US2130162A

US2130162A - Tuning indicator tube

Info

Publication number: US2130162A
Application number: US80474A
Authority: US
Inventors: Harry C Thompson
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1935-06-27
Filing date: 1936-05-19
Publication date: 1938-09-13
Anticipated expiration: 1955-09-13
Also published as: DE692964C; GB481790A; NL57947C; GB481791A; NL46087C; CH203784A; FR807964A

Description

P 1933- H. c. THOMPSON 2,130,162

TUNING INDICATOR TUBE Original Filed June 27, 1935 INVENTOR HARRY C.THOM PSON ama Patented Sept. 13, 1938 UNITED STATES PATENT OFFICE TUNING INDICATOR TUBE tion of Delaware Original application June 27, 1935, Serial No. 28,665. Divided and this application May 19,

1936, Serial No. 80,474

4 Claims.

My invention relates to electron discharge devices, more particularly to such devices useful as visual indicators of voltage and having a fluorescent electrode which is rendered luminous, and has the appearance of a pattern of light which may be of constant height or length and varying width and which changes in response to the change in the magnitude of the applied voltage, a device of this character being particularly useful as a tuning indicator in radio receiving sets.

This application is a division of application No. 28,665, now Patent No. 2,051,188, issued August 8, 1936, filed June 27, 1935 and assigned to the same assignee as the present application.

It is an object of my invention to provide an improved electron discharge device of the kind described, which is particularly suitable for use as a visual tuning indicator in a radio receiving set and in which resonance is indicated by a brilliant luminous glow on an electrode.

In general my invention comprises an envelope having within it a straight thermionic cathode having two separate electron emitting sections around one of which are positioned at least one grid and an anode. Around the other section are mounted the visual tuning indicator elements comprising preferably a straight control electrode parallel to the cathode, and an anode which may be flat or cylindrical and may be of sheet or of mesh material and coated with material which fluoresces in response to electron bombardment. In operation the electrons flow from the cathode to the anode with suflicient, velocity to bombard the plate and render it luminous. The control electrode is electrically connected to the anode surrounding the grid and the elements of the tube are so connected in a radio receiving circuit that when the circuit is tuned to resonance with an incoming signal the luminous portion of the indicator anode is of a predetermined size. In one form of the device the connection is such that the luminous portion of the anode is of a maXi mum width and hence the dark space of minimum width when the circuit is tuned to reso nance, the height or length remaining constant.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which Figure 1 shows an electron discharge device embodying my invention with parts broken away to show details of construction; Figure 2 is an enlarged top and side view showing details of construction of the voltage indicating elements of the tube shown in Figure 1; Figure 3 shows a circuit arrangement using a tube made in accordance with my invention; and Figures 4 and 5 are top views of further modifications of the tuning indicator elements of the electron discharge device shown in Figure l.

The electron discharge device or tuning indicator tube shown in Figure 1 comprises an evacuated envelope l provided with the usual stem and press II, and base I 2. Supported from the press are a cathode l3, preferably the conventional indirectly heated equipotential type, a grid l4 and anode l surrounding the cathode.

In accordance with my invention I mount in the dome portion of the envelope Ill the visual indicating portion of the tube comprising a cathode, a control electrode and an anode having preferably a fiat surface presented to said cathode and control electrode and provided with a coating which fiuoresces when subjected to electron bombardment. While the anode having the fiuorescent coating may be of the mesh type and viewed from either side and might have fiat or curved surfaces, I may make it of fiat or curved sheet material and coat only one side, which may be directly viewed.

As shown in Figures 1 and 2 the cathode I3 is extended into the dome portion of the envelope as shown at I6 and has a second emitting section 16' for applying the electrons in the visual indicating device. A control electrode 25 in the form of a cylinder provided with a longitudinal opening 26 through which electrons pass from the cathode emitting portion Hi to the flat coated anode 21 surrounds the cathode and is supported from a cross bar [8 electrically connected to the side rods 19 of the anode !5. This control electrode determines the pattern of the luminescent portion of the anode Zl, which is shown as made of sheet material and coated with any conventional luminescent material, and is supported by rods 2! extending from the press II.

In operation the voltage on the anode I5 is applied to the control electrode 25, the voltage on this electrode determining the width of the pattern of light on the anode 21, the height of the pattern of light being constant and equal to the height of the anode. The less negative this control electrode 25 is biased with respect to the anode 2'? the wider will be the luminescent area (b) on the anode 21 inasmuch as the beam of electrons from the cathode becomes less sharply focused than when the negative bias on the control electrode is large and the luminescent area (a) is narrower. In this embodiment of my invention the luminescent portion of the voltage or tuning indicator may be viewed from the side of the tube with ease. The emitting area l6 of the cathode I6 is confined as shown to prevent the control electrode 25 drawing anysubstantial amount of current.

Referring to Figure 2, which shows a top view of the tuning indicator portion of the invention shown in Figure 1, the beam control electrode 25 is so biased that when no signal is being received the voltage difference between the control electrode 25 and the anode 21 is such that only the portion a of the anode is luminescent. As the set is tuned to resonance the voltage difference between the anode 21 and the electrode 25 becomes less, so that the control effect of the electrode 25 on the electrons leaving the cathode I6 is less, permitting electrons from the cathode IE to reach more of the anode 21 so that when the set is tuned to resonance the anode is luminous over the surface as shown by lines I).

