US2443794A - Electrical apparatus - Google Patents

Description

June 22, 1948..

E. F. M NlcHoL, JR 2,443,794

ELECTRICAL APPARATUS Filed Feb. 19, 194

| I I l I I i ee l I I I I [GENE/PA TOR| I INVENTOR. F JEDW4RD F MAcN/CHOL JR.

Patented June 22, 1948 Edward F. MacNichol, Jr., Wenham, Mass., as-

signor, by mesne assignments, to the United States of America as represented by the Scoretary of War Application February 19, 1945, Serial No. 578,766 8 Claims. (01. 315-370) This invention relates to electrical apparatus, and particularly to means for determining certain characteristics of electron tubes.

Expandinguses of electron tubes above and beyond the types of operation knownin the prior art have madenecessary other types of tests of these electron tubes than those .known and used heretofore, and other means for making these tests, so that the operational and dependability characteristics of the electron tubes may be determined under these new conditions of use. Uses now made of electron tubes, such as in pulse gen.-

.erators, pulse amplifiers and other associated work require the provision of tube performance data or characteristics which would not be available ordinarily. The required characteristics'in the type of work contemplated by the present invention include the ratio various electrodes. i i

In accordance with the present invention there is provided apparatus for determining the characteristics of an electron tube under conditions of pulsed operation. The electron tube under test must have at least a first, second and third electrode. The apparatus comprises a source of power connected to the electrodes of the electron tube and a pulse source. A coupling means is used for feeding the pulses from the pulse source to. the first electrode of the electron tube. The pparatus also includes an indicating means which is connected to the circuit of. the first electrode and one of the other remaining elec: trodes of the electron tube. The circuit of the first electrode includes a resistor and the circuit of said one of the other electrodes includes a potentiometer. The-potentiometer is adapted to indicate the ratio of the current in the potentiometer to the current in the resistor when a pulse is fed to the first electrode and the indicating means shows the resistances in the efiective part of the potentiometer and in the resistor are properly proportioned.

Hence, an object of this invention is to provide means for expeditiously determining the required of the currents in the tube characteristics.

' Other objects of the invention will be apparent from the following description and the appended claims, taken in connection with the accompany ingdrawings,in which: '1 Fig. 1 shows a. schematic diagram of one em- 2 bodiment of electrical apparatus which may be used for determining characteristics of electron tubes;

Fig. 2 shows a schematic wiring diagram of an--;. other embodiment of electrical apparatus which may be used for determining characteristics of electron tubes; and,

Fig. 3 is a fragmentary schematic diagram of a circuit which is adapted for combining the features of the apparatus illustrated in Figs. 1 and 2..

Referring now more particularly to Fig. 1 of the drawings, there is shown in this embodiment.

of the invention a circuit for determining the ratio of the plate current to the grid current of an electron tube. The circuit, as shown, includes.

a pulse source I I preferably a pulse generator and a coupling means I2 preferably a pulse transformer. The couplin means I2 is adapted to couple the pulse source i I to a grid ll of an electron .tube l3'so that the pulse to the grid I1 will be a positive going pulse. The tube i3 is the tube being tested and may be any electron tube :with at least three electrodes. However, in the illustrations in Figs. 1, 2, and 3 the tube is a triode.

A grid load resistor I4 is connected as shown be tween the transformer l2 and a source of negative bias sufficient to maintain the tube I 3jat the desired operating point, normally at cutofli A potentiometer consisting of a plate load resistor l5 and a variable tap I6, is connected between an anode ll; of the tube l3 and a source of positive voltage which is normally between +300 and +1000 volts. The resistor I 5 is equal in magnitude to the resistor I4. i The potentiometer I5-l 6 may be calibrated in a manner hereinafter described so that from the calibration the characteristicsof tube l3 may be read directly. A cathode IQ of the tube I3 is connected toground as shown. An indicating device 2| such as a cathode ray oscilloscope, peak readingvoltmeteror other peak reading device is includedin this circuit to show the relative amplitudes of voltages developed across the grid resistor l4 and across the effective portion of the potentiometer Iii-l6. One side of the indicating device is connected to the potentiometer l5'|6 through a coupling ca pacitor 22 and the other side is connected through afcoupling capacitor 23 to a point between the secondary of transformer l2f and the'resistor I 4. The rest of the connections of the indicatin 3 meansare not shown but are connected in any suitable manner well known in the prior art.

