DE1071238B - - Google Patents

Description

The invention relates to a cathode ray tube with a beam generating system, which consists of at least one Triode part with cathode, grid and anode and which is intended for operation in a circuit to which the modulation of the cathode is fed.

It is known that the steepness of the modulation characteristic of a cathode ray tube, ie the ratio between the change in the electron beam current and a given change in the signal voltage supplied to the cerium tube, is determined by the parameters and the spacing of the electrodes which form the triode part of the tube . Other electrodes, which may be arranged beyond this part, have little or no effect on this characteristic. . _:

It is also known to increase the steepness of the modulation characteristic of a cathode ray tube by using an electron beam generating system in which the anode of the grid is 0.152 mm or less apart. In the known arrangement, the openings in the Gittej and anode both have the same diameter. ■ ■. . ; _; :.

Furthermore, a cathode ray tube is known which is operated in 'normal grid control'; and at for the purpose of limiting the beam cross-section, -the .., The anode opening is smaller than the opening of the positive acceleration electrode. As a result of the different training the rest of the electrode system and the different mode of operation of this known arrangement however, no increase in slope can be achieved. .

Surprisingly, it has been found that with a cathode-modulated cathode ray tube a significant increase in slope can be achieved that one not only measures the distances between the individual electrodes in a suitable manner, but that In addition, one also places the electron passage openings of the individual electrodes in a certain one Brings relationship to each other. It is therefore an object of the invention to provide a cathode ray tube, which has a significantly steeper modulation characteristic without the need for special additional electrodes in the tube would have to be inserted.

According to the invention it is proposed that the distance between the electron passage openings of the grid and the anode is 0.152 mm or less, preferably 25 µ, and that the electron passage opening of the grid is made larger than that of the anode.

The invention is explained in more detail. Calculations of the slope of cathode ray tubes with cathode modulation are explained.

It should be noted that the following expression is not an exact specification of the slope, but rather represents the dynamic characteristic of the tube. It is therefore called G, quality factor. .

Applicant:

Electric & Musical Industries Limited,
Hayes, Middlesex (Great Britain)

Representative: Dr.-Ing. B. Johannesson, patent attorney, ■ -. Hannover, Göttinger Chaussee '76 '. · .;

Claimed priority:, V:
Great Britain January 10, 1956 and January 7, 1957

Kenneth Edward Groves, Hillingdoii, Middlesex

(Great Britain),
has been named as the inventor

Assuming that the G + factor in grating modulation is a constant for a certain arrangement of the beam generating system, the factor can be defined as ... ^:> . ';

I. max

G _n =

where Ic max is the cathode current of the tube at 0 volt grid voltage, measured in μΑ, and Vco _{g is} the grid blocking voltage, measured in volts.

Itt the above definition of the G factor becomes the modulation of the electron beam is fed to the grid, but in normal use of television picture tubes the Modulation applied to the cathode.

In order to obtain an indication of the mode of operation of an electron gun in the case of cathode modulation, another G factor G _{c is} defined as

G ₀ =

I. max

Vco

where Ic max is the cathode current, measured in μΑ, with V _e = 0 and with cathode modulation _{and Vco c} the reverse voltage, measured in volts. ' ■■: .- ■■

For a particular system arrangement using cathode modulation, the cathode current is with 0 volts at the cathode in relation to the grid always greater than with grid modulation, provided that that the accelerating voltage in each Case is tuned so that it gives the same modulus of the reverse voltage. When a system for a

909 689/473

specific cathode current is designed and the beam current is blocked, once by grid modulation and another time by cathode modulation, then consists the following relationship between the two reverse voltage potentials:

Let Ig max = I _c max

Let Va ₁ be the voltage supplied to the first anode, which is assigned to a grid reverse _{voltage potential of Vco g} volts and a cathode reverse _{voltage potential of Vco c} , in the case of grid or cathode modulation.

Two operating conditions of the beam generating system are shown below and these are in fact identical. In the case of cathode modulation, the potentials are given in relation to the grid potential, while im In the case of lattice modulation, they relate to the cathode are specified.

Cathode modulation Lattice modulation Cathodes
tension
Grid voltage ..
Tension the
first anode .. VcOc
0 0
- Vcoc
Va ₁ - VcOe Vcog = mV _ai + b (see equation 4) where VCOg is a negative quantity; Lattice modulation
results in bowel Vco _c =
From right to left = m (F ₀₁ - Vco _e ) + b,

which, inserted from equation (4), gives:

Vco _c =

Vco _a

(3)

V COg - mV _ai + b

(4)

G, =

I ₀ max (m + 1) '

Vco '

(5)

and by substituting in (5) of (1) that
G _c = G ₀ (m + 1) ^{T of} the G factor, is important for television picture tubes with cathode modulation Gc . From (6) it can be seen that in order to obtain a high value for G _{c it is} necessary to make Gg and m as high as possible. It has been found that G ₃ and m depend on the geometry of the electrode arrangement, but that m decreases as Gg increases. However, the change in m is far greater than that of G _g , and high values of G ₀ are achieved when the value of Gg is small and that of

is great. It has been found that m increases with the decrease in the distance between the cathode and the grid and the distance between the grid and the first anode and with the enlargement of the grid opening. An even greater increase in m results if the grid opening is made so large that it is larger than the opening in the first anode.

