US1993569A

US1993569A - Discharge tube

Info

Publication number: US1993569A
Application number: US645980A
Authority: US
Inventors: Schubert Georg
Original assignee: FIRM FERNSEH AKTIEN GES
Current assignee: FIRM FERNSEH AKTIEN GES; FIRM FERNSEH AKTIEN-GESELLSCHAFT
Priority date: 1931-12-12
Filing date: 1932-12-06
Publication date: 1935-03-05
Anticipated expiration: 1952-03-05
Also published as: FR746564A; GB392472A

Description

March 5., 1'935.

G. lSGHLJBERT DISCHARGE TUBE Filed Dec. e, 19:52

3 Sheets-Sheet l aba-4215062125@ m4 I /n ventop:

' www@ G. SCHUBERT DISCHARGE TUBE March @35 Filed Deo. 6, 1952 3 Sheets-Sheet 2 19o 120 isa 1'40 150 16a March 5` l935- G. SCHUBERT .DISCHARGE TUBE Filed Dec. 6, 1952 5 Sheets-Sheet 3 Gene/'afar' Patented Mar.j5, 1935 UNITED STATES DISCHARGE TUBE v Georg Schubert, Berlin,

Germany, assignor to firm Fernseh Aktien-Gesellschaft, Zehlendorf,

, near Berlin, Germany Application December 6,

i932, serial Nn. 645,980

In Germany December 1 2,A 1931 6 Claims. (Cl. 176-124) 'I'he invention relates to a method. of controlling discharge tubes of the positive column type for television purposes. f

'Ihe mai object of the invention is to control -5 v discharge tu es filled with sodium 4vapor and having a positive luminous column by adjusting the operating temperature of the tube in such manner that the light density ofthe luminous column is substantially a linear function of the grid volt- L age of the lthermionic valve which controls the discharge tube and normallyforms the output Valve of the receiver amplifier.

In ordento receive'an undis'torted reproduction of television transmission it is essential, that not ,5 only all parts of the transmission system operate? faultlessly, but also that the intensity of the controlled source of light at the receiver v ariesV in proportion to the iiuctuations of the grid potential of the output tube of the receiver amplifier.

Assuminthat the controlled source of light is arranged inthe anode circuit of this output tube, which is the most simplied arrangement,

then the above condition is fulfilled provided a linear function exis on one hand between theY ,5 grid potential and the anode current, and on the other hand between e anode current and the intensity of light. For the purpose of obtaining,- proportionality between the fluctuations 'of the grid potential and the fluctuations of the anode 0 current it is necessary that the working characteristic be a straight line, which inturn'occurs only whenwhile operating inthe straight region of the static characteristic of the tube-the A'. C.

Q resistance of the anode circuit (in this case substantially the controlled source of light) is constant.

While it was not difllcult to yfulfill these conditions when employing the well known sources of light such as glow lamps and kino lamps, it was 0 at first extremely dicult to operate discharge tubes of the positive-column type, for example the new Na-surface lamps, which only very rei cently have been employed for television purposes. It is now an yimportant object of the present 3 invention .to overcome-these difficulties'encountered in the control of discharge tubes filled withy sodium vapor. Experiments have shown that the A. C. resistance of these'sodium lled lamps is not constant, and furthermore that there 1s no l linear function between their intensity 'of light and the strength of their operating current. According to the invention, however, these diilculties mayf be largely overcome by Aoperating the lamp at a predetermined and properly adjusted i operating temperature. In. the following the inventi/on is described by way of example based on experiments made with Na-surface lamp. The same considerations, however; apply also to other discharge tubes having a positive column and a heated cathode. i

As well known, tsea-surface lamp is operated with an additional exterior heating-means. Other discharge tubes,N however, need only be provided with some heat protecting means to prevent ex-` cessive loss of heat and to nablethe tube' to 10 create its own operating temperature, In -these last vmentioned tubes the adjustment of therequired operating tenfperature according to the inventionmayfbe obtained by suitably selecting an `average operating current. n ,'15

In the drawings: l

Fig. 1 shows thestatic resistance characteris-` tic of anA Na-surface lamp at three different op- .eratingx temperatures. It willfbe noted that all three characteristics are descending, only the one taken at 180* C., is approximately linear, so vthat in this case the A. C. resistance is practically constant within a certain range of current. v

Fig. 2 lshows the relationshiplbetween the intensity of light and the current intensity at the three operating temperatures recorded in Fig. 1 and it can be seen that only .when in this particular lamp the operating temperature is 180 C., the light intensity is a linear function of the current intensity, Whereas the same deviates very l3() appreciably ,from the desiredproportionality at temperatures which are only above or below this value.

