HP 712B Owner's manual

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OPERATING AND SERVICING MANUAL
MODEL 7121
POWER
SUPPLY
Serial 511 and Above
HEWLETT-PACKARD COMPANY
275 Page Mill Road • Palo Alto, California, U.S.A.

OPERATING AND SERVICING MANUAL
FOR
MODEL 7128
POWER SUPPLY
Serial 511 and Above
Copyright 1954 by Hewlett-Packard Company
The information contained in this booklet
is intended for the operation and main-
tenance of Hewlett-Packard equipment and
is not to be used otherwise or reproduced
without the written consent of the Hewlett-
Packard Company.
HEWLEn·PACKARD COMPANY
275 PAGE MILL ROAD, PALO ALTO, CALIFORNIA, U.S.A.
7121004.1

TABLE OF CONTENTS
FOR
MODEL 712B POWER
SUPPLY
Para.
Page Para. Page
SECTION I
SECTION IV
GENERAL DESCRIPTION MAINTENANCE
1 -1 General.
·1
-1 4-1 Cover and Bottom Plate
1 -2 Inspection.
1 -1
Removal
4-1
4-2
Replacements
···. .
4-1
4-3
Adjustments
··
4-3
SECTION II
4-4
Line Regulation
Adjustment 4-3
2-1
Controls and Terminals.
2-1
4-5
Adjustment of Fixed -300
2-2 Operation
······
2-2 Volt Bias Supply Output
Voltage
· · ····· ·
4-5
4-6
Adjus tment Of HV Supply
SECTION III Output Voltage •····
4-5
4-7
Setting Variable Resistor
3-1
General
.· · .····
3-1
R39
.····· · · ·
4-5
3-2 High Voltage Regulator
4-8
Setting the Stop on the H V
Circuit
.··.····...
3-1
Control
····· · · ·..
4-7
3-3
Bias Supply Circuit.
··
3-3
SECTION V
TABLE OF REPLACEABLE PARTS

TABLE OF SPECIFICATIONS
OUTPUT VOLT AGES
I,
DC REGULATED HIGH VOLT AGE:
DC REGULATED FIXED BIAS:
DC VARIABLE BIAS:
AC UNREGULATED:
o to +500 volts (without switching), 200 ma maximum load.
-300 volts, 50 ma maximum load.
o to -150 volts, 5 ma maximum load.
6.3 volts CT, 10 amps maximum load.
OUTPUT VOLTAGE REGULATION (for constant line voltage)
DC REGULATED HIGH VOLT AGE:
DC REGULATED FIXED BIAS:
DC VARIABLE BIAS:
LINE VOLTAGE REGULATION
RIPPLE
INTERNAL IMPEDANCE
DC REGULATED HIGH VOLTAGE:
RECOVERY TIME
METERING
CURRENT METER:
VOLTMETER:
TERMINALS
OVERLOAD PROTECTION
POWER SUPPLY
DIMENSIONS
WEIGHT
Less than 50 millivolts change no-load to full-load at any output
voltage.
Less than 50 millivolts change no-load to full-load.
Is tied to fixed bias, hence source regulation is same as for fixed
bias. Internal impedance 0 to 10, 000 ohms, depending on bias
control setting.
Regulated DC output voltages vary less than ±l00 millivolts for
line voltage variations 115 volts ±1O%.
Less than 500 microvolts.
(For frequencies above 20 cps.) Full-load: 0.1 ohm in series
with 25 microhenries maximum. No-load: 1 ohm in series with
50 microhenries maximum.
Upon application of full-load: 0.1 millisecond maximum. Upon
decrease from full-load to:
(a) 0 ma, 0.5 millisecond maximum.
(b) 25 ma, O. 1 millisecond maximum.
Maximum transient voltage, 1 volt.
o to 200 ma. (high voltage only.)
Three ranges, 0 to +500 volts, 0 to +150 volts and 0 to -150 volts.
Panel switch connects meter to DC regulated high voltage or DC
variable bias and selects range.
Either positive or negative DC regulated high voltage terminal may
be grounded. Positive terminals of both bias supplies and nega-
tive terminals of DC regulated high voltage are common.
AC line, DC regulated high voltage, DC regulated fixed bias and
filament supply are separately fused. DC regulated high voltage
drops to a safe value if bias fuse blows.
115 volts ±10%, 50 to 60 cps. Approximately 120 to 450 watts
depending on load and line voltage.
Cabinet Mount: 12-1/2" high, 20-1/2" wide, l4-l/4"_deep.
Rack Mount: Panel 10-1/2" high, 19" wide, 14-1/4" deep.
Cabinet Mount: 6!1lbs. shipping weight approx. 104 lbs.
Rack Mount: 62 lbs. shipping weight approx. 98 lbs.

