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Патент USA US2409314

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4 Oct. 15,1946.
_ J’, B, REEVES
CURRENT
REGULATOR
Filed Feb. 5, 1945'
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2,409,312
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2 Sheets-Sheet l
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15, 1945-
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‘J. B. REEVES
I I
2,409,312‘
CURRENT REGULATOR
Filed Feb; 5, 1945
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2 Sheets-Sheet 2
Patented Oct. 15, 1946
2,469,312
UNITED STATES PATENT OFFICE
2,409,312
I
CURRENT REGULATOR
James B. Reeves, White?sh Bay, Wls., assignor to
' Cutler-Hammer, Inc., Milwaukee, Wis., a cor
notation of Delaware
Application February 5, 1945, Serial No. 576,335
6 Claims. (01. 172-239)
1
.
The invention relates to the current control of
dynamo-electric machines or other translating
circuits, and while not limited thereto, it is par
ticularly applicable to the control of motors which
are supplied with armature current from a varia
ble voltage generator where it is desired to limit
the current ?owing between the-generator and
motor upon changes of the motor load or changes
of the generator voltage.
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electron tubes l4 and I5. The electron tube_ 14.
is a duplex tube, having cathodes Ma and M“,
anodes MC and W‘, respectively, and control elec
trodes Me and [4‘, respectively.
5
The electron tube [5 is provided with a cathode.
I55, an anode I5‘), and a control electrode l5°.
The anodes Illc and W1 are jointly connected to__
a bus bar L1 which constitutes one terminal ‘of, a
‘
source of direct current of constant potential;
An object of the invention is to provide im 10 the other terminal of said source being a bus bar',
proved means> for automatically controlling the.
L2. The cathode I53 is connected to the bus bar‘
armature current of a motor by controlling the
L1, through a voltage divider l6, which is provided‘
?eld excitation of a generator supplying said
with an adjustable contact. The anodeltl‘? is‘
armature current.
connected to the bus bar L1, through a resistorv
Another object is to provide in a system of the
l1, while the cathode I5a is connected to the bus
aforementioned type for limiting through control
of the generator excitation the maximum torque
tof the motor upon changes of load thereon.
Another object is to provide in a system of the
aforementioned type for affording different limits
of motor currents for different operating condi
tions of the motor.
1
bar L2, through a resistor l8, which is preferably
paralleled by a voltage regulating tube‘ l9. The
grid [5° is connected to the two cathodes Ma and
I4‘), and is also connected through a resistor 2!],
to the bus bar L2. The grid Me is connected to.
the terminal of the current shunt l2, which isv
nearest to the generator, while they grid It1 is
- Another object is to provide in a system of the
aforementioned type for varying the excitation
connected .to the terminal of the current shunt‘
l3, which is nearest to the motor H. The oath-p
of the generator so as to maintain a constant
odes Ill‘3L and Nb‘ are also connected to the nega
motor current upon tendencies of such current
tive terminal ofv a biasing battery 2l,.,which ‘is
paralleled by a voltage divider 22, which is pro
to increase.
.
'
Another object is to provide for controlling, in
videdwith adjustable contacts 22a, 22b, 22fJ and
a system of the aforementioned type, the accel
erating current in response to the motor speed. 30 -. The field winding‘ ll)” of the generatorv is sup-'
- Otherobjects and advantages will hereinafter
plied with current from the lines‘ L3, L4 of an.
22d.
appear.‘
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k
‘
'I'hehaccompanying drawings are illustrative of
an embodiment of the invention.
. Figure '1 illustrates a system in which a sepa_-'_
7
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.
.
alternating current source of‘ supply, through a
transformer 23, which has a primary winding‘. 23";
and a centerjtapped secondary winding 23“. The
secondary winding ‘is further provided with addi:
rately excited reversible direct current motor is
tional .taps oneach'side of the center tap inter
mediate between the latter and the end terminals
erator, while
- .
