Vacuum Tube Characteristics Research Articles

The Legacy of the CE and BMET: Safer Healthcare Technologies

The Legacy of the CE and BMET: Safer Healthcare Technologies

X-ray emission from broadcast transmitters

During the past few years amplitude-modulated transmitters employing efficient pulse-width modulators have come into common use. These transmitters are reliable, relatively insensitive to vacuum tube characteristics, and offer excellent audio fidelity. Their architecture requires, however, supply voltages in the 20-30-kV range, which greatly enhances the production of ionizing radiation in the form of X-rays. Recent analysis by Voice of America indicates that these X-rays are being emitted in short, high-intensity bursts focused into broad radial beams. The general aspects of ionizing radiation of interest to communications engineers are reviewed. The spectral and time-domain characteristics of X-ray radiation from transmitters are examined, a method for estimating fault-condition radiation values is suggested, and the findings of the Voice of America are discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Historical Introduction

This program has been organized by the EMSA to commensurate the 50th anniversary of the experimental verification of the wave nature of the electron. Davisson and Germer in the U.S. and Thomson and Reid in Britian accomplished this at about the same time. Their findings were published in Nature in 1927 by mutual agreement since their independent efforts had led to the same conclusion at about the same time. In 1937 Davisson and Thomson shared the Nobel Prize in physics for demonstrating the wave nature of the electron deduced in 1924 by Louis de Broglie.The Davisson experiments (1921-1927) were concerned with the angular distribution of secondary electron emission from nickel surfaces produced by 150 volt primary electrons. The motivation was the effect of secondary emission on the characteristics of vacuum tubes but significant deviations from the results expected for a corpuscular electron led to a diffraction interpretation suggested by Elasser in 1925.

Console Comparator Microphotometer Featuring High Screen Intensity and a Null-Ratio Measurement System

A Comparator Microphotometer of new design is described. An optical system has been developed in which all of the available light flux is used for both viewing the spectrum and measuring the transmission of selected spectral lines. Besides high viewing screen intensity and great sensitivity, a unique electronic system is employed. The advantages of this null-ratio system include: reduced drift and noise, independence of individual vacuum tube characteristics, and freedom from the logarithmic damping response characteristic of galvanometers and meters.

An AM-FM Electronic Analog Multiplier

This paper describes an electronic multiplier wherein the input voltages are made proportional to the respective indices of amplitude and frequency modulations of a radio frequency carrier with the aid of feedback stabilization. The desired product of the input voltage is obtained from a Foster-Seeley discriminator whose output is independently proportional to each modulation index after the carrier component is subtracted out. Performance of the AM-FM multiplier is essentially independent of vacuum tube characteristics by virtue of the feedback stabilization and is limited primarily by the stability of the discriminator parameters. Other features of the multiplier are: ease and rapidity of adjustment; conventional AM and FM receiver circuitry; long-time multiplication error of less than 1 per cent of full scale output; usable bandwidth (flat amplitude response and less than 15 degrees phase-shift for highest frequency component) approximately 1 per cent of carrier frequency.

The effect of filament voltage upon vacuum tube characteristics

One means of increasing vacuum tube life and at the same time decrease filament power supply requirements, heat dissipation problems, and d-c drift, is to operate the vacuum tube with reduced filament supply voltage. If the tube is operating well below temperature saturation, which is the case for the majority of circuits other than power amplifiers, the effect of reduced filament power will be to decrease the initial velocity of electrons emitted from the cathode. This reduces the magnitude of the charge at the virtual cathode, and increases the charge density at the grid, which decreases the velocity of electron flow through the grid. By creating an imaginary cathode, called an image cathode, which is located behind the real cathode, and defined as the plane from which the electrons appear to be emitted, the principles of electrostatics can be applied to determine the effect of lowered cathode temperature upon amplification factor. As the cathode temperature decreases, the charge of the virtual cathode decreases, and the distance from the real cathode to the image cathode decreases. The apparent grid to cathode distance has thus been decreased and amplification factor goes up. This is experimentally verified by tests on a 6C4 triode and a 6AG5 pentode. The effects of decreasing filament voltage upon μ, r <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> , and G <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> are plotted. It is shown that μ increases, r <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> increases, and G <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</inf> decreases. The actual gain that may be achieved in a voltage amplifier increases. Increases in gain of 1.5 times have been measured when the filament voltage was decreased from 6.3 volts to 3.0 volts.

