US1936758A - Electron discharge device - Google Patents

Description

NOV. 28, 1933. M HAFFCKE 1,936,758

ELECTRON DI SCHARGE DEVICE Filed March 30, 1931 3 6 W007 1 11 our ur 17 l/ 10 7 l l i l ii l l l l INVENTOR PAM A7. l/af/ke Patented Nov. 28, 1933 UitITED STATiiiii OFFICE ELECTRON DISCHARGE DEVICE Philip M. Haficke, New Haven, by mesne assignments, to

Conn, assignor, Radio Research 9 Claims.

My present invention relates to electron discharge devices useful for rectifiers, detectors, amplifiers and other purposes, and is an improvement upon the invention of Heany and Barnett forming the subject matter of their United States patent application Serial No. 522,297 filed March 13, 1931, entitled Electron discharge devices. In brief, that invention comprised an electron discharge device or tube containing a remarkably high gas content as compared with the usual and previous practice in connection with radio tubes and further comprised a hot cathode for initiating electron emission to ionize said gas by collision to produce additional electrons, the operation of said tube being controlled within working limits by the special construction thereof and by an unusually large space relation between the plate and the cathode in connection with high gas content and the electrical potentials employed.

My present improvement provides an intensifier or accelerating or sustaining electrode or element preferably located approximately midway of the grid of the tube and relatively close thereto, to which is applied an electrical potenial which is positive relatively to the cathode and negative relatively to the plate.

An object of this improvement in electron discharge devices is to attract and sustain an electron flow past the grid and thereby maintain a signal path to the plate at all times, which otherwise might be interrupted by a heavy negative swing of the potential on the grid.

Another object is to provide means which will 35 sustain the ionization and the electron flow from the cathode to the plate in the Heany-Barnett tube at all times even during heavy negative charges on the grid.

Another object is to provide the foregoing means under conditions of spacing and pressure which will increase the amplification factor of the tube.

illustrative of the present invention are the devices shown in the accompanying drawing wherein Fig. 1 shows one form of embodiment of the invention in connection with a Heany- Barnett electron discharge tube; Fig. 2 shows an alternative preferred, more commercial embodiment; and Fig. 3 shows the improved tube diagrammatically together with the various battery and input and output connections irrespective of the position of the tube in the radio receiver or its interstage hook-up with respect to other tubes thereof.

55 In the various figures, 1 designates the envelope of the tube; 2 the press; 3 the emitting cathode; 4 the control grid; 5 the accelerator; 6 the plate or anode; 7 is the source of current for heating the cathode; 8 is the ordinary B battery in the output circuit with its positive pole connected to the plate through the resistor or other suitable form of interstage coupling 11. A tap 9 is taken from a suitable intermediate point 01 the battery 8 to the accelerator 5. The output circuit is shown bridged across the coupling 5 11 in accordance with the usual practice; and the input circuit is connected as usual between the cathode 3 and the grid 4.

The electron emitting heated cathode may take a variety of forms. Thus, it may be a filamentary cathode either of the oxide coated type operating at comparatively low temperature, or may consist of an alloy of a thoriated tungsten type, or it may be a pure metal filament operated at incandescence. Also, it may consist of an oxide coated cathode separately heated by a hot filament. In any case, the temperature of the cathode will be similar to that used in the hard vacuum tube for the same type of cathode. In-

stead of being strung between supports, the cath- 30 'ode may consist of a thin metallic ribbon coated with an emitting oxide and wound around a small diameter suitably supported tube of insulating material, since this form of cathode also gives very good results in practice and corre- 35 sponds with the cathode disclosed in United States patent application Serial No. 507,133 entitled Electrode for electron discharge devices filed January 7, 1931, by David A. Barnett.

In the embodiment shown in Fig. 1, the con- 9 ducting support 12 for the plate 6 is preferably encased within an insulating tube 13 to prevent stray ionization from said conductor to the cathode.

The accelerator 5 in the form illustrated consists of a small wire loop surrounding the grid at its mid point and separated from it by a clearance of approximately 3 2 of an inch. A conductor 19 supports the accelerator 5 from the press and extends out of the tube through the stem. The wires 16 and 17 extend through the stem and press to the ends of the filament 3; and in the same way the wires 18 and 20 form the connections respectively to the grid 4 and the plate 6.