~l
of the winding 23”. Each end terminal. of the
Fig. 2 illustrates a non-reversible system in
Winding"23b is connected to one of the ‘anodes 24b
cludingcertain modi?cations of the control of 40 and 25‘), respectively, of gaseous electron tubesj24
the generator ?eld.
and 25, respectively, which tubes are also provided
supplied with energy from a variable voltage gen
Referring to Fig. l, the same illustrates a var
with cathodes 24a and 25*‘, respectively, and 'con-.
iable voltage generator l0, having an armature
trol electrodes 24? and 25°, respectively. 'The'
l0“, and a separately excited regulating ?eld
tubes 24 and 25 are reversiblyvconnectable to the
winding lllb.
he generator supplies current to 45 ?eld winding lob, by a pair of‘ electromagnetic
the armature Hat of a motor II which is also
reversing switches 26 and 21, each provided with
provided with a ?eld winding lib. The latter
may be energized from any suitable direct current‘
source, the energizing current being adjusted to
two normally open main contacts 26b and 26°, and
21b and 210, respectively, normally‘ open auxiliary,
a suitable value.
The armatures Illaand II“ are
connected into a closed loop which includes cur
rent shunts I 2 and I3 connected in serieswith
each other and with the generator and the motor
armature.
.
The control system comprises two high vacuum
contacts 26d, 213‘, '26g and 21d, 21‘. and 21B, respec
tively, normally closed auxiliary contacts 266 and‘
21° respectively; and energizing windings 26*‘.and
21“, respectively. One terminal each of the con
tacts 26b and 21b is jointly connected to one'ter-.
minal of the Winding ID"; the other terminalof
'_ which is connected to one terminal of. the contacts.
2,409,312
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26° and 21°. The cathodes 24° and 25a are jointly
connected to the second terminal of the contacts
26*’ and 21°. The center tap of the winding 23b
21K, 261 and 2'!I is connected to the sliding con
tacts 22°, 22b, 22(1 and 221, respectively.
To start the equipment, the lines L1, L2 and the
lines L3 and L4, as well as the motor ?eld l U’, are
is connected to the other terminal of contacts 26°
and 2'!b and to one terminal of the primary wind in energized and the generator armature is rotated
by its prime mover. The energization of the field
ing 29a of a transformer 29 which also has a cen
ter tapped secondary winding 29*’.
The other
terminal of the winding 29‘1 is connected to one
intermediate terminal of the winding 2311 through
winding I lb establishes the desired magnetic ?eld
in the motor ll, while energization of the lines
L3, L4 causes a potential to be impressed by the
a condenser 30 and to the other intermediate 10 transformers 23 and 29 upon the anodes of the
tubes 24 and 25. A potential is also impressed
terminal of the said winding 23b through a varia
upon the control electrodes 24° and 25°. By ad
ble resistor 3|. The condenser 30, the resistor 3|
justment of the resistor 3!, the phase relation
and the winding 298L form a phase shifting net- >
of the‘ potential impressed upon the anodes 24°
work by means of which the phase. anglev of the
voltage impressed upon the control electrodes of 15 and25b, with respect to the phase angle of the
voltage impressed upon the control electrodes 24"
tubes 24 and 25, in relation to the phase angle of
and 25°, and thus. the maximum current passed
the voltage of the lines L3 and L4, may be- varied.
by tubes 24 and 25 to the winding lab, and thus
The control electrodes 24° and 25°, respectively,
the maximum voltage of the generator 10 may be
are each connected to one of the end terminals
of the secondary winding 29b of the transformer 2-0 adjusted.
If it is now desired to operate the motor in a
29.
The windings 25° and 21“ may be selectively en
forward direction, the control lever 32° of the
control switch 32 is moved to make contact with
ergized from the line L3 and L4 through. a man
the stationary contacts 32° and 32°, whereupon a
ually operated pilot switch 32, which has a center
bias lever 32° operable in one direction to make 25 circuit is established from line L3, over lever 32",
contact 328, contacts 21°, through the energizing
contact with stationary contacts 32b and 32d, and
winding 26° to line L4, and the forward switch 26
operable in the opposite direction to make con
is actuated.
“
tact with stationary contacts 32° and 32°.
Energization of the forward switch 25 com
The pilot switch 32 is preferably so arranged
pletes a circuit from line L3 over contact lever
that, upon movement of the lever 32a to the re
spective operating position... it closes circuit with
32“, contact 32°, contacts 26d, coil 34a, to line L4,
contacts 32°, 32c prior to closure of circuit with
and the relay 34 is actuated to close its contacts
contacts 32b or 32°.
The energizing winding 33a of an electromag
34b, 34(1 and 34f, thereby connecting the anode
netic voltage responsive relay 33 is connected
across the terminals of the motor armature l|°.