SECTION I
GENERAL DESCRIPTION
CAUTION
Voltages which are dangerous to life
are present at the terminals and
within this instrument.
1-1 GENERAL
The Model 7l2B Power Supply is a very stable
source of continuously variable direct cur-
rent for plate and bias circuits. It also pro-
vide s up to 10 amper es, 6.3 volts alternat-
ing curr ent for filament cir cuits • A two-
range voltmeter and a milliammeter (high
voltage only) are provided to measure the
direct current output. This power supply is
veryusefulas apower sourcefor small trans-
mitters, oscillators, complex systems, cer-
tain types of klystrons, and general labora-
tory use.
CAUTION
The AC power should be turned on
for at least 30 seconds before switch-
ing on the high voltage. This allows
the regulator circuits to reach their
proper operating point and avoids
exces sive voltage at the high voltage
terminals.
1-2 INSPECTION
This instrument was thoroughly tested and
inspected before being shipped and is ready
for use when received.
After the instrument is unpacked, it should
be inspected for damage received in transit.
If any shipping damage is found, follow the
procedure outlined in the "Claim for Damage
in Shipment" page at the backof this instruc-
tion manual.
1 -1

SECTION II
OPERATING INSTRUCTIONS
2-1 CONTROLS AND TERMINALS
AC POWER
This toggle switch controls the power sup-
plied to the instrument from the power line.
When the switch is in the ON position the
red indicator lamp above the switch will
glow.
LINE 4 AMP
The fus eholder, located on the control panel,
contains a 4 ampere cartridge fuse for the
protection of the whole instrument. The
fuse may be replaced by turning the fuse-
holder cap, removing the old fuse, and in-
serting a new fuse. Replacement fuses for
this instrument must be of the "Slo-Blo"
type as specified in the Replaceable Parts
List.
-300V 1/16 AMP
The fus eholder, located on the control panel,
contains a 1/16 ampere cartridge fuse for
the protection of the -300 volt fixed bias
supply. The fus e may be replaced by turn-
ing the fuseholder cap, removing the old
fuse, and inserting a new fuse.
NOTE
If this fuse blows, the positive
high - voltage regulator circuit
will drop the HV voltage level to
less than 100 volts, thus protect-
ing external equipment or cir-
cuits against the pos s ibility of
damage due to loss of bias •. When
the openfuse is replaced, all cir-
cuits restore to normal.
+HV 1/2 AMP
The fus eholder, located on the control panel,
contains a .5 amper e cartridge fus e for the
protection of the high voltage de cir cuit.
The fuse may be replaced by turning the
fuseholder cap, removing the old fuse, and
inserting a new fuse.
2-1
CAUTION
If this fuse blows, immediately
turn off the AC POW ER switch,
and then replace the fus e. Con-
tinued operation of the instrument
with the +HV 1/2 AMP fuse open
will damage the screen grids of
the series regulator tubes (V3,
V4, V5, V6).
HIGH VOLTAGE
This toggle switch turns the high voltage
direct current off and on. The switch also
controls the red indicator light above it on
the control panel. When the switch is on,
the indicator lamp glows as a warning that
the high voltage is turned on.
6.3V AC, 10 AMP
The two fuseholders, located on the control
panel, each contain a15 ampere cartridge
fus e for protection of the 6.3 volt AC fila-
ment supply circuit. Each fuse may be re-
placed by turning its fus eholder cap, re-
moving the old fuse, and inserting a new
fuse. Replacement fuses must be of the
"Slo-Blo" type as specified in the Replace-
able Parts List.
6.3V AC 10 AMP CT
These binding posts are terminals for the
unregulated AC filament supply.
6.3V AC 10 AMP
These are the terminals for the 6.3 volt
unr egulated alternating current.
CT
This binding post is the terminal for the
center tap of the secondary winding from
which the unregulated AC is taken.
-300V 50 MA 5!vIA GND
These binding posts are terminals for the
bias supply output and chassis ground.
-300V 50 MA
Output terminal for the fixed -300V regu-
lated voltage supply.