A Simple Electronic Correlator

Attention has been drawn in the literature to the possible utility of correlation techniques in the reception of acoustic signals. In applying such techniques, it is often necessary to find the average of the instantaneous product of two electrical signals; the black box which performs this function, which is that of a generalized detector, may be called a correlator. By use of the quarter-squares method of multiplication [AB = 14(A + B)2 − 14(A − B)2], correlators can be constructed using common triodes as the square-law devices. In practice, however, such multiplier-averagers depend strongly upon the vacuum tube characteristics which in turn require, for stability, regulated plate and heater supplies and frequent balance adjustments. If the square-law vacuum tubes in the circuit mentioned above are replaced by linear rectifiers, as many have suggested, it is shown that the resulting circuit is similar in action to a correlator. The output of this “linear rectifier correlator” is a somewhat distorted replica of the un-normalized cross-correlation function of the input signals, but the output signal-to-noise ratio for small input signal-to-noise ratios is not appreciably less than that for a multiplier-averager. The linear rectifier correlator has the practical advantage of being completely independent of power supplies, if contact rectifiers are used, and requires no balance adjustments if care is used in its construction.

A New Logarithmic Electronic Indicator

Acoustic measurements are often facilitated by the use of an electronic device with output consisting of a direct current which is proportional to the logarithm of the a.c. input voltage. A uniform decibel scale is obtained when such a device is used in conjunction with a linear indicator, such as a cathode-ray tube or a d.c. meter. The several circuits to perform this function which have been described previously have depended upon approximate logarithmic characteristics of vacuum tubes. The present paper outlines methods for securing from combinations of passive circuit elements a response which in principle is rigorously logarithmic. The logarithmic time-voltage characteristic of an impulse-excited resistance-capacity circuit is considered in particular. A brief description is given of a specific circuit which produces logarithmic indication over a 20–30 db range. The more important practical design limitations are mentioned.

Characteristics of Vacuum Tubes for Radar Intermediate Frequency Amplifiers

The desired characteristics for vacuum tubes for use in broad-band intermediate frequency amplifiers are primarily high transconductance, low capacitances, high input resistance, and good noise figure. These characteristics determine the frequency bandwidth, amplification, and signal-to-noise ratio attainable with such an amplifier. The maximum operating frequency is generally limited by the input resistance of the tube which decreases as the frequency is increased, and, in some cases, by the tube noise which increases with increasing frequency. Three other characteristics which are also important are small physical size, low power consumption, and ruggedness. The present paper describes how these characteristics are related to the performance requirements for intermediate frequency (IF) amplifiers used in radar systems and shows how the requirements were met in the design of the Western Electric 6AK5 Vacuum Tube.

Visual Demonstration of Vacuum Tube Characteristics

Visual Demonstration of Vacuum Tube Characteristics

Sharp cutoff in vacuum tubes, with applications to the slide-back voltmeter

That the current-voltage characteristics of vacuum tubes obey an exponential law near cutoff is pointed out. The larger the coefficient k appearing in the exponent, the steeper will be the current-voltage curve, and the better suited the tube will be for use in a slide-back voltmeter. The problem of obtaining high values of k is considered, and a simple theory of rectification by an exponential conductor is given. The error inherent in slide-back voltmeters of the ordinary type is discussed, and a correction factor applicable to sine waves is derived. The circuit of a slide-back vacuum-tube voltmeter which includes means for measuring the k of the tube is shown.