Instead of the disk form of plate 6 in Fig. 1, a tubular plate 6 is substituted in Fig. 2 supported on wire 12 connecting through the press with the lead-in wire 20. Also, in Fig. 2, the filament 3 constituting the cathode is supported in the axis 110 of the tubular plate between the ends of supporting wires projecting from the press which in turn are connected with the lead-in wires 16 and 17. The grid 4 consists of a wire helix surrounding the filament 3 and supported on a wire from the press connected with the lead-in wire 18. The accelerator 5 consists of a coiled wire concentrically surrounding the control grid 4 midway of its length and is supported on a wire 14 from the press connected with the lead-in wire 19. This supporting wire 14 is surrounded by a tube of insulating material 15 to serve like the tube 13 in Fig. 1 to prevent stray ionization from the support wire to the cathode.

As a specific illustration, a tube constructed in accordance with the invention on the general design of Fig. 2 for use as a detector or amplifier consisted of a thoriated tungsten filament .004 inches in diameter surrounded by a grid in the form of a fine wire helix 1% of an inch inside diameter and one inch in length and having thirty-two turns to the inch; and the plate or anode consisted of a metal tube of an inch in diameter and one inch long; the grid being surrounded at its mid point by a small wire loop 5 separated from the grid by a clearance of approximately 01 an inch.

In this specific tube the gas content was nitrogen at a pressure approximately equal to one millimeter of mercury. The voltage applied to the filament was slightly higher than in a hard vacuum tube on account of the presence of the gas and was just sufficient to raise the filament to a temperature similar to that in a hard vacuum tube. The potential applied to the accelerator was slightly greater than the ionizing potential oi the gas; this varying slightly with the pressure but more particularly with the kind of gas used. The plate potential was from 45 to volts above the accelerator potential. When the described tube was connected in a radio receiver, either as a detector or amplifier with the various constants adjusted to suit the characteristics of this tube, very excellent results were secured, Iully as good as or better than the performance of tubes of the usual kind.

Other gases than nitrogen may be used, such as neon or any other gas operative for the purpose which will be inert or without chemical effect on the electrodes.

The plate spacing will be as in the Heany- Barnett tube. As to this it may be said that there is no definite plate diameter or cathode-plate space relation that may be said to be applicable to all kinds of tubes, because this relation varies depending upon whether the tube is a detector, amplifier, power or screen grid tube, etc. However, as a relative statement it may be said that the best or preferred cathode-plate spacing for my improved tube is similar to the Heany-Barnett tube, and will be substantially twice or possibly more than twice the cathode-plate spacing in a hard vacuum tube oi the same kind. The object is to spread out or thin out the glow discharge between the cathode and anode over a surface which is sufiiciently large and a gap which is sufiiciently long so that the pop-over or arcing stage is past and so that easy control of the operation of the tube is obtained.

The actual gas pressure in the improved tube may be the same as in the Heany-Barnett tube and not being critical may vary over an extremely wide range. The minimum pressure may be described as that which is sufiicient to allow a perceptible discharge glow surrounding the cathode, which is particularly noticeable with the emissive oxide coated filament type because of its low operating temperature and the particularly rich emission of electrons from this type of cathode. The gas pressure measured by a McLeod gauge may be as low as of a micron. However, considerably, better performance is secured by increasing this pressure from this operable minimum until a pronounced glow discharge is seen. Creditable performance is secured with gas pressures ranging all the way from 1 to '15 millimeters of mercury and higher. The tube is operative with gas pressures which are so high that they are past the point at which there is a visible glow discharge provided the plate potential is made sufiiciently high. With thoriated tungsten filaments we have secured very excellent results with gas pressures corresponding to 6 to 12 millimeters of mercury. All this is in marked contrast to the ordinary hard vacuum tube which is usually pumped to a pressure of of a micron of mercury and then flashed so that the final gas pressure in the tube is only a very small fraction of a micron. With this tube a gas pressure is suitable which will give a distinct glow through the tube when tested by the usual spark coil test method with the spark gap adjusted to of an inch or less, whereas such a gas content would be prohibitive for operation in the usual tube.

In Fig. 3 the accelerator 5 is shown connected by the wire 19 with an intermediate tap 9 of the B battery 8 so as to apply a potential to the accelerator which will be positive relatively to the cathode 3 and negative relatively to the plate 6, the potential applied to the accelerator being preferably slightly greater than the ionizing potential of the particular gas used in the tube.

During the normal or preferred operation of 115 the tube, a distinct glow discharge is seen surrounding the cathode, and furthermore a distinct additional glow discharge will be visible around the accelerator when connected to its proper potential.

