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Патент USA US2131538

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Sept. 27, 1938.
Filed Dec. 31, 1936
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Patented Sept. 27, 1938
2,131,538 ‘ _
' 2,131,538
Henry J. McCarthy, Danvers, Massg’assignor to _
Hygrade Sylvania Corporation, Salem, Mass., a '
corporation ‘of Massachusetts
Application December 31, 1936, Serial No. 118,532
4 Claims.
(01. 179~—171)
This invention relates to- wave signaling sys
tems and more especially to such systems as
employ electron discharge tubes of the suppressor
grid type.
‘The invention is in the nature of an improve‘
ment on the type of system disclosed in appli
cation Serial No. 13,047, ?led March, 26th, 1935. >
There is disclosed in said application a system
employing a pentode tube of the suppressor grid
10 type wherein the suppressing action is achieved
without employing a conductive or metallic con
necticn between the suppressor grid and the
cathode. The present invention relates to this
same type of system and one of its principal ob
15. jects is to provide a wave repeater or ampli?er
employing a suppressor grid pentode tube where—
in the suppressor grid is capable of eifecting sup
pressor action without conductive connection to
the cathode, and at the same time it maintains
20 theinterelectrode capacity between the anode
and control grid at a minimum.
A feature of the invention relates to a sys
velope either of the metal or glass type. Suitably
supported within the envelope is a pentode
mount comprising an electron emitting cathode
2 with its insulated heater ?lament 3; a control
grid 4; a shield grid 5; a suppressor grid 6; and
an anode or plate-1; It will be understood that
any Well-known structure and arrangement of
the electrodes may be employed, for example the
mount may be similar to that embodied in the
tubes designated commercially by the type num- loi
bers 39/44, 41, 5'7, 78 and the like and while the
invention is primarily applicable to- radio fre
quency pentodes it also has desirable applica
tions to so-called power ‘output pentodes repre
sented for example by tubes of the type <53, 47 and 15»
the like.
. The signals to be repeated or ampli?ed are
impressed across the control grid 4 and the
cathode 2 by any well-known form of signal
input coupling circuit represented by the sec- 20,
ondary winding 8 of the coupling transformer.
_ Preferably the grid 4 is biassed with respect to
tem‘employing a suppressor grid pentode tube the ‘cathode by any well-known means, for ex~
wherein the suppressorgrid is insulated from the
25 cathode so far as direct current is concerned, by
a condenser. With this arrangement the sup
pressor grid acts ef?ciently to prevent the re
turn of any appreciable number of secondary
electrons from the plate or anode to the shield
30 grid, and it also supplements the shield grid in
reducing to a desirable minimum, the interelec
trode capacity between the anode and the con
trol grid.
Other features and advantages not speci?cally
3,. enumerated will be apparent after a consider
ation of the following detailed descriptions and
the appended claims.’ While the invention will
be disclosed herein in schematic form and in con
nection with certain well-known types of pentode
tubes, it- will be understood that this is done
merely for explanatory purposes and not by way
of limitation thereto. Accordingly in the draw
Fig. 1 is a typical schematic wiring diagram of
45 a system embodying features of the invention.
Fig. 2 is a typical series of characteristic curves
showing the relation between plate current and
plate voltage in a tube connected according to
Fig. 1.
Fig. 3 is a curve showing the relation between
the interelectrode control grid-to-plate capacity
for different values of the suppressor grid return
Referring to Fig. 1, the numeral I represents
55 any well-known form of evacuated enclosing en
ample by the resistor 9 shunted by condenser 50.
The signal output coupling circuit may be of any 25
suitable type and merely for purposes of expla
nation it is shown as of the resistance-capacity
type in which the plate 1 is connected to the
positive potential tap ll through a coupling re
sistor I2.
The potentials across resistor l2 are
coupled through capacity 13 to the input of a
succeeding stage or to a signal reproducing de
vice, the input terminals of which are represented
by numerals I4, l5. In accordance with the
usual practice, a leak resistor l6 may be provided.