Sharp Cutoff in Vacuum Tubes, With Applications to the Slide-Back Voltmeter

That the current-voltage characteristics of vacuum tubes obey an exponential law near cutoff is pointed out. The larger the coefficient appearing in the exponent, the steeper will be the current-voltage curve, and the better suited the tube will be for use in a slide-back voltmeter. The problem of obtaining high values of k is considered, and a simple theory of rectification by an exponential conductor is given. The error inherent in slide-back voltmeters of the ordinary type is discussed, and a correction factor applicable to sine waves is derived. The circuit of a slide-back vacuum-tube voltmeter which includes means for measuring the k of the tube is shown.

Use of Vacuum Tubes in Measurements

For the benefit of those who may wish to use vacuum tubes in meeting specific problems in the field of measurement, the comprehensive bibliography contained in this paper has been prepared. Some 600 references are included in this list, selected from a total of about 1,500 papers or books published since approximately 1920. The first portion of the bibliography contains publications dealing with the characteristics of vacuum tubes, and the second portion contains references to specific applications to measurement problems.

Vacuum tube characteristics in relation to the selection of coincident pulses from cosmic ray counters

Vacuum tube characteristics in relation to the selection of coincident pulses from cosmic ray counters

Vacuum Tube Characteristics in the Positive Grid Region by an Oscillographic Method

A method of determining plate and grid characteristics of vacuum tubes in the positive grid region by means of oscillographic recording has been developed. A condenser of high capacity furnishes a single pulse of grid excita tion which can be made to cover the entire region from any desired positive grid voltage to zero. Due to the rapidity of this excitation instantaneous power input to the tube of twenty to thirty times nominal rating has been recorded without danger to the tubes. Several typical complete charts of plate and grid characteristics obtained by this method for an experimental tube of the so-called 50-watt type are given. The experimental procedure in obtaining these characteristics is discussed in detail. Also the circuit for obtaining oscillographically the highly important composite diode line, with E p = E g , is described. The inadequacy of the usual logarithmic extrapolation of zero-grid characteristics into the positive grid region is discussed. The complete plate and grid current charts, which can be obtained accurately only by an oscillographic method, are practically indispensable in precalculation of class B and class C performance. The method has been successfully used in studying the characteristics of the smallest and the largest existing tubes in this country.

Audio-frequency transformers: Voltage-ratio characteristics determined by the low-voltage cathode ray oscillograph

The usual method of determining the voltage ratio of audio-frequency transformers employs a three-element vacuum tube in the circuit. Due to the fact that the results are a combination of both transformer and vacuum tube characteristics this method is not entirely satisfactory. This paper describes a new method, using a low-voltage cathode ray oscillograph, by means of which the voltage ratio of a transformer is determined independent of any other apparatus This newly developed method is accurate and simple in operation, and gives the actual characteristics of the transformer for all frequencies and d-c. components. The ratios of several makes of transformers were determined over a frequency range of 20 to 10,000 cycles and at different degrees of magnetic saturation. The results indicate that the ratios are very good between frequencies of 40 and 3000 cycles. Saturation within the usual operating limits was found to have little effect. The method developed was found to be exceptionally good, as the results are accurate and are readily reproduced. However, precautions must be taken to eliminate stray fields which may influence the tube unless properly shielded.

Harmonic Production in Ferromagnetic Materials at Low Frequencies and Low Flux Densities