Under preferred conditions of electrode spacing and gas pressure, the accelerator 5 materially increases amplification by the tube; and in most cases the accelerator is an important element of the tube due to the fact that its positive potential relative to the cathode attracts and sustains an electron flow past the grid at this point and thereby maintains a signal path to the plate at all times which otherwise might be interrupted by a heavy negative grid swing.

Instead of a ring surrounding the grid approximately at its mid point, the accelerator may consist of a short are or portion of a ring or of merely an exposed wire point close to the outside of the grid in the same position.

Like the Heany-Barnett tube, the present tube may be used with any oi. the forms of interstage coupling generally employed in radio receivers with suitable change in the constants of the hook-up to secure the full advantages in recep- 140 tion, sensitivity and amplification.

It will be understood that the sizes, figures and data above given are only specific for certain conditions such as the kind of gas employed, the spacing of the electrodes, the electrical potentials 5 used and the electrical characteristics of the circuits employed, etc.

What I claim is:

1. Electric discharge apparatus comprising a receptacle having a useful gas content ata pres- 150 sure of at least one millimeter of mercury; a heatable electron emissive cathode; a control grid; a plate; an auxiliary electrode intermediate said grid and plate; means including said cathode and plate for creating a glow discharge in said gas; and means for applying to said auxiliary electrode a positive potential relatively to said cathode and a negative potential relatively to said plate suflicient to maintain said glow discharge at all values of negative signal potential applied to said grid.

2. Electric discharge apparatus comprising a receptacle having a useful gas content at a pressure of at least one millimeter of mercury; a heatable electron emissive cathode; a control grid; a plate; an auxiliary electrode intermediate said grid and plate; means including said cathode and plate for creating a glow discharge in said gas, the space between said cathode and plate being long enough to prevent arcing therebetween; and means for applying said auxiliary electrode a positive potential relatively to said cathode and a negative potential relatively to said plate suflicient to maintain said glow discharge at all values of negative signal potential applied to said grid.

3. Electric discharge apparatus comprising a receptacle having a useful gas content; a heatable electron emissive cathode; a control grid; a plate; an auxiliary electrode intermediate said grid and plate; means for creating a glow discharge in said gas; and means for applying a potential to said auxiliary electrode suflicient to maintain said glow discharge at all values of negative signal potential applied to said grid.

4. Electric discharge apparatus comprising a receptacle having a useful gas content at a pressure of at least one millimeter of mercury; a

heatable electron emissive cathode; a control grid; a plate; an auxiliary electrode intermediate said grid and plate; means for impressing on said plate a positive potential sufficient to create a glow discharge in said gas when said cathode is operating, the distance between said anode and said other electrodes being long enough to prevent arcing therebetween; and means for applying to said auxiliaryelectrode a positive potential relatively to said cathode and a negative potential relatively to said plate suflicient to maintain said glow discharge at all values of negative signal potenial applied to said grid.

5. Electric discharge apparatus comprising a receptacle having a useful gas content at a pressure of at least one millimeter of mercury; a heatable electron emissive cathode; a control grid; an anode; means including said anode and cathode for creating a glow discharge in said gas; an auxiliary electrode closely adjacent said grid and intermediate said grid and anode; and means for applying a potential to said auxiliary electrode sufficient to maintain ionization through said grid at all values of negative signal potential applied to said grid. 1

6. Electric discharge apparatus comprising a receptacle having a useful gas content at a pressure of at least one millimeter of mercury; a heatable electron emissive cathode; a control grid; a plate; an auxiliary electrode intermediate said grid and plate; means for applying a positive potential to said auxiliary electrode relatively to said cathode somewhat greater than the ionizing potential of said gas content and for applying a higher positive potential to the plate relative to the cathode suflicient to create electron fiow from said cathode to said plate.

'7. Electric discharge apparatus comprising a receptacle having a useful gas content; a thermionic cathode; a signal control grid; an anode; the spacing being such as to render the device non-self-restoring when an excessive negative potential is applied to said grid, and an auxiliary electrode for rendering said cathode-anode space self restoring for all values of negative signal potential applied to said grid.

8. An electric discharge device comprising a receptacle having a useful gas content; a thermionic cathode for liberating electrons in said gas; a plate adapted to have impressed thereon a positive potential suflicient to create a glow discharge between said electrodes when said cathode is operating; a control grid intermediate said cathode and plate and an auxiliary electrode in the path of said discharge for rendering said discharge self restoring for all values of negatve signal voltage on said grid.

9. A device in accordance with claim 8 wherein said auxiliary electrode is a ring-like electrode substantially surrounding the mid-point of said grid.

PHILIP M. HAFFUKE.

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