Vacuum Tube Technology: A Perspective Circa 1950

The definitions listed here are from Standards on Electron Tubes: Definitions of Terms, published in 1950 by the Institute of Radio Engineers, the organization that later became the IEEE. About 200 scientists and engineers collaborated on the standard, which replaced the one that the IRE issued in 1938.

Newly developed specialty tubes abound. By 1950 we see disectors, orthicons, monoscopes, kinescopes, and iconoscopes, which were developed for television and imaging applications, enter the standard vocabulary. The hexode, heptode, and octode also become standard.

One of the most common applications for multigrid tubes is in the heterodyne circuit for radio receivers, in which the input radio frequency signal is converted to a fixed intermediate frequency for further amplification and demodulation. With a pentagrid converter tube (officially defined by the IRE as a heptode), a single electron stream is used for both a local oscillator and a mixer, operations previously requiring two separate tube circuits. More generally, an electronic circuit that changes one frequency to another is defined by the IRE committee as a transducer, a term that appears quite often in the standard.

The definitions below describe tube parameters in terms of admittances rather than impedances. Since they are reciprocals of each other, each is easily translated into the other. Admittances are more convenient when viewing tubes as controlled current sources. This can be seen, for example, in Thomas Martin's treatment of common-cathode amplifiers in Electronic Circuits (Prentice-Hall, 1956).

Accelerating Electrode. An electrode to which a potential is applied to increase the velocity of the electrons in the beam.

Accelerating Electrode (of an Electron-Beam Tube). An electrode the potential of which provides an electric field to increase the velocity of the beam electrons.

Amplification Factor. The μ-factor for the plate and control-grid electrodes of an electron tube under the condition that the plate current is held constant.

Anode (of an Electron Tube). An electrode through which a principle stream of electrons leaves the inter-electrode space.

Anode Breakdown Voltage (of a Glow-Discharge Cold-Cathode Tube). The anode voltage required to cause conduction across the main gap with the starter gap not conducting and with all other tube elements held at cathode potential before breakdown.

Anode Voltage Drop (of a Glow-Discharge Cold-Cathode Tube). The main gap voltage drop after conduction is established in the main gap.

Astigmatism (Electron Optical). In an electron-beam tube, a focus defect in which electrons in different axial planes come to focus at different points.

Available Conversion Power Gain (of a Conversion Transducer). The ratio of the available output-frequency power from the output terminals of the transducer to the available input-frequency power from the driving generator. (Note - The maximum available conversion power gain of a conversion transducer is obtained when the input termination admittance, at input frequency, is the conjugate of the input-frequency driving-point admittance of the conversion transducer.)

Available Power. From a generator or an electric transducer, the power that would be delivered to the output external termination of the generator or transducer if the admittance of the external termination were the conjugate of the output driving-point admittance of the generator or transducer.

Available Power Gain (of an Electric Transducer). The ratio of the available power from the output terminals of the transducer to the available power from the driving generator. (Note - The maximum available power gain of an electric transducer is obtained when the input termination admittance is the conjugate of the driving-point admittance at the input terminals of the transducer. It is sometimes called completely matched power gain.)

Average Electrode Current. The value obtained by integrating the instantaneous electrode current over an averaging time and dividing by the averaging time.

Beam-Deflection Tube. An electron-beam tube in which current in an output circuit is controlled by transverse movement of the electron beam.

Beam-Power Tube. An electron-beam tube in which use is made of directed electron beams to contribute substantially to its power-handling capability, and in which the control grid and the screen grid are essentially aligned.

Camera Tube (Pickup Tube). An electron-beam tube in which an electron-current or charge-density image is formed from an optical image and is scanned in a predetermined sequence to provide an electrical signal.

Cathode (of an Electron Tube). An electrode through which a primary stream of electrons enters the inter-electrode space.

Cathode Heating Time (of a Gas Tube). The time required for the cathode to attain operating temperature with normal voltage applied to the heating element.

Cathode Heating Time (of a Vacuum Tube). The time required for the time rate of change of the cathode current to reach maximum value. (Note - All electrode voltages are to remain constant during measurement. The tube elements must all be at room temperature at the start of the test.)

Cathode Ray Tube. An electron-beam tube in which the beam can be focused to a small cross section on a surface and varied in position and intensity to produce a visible pattern.

Class-A Amplifier. An amplifier in which the grid bias and alternating grid voltages are such that plate current in a specific tube flows at all times.

Class-AB Amplifier. An amplifier in which the grid bias and alternating grid voltages are such that plate current in a specific tube flows for appreciably more than half but less than the entire electrical cycle.

Class-B Amplifier. An amplifier in which the grid bias is approximately zero when no exiciting grid voltage is applied, and so that plate current in a specific tube flows for approximately one-half of each cycle when an alternating grid voltage is applied.

