Geiger Tube Quenching Circuit for a Negative High Voltage SupplyRichard John Watts Citation: Review of Scientific Instruments 20, 699 (1949); doi: 10.1063/1.1741653 View online: http://dx.doi.org/10.1063/1.1741653 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/20/9?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Improved Quenching Circuit for Geiger Counters Rev. Sci. Instrum. 29, 245 (1958); 10.1063/1.1716160 Pulse Type Regulated High Voltage Supply for GM Tubes Rev. Sci. Instrum. 21, 342 (1950); 10.1063/1.1745579 A New Quenching Circuit for Geiger Counters Rev. Sci. Instrum. 19, 500 (1948); 10.1063/1.1741311 A Combined Voltage Regulating and Quenching Circuit for the GeigerMüller Counter Rev. Sci. Instrum. 14, 222 (1943); 10.1063/1.1770167 A Light Weight, High Voltage Supply for Geiger Counters Rev. Sci. Instrum. 12, 140 (1941); 10.1063/1.1769844

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

128.240.225.44 On: Fri, 19 Dec 2014 23:30:48

LABORATORY AND SHOP NOTES 699

tubes tested.1 This amplifier was made with a 4.7-meg. input resistor. This has been recently increased to 10 meg. with no noticeable difference in performance. When the input leads are open circuited, some of the poorer tubes tested gave more than the quoted drift for line voltage variation. However, when the input is connected to a source of a few thousand ohms (such as the bioelectric source used here), the fluctuations are greatly diminished.

In the two-stage amplifier shown here, most of the gain is used in cathode degeneration for stability; linearity is provided at the same time. In order to have sufficient output gain for feedback to give a good integrating or differentiating amplifier, another stage should be employed. The extra stage (simply inserted between the two shown) can have its cathodes tied together and resistors in the plates and the common cathode about equal. With a polystyrene (or a good paper condenser) of a few microfarads, integration over a period of several minutes can be performed.

The two-stage circuit has also been used with a photo-tube input to make a light intensity meter. This is suitable for determination of exposure time for photo-micrographs, and so on.

The original idea for this type of circuit was developed by Mr. A. W. Vance of the RCA Laboratories. The amplifier described here has been extensively used and tested by Dr. R. W. Ramsey of the Physiology Department of the Medical College of Virginia.

1 Some makes. sllch as TungsoI. had a much smaller unbalance than others and gave more stability against line voltage variations.

Geiger Tube Quenching Circuit for a Negative High Voltage Supply

RICHARD JOHN WATTS

Los Alamos Scientific Laboratory,* Los Alamos. New Mexico April 20, 1949

T HE following circuit (Fig. 1) illustrates a method of assisting the quenching action of a Geiger-Muller tube. It may be

considered a Neher-Harper circuit with two modifications (1) a negative high voltage supply is used. (2) No high voltage need be placed across receiving type tubes not designed for this purpose. Inasmuch as the circuit was designed for portable work a CK569AX tube was selected. However, the method is applicable to heater type tubes.

It should be pointed out that if a very high impedance voltmeter is placed across the electronic tube of a Neher-Harper quenching circuit, it can be ascertained that the tube behaves as a shunt regulator for the high voltage supply. This can lead to some con­fusion in the length of a G-M tube plateau since the voltage across the G-M tube does not change linearly with supply voltage. If supply voltage changes are used for plotting plateaus with this circuit, it then appears that the length of the plateau has been increased considerably over the plateau obtained from a non­quenching circuit.

In the present circuit one cannot expect this increment in plateau since the high voltage is not across a non-linear medium.

The operation of the circuit is as follows: The circuit constants are chosen such that the plate voltage in the quiescent condition of the CK569AX is 70 volts. When the G-M tube fires there is observed across the one-megohm resistor in series with the high voltage supply a sharp positive pulse of voltage. This pulse is of the order of 100 microsec. in duration with the circuit constants given. The rise time of this pulse as observed with a Tektronix 511 AD oscilloscope is less than 0.2 microsec. This sharp positive pulse of voltage is applied to the grid of the CK569AX. The tube thereby conducts and the plate voltage goes negative sharply. Inasmuch as the central wire of the G-M tube is connected directly to the plate of the CK569AX the G-M tube voltage will be thrust below threshold rapidly.