A pulse is applied to the tube 13 from the pulse generator I! through the. pulse transformer 2. The current ig which flows in the grid circuit will produce a variational voltage at 24 of the form shown at 24 in Fig. l and is equal to:

where V24 is voltage at 24 relative to bias is is grid current R14 is resistance of resistor I 4 When the grid is driven positively above cutoff.

plate current in will flow causing a Variationalvoltage to appear at 25 of the form shown at 2.5 in Fig. l and is equal to:

Where V25 is voltage at 25 relative to plate battery ip is plate current r is the resistance of resistor I5 from tap [6 to Also referred to as the efiective resistance of potentiometer li5-l 6.

It is assumed that grid bias is su'fficient to eliminate both grid and plate current except during the pulses; if this is not the case only the changes in current and voltage should be used. This might .be otherwise expressed in terms of pulse voltages since only the variations can pass the blocking condensers to the oscilloscope. The tap [B is adjusted so that the peak voltage value V25 is equal to peak voltage value V24. This equality is indicated by no deflection on the oscilloscope 2.1 when connected .as shown in Fig. 1. We then have that: (3.) V124=V25 From the above three equations we .get:

5, plate cur-rent -"i r grid current However, since resistor 44 is equal in magnitude toiliesistor r-| fiithen The tapped resistor 1.5 may now be'calibr-ated .to

the cathode :current to the .-.grid- :current of an electron tube. The circuitsas shown, includes a pulse source 31 #preferably arpulse generator :3! and arcoupling' means32 preferably'a pulse transformer :connected "to transfer pulses from the pulse generator 134 .toa grid 3411f anelectrontube 33. The i-pulse at the grid iJLncrmally is aposttive goin-g ;pulse. n grid load resistor .34 is .connected ras shown between the coupling :-means .32 and .asource .of negative .bias. The inegative bias appliedto thesgrid 3.1 through.the..resistor,34 .has

a value whichiis :suitable .to maintain the tube .33

normallyat .cutofi. Theconnection'ofrthe resistor 34 permits the current flowing in the circuit of the grid 31 to develop a voltage across this resistor 34. A potentiometer consisting of a cathode load resistor 35 and a variable tap 3B is connected between a cathode 38 of the tube 33 and ground. The resistor 35 is equal in magnitude to the resistor 34. An anode 39 of the tube 33 normally is connected directly to a source of positive voltage as shown. The same conditions of biasing will normally be used in the circuit in Fig. 2 as are used in the circuit in Fig. 1. An indicating device 4| such as an oscilloscope, peak reading voltmeter or other peak indicating device is included in the circuit in Fig. 2 to show the relative amplitudes ef-voltages developed across the grid resistor 34 I and across the effective portion of the potentiometer '35--36. The indicating device is connected to the potentiometer 35-36 and to a point between the resistor 34 and the secondary of the transiormer 82 as shown in Fig. 2. The rest of the connections of the indicating means 4| are not shownbut are made in a suitable manner well known in the prior art. As will be noticed, the connections of the indicator 2| in Fig. 1 are different from the connections of the indicator 4! in Fig. .2. The reason for this is because of the opposite polarities of the two voltages being come pared in'Fig. 2.

A pulse is applied to the tube 33 from pulse generator 3| through the pulse transformer 32. The current i which flows in the grid circuit will produce a variational voltage at 42 of the form shown at 42 in Fig. 2 and is equal to:

(7) Vaz i Rai where V4215 voltage at 42 relative to bias z is grid current R34 is resistance of resistor 34 When the grid .31 is driven positively above cutofi, cathode current i1: will flow causing a Variational voltage to appear at 43 of the form shown at 43 in Fig. 2 and equal to:

where The tap 36 is adjusted so that the peak voltage value VA3 is equal to the peak voltage value Va. This equality 'isindicated on the oscilloscope 4! of Fig. 2. We then have:

('95) tVaz Vaa and solving the .above' three equations we ohtainz,

i ii cathode current a z rid current However, since resistor .34 is equal in magnitude toresistorBEthen:

'2 T The tapped resistor 35 may now be calibrated to read the ratio .Raa/r and the reading when the two aforementioned voltages are equal will be the desired characteristic under the ,biasing con-d1 tions used. From Equation IQ-itmaybeseemthat if resistor .35 is calibrated to .read the. iresistance ofthe resistor-'34 divided by r(R,s4/r) then resistor 35 need not equal resistor 34 in magnitude.