When a multi-channel communication circuit includes a non-linear element such as a ferromagnetic core coil, distortion of the wave form impressed upon the circuit is produced. In terms of the single frequency components, this distortion is manifested in the appearance of new components. This distortion may give rise to the reduction of quality in any channel, and it may also introduce crosstalk and interference, which consists of new frequencies not present in the impressed wave of any channel under consideration, produced by independent channels. In view of the recent increased use of multi-channel systems, it has become necessary to investigate the effects of this type of distortion, to determine the dependence of this distortion upon the properties of the magnetic materials constituting the cores of inductance coils and transformers, as well as upon the circuit impedances, and to determine those constants of core materials which are significant in the distorting process. The behavior of magnetic materials to complex waves of magnetizing force is ordinarily a highly involved process, so that a direct correlation between distortion and some of the easily measured constants of materials is a matter of some difficulty. It has been established experimentally, as a confirmation of theoretical speculations, that the third harmonic e.m.f. generated by a sinusoidal wave of magnetizing force may serve as an index of the distortion with a complex wave of magnetizing force. This relation is valid for low flux densities and for frequencies at which the screening effect of eddy currents is not important. The paper is therefore devoted to an investigation of the third harmonic production in its dependence upon the properties of hysteresis loops. These loop constants in turn are shown to be deducible from AC bridge measurements on a coil of known dimensions having a core of the magnetic material under investigation. The loop constants for a few materials are included in the text. An analogy exists between the treatments of hysteresis loop and of three-element vacuum tube characteristics which enables us to compare simplifying relations introduced by Rayleigh and by H. J. van der Bijl in the two cases. The theoretical deductions are found to be in general agreement with experiment, and are applied to a number of cases of practical interest. These include the effects of air gaps and dilution, and the choice of core material in third harmonic production by inductance coils and transformers. Finally, the amount of third harmonic current flowing out of long lines is deduced with both lumped and continuous loading.

Use of an Oscillograph for Recording Vacuum-Tube Characteristics

This paper describes the method involved and results obtained in using an oscillograph for plotting photographically vacuum-tube characteristics. The main requirement is an alternating voltage of fairly pure wave-form with as few harmonics as possible. The "dynatron" action of vacuum tubes is shown very clearly when large alternating e.m.f.'s are applied to the grid. Static and dynamic characteristics can also be quite easily recorded.

The Unilateral Dynamic Characteristics of Three-Electrode Vacuum Tubes

Unilateral dynamic characteristics of vacuum tube when plate circuit includes resistance, inductance or capacity.---(1) Theoretical equations. For the case of pure resistance ($R$), the Van der Bijl parabolic relation between plate current and effective grid voltage is expressed as a power series in $e$ sin pt, the impressed simple harmonic grid voltage. The coefficients of the various harmonics involve $R$, the $n$th harmonic reaching a maximum value when $R$ equals $\frac{(n\ensuremath{-}2)}{3}$ times R0 the tube resistance. For the fundamental the maximum energy output for a given plate battery is secured when $R=0.81 {R}_{0}$. The dynamic characteristic was obtained by compounding the harmonics into a single curve; it approaches a straight line as the resistance is increased. For the case of pure inductance, the plate current is expressed as a Fourier series. The dynamic characteristic is a closed loop whose area is proportional to the energy in the inductance. This loop reduces to an ellipse for small values of $e$, in which case the tube functions as an alternator whose internal impedance is a function of the external load. The insertion of a condenser instead of an equivalent inductance gives identical results except that the phase angle of the various harmonics is shifted. (2) Experimental verification. The effects on the plate current of varying the alternating grid voltage $e$, the static grid voltage ${E}_{c}$ and the plate voltage ${E}_{b}$, for a given value of resistance $R$ or inductance $l$, and the effect of varying $R$ or $l$ with constant ${E}_{b}$, ${E}_{c}$ and $e$ (15 or 20 volts), were determined and are shown in curves together with the corresponding theoretical values. A. W. E. 205B tube was used. The results show that the equations predict the harmonic constituents of the plate current as high as the fourth, for values of $e$ up to 15 or 20 volts (depending on ${E}_{b}$), the range for which the fundamental equation holds. For this range the coefficients of the various harmonics in the equation are proportional simply to ${e}^{n}$. The fundamental becomes greater while the other harmonics diminish as we approach the straight portion of the static characteristic and as we increase the plate potential.Circuit for producing pure sine wave electromotive force with frequency of 200,000 cycles.---The oscillating circuit and filters used are shown diagrammatically in Fig. 1.Pure resistance for high frequencies.---A platinized quartz fiber (diameter 0.01 mm.) with a resistance of 100 ohms per inch will carry 0.06 ampere when immersed in acidfree paraffin oil and has a negligible skin effect.