
4·8 POWER TRANSFORMER PRIMARY CONNEC-
TIONS
Connections
from
the
primary
winding of
power
transformer
T1
are
brought out to a
terminal
strip
(identified in
Figure
4-3) mounted on
under
side
of
the
deck,
at
the
rear
of
the
instrument.
The two
sections
of the power
transformer
primary
are
strapped
at
the
factory
for
115-volt
operation.
If
the
instrument
is
to be
operated
from
a230-volt
power
source:
a. Change
the
strapping to connect the
two
sections
of the
primary
in
series,
as
indicated
for
230-
volt operation on the
schematic
diagram.
b. Replace 1.
6-ampere
fuse F1 with a
O.
8-ampere
cartridge
fuse of the
same
slo-blo
type (see F1
description
in
the
Table
of
Replaceable
Parts,
Section
V).

Sect. IV Page 4
4·9 TROUBLE SHOOTING CHART
The following chart lists various symptoms of trouble
and for each indicates the
part or parts of the circuit
which should be checked. In the main. for purwses
of simplification, only tubes are referenced, but it
should be remembered that components associated
with referenced tubes also are failure possibilities.
With each section of the chart, checking should be
performed in the order given since it is assumed
throughout a procedure that the parts checked pre-
viously are functioning correctly.
When testing the Model 711A, it is recommended that
line voltage be applied to the instrument through a
variable transformer, and that the transformer be
adjusted to deliver a voltage at the low end of the
rated 103- to 127-volt range. An instrument in good
condition
operates satisfactorily from any line volt-
age within rated range, but where there is marginal
operation (from weak tubes, etc.) weaknesses be-
come easier to trace at low line voltages.
Table 4-1. Trouble Shooting Chart
SYMPTOM AND POSSffiLE CAUSE TEST PROCEDURE
1. Instrument NOT operating;AC volt-
age indicator light NOT lighted.
a. Fuse open due to defective fuse
or overload in power supply. a. Replace fuse.
If this fuse blows:
(1) Remove all tubes and K1; again replace fuse.
(2) If this fuse does not blow:
A. Check voltage across C1, C2-3 (with COARSE con-
trol max ccw), C6(from terminal 3to 1).
1. If output voltages are somewhat higher than those
shown on the schematic, proceed to
step B.
2. If output from any rectifier less than normal, check
rectifier and associated electrolytic capacitor.
B. Replace V3, V4, V5.
1. If fuse does not blow, proceed to step C.
2.
If fuse does blow:
a. Check tubes by substituting tubes known to be good.
b. If trouble is not in tubes, check resistors, capaci-
tors, and wiring in secondary regulator and V4B
circuits; tolerances given in Table of Replaceable
Parts.
C. Check that no load is connected to d-c output termi-
nals. Reinstall V1 and V2, but not K1.
1.
If fuse does not blow, replace K1.
2. If fuse does blow, check V1 and V2 by removing one
6L6 and leaving
other in circuit.
3.
If fuse blows when K1 is installed, K1 may be defec-
tive and arcing to ground.
(3) If 2nd fuse does blow, localize as follows:
A. Disconnect rectifiers from their respective T1 sec-
ondary windings: one grey T1 lead from SR1, red
T1lead from SR3, one green T1lead from SR4.
Replace fuse.
1.
If fuse does not blow, proceed to step B.
2. If fuse does blow, short is in the primary or a fila-
ment winding. Disconnect green lead from pin 2,
V2, and replace fuse. If fuse does not blow, trouble
is in Vl-V2 filament supply. If fuse blows, trouble
probably
is in V3-V4 filament supply, though it can
be in a-c supply, iJxUcator light circuits, or primary.