The relay 33 is also provided with two normally
open contacts 33b and 33°. One terminal of each
of said contacts is connected to the line L3.
15b to the cathodes 24a and 25°, the movable
contact of the voltage divider IE to the center tap
of the transformer Winding 29". Closure of con»
tacts 26b and 25° establishes a circuit from one
end terminal of winding 2311, through tube 24,
through contacts 26b, winding Nib, contacts 26°,
The second terminal of the contact 33b is con 40 to the center tap of winding 23", and through said
Winding back to tube 24, and alternately from the
nected to the contact 32b while the second ter
other end terminal of winding 23b, through tube
minal of the contact 33° is connected to the con;
tact 32°. One terminal each of the windings 26a
25, contacts 26”, winding lob, contacts 26°, to the
center tap of the winding 23b. The generator
and 21'1 is connectable to the line L4. The sec
?eld Illb is thus supplied with recti?ed direct cur
ond terminal of the winding 26“ is connectable
rent, and a voltage is induced in the generator
through the normally closed contacts 21° to the
armature Ilia to cause a current flow from said
terminal 32°, while the second terminal of the
armature through the shunts l2 and IS, the motor
winding 21° is connectable through the normally
armature I I3 back to the generator armature 10*‘.
closed contact 26° to the terminal 32*’.
An electromagnetic‘ relay 34 has an energizing 50 As the‘ current supplied to the motor armature l I"
accelerates the latter, the terminal voltage of
winding 34“, one terminal of which is connected
the armature H“ increases until the voltage im
to the line L‘, while the other terminal is'con
pressed upon the energizing coil 33a is su?icient
nected to one terminal each of the normally open
to cause closure of the contacts 33b and 33°, Clo
contacts 28“ and 21°. The other terminal of con
sure of these contacts parallels the circuit between
tact 26° is connected to contact 32° and the sec
the contact arm 3-2 and the contact 32° so that
ond terminal of contact 21° is connected tc‘con
the lever 32° may be returned to the neutral posi
tact 32°‘. The relay 34 has normally ‘open con
tion to break circuit with the contact 32°, but
tacts 34b, 34‘1 and 341, and normally closed contacts
the switch 26 remains energized until the ener
34°, 34° and 34@. The contacts 34b are inter
posed in a circuit between the cathodes 24a and 60 gization of the coil 33a is insufficient to maintain
the contacts 33b and 33° closed. The circuit
25', and the anode IS”. The contacts 34° are
which responds to the voltage drop in the shunts
interposed in a circuit between the center tap of
l2 and I3 is so adjusted that when no current
the winding 29b and the anode IS”. The con
?ows between the generator and the motor both
tacts 34° are interposed between the cathodes
halves of the tube i4 conduct only a small cur
24' and 25“, and the movable contact of the volt
rent. As the current supplied by the generator
age divider IS; the contacts 34d are interposed
increases, it produces potential differences in the
between the center tap of the Winding 29b and
shunts l2 and 13, which render the grid 14° less
the movable contact of the voltage divider l6;
positive and the grid l4f more positive with re
one terminal of contacts 34t and 34K is connected
spect to their respective cathodes, so that the po
to the common terminal of the shunts l2 and I3;
tential of the grid 14° is ultimately su?icient to
the second terminal of contact 341 is'connected to
stop current conduction in the left half of the
one terminal of each of the contacts 26! and 218,
tube l4, whereas the current ?owing through the
while the second terminal of contact 348 is con
right half of the tube I4 is increased. The rela
nected to one terminal of each of the contacts 26f
tion between the variation of the current in the
and 21‘. The second terminal of contacts 26K,
2,409,312
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tw'oihalves of the tube l4 and the potential of the
is closed from said common terminal through
grids W’ and I41 may be adjusted in a well known
manner by adjustment of the supplemental grid
bias afforded by the voltage divider 22.
contacts 348 and 261, to contact 22d. Hence, the
biasing potential for the tube 14 has been changed
so that the system is regulated to afford a decel
erating current which is higher or lower than the
- This supplemental grid bias is equal to the volt
age between the adjustable contact of the voltage
divider 22, which is connected to the common
terminal of the shunts l2 and i3, and the nega
tive terminal of the battery 2 I. During operation
of the motor in the forward direction, that is,
While the switch 26 and the relay 34 are energized,
accelerating current, depending upon the relative
position of the contacts 22° and 22“.