The application of an electron discharge de vice made in accordance with my invention to a radio circuit is shown in Figure 3. Normally the anode 15 of the triode section of the tube is electrically connected through a resistor 49, to a source of voltage 4|. The indicator anode is connected directly to the source of voltage 4|. With no voltage on the grid 14 a certain predetermined amount of current flow through the triode section of the tube causes a drop in resistor 40, so that the Voltages applied to anode l5 and indicator anode 21 have the greatest differential, the voltage on anode l5 being at the lower potential. The voltage on anode 21 does not change While that on the anode [5 decreases, due to the drop through resistor 40. This makes the control electrode 25 negative with respect to anode 21, thus reducing the width of the luminescent portion of the anode 21. As the voltage on the control grid 14 increases in the negative direction the current flow to the anode l5 decreases so that the voltage drop through the resistor 40 decreases. Under these circumstances the voltage differential between anode l5 and indicating anode 21 decreases: so that the control electrode 25 becomes less negative with respect to the anode 21. This permits the width of the luminescent portion to increase. Thus the luminescent portion increases as the negative bias on the control grid l3 increases. This characteristic of the tuning indicator tube is made use of when connected to a conventional automatic volume control circuit. The rectifier tube 42 has an anode 43 connected to one side of the radio frequency or intermediate frequency transformer 44 coupled to the receiving circuit not shown, and a cathode 45 connected through a grid leak 46 and by-pass condenser 41 to the other side of the transformer 44. The cathode side of the transformer 44 is connected through resistor 48 to control grid 1 4 of the tuning indicator tube. A radio frequency by-passing condenser 49 connects the grid to ground, and the conductor 50 may be connected to other parts of the circuit to provide automatic volume control. As the receiving circuit is tuned to resonance and rectification takesplace through the tube 42, the cathode side of the radio frequency transformer becomes negative with respect to ground due to the current through resistor 46. This negative voltage is applied to the control grid 14 as a negative bias with the result that the current through the triode portion of the tube is reduced, thus causing the width of the luminescent portion of the tuning indicator anode 21 to increase as explained above. In this arrangement the control electrode is positive with respect to the cathode. Several advantages follow from this arrangement over that in which the control electrode is biased negatively with respect to the cathode. The boundaries of the electron beams are sharp and well defined. There can be a high concentration of electrons at the edges of the luminous areas so that the luminosity is uniform. The high current to the luminescent portion of the screen can be obtained at low voltages and hence a high luminosity is the result. A positive control electrode is suitable for direct coupling to an amplifier, that is it may be directly connected to the plate of an amplifier tube as shown in Figure 1 for example. Furthermore, a tube made in accordance with my invention is not critical to variations in cathode temperatures and is susceptible for use with alternating and direct voltages and current:

In Figure 4 the control electrode 30 is a V- shaped member on one side of the electron emitting cathode l6 and the luminescent anode is similarly shaped with the coating on the side facing the cathode. Figure 5 shows an arrangement very similar to that shown in Figure 4 except that the control electrodes 35 and anode 36 are flat.

In the embodiment shown in Figures 4 and 5 the control electrodes 30 and 35 may be connected to the grid of the triode section, so that they are biased negatively with respect to the cathode. With this connection the luminescent portions between the lines a and b in Figures 4 and 5 indicate the luminescent portions when the circuit in which the tube is used is tuned and untuned to an incoming signal.

While I have indicated the preferred embodiment of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing-from the scope of my invention as set forth in the appended claims.

What I claim as new is:

1. An electron discharge device having an envelope enclosing a straight thermionic electron emitting cathode, an anode having a flat surface adjacent said cathode and having a fluorescent coating thereon, a control electrode comprising a pair of straight conductors parallel to and on the opposite side of the cathode from said anode for determining the extent of the anode reached by the electrons emitted by the cathode.

2. An electron discharge device having an envelope, a cathode within the envelope having a plurality of electron emitting surfaces along its surface, a grid and anode surrounding one of said electron emitting surfaces and a fluorescent anode having a flat surface adjacent another of the electron emitting surfaces of said cathode and a, control electrode positioned on the opposite side of the cathode from said fluorescent anode and comprising a conductor parallel to the cathode and connected to the anode surrounding the grid for producing on said fluorescent anode a beam of substantially constant length and of a width depending upon the voltage applied to said control electrode through the anode around the grid.

3. An electron discharge device having an envelope, a straight thermionic cathode within said envelope for emitting electrons, a V-shaped anode adjacent the cathode and coextensive therewith and coated with a material which fluoresces when struck by electrons from said cathode and a control electrode comprising a V-shaped member on the other side of said cathode from said anode and coextensive with said cathode and anode, the width of the luminescent portion of the anode struck by said electrons being dependent on the voltage applied to said control electrode.

terial and electrically connected to and sup-port- 10 ed by the anode surrounding said grid.

HARRY C. THOMPSON.