(12) reading=ratio E Fig. 3, as hereinbefore stated, illustrates one means of combining the-features of the circuits illustrated in Fig. 1 and Fig. 2. By means of a switch 5|, there may be inserted in the plate circuit of a tube 52 either a resistor 53 or a shunt 54. By means of a switch 55, mechanically connected to switch 51, there may be inserted in the cathode circuit of tube 52 either a shunt 56 or a resistor 53. By means of switch-59 alsomechanicallyconnected to switch 5i the appropriate connections aremade to oscillograph 6! as in Figures 1 and 2. It will be observed that placing the resistor 53 in the'plate circuit places the shunt in the cathode circuit and vice versa. The grid of tube 52 is connected through grid resistor 64 and coupling transformer 62 fed by pulse generator 63, with a terminal 65 corresponding to terminals 34 and 42 in Figs. 1 and 2. The tap 57 on resistor 53 is connected to an indicating device. If the indicating device is an oscilloscope, then the tap 5'! is connected to the oscilloscope through switch 59 as in Figs. 1 and 2. With the tube 52 connected in the manner just described it is possible to measure with one system both the ratio of cathode current to the grid current and the ratio of anode current to the grid current.

While there has been described what is at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. An' apparatus for determining the characteristics of an electron tube under conditions of pulsed operation, said tube including at least a cathode, a grid, and an anode, said apparatus comprising a power supply having at least a positive terminal, a negative terminal, and an intermediate terminal; a pulse source; a pulse transformer for coupling said pulse source to said grid; a grid load resistor connected in series with said negative terminal, said pulse transformer and said grid; at second load resistor, equal in magnitude to said grid load resistor and having a variable tap, said second load resistor being calibrated to give the ratio of the resistance of said second load resistor to the resistance of said second load resistor from said tap to one end of said resistor; means for switching said load resistor selectively between said anode and said positive terminal with said end of said load resistor connected to said positive terminal and between the cathode and said intermediate terminal with said end of said load resistor connected to said intermediate terminal; means operative with said switching means to close the electrode circuit into which said second load resistor is not connected; and means for comparing the voltage developed across said grid load resistor by the current flowing through said grid load resistor, with the voltage developed across the portion of said second load resistor from said tap to said end by the current flowing through said second load resistor, said tap being adjustable to cause said two voltages to be possible of equalization in magnitude so that the ratio of current through said second load resistor;

to the current through said grid load resistor may be read from the calibration of said load resistor. r i i q 1' a 2. An apparatus for determining the characteristics of an electron tube under conditions: of pulsed operation said tube including at least; a first, second, and third electrode, said apparatus comprising a power supply having at least a positive terminal, a negative terminal, and an. intermediate terminal; a pulse source; a pulse transformer for coupling said pulse source tosaid second electrode; a first load resistor connected in series with said negative terminal, said pulse transformer and said second electrode; a second load resistor having a variable tap, saidsecond load resistor being calibrated to give the ratio of the resistance of said first load resistor to the resistance of said second load resistor from said tap to one end thereof; means for switching said second load resistor selectively, between said third electrode and said positive terminahwith said end of said second load resistor connected to said positive terminaLand between said first electrode and said intermediate terminaLowith said end connected tosaid intermediate terminal; shunt means operative with said switching. means to close the electrode circuit into which said second load resistor is not connected; and means for comparing the voltage developed across said first load resistor by the current flowing through said first load resistor, with the voltage developed across the portion of said second load resistor from said tap to said end by the current flowing through said resistor, said tap being adjustable to make possible equalization of the two said voltages so that the ratio of the current flowing in said second load resistor to the current flowing in said first load resistor may be read from thecalibration of said secondload resistor.

3. An apparatus for determining the characteristics of an electron tube under conditions of pulsed operation, said tube including at least a cathode, a grid, and an anode, said apparatus comprising a power supply. having at least a positive terminal, a negative terminal, and an intermediate terminal; a pulse source; means for coupling said pulse source to said grid; a grid load resistor connected in series with said negative terminal, said coupling means, and said grid; a plate load resistor connected between said anode and said positive terminal, equal in magnitude to said grid load resistor, and having a variable tap, said plate load resistor being calibrated to give the ratio of the resistance of said plate load resistor to the resistance of said plate load resistor from said tap to said positive terminal; and means associated with said grid load resistor and said tap for comparing the voltage developed across said grid load resistor by current flowing through said grid load resistor, with the voltage developed across that por tion of said plate load resistor from said tap to said positive terminal by current flowing through said plate load resistor, said tap being adjustable to make possible equalization of the two said voltages so that the ratio of the current flowing in said plate load resistor to the current flowing in said grid load resistor may be read from the calibration of said plate load resistor.

