US2124401A - Cathode-ray tube - Google Patents

Description

Jul 19, 1938. w, HEWNN 2,124,401

CATHODE RAY TUB-E Filed May 11, 1955 Fig. I

Inventor: Walter Heimann,

Patented July 19, 1938 CATHODE-RAY TUBE Walter Heimann, "Berlin Reinickendorf, Ger.-

many, assig nor to. General Electric Company, a corporation of New York Application May 11, 1933,.Serial No. 670,551

I In

The present invention .relates to. cathode-ray tubes provided with an electrostatic control member and used in :theinvestigation of electric or magnetic phenomena.

In tubes of this sort, the electrons emitted by the cathode and accelerated by :the .anode are causedto. be focused on afiuorescent screen by means of an electrostatic member whichis sometimes known as..a Wehnelt cylinder". In

lan order to increase the concentration .ofthe electrons, there. may be provided .an inert gas within the envelope, asis well known. The cathode rays. are usually deflected: across. the:v screenby means of a pair .or pairs f plates. to which; the

.15 voltage. under investigationis applied.

It has been found that when the voltage-ape plied. .to the deflecting. plates is less :thanablout 100,000 cycles vper second,- thecombined effect of thefocusing member and the gas is usuallysuiificient to produce a sharpandiwell-defined light spoton the screen. However, at: the higher frequencies, i. e. above 100,000 cycles. per -::second, the'light image becomes fuzzy with an indefinite outline. In order to improve the light char- 5 acter of the spot at these higher frequencies, the use of a gas of very low atomic weight has been proposed, for example hydrogen, which tends to constrain the electrons to a beam of uniform density in cross section. Notwithstand- I 30 ing the improvement in the focusing effect obtained by the use of such a gas, it has still been found that the light spot does not present a clearly defined'image when the cathode-ray beam is deflected at frequencies above the order of 35 100,000 cycles per second.

An object of the present invention is to improve the light image when the tube is used under high frequency conditions. It has been found that the indefinite character of the light 40 image is due in a large degree to the deleterious electrostatic effects produced on the control member and having their origin in the deflecting plates. In accordance with my invention, I propose to electrostatically shield the focusing mem- 45 ber from these effects and for this purpose,

provide a metal enclosure which completely surrounds the member. The invention will be more 1 fully understood when reference is made to the following specification and accompanying draw- 50 ing in which Fig. 1 represents an elevational view, partly broken away and in section, of a cathode-ray tube improved in accordance with my invention. Fig. 2 is an enlarged view, in cross section, of an exemplary form of cathode 55 which may be used in the tube.

end of the envelope is coated onthe interior carrying a metal cup member 5..

Germany May 30,1932 3Claims. (o1. sac-27.5w

. Referring to Fig. 1, numeral 1 designates-the envelope of a cathode-ray tube which is pro.- vided with .the usual flared-out portion terminated bya spherical glass wall. The spherical with .a well-known substance which fluoresces whenlstruck by electrons. The other .end' of the envelope terminates in a reentrant stem 2 which supports the entire electrode structure except the deflecting: plates. The cathode, as shown n more clearly in Fig. 2, is. constituted. of a metal cylinder provided at the upper end (as shown) with a transversely extending metal plate 4 The interior of the cup may be coated with an electronically active material. ,At the extreme upper; end of the cylinder there is a metal cap 6 provided-at :the center with an. electricdischarge opening 1.

Within the cylinder 3., there is a helical form. of

heater fl secured at the upper end to the trans.- .verse disk 4. Leading-in conductors which also serve. the purpose of supporting thecathode structure-are taken, respectively from the lower end of the heater and from the cylinder 3,

through the stem 2 to the exterior.

The anode may take the form of a metal plate 9 having a central discharge opening Hi. In order to focus or otherwise control the electrons passing between the cathode 3 and the anode 9, there may be provided a cylindrical focusing member ll, mounted in line with the openings I and In, as shown. The member ll conveniently may be supported from the stem 2 by means of a rigid leading-in conductor I2.

In addition to this electrode structure, the envelope I also contains two pairs of deflecting plates l3, l4, rigidly mounted in the envelope by means of stiff wires which extend transversely across the envelope. The respective pairs of plates arearranged in different transverse planes with respect to the envelope and with respect to one another.

The envelope may contain an inert gas such as argon at a relatively low pressure.

When a tube of this sort is operated under conditions of high frequency, i. e. when high frequency voltage undulations are applied to the deflection plates I3, I 4, it has been found that notwithstanding the presence of a gas within the tube and the focusing cylinder ll charged to a proper potential for focusing, the light spot on the fluorescent screen I5 becomes blurred or fuzzy.

In order to reduce this effect, and in accordance with my invention, I provide an electrostatic shield I6 about the focusing member I I. This shield conveniently may take the form of a metal cylinder secured directly to the anode, hence maintained at anode potential, and the bottom of which is completely closed except for a small discharge opening I! in line with the opening in the cathode. The electrostatic control member II is thus surrounded on allsides by the metal member except for a discharge opening at the top and the bottom of the member through which electrons pass on their way to the screen.

It is evident that while I have shown the member l6 as being made of solid metal, this member may take the form of a metal cage or mesh enclosure, since its function is solely that of providing a positive field about the member II which serves to shield the member from the high frequency oscillations applied to the deflecting plates I3, M. It is also apparent that the positive field as exerted by the metalenclosure [6 incidentally functions to accelerate the electrons between the cathode 3 and the control member I I. The enclosure Hi can conveniently serve as a support for the anode 9 and for this purpose, there may be provided a rigid leading-in conductor l8 sealed in the reentrant stem 2 and secured to the bottom member of the enclosure.

While I have shown the metal enclosure l6 as being secured directly to the anode, hence maintained at anode potential, it is evident that the enclosure may be mounted separate from the anode and charged to any suitable positive potential.

It has been found in accordance with my invention, that when the focusing member H is completely surrounded by a positively charged metal member, the electric fields produced at the deflecting plates l3, I4 have substantially no effect on the action of the focusing member and hence, the latter is free to exercise its focusing or other controlling eflect on the electron stream as it passes through the anode and between the deflecting plates on its way to the fluorescent screen. By the use of the improved shielding member IS, the light spot on the screen is sharply defined, even when the electron beam is deflected at a rapid rate by voltages having frequencies, as high as 200,000 cycles per second or over, applied to the plates I3, M. I

While I have described my invention in connection with a cathode-ray tube of the gaseous type, it is to be understood that the positively charged shield I6 also ofiers an advantage by way of increasing the electrostatic controlling effect of the member H in a highly evacuated tubecontaining no gas.

What I claim as new and desire to secure by Letters' Patent in the United States is:

1-. A cathode-ray tube comprising an envelope containing a cathode, an electrostatic control member and electron-deflecting plates, and means for electrostatically screening said control member from the. deflecting plates, said means including a cylinder completely enclosing said member except for discharge openings and adapted to be'maintained at a positive potential with respect to the cathode;

2. A cathode-ray tube comprising an envelope containing inert gas, a cathode, an electronfocusing member and electron-deflecting plates, and means for electrostatically. screening the focusing. member from the deflecting plates, said means including a cylinder adapted to be maintained at a positive potential with respect to the cathode and completely enclosing solely the electron-focusing member except for discharge openmgs.

3. A cathode-ray tube comprising an envelope containing gas, a cathode, an anode, an electronfocusing member and electron-deflecting plates,

said anode comprising a cylinder completely closed by a metal wall except for discharge openings and enclosing the focusing member.

WALTER HEIMANN.

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