5 MA
Output terminal for the variable (0-150
volt) regulated bias voltage supply.
GND
Terminal for making connection to the
chassis. Anyone of the output terminals
may be connected to the chassis by con-
nection to terminal GND.
COM +HV GND
These binding posts are terminals for the
high voltage supply, common conductor,
and chassis ground.
+HV
Output terminal for the regulated 0-500
volt voltage supply.
COM
Output terminal common to the HV, 5 MA
(variable bias), and -300V 50 MA (fixed
bias) cir cuits •
GND
Terminal for making connection to the
chassis.
-BIAS CONTROL
This control varies the output of the regu-
lated bias voltage supply from 0 to 150 volts.
HV CONTROL
This control varies the output of the regu-
lated high voltage supply from 0 to 500 volts.
METER RANGE
This switch connects the regulated high
voltage supply circuit to the voltmeter on
either the 0-150V or 0-500V range. Opera-
tion of the switch to 0-150 -BIAS connects
the variable bias supply circuit to the volt-
meter.
2-2 OPERATION
CAUTION
Avoid electric shock by turning the
high voltage switch to the off posi-
tion before making any connections
to the instrument.
2-2
The procedure for operating the Model 712B
Power Supply is as follows:
a. Connect the power cable to aIlS V power
line and turn the AC POWER switch to
ON.
NOTE
The triple -conductor power cable is
supplied with the new NEMA approv-
ed three-prong plug. The third con-
ductor provides a chassis ground.
An adapter may be obtained to per-
mit use of this plug with two-conduc-
tor receptacles.
b. With the HIGH VOLTAGE switch in the
off position, connect the output terminals
to the load.
c. If the bias supply is to be us ed, set the
METER RANGE switch to the 0-150V
-BIAS position and adjust the -BIAS CONTROL
for the desired voltage.
NOTE
The internal impedance of the vari-
able bias circuit can be as high as
10, 000 ohms, depending on the set-
ting of -BIAS CONTROL.
d. Set the METER RANGE switch at the 0-
150V or 500V position, and adjust the
HV C ONTR OL for the des ired output voltage.
e. Turn the HIGH VOLTAGE switch to ON,
check the bias voltage, and readjust -BIAS
CONTROL if necessary.
f. If the Model 712B is to be used for an
application which requires a power sup-
ply of more than 500 volts, up to 300 volts
additional may be made available by connect-
ing the load across +HV and -300V 50 MA.
Ground may be connected to either terminal,
as desired.