4. An apparatus for determining the characteristics of an electron tube under conditions of pulsed operation, said tube including at least cathode, grid, and plate elements, said apparatus if 2 comprising-a power supply having at least a positive terminal, a negative terminal, and an intermediate terminal; a pulse source; means for coupling said pulse source to said grid; a grid load resistor connected in series with said negative terminal, said coupling means and said grid; a cathode load resistor, equal in magnitude to said grid load resistor and connected between said cathode and said intermediate terminal and having a Variable tap, said cathode load resistor being calibrated to give the ratio of the resistance of said cathode load resistor to the resistance of said cathode load resistor from said tap to said intermediate terminal; and means associated with said grid load resistor and said tap for comparing the voltage developed across said grid load resistor by current flowing through said grid load resistor, with the voltage developed across that portion of said cathode load resistor from said tap to said intermediate terminal by current flowing through said cathode load resistor, said tap being adjustable to make possible equalization of the two said voltages so that the ratio of the current flowing in said cathode load resistor to 'the current flowing in said grid load resistor may be read from the calibration of said cathode load resistor.

5. Apparatus for determining the characteristics of an electron tube under conditions of pulsed operation, said electron tube including at least a first, second and third electrode, said ap paratus comprising a source of power connected to the electrodes of the electron tube; a pulse source; means for coupling said pulse source to said first electrode of the electron tube; indicating means; means for connecting said first electrode to said indicating means, said connecting means including a first resistor; potentiometer means connected to said indicating means; and switching means associated with said potentiometer means for connecting said potentiometer in series circuit with one of said remaining electrodes and closing a circuit to the remaining of said electrodes, said potentiometer being adapted to indicate the ratio of the current in said potentiometer to the current in said resistor when a pulse is fed to said first electrode and said indicating means showing that the resistances in the effective part of said potentiometer and in said resistor are properly proportioned.

6. Apparatus for determining the characteristics of an electron tube under conditions of pulsed operation, said electron tube including at least a first, second, and third electrode, said apparatus comprising a source of power connected to the electrodes of the electron tube; a pulse source; means for coupling said pulse source to said first electrode of the electron tube; indicating means; means for connecting said first electrode to said indicating means, said connecting means including a resistor; and means for connecting said second electrode to said indicating means, said second connecting means including a potentiometer, said potentiometer being adapted to indicate the ratio of the current in said potentiometer to the current in said resistor when a pulse is fed to said first electrode and said indicating means shows that the resistances in the effective part of said poentiometer and in said resistor are properly proportioned.

'7. Apparatus for determining the characteristics of an electron tube under conditions of pulsed operation, said electron tube including at least a first, second, and third electrode, said apparatus comprising a source of power connected to the electrodes of the electron tube; a pulse source; a pulse transformer for coupling said pulse source to said first electrode of the electron tube; indicating means; means for connecting said first electrode to said indicating means, said connecting means including a first resistor; and means for connecting one of the other of said electrodes to said indicatin means, said second connecting means including a potentiometer, said potentiometer being adapted to indicate the ratio of the current in said potentiometer to the current in said resistor when a pulse is fed to said first electrode and said indicating means shows that the resistances in the effective part of said potentiometer and in said resistor are properly proportioned,

8, Apparatus for determining the characteristics of an electron tube under conditions of pulsed operation, said electron tube including at least a first, second, and third electrode, said apparatus comprising a source of power connected to the electrodes of the electron tube; a pulse source; means for coupling said pulse source to said first electrode of the electron tube; indicating means; means for connecting said first electrode to said indicating means, said connecting means including a resistor; and means for connecting one of the other of said electrodes to said indicating means, said second connecting means including a potentiometer, said potentiometer being adapted to indicate the ratio of the current in said potentiometer to the current in said resistor when a pulse is fed to said first electrode and said indicating means shows that the resistances in the efiective part of said potentiometer and in said resistor are properly proportioned.

EDWARD F. MACNICHOL, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,831,744 Laurent Nov. 10, 1931 2,213,099 Adorjan Aug. 27, 1940 FORMGN PA'I'ENTS Number Country Date 753,659 France Oct. 21, 1933

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