H. V.

+

1.5V

1.0M I/2W

FIG. 1.

1M I/2W

2M I/2W

90V

It should be noted that the negative pulse obtained by electron collection on the central wire of the G-M tube is the same polarity as the plate voltage drop. Thus the circuit is in a sense regenerative. With the circuit given, the negative voltage pulse on the anode of the CK569AX has been observed to be 250 microsec. in duration with a fall time of about 0.5 microsec. The circuit constants given are not optimum. They were chosen with regard to reasonable battery drain for portable operation. The Geiger tube used was a standard size in common use with a neon-amylacetate filling. The tube was operated in the plateau region at 900 volts.

* This document is based on work performed at Los Alamos Scientific Laboratory of the University of California under Government contract W-7405-Eng-36.

Extended Range D.C. Bias Control of Thyratron Plate Current LEONARD REIFFEL

Armour Research Foundation, Technology Center Chicago, Illinois May 26, 1949

T HERE are three important basic circuits useful in controlling the average current in a thyratron with alternating plate

voltage. These are:

1. The d.c. grid bias control 2. Variable phase grid voltage control 3. Constant phase plus bipolar d.c. grid bias control.

It is the purpose of this paper to describe the basis of a new technique for thyratron plate current control applicable to shield grid tubes.

Before proceeding, it will be helpful to review briefly the ad­vantages and disadvantages of the already extant methods.

1. The d.c. grid bias control: This system consists merely in applying variable d.c. voltage to the thyratron control grid. The point of firing is delayed as the bias voltage is made more negative.

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

128.240.225.44 On: Fri, 19 Dec 2014 23:30:48

700 LABORATORY AND SHOP NOTES

The maximum delay attainable by this method is 90 degrees of the plate voltage cycle. This delay angle. corresponds to approximately 50 percent of maximum d.c. plate current (i.e., the variable bias provides continuous control from full d.c. plate current to one-half of full current). Any attempts to advance the firing point beyond 90 degrees by further reduction in bias cause the plate current to drop abruptly to zero.!

FIG. 1.

This technique has the advantage of extreme simplicity. How­ever, the control range is limited and the bias required for a given current varies somewhat during the tube life because of changes in the critical grid voltage curve. These changes become very im­portant near the 90 degree delay point since the critical grid voltage curve intersects the bias curve nearly tangentially.'

2. Variable phase grid voltage control:8 This method consists in applying to the grid an alternating voltage of (usually) the same frequency as the plate voltage. As the phase angle of the grid voltage with respect to plate voltage is varied from approximately zero degrees lagging to 180 degrees lagging, the d.c. plate current varies smoothly from the maximum (full one-half cycle of con­duction) to very nearly zero.

This method, probably the most widely used, has the advantages of full 180 degrees delay range and a high degree of immunity to fluctuations in d.c. current due to changes in the critical grid voltage curve (because of the large angle of intersection between

FIG. 2.

e

~~------~------------___ r

~------~~-------------.-t

FIG. 3.

this curve and the grid voltage curve for large amplitudes of grid voltage). This system, however, requires a variable phase shift circuit with its attendant saturable reactor4 (or manually variable reactor) center tapped transformer and phasing condenser. Usually, when the controlling signal is d.c. a triode etc., is used to control the inductance of the saturable reactor and thus control the phase shift and d.c. plate current. The primary controlling parame­ter thus becomes the triode grid bias voltage.

3. Phase-bias control:6 This method is an extension of method 1 in which a phase-shifted (90-150 degrees behind the plate Voltage) a.c. voltage is added to the variable d.c. applied to the grid. If the amplitude of the a.c. applied to the grid is EM, then in order to get full 180 degree control, the d.c. bias must vary from EM to -EM.