However, it is applied to the tubes 24 and 25
in the reverse direction from that during accel
eration of the motor I I, thereby advancing the
moment of ignition of the respective tube during
the positive half cycle and tending to increase
the current of the ?eld winding of the generator,
a circuit is established from the common terminal
of the shunts l2 and I3, through contacts 341, 25g’
and 22°, through part of the voltage divider 22,
to decrease the dynamic braking effect. Thus,
to the cathodes I42:‘ and Nb. Thus the adjust 15 the system maintains the braking current of the
ment-of the contact 22° determines the supple
motor at a constant value which may be sub-‘
mental grid biasing voltage and therefore the
stantially the same as the accelerating current,
relation between the current flowing in the gen
so that the motor is brought to a standstill with
erator-motor loop and the conduction of the two
the maximum allowable torque and in'the' short
halves of the tube 14, so that upon moving the 20 est possible time. When the‘motor speed ap
contact 22° toward the positive terminal of the
proaches zero, the voltage impressed upon the
voltage divider 22, the current conducted by the
coil 33“ is insuflicient to maintain the relay 33
tube I 4 for a given current in the motor-gen
energized. Thus the contacts 33b and 33° are
erator loop will be increased.
’
opened, which opens the maintaining circuit for
As the conduction of the right half of the tube 25 the forward switch coil 26a and causes disconnec
l4 increases, the potential of the grid |5° becomes
tion of the generator ?eld Ii)b from the tubes '24
more positive, thereby increasing the conduction
and 25, and the equipment returns to the initial
of the tube 15 which increases the current in the
condition.
resistor H, which in turn reduces the positive po
Operation of the motor in the opposite direc
tential of the anode l5". The potential derived 30 tion is obvious from the foregoing. To start the
from the voltage divider I6 is so adjusted that
motor in reverse direction, the switch arm 32% is
a desired potential di?erence exists between the
moved to make circuit with the contacts 32d'and
anode 15b and the movable contact of the voltage
32b, thereby energizing the reverse switch 21. The
divider It. This potential difference is impressed
functioning of the various elements of the system
upon the grids 24° and 25°, as will be apparent
upon reverse operation will be obvious from the
from the diagram, and is superimposed upon
foregoing description and the accompanying
the potential impressed by the winding 29'’, the
drawings. However, it is to be pointed out that
polarity of the superimposed potential being such
since during acceleration upon reverse operation,
as to delay the moment of ignition of the tubes
the contact 22b is connected to the common ter
24 and 25, during the respective conducting half a minal of the shunts l2 and I3, the position of
cycle, so as to tend to decrease the current sup
said contact determines the accelerating current
plied to the generator ?eld I0", to a value which
of the motor for reverse rotation. Upon reopen
will result in a desired constant current ?owing in
ing of the pilot switch 32 and during subsequent
the generator-motor loop. As a result, the motor
deceleration, the contact 22“ is connected to the
is accelerated with‘a constant torque. Further
' common terminal of the shunts l2 and I3, so that
more, after the motor has reached its maximum
speed, the current cannot exceed the full load
the position of the latter contact determines the
decelerating current. Hence, during forward op
value, such value being adjustable by adjust‘
eration, the positions of the contacts 22°and 22d
determine the current in the mot0r~generator
ment of the resistor 22.
If it is now desired to stop the motor, the oper- q‘ loop during acceleration and deceleration, respec
ator returns the lever 323 to the neutral position.
As the voltage impressed on the coil 33“ is the
tively, while for reverse operation the positions
maximum terminal voltage of the motor, the
relay 33 remains energized, thus maintaining the
rent in the motor-generator loop during accelera
switch 26 energized, which in turn maintains the
connection between the recti?er tubes 24 and 25
and the generator ?eld winding 10b. However,
opening the connection between the contact lever
32“, and the contact 32°, opens the circuit of the
energizing coil 34*‘, so that the relay 34 opens
crating currents for both directions of rotation
and equal decelerating current for both directions
or equal accelerating and decelerating currents
of the contacts 22b and 22*’L determine the cur
tion and deceleration, respectively. Obviously, the
controller may be arranged to afford equal accel~
of one value for one direction and of another
(ii
the contacts 34b and 34“, thereby reversing the
value for the other direction, or the currents may
be adjusted for the same value under all condi
connections between the anode l5h and the mov
able contact of the voltage divider It on one hand,
and the cathodes 24a and 25a and the center tap
tions of operation. For certain of said condi
tions, some of the commutating circuits for the
of the winding 291), respectively. As now the
action of the generator and motor is reversed,
current‘ flows in the motor-generator loop in the
reverse direction, so that now the left half of the
tube l4 becomes conducting and the right half
becomes non-conducting.