SECTION III
CIRCUIT DESCRIPTION
3-1 GENERAL
The Model 7l2B Power Supply furnishes two
separate regulated supplies: a positive high
voltage in the 0-500 volt range and a bias
voltage. A block diagram of the Model 7l2B
is shown in Figure 1 •
Voltage level of the high voltage supply is ad-
justed by means of a panel knob, HV CON-
TROL, which controls the setting of variable
autotransformer Tl. The autotransformer
supplies primary voltage to the high voltage
power transformer, T2. The comparis.on
voltage in the regulator circuit is adjusted by
means of variable resistor R39 which is me-
chanically coupled to the autotransformer
shaft. This arrangement maintains the regu-
lator circuit at its optimum operating point,
regardless of output voltage level.
After the high voltage has been rectified (dual
diodes VI and V2) and filtered, it is applied
to a group of series regulator tubes (pentodes
V3-V6), to the DC milliammeter, and then
to the high voltage output terminal, +HV. The
conduction of the series regulator tubes is
controlled by a cascade differential amplifier
(dual triodes V12 and V13). The differential
amplifier compares a sample of the output
voltage with the voltage developed across
voltage reference tube VII; any difference
between thes e voltages is amplified and the
conductivity of the series regulator tubes is
changed accordingly.
The fixed bias voltage (-300V) supply con-
sists of a conventional power transformer,
full-wave rectifier (dual diode V7), and capa-
citor -input filter. The voltage is regulated
by means of a series regulator tube (pentode
VB), which is controlled in turn by a cascade
differential amplifier (dual triodes V9 and
VlO). Operation of the regulator circuit is
similar to the +HV regulator described above.
A source of variable bias voltage is provided
by means of a voltage divider (variable re-
sistor R46) which is connected between the
-300V 50 MA terminal and the COM terminal.
This voltage is regulated against line voltage
variations only. Since the internal impedance
may be as high as 10, 000 ohms, depending
upon the setting of resistor R46, the voltage
will depend upon the actual load current be-
ing drawn (5 rna. max.). This voltage can
be measured by turning the METER RANGE
switch to the -150 V -BIAS position.
3-2 HIGH VOLTAGE REGULATOR CIRCUIT
The regulator circuit is so arranged that a
slight voltage change in the sampled output
in the positive directionwill result in a rela-
tively large voltage swing in the negative di-
rection on the grids of the series regulator
tubes, and vice versa.
Figure 2 shows the arrangement of dual tri-
odes V13 and V12 which, connected in cascade,
form a two stage differential amplifier. In
each tube, cathode connections are common
for the two sections. Thus any variation in
plate current in one section appears across
the cathode resistor common to both sections,
and results in a difference voltage in each of
the output circuits.
In the first stage, a fixed bias supplied by
voltage reference tube VII is applied to one
grid of dual triode V13. The bias on the other
grid of V13 is a portion of the +HV voltage,
sampledwithrespectto the -300voltbias sup-.
ply through a voltage divider. Any variation
in the level of the output voltage results in
voltage changes in the plate circuits of both
sections of V13, and corresponding changes
in the bias es on the grids of dual triode VIZ in
the next stage.
For example, if the voltage of the sampled
output swings in the positive direction, in-
creased current will flow through the right-
hand section of V13, which will raise the cath-
ode voltage and lower the right-hand plate
(pin 1) voltage. Since the bias on the grid in
the left-hand section of V13 remains fixed,
the increas ed cathode voltage will decrease
conduction in the left-hand half of the tube,
which result in an increase in voltage on the
left-hand plate (pin 6).
3-1

/
OUTPUT I--~_-o_ +HV
CURRENT
HIGH
VOLTAGE
SUPPLY
HV
CONTROL
~------------------------~
I
SERIES !
1 '.
REGULATOR I
""'--+ ......... ~
r---..&.- __ ~
VARIABLE
..- I--
TRANSFORMER
DIFFERENTIAL
r--o+- AMPLIFIER ~
POWER
INPUT
115V
5O-IOOO/V
VOLTAGE
REFERENCE
TUBE
DIFFERENTIAL
~ AMPLIFIER
/
OUTPUT
VOLTAGE
-
-
+
-300
VOLT
SUPPLY
SERIES
REGULATOR
__ ._ ...... -------+--00_ COM
~
">4o-------4II~O_ 5 MA
o -BIAS CONTROL
lGND
-
-300V
--
50MA
-
6.3V AC
_ CT
IOAMP
-
'FILAMENT
TRANSFORMER
...... --------------------0
Figure 1. Model 7l2B Block Diagram
3-2