This method will thus yield smooth current control over the entire half-cycle6 but bipolar d.c. bias must be provided and the circuit is not as independent of critical grid voltage curve changes as the preceding method unless EM is large. This leads to difficulty in supplying the bipolar d.c. bias. Regardless of the amplitude re­quired, if electronic control is to be used, the bipolar bias requires additional circuits.'

New circuit.-The principle of the new technique for control of thyratron plate current is illustrated in Fig. 1.

An alternating voltage of amplitude E is applied to the plate of thyratron T, and an a.c. voltage of amplitude Eo is applied to the shield grid. This voltage Eo is shifted approximately 90 degrees behind the plate voltage by the fixed phase shifting network con­sisting here of R! and C!. This phase-shifted shield grid voltage introduces an asymmetry in the critical grid bias control curve of the thyratron, since at the beginning of the positive half-cycle of

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

128.240.225.44 On: Fri, 19 Dec 2014 23:30:48

LABORATORY AND SHOP NOTES 701

PC CtWr1I!bL 8/"15

r-----+-~--T----------.-t

COIVnt:.Ol... CO,cV£

~--------~~------~~t

FIG. 4.

plate voltage the shield grid is negative by E g , while at the end of the positive half-cycle the shield is positive by Eg. Thus the critical control grid voltage is more positive at the beginning of the positive plate half-cycle (0 degrees) and more negative at the end (180 degrees) than it would be ordinarily. This gives rise to a new critical grid voltage curve with its minimum shifted considerably toward the 180 degree point of the plate voltage as shown by the construction in Fig. 2.

By inspection of Fig. 2 it is evident that the point of firing of the thyratron may be delayed more and more by increases in the negative bias on the control grid until the point a is reached, at a bias EK and firing point O. With the simple circuit of Fig. 1, it has been found that 0 can be made as large as 145 degrees.

It is to be noted, however, that there are a number of inherent limitations in the simple system just described. First, the change in the critical grid voltage for a unit change in shield grid voltage at constant plate voltage becomes increasingly less as the shield grid goes more and more positive. This tends to flatten the critical grid voltage curve near point a and leads to the limit of 145 degrees maximum delay mentioned above. A possible means of extending this limit will be discussed. Second, during the first 90 degrees of the plate voltage cycle, the shield grid may be sufficiently negative to require a positive grid voltage for firing. This throws the circuit open to the same criticism leveled against the phase-bias system of control. This objection may be overcome in a number of ways, among which are:

1. The shield grid may be biased positively if this is not obviated by other considerations. 8

2. A rectifier (IN34) may be used to eliminate the negative half­cycle of shield grid voltage; however, the firing point stability will suffer during the first quarter-cycle of plate voltage.

1--.t l

I

~ ~ /0

~ o " U ~.$

o -.1

C(/te~ENT CONr~oL

FIG. 5.

7,Ptt" 20.5'0 TIl YR"fT'lfolll

-2

3. Tubes may be employed which will fire at negative control grid voltages even with the shield grid near - Eg. This is, of course, the most desirable condition and uses the simplest circuit.

The first two suggestions lead to the circuits and control charac­teristics shown in Figs. 3 and 4. Figures 1 and 2 refer to method three.

As an example the circuit of Fig. 4 was employed with a type 2050 thyratron, a tube not fulfilling conditions in 3 above, and yielded the results shown in Fig. 5 for I d.c. versus Ebi ••.

From the figure it is seen that continuous control of the d.c. plate current may be had with the circuit.of Fig. 4 over a range extending from 100 percent to about 15 percent of full current. There is a small region of jitter when the bias is near point b of Fig. 4, just before the rectifier applies the shield grid voltage. This may be eliminated by shifting the phase of the shield grid voltage

e

~----~----~---------t

~------+-+-Ir-----t

FIG. 6.

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

128.240.225.44 On: Fri, 19 Dec 2014 23:30:48

702 NEW INSTRUMENTS

by only about SO degrees with a slight reduction in the control range.

Method one above yields similar results and is preferable from the stability point of view.