Practical experiments which were made with an electron gun of the basic form shown in Fig. 1, which contains an indirectly heated cathode 1, a grid electrode 2 with electron passage and a first anode labeled 3 and a second anode labeled 4, the anodes 3 and 4-4, forming a two-cylindrical electrostatic lens, have shown that the value of G _c increased from a presently normal value of 3 to 4 to a value on the order of 6 to 8.

The results achieved, which show the change in the electrode geometry and the corresponding changes in Gg, m and G ₀ , are summarized in the following table:

35

40

where Vco _{c is} the reverse voltage potential for cathode modulation, VCOg is the reverse voltage potential for grid modulation and m is the steepness of the curve of the voltage of the first anode V _ai plotted against Vco _g.

It has been found experimentally that m is a constant for a particular system, but that this depends on the electrode geometry. The curve V _ai plotted against Vco _g is a straight line.

tube C / G-
Away- Lattice
Public GIA ₁ -
Away- ^ -Off ^G 'j m G ₁ . No. was standing tion was standing tion 1 0.017 0.030 0.010 0.030 2.47 0.165 3.17 2 0.012 0.030 0.010 0.050 2.8 0.205 3.66 3 0.020 0.030 0.010 0.030 2.6 0.137 3.18 4th 0.010 0.020 0.010 0.030 2.96 0.147 3.61 5 0.010 0.020 0.010 0.030 2.89 0.127 3.45 6th 0.010 0.020 0.010 0.050 3.12 0.068 3.44 7th 0.010 0.050 0.010 0.030 0.99 2.50 6.43 8th 0.010 0.050 0.010 0.030 0.67 4.53 8.18 9 0.010 0.040 0.010 0.020 1.6 1.15 5.03 10 0.010 0.050 0.010 0.040 1.02 1.75 5.73

50

where b is a constant which means the intersection of the straight line with the Vco _g axis; b has been found to be positive in all cases, and .for changes 5-30 volts and further attempts certain relationships between b and V _ai have _shown; Substituting in (2) and (3) it follows that

60

(6)

when / "max in equation (1) is made equal to I ₀ max in equation (2).

To achieve an increase in the slope of the modulation characteristic or, as expressed here, an increase. It can be seen that the tubes No. 7, 8, 9, 10 have a noticeable increase in G ₀ compared to other tubes, but G _c only gives the maximum available current for a certain blocking and therefore gives no indication of whether there is any increase in cathode current for a given level. Measurements of cathode drive voltage versus cathode current for tube numbers 3 and 8 were made for various voltages A _x and a number of curves representing these measurements are shown in the graph of FIG. From the diagram it can be seen that for a given reverse voltage, the cathode current is increased by a factor between 2 and 3, and for tube no. 8 the voltage applied to the first anode is much lower than that required for tube no.

It is possible for systems in which the grid opening is larger than the anode opening to experience beam divergence show, if one modulates the beam current, which is large enough that part of the beam from the Opening of the first anode is stopped. The consequence of this is that, with further modulation, the one reaching the screen Beam current will be less than the measured cathode current. To control this, the

The anode current of the last anode is measured and compared with the cathode current. No difference was found for tube # 3, but for # 8 an expected difference was noted. However, the anode current was almost twice that of tube no.3. The elimination of the stopping of the beam at the opening of the first anode while maintaining a high G _c factor appears possible if one looks at the plane of the opening of the first anode can coincide with the plane in which the ray crossing point is located. It should be noted that the beam crossover point obviously moves with the modulation and that the coincidence of the two levels should take place at maximum modulation voltage.

The electron beam from cathode ray tubes with systems that contain a triode part described above, can be focused by magnetic means, or another electrode can be provided, such as shown in Fig. 1 so that the electron beam is focused by an electrostatic lens.

Tubes containing an electrostatic system of the type shown in Fig. 1, in addition to the high value of G _{0, have} the further advantage that the astigmatism has a tendency to become very small. The reduction in astigmatism appears to be related to the fact that the grating opening can tolerate a greater degree of axial tilting before severe astigmatism occurs.

The arrangement described has been explained on cathode ray tubes for television purposes, it can but also find application in other cathode ray tubes, e.g. B. in oscilloscope tubes.

Claims (2)

Patent claims: 1. Cathode ray tube with a beam generating system, that consists of at least one triode part with cathode, grid and anode and that for the Operation in a circuit in which the modulation is applied to the cathode is determined thereby characterized in that the distance between the electron passage openings of the grid and the Anode 0.152 mm or less, preferably 25 μ, and that the electron passage opening of the Grid is made larger than that of the anode. 2. Cathode ray tube according to claim 1, characterized in that one or behind the first anode several further electrodes are arranged. Considered publications:
British Patent Nos. 597 468, 707 064. 1 sheet of drawings