Class-C Amplifier. An amplifier in which the grid bias is appreciably greater than the cutoff value so that the plate current in each tube is zero when no alternating grid voltage is applied, and so that plate current in a specific tube flows for appreciably less than one-half of each cycle when an alternating grid voltage is applied. (Note - To denote that grid current does not flow during any part of the input cycle, the suffix 1 may be added to the letter or letters of the class identification. The suffix 2 may be used to denote that current flows during some part of the cycle.)

Cold Cathode. A cathode that functions without the application of heat.

Cold Cathode Tube. An electron tube containing a cold cathode.

Collector. An electrode that collects electrons or ions which have completed their functions within the tube.

Composite Controlling Voltage. The voltage of the anode of an equivalent diode combining the effects of all individual electrode voltages in establishing the space-charge-limited current.

Condensed-Mercury Temperature (of a Mercury Vapor Tube). By definition, the temperature measured on the outside of the tube envelope in the region where the mercury is condensing in a glass tube or at a designated point on a metal tube.

Conductance for Rectification. The quotient of the electrode alternating current of low frequency by the in-phase component of the electrode alternating voltage of low frequency, a high-frequency sinusoidal voltage being applied to the same or another electrode and all other electrode voltages being maintained constant.

Constant-Current Characteristic. The relation, usually represented by a graph, between the voltages of two electrodes, with the current to one of them as well as all other voltages maintained constant.

Control Characteristic (of a Gas Tube). A relation, shown by a graph, between critical grid voltage and anode voltage.

Control Electrode. An electrode on which a voltage is impressed to vary the current flowing between two or more other electrodes.

Control Grid. A grid, ordinarily place between the cathode and an anode, for use as a control electrode.

Control Ratio (of a Gas Tube). The ratio of the change in anode voltage to the corresponding change in critical grid voltage, with all other operating conditions maintained constant.

Conversion Transconductance (of a Heterodyne Conversion Transducer). The quotient of the magnitude of the desired output-frequency component of current by the magnitude of the input-frequency (signal) component of voltage when the impedance of the output external termination is negligible for all of the frequencies which may affect the result. (Note - Unless otherwise stated, the term refers to the cases in which the input frequency voltage is of infinitesimal magnitude. All direct electrode voltages and the magnitude of the local-oscillator voltage must remain constant.)

Conversion Transducer. An electric transducer in which the input and the output frequencies are different. (Note - If the frequency-changing property of a conversion transducer depends upon a generator of frequency different from that of the input or output frequencies, the frequency and voltage or power of this generator are parameters of the conversion transducer.)

Conversion Voltage Gain (of a Conversion Transducer). The ratio of (1) the magnitude of the output-frequency voltage across the output termination, with the transducer inserted between the input-frequency generator and the output termination, to (2) the magnitude of the input-frequency voltage across the input termination of the transducer.

Converter Tube. An electron tube that combines the mixer and local-oscillator functions of a heterodyne conversion transducer.

Critical Grid Current. In a gas tube, the instantaneous value of grid current when the anode current starts to flow.

Critical Grid Voltage. In a gas tube, the instantaneous value of grid voltage at which the anode current starts to flow.

Cutoff Voltage (of an Electron Tube). That electrode voltage which reduces the value of the dependent variable of an electron tube characteristic to a specified low value. (Note - A specific cutoff characteristic should be identified as follows: current versus grid cutoff voltage, spot brightness versus grid cutoff voltage, etc.)

Decelerating Electrode (of an Electron-Beam Tube). An electrode the potential of which provides an electric field to decrease the velocity of the beam electrons.

Deflecting Electrode. An electrode the potential of which provides an electric field to produce deflection of an electron beam.

Deflecting Yoke. An assembly of one or more coils the current through which provides a magnetic field to produce deflection of an electron beam.

Deflection Factor (of a Cathode-Ray Tube). The reciprocal of the deflection sensitivity.

Deflection Sensitivity (of a Cathode-Ray Oscillograph Tube). The quotient of the displacement of the electron beam at the place of impact by the change in the deflecting field. (Note - Deflection sensitivity is usually expressed in millimeters per volt applied between the deflecting electrodes or in millimeters per gauss of the deflecting magnetic field.)

Deflection Sensitivity (of an Electrostatic-Deflection Cathode-Ray Tube). The quotient of the spot displacement by the change in deflecting potential.

Deflection Sensitivity (of a Magnetic-Deflection Cathode-Ray Tube). The quotient of the spot displacement by the change in deflecting magnetic field.

Deflection Sensitivity (of a Magnetic-Deflection Cathode-Ray Tube and Yoke Assembly). The quotient of the spot displacement by the change in deflecting-coil current.

Deionization Time (of a Gas Tube). The time required for the grid to regain control after anode-current interruption. (Note - To be exact, the ionization and deionization times of a gas tube should be presented as families of curves relating such factors as condensed-mercury temperature, anode and grid currents, anode and grid voltages, and regulation of the grid current.)

Diode. A two-electrode electron tube containing an anode and a cathode.

Diode Characteristic (of a Multielectrode Tube). The composite electrode characteristic taken with all electrodes except the cathode connected together.