The shield grid 5 is connected to a suitable
positive potential tap l'l preferably of a lower
voltage than the tap H for purposes well under
stood in the electron tube art. Heretofore, the
suppressor grid 6 has been conductively connected
to either the cathode or to ground so as to be
at or near cathode potential. This usual con
ductive connection of the suppressor grid to the
cathode, performs. the function of preventing the
return of any appreciable number of secondary
electrons from the anode to the shield grid, and m
at-the same time it tends to supplement the shield
grid in reducing the interelectrode capacity be
tween the plate and the control grid. As dis
closed in my prior application Serial No. 13,047, 50
I have found that the suppressing action of grid
6 may be obtained without a conductive connec
tion to the cathode. In this lattercase, it is
necessary to employ a suppressor grid which be
cause of its composition or because of its surface 55
characteristics has the property of emitting few
secondary electrons under bombardment either
by the primary electrons from the cathode or by
by 3 volts; the shield grid 5 was positively biassed
with respect to the cathode by 100 volts; the plate
‘I had applied thereto a positive potential of 250
secondary electrons.
volts. vUnder these circumstances the condenser
I 8 had a capacity of 0.01 mfd. The curves of Cl
For example as disclosed
in said application Serial No. 13,0517 the grid may
be coated with ceramic or any other material
Fig. 2 show the relation between plate voltage
that has the property of reducing secondary and plate current for di?erent values of negative
emission as is well known in the electron tube
art. With such a grid it is possible to allow it to
10 ?oat, -without any conductive or other connec
tion to the cathode, and the desirable pentode
plate current plate voltage characteristics are
I have found however that with this
type of suppressor grid ?oating, While the sup
15 pressor action is obtainable, nevertheless the grid
does not supplement the shield grid in reducing
the interelectrode capacitance. However, I have
also found that by returning the suppressor grid
to the cathode through a condenser such as con
.20 denser l8, it is possible to obtain the suppressing
action and at the same time the suppressor grid
supplements the shield grid in reducing the inter
electrode capacitance. While this method; of
suppressorgrid return ?nds its greatest useful
25 ness in a tube wherein the suppressor grid has
a surface capable of inhibiting the emission of
bias on the control grid, the» curve “a” being at
minus 1 volt, curve “b” at ‘minus 3 volts, and
curve “0” at minus 10 volts. It will be under
stood of course that various changes and modi
?cations may be made in the various voltages
without departing from the spirit and scope of
the invention.
What I claim is:
1. In a wave repeater the combination of an
electron discharge tube having a cathode, an
anode, a control grid, a shield grid and a sup
pressor grid, means to impress signals on the
control grid, means to apply a steady positive 20
potential to the shield grid, and a connection
between the supressor grid and cathode to con
ductively insulate said suppressor grid from the
cathode while allowing said suppressor grid to pre
vent secondary electrons from reaching said 25
shield grid from said anode.
secondary electrons, nevertheless it isalso useful
2. In a wave repeater the combination of a
as applied to the ordinary type of pentode
wherein the suppressor grid is not specially
formed or treated to inhibit secondary emission.
While the capacitance of condenser I8 is not
critical nevertheless it is preferable to employ a
condenser having a capacity not materially less
than 0.001 mfd., so that the control grid-to—plate
pentode tube of the suppressor type, and means
to return the suppressor grid‘to the cathode
without a conductive connection thereto, said 30
capacitance is at or near a minimum. Fig. 3 is
a curve showing the relation between the inter
electrode control grid-to-plate capacity of a type
'78 tube for various values of condenser l8. From
this it will be seen that the interelectrode capac
403 ity rises abruptly for very low values of capacity
it. For example if the tube of Fig. 1 is a type
78 tube the condenser l8 should have a capacity
of the order of 0.01 mfd. Thus in one particu
lar connection which was found to produce the
desired pentode characteristics the control grid 4
was negatively biassed with respect to the cathode
means comprising a condenser.
3. A wave repeater according to claim 2 in
which the condenser has a capacity not mate
rially less than 0.001 mfd.
4. In a wave repeater the combination of a
pentode tube of the suppressor grid type, the sup
pressor grid having its surface specially designed
to reduce the emission of secondary electrons
therefrom whereby the suppressing action may
be obtained while maintaining said suppressor 40
grid conductively insulated from the cathode, and
a condenser connected in series between the sup
pressor grid and the cathode to allow said sup
pressor grid to supplement the shield grid in re
ducing interelectrode capacitance.
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