Fig. 3 shows the relationship between the light f intensity. and the operating temperature at three different currents. It can be seen that at an operating temperature of 180 C. (which has been 'foundto be most favorable) the maximum current amplitudes vof approximately- 1D0-'140 milliampere (at an average supply current of approxi- 40 mately 450-'70 milli-ampere) ,'v produce approximately the maximum intensity' of light which the lamp maycreate at its best. According to the invention, the discharge tubes are maintained during their operation at .a temperature-at' which 45 (1) 'the light' intensity varies in proportion to the current intensity, (2) the A. C. resistance is approximately constant, and y(3) approximately the maximum light intensity is obtained. Obviously, the condition that the A. C. resistance should be constant is also fulfilled when the `saine lis zero; this means, however, that the potential at thel lamp must be constant. f

Fig. 4 shows that by superimposing a properly selected high frequency currentover the operatliliy ing D.- C., the characteristic of the lamp may be changed in such manner, that the voltage at the lamp'is constant over the' greater part of the current' 'range employed during the modulationor in other words that the A. C. resistance is practically zero. The light intensity of the lamp remains practically unaffected by the superposedhigh frequency current. i

. Fig. 5 shows diagramrratically the circuit used with the discharge tube. In thisv figure 1 is the output valve of -the receiver amplifier; 2 is the discharge tube with a positive luminous column`V and a ligatedcathode; 7 represents the anode circuit of the amplifier in which the discharge tube 2 is arranged; 5 is an adjustable resistance for controlling the `current passing through the discharge tube, 6 is a condenser in shunt to said resistance 5; and 3 indicates a high frequency generator for capacitycoupling oi.' tube 2 to the high frequency circuit by means 'of a metallic plate 4.. This high frequency generatorgisused for superposng -a high frequency current over the operating D. C. asshown in Fig. 4. The discharge tube 2 is placed in a casing 9, preferably of heat insulating material. An electric heating resistance -10 vmay be employed to maintain the desired-operating temperature for' the tube 2 vwithinl the casing. I

which occur in any one of the transmission'means may likewise be compensated by a suitable selection of the opeating temperature of the discharge tube. l c I It is, of course, understood that the invention is not limited' by the specific description set forth in the above, and that numerous modifications are quite possible within the scope of the appended claims.

What I claim asmy invention is:

I 1. A method of controlling discharge tubes lled with sodium vapor and operating with positive column and heated cathode, consisting in so adjusting lthe operatin temperature of the discharge tube that the te'nsity of light is a substantially linear function of the grid potential of the audion controlling the discharge tube.

2. A method of ,controllingV discharge tubes lledwith sodium vapor and operating with positivecolumn vand heated cathode, consisting in so adjusting the operating temperaturev of the discharge tube that the A. C. resistance is approximately constant, and thatat the same time at this temperature the intensity of light is directly proportional to -the current intensity.

3. A method of controlling discharge tubes filled with sodium vapor and operating with positive column andnheated cathode, consisting in ad- The maintenance of aconstant A. C. resistance dusting' the Opeiating temperature 0f the diS- andof a linear function between 'the intensity of light and the strength of the operating current (characteristic of intensity of light) make possible a distortinless television reception. But it is als.possible to prevent distortions in the reproduction of the television image by co c pensating for any variation of the A. C. resistance by a ,corresponding non-proportionality of the `characteristic of the intensity of light,-Whichv in `sistance of the lamp has been m ntioned,` it should be understood that always the A. C. resistance was meant as it results from the statically recorded characteristic yof the lamp. The A. C'. resistance, however, may also depend upon the fre-A quencyor uponA that condition of operationof the lamp which prevailed at the immediately preceding/instant.v This, however, does not-result in any appreciable variation in the working diagram of the lamp, which for the sake of simplicityd has been considered to follow th static characteristics, sincevthe' principle is\the same.,

'I'he above considerations and Athe diagrams shown in the Figs. 1-4, apply in the first place" when the discharge tubes-are operated with D. C.' potential. 'I'he same considerations', however,

\ may be applied correspondingly when the dis.-

frequency current `mission means in the system do not operateu charge tubes are operated exclusivelyf'with high When the Jvarious translsuperposing a high frequency current over the D. C.for the purpose of acquiring constancy of the A. C; resistance, substantially as described.

5.` In a method for controlling a hot-cathode discharge tube filled with sodium vapor and having a positive luminous colunn, said discharge tube being arranged in the anode circuit of the output valve of an amplifier, the step of adjusting the operating temperature of the discharge tube in such manner that the light intensity of said positive luminous column is substantially a linear function of` the grid voltage of said output valve. l

6. -In a method for controlling a hot-cathode discharge tube filled with sodium vapor and having a positive luminousv column, said discharge tube being arranged in the anode circuit of the output lvalve of, an amplifier, theD step of adjusting the operating temperature of the discharge tube in such manner that the light intensity of said positive luminous columnis substantially a linear function of the grid voltage of vsaid output valve, whereby at this operatingtemperature the highest intensity of lightis produced.

GEORG SCHUBERT.