Thus it is possible to obtain continuous control of d.c. plate current over a range corresponding to a delay angle of near 0 degrees to about 145 degrees using the proper circuit of those shown previously. This control may be achieved with variable monopolar control grid bias. By using moderately large shield grid voltages,9 the slope of the critical grid voltage curve may be made large which minimizes the effect of aging and small changes in plate voltage as mentioned earlier.

If it is desirable to extend the range of control even further, a peaked wave form, such as generated by a fixed saturable reactor, may be applied to the shield grid. This will give greater rates of change of shield grid voltage in those regions where the critical grid voltage varies slowly with shield grid voltage. This scheme is illustrated in Fig. 6 and should permit extension of the control range to about 165 degrees.

1 Millman and Seely. Electronics (McGraw-Hill Book Compaony, Inc., New York, 1941), first edition, pp. 432-3.

2 This same characteristic of large variation in d.c. current at fixed bias for small changes in the critical grid voltage curve has prevented wide use of an a.c. bias amplitude control system. See H. J. Reich, Theory and Applications of Electron Tubes (McGraw-Hill Book Company, Inc., New York, 1944), second edition, p. 509.

• See reference I, pp. 428-432. 'J. C. May et al .. "Thyratron phase control circuits," Electronics, 107-9

(July 1948). • See reference I, PP. 434-5. 6 Neglecting tube drop, of course as in all the preceding discussion. 7 See reference 4, P. 108. S A circuit which interchanges the role of the control and shield grids is

now under investigation. • The voltage which may be applied is, of course, limited by the possibility

of shield grid to cathode breakdown.

New Instruments W. A. Wildhack: Associate Editor

in Charge of this Section National Bureau of Standards, Washington, D. C.

These descriptions are bastd on information supplied by the manufacturer and in some cases from independent sources. THE REVIEW assumes no re­sponsibility for their correctness.

Oscillator Model M oscillator has been de-signed as a source of power cover­

ing the frequency range of 0.25 to 120,000 cycles per second. The frequency is continuously variable from 1 to 120,000 cycles per second in five overlapping ranges, and provision is made for fixed frequencies determined by plug-in units for frequencies as low as 0.1 cycle per second.

The circuit is a new arrangement of the bridge-stabilized type of oscillator, using two separate amplifiers connected together by a four-terminal bridge network. This arrangement affords a means of reducing to a minimum the influence of amplifier parameters on the frequency of oscillation. The circuit is self-balancing. The amplifiers operate in phase opposition, and their output is es­sentially free of even harmonic distortion. Third harmonic distortion is generated in the AVC element, but it has been kept to a low value by the use of an element with a long thermal time constant.

The power supply is electronically regulated. Deposited carbon resistors are used in the frequency determining networks.

Calibration is accurate within 1! percent plus 0.1 cycle. Some specifications on "undesired voltages" are as follows: power supply noise, less than 0.01 percent of the output signal; harmonic dis­tortion, less than 0.2 percent at all frequencies from 20 cycles per second to 15,000 cycles per second; microphonic noise, less than 0.01 percent of the output signal.

Power consumption is 140 watts at 115 volts, 60 cycles per second. Dimensions are n in. high, 1S! in. long, and 12 in. deep. Weight of the unit is 43.5 pounds.-SoUTHWESTERN INDUSTRIAL ELECTRONIC COMPANY, 2831 Post Oak Road, Houston, Texas.

Polinear Recorder Model PFR polinear recorder offers the engineer means for re­

cording complete characteristics of electroacoustic and electronic devices with one instrument. The combined features of polar and rectilinear movement permit the recording of angular patterns, frequency response characteristics, and other measurements.

The instrument can record either d.c. or a.c. voltages, selectable by the operator. The turntable, S! in. X 11 in., is driven linearly by a synchronous motor and is rotated by a selsyn repeater. The latter allows the test turntable to be placed at any distance and any location from the recorder. The turntable of the recorder is equipped with a friction slip clutch which allows the operator to set it at any angular position independent of the selsyn position, or any linear position independent of the drive motor. Both linear and polar motions are reversible.

This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP:

128.240.225.44 On: Fri, 19 Dec 2014 23:30:48