During deceleration in the forward rotation
of the motor, the contacts 34! are open and con
tacts 3,4? are closed.‘ Therefore, the circuit be
tween the contact 22° and the common terminal
of the shunts l2 and I3 is opened, while a circuit
biasing resistor 22-may be combined or omitted,
as will be apparent.
-
Referring now to Fig. 2, the same illustrates
a system in which the motor is required to operate
only in one direction. However, in the system of
Fig. 2, the accelerating current of the motor is
controlled in accordance’ with the speed of the
latter so ‘that the rate of acceleration and the
motor current are'relatively low upon starting‘and:
increase progressively as the motor attains speed.
The'connections and the elements of the sys
tem‘ are substantially the same as illustrated and
2,409,312
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described in connection with Fig. 1, except ‘for
the following: The electromagnetic reversing
switch 21 has been omitted; the reverse speed
armature for controlling maintenance of said
connection of said electron tubes to said field
winding independent of said manual means, and
contacts 32b and 32d of pilot switch 32 have been
means to render said electronic means responsive
omitted; contacts 2B8, 25‘, 26g of switch 25, con
tacts 33b of switch 33 and sliding contacts 22“,
22b of voltage divider 22 have been omitted.
to the current circulating between said armatures
to control and limit such current and including
means for predetermining the limit.
A voltage divider 50 has been added, one of its
2. In combination, a generator, having an ar
mature and a ?eld winding, a pair of electron
terminals being connected to the positive termi~
nal of the motor, while its other terminal is con~
nected to the common terminal of the shunts I2
and I3. The voltage divider 50 is provided with
a movable contact 59a which is connected to one
terminal of each of the contacts 341][ and 3%,
while the connection of said contacts to the com
mon terminal of the shunts I2 and I3 has been
tubes, each having a control electrode, manual
means for establishing connection of said tubes
to said ?eld winding for supplying energizing cur
rent to the latter, adjustable means including
exciting current of the generator I0 is relatively
opposite directions selectively, adjustable means
electronic means for impressing a voltage on said
control electrodes for regulating the current sup—
plied by said tubes, a motor having an armature
connected in circuit with said generator arma
omitted. Furthermore, the movable contact 22‘1
ture, means responsive to the speed of said motor
is directly connected to the second terminal of
armature for controlling maintenance of said
contact 348, while the movable contact 22° is di
rectly connected to the second terminal of the 20 connection of said electron tubes to said ?eld
winding independent of said manual means, and
contact 34‘.
The operation of the system is substantially the
means to render said electronic means responsive
to the magnitude and direction of current circu
same as that illustrated in Fig. 1, except that the
supplemental voltage existing between the mov
lating between said armatures to control and limit
such current and including means for predeter
able contact Slla and the negative terminal of the
voltage divider 50 is added to the bias supplied by
mining different limits for different directions of
said circulating current.
the voltage divider 22 to the cathodes Me and I6“.
Upon starting, the voltage of the generator ar
3. In combination, a generator, having an ar
mature IIBL is substantially zero. Therefore, the
mature and a ?eld winding, a pair of electron
bias of the grids I48 and I4f with respect to the - tubes, each having a control electrode, reversing
cathodes I4,1 and Nb, respectively, is a minimum.
means including a pilot switch for establishing
This as has been aforedescribed results in a high
connection of said tubes to said ?eld winding
impedance of the tubes 24 and 25, so that the
for supplying energizing current to the latter in
low and the motor I I accelerates with a relatively
for impressing a voltage on said control elec
low torque. As the motor starts to rotate, and its
speed increases, the supplemental voltage sup~
plied by the voltage divider 50 progressively in
creases, thereby reducing the positive bias of the
grids Me and “If with respect to the cathodes IIIa
and I41’, respectively, which in turn increases the
trodes for regulating the current supplied by said
current passed by the tubes 24 and 25, so as to
cause an additional increase of the generator
dependent of said pilot switch, and electronic
means responsive to and controlling the current
tubes, a motor having an armature connected in
circuit with said generator armature, means re
sponsive to the speed of 'said motor armature
for controlling maintenance of said connection
of said electron tubes to said ?eld winding in
voltage to increase the torque and the accelera
circulating between said armatures for impres
ing a supplemental voltage on said control elec
tion afforded by the motor II. Hence, at low
speeds, the accelerating current and torque of the
trodes to limit such current, said last named
motor I I are relatively low, while at higher speeds
means including means for predetermining the
they are relatively high, the variation being ad
limit.
lustable by adjustment of the sliding contact 5%.
‘i. In combination, a generator, having an ar—
This system is particularly suitable for large 5 I.) mature and a ?eld winding, a pair of electron
centrifugal extractors which must be started at
tubes, each having a control electrode, revers
a very low rate in order to prevent undue unbal
ing means including a pilot switch for establish
ance of the rotating parts of the extractor. As
ing connection of said tubes to said ?eld wind
the extractor accelerates, the parts balance au
ing for supplying energizing current to the lat
tomatically and it is then permissible to increase . ter in opposite directions selectively, adjustable
the rate of acceleration and the accelerating cur
means for impressing a voltage on said control
rent.
The system shown in Fig. 2 may, of course, also
be applied to reversible controllers, and it is fur
electrodes for regulating the current supplied by
thermore possible to provide for a high rate of ac
celeration at low speed and a low rate of accel
eration at high speed, the changes required for
such operation being obvious.
I claim:
1. In combination, a generator, having an ar
mature and a field winding, a pair of electron
tubes, each having a control electrode, manual
means for establishing connection of said tubes to
said ?eld winding for supplying energizing cur
said tubes, a motor having an armature con
nected in circuit with said generator armature.
means responsive to the speed of said motor ar
mature for controlling maintenance of said con
nection of said electron tubes to said ?eld wind
ing independent of said pilot switch, and elec
tronic means responsive to and controlling the
current circulating between said armatures for
impressing a supplemental voltage on said con
trol electrodes to limit such current, said last
named means including means for-predetermin
ing a plurality of limits, respectively, for differ~
rent to the latter, adjustable means including “' ent operating conditions.
electronic means for impressing a voltage on said
control electrodes for regulating the current sup
plied by said tubes, a motor having an armature
connected in circuit with said generator arma
ture, means responsive to the speed of said motor 75
5. In combination, a- generator, having an ar
mature and a ?eld winding, a pair of electron
tubes, each having a control electrode, reversing
means including a pilot switch for establishing
connection of said tube to said ?eld winding for
2,409,312
9
,
supplying energizing current to the latter in op
posite directions selectively, adjustable means
connection of said tubes to said ?eld winding for
supplying energizing current to the latter in op
posite directions selectively, adjustable means
for impressing a voltage on said control elec
trodes for regulating the current supplied by said
tubes, a motor having an armature connected in.
circuit with said generator armature, means re
sponsive to the speed of said motor armature
for controlling maintenance of said connection“
of said electron tubes to said ?eld winding inde-. '
for impressing a voltage on said control elec
0
trodes for regulating the currentsupplied by said
tubes, 2. motor having an armature connected in
circuit with said generator armature, means re
sponsive to the speed of said motor armature for
controlling maintenance of said connection of '
pendent of said pilot switch, electronic means 10 said electron tubes to said ?eld'winding inde
for supplying a supplemental voltage varying in,
pendent of said pilot switch, velectronic means for
accordance with variations of the current circu
supplying‘ a plurality of supplemental voltages
lating between said armature's, means to Vary
varying in accordance with variations of the cur
the response of said electronic means to said cir- '
culating current, and electromagnetic means
controlled by said reversing means and said speed
responsive means, for impressing said supple
mental voltage upon said control electrodes to
limit such circulating current.
rent circulating between said armatures, means
to vary the response of said electronic means to
said circulating current, and means including
electromagnetic means responsive to said revers
ing means and said speed responsive means for
selectively impressing one of said supplemental
6. In combination, a generator, having an ar 20 voltages upon said control electrodes to limit such
mature and a ?ield winding, a pair of electron
circulating current to different values for differ
tubes, each having a control electrode, reversing
means including a pilot switch for establishing
ent operating conditions.
JAMES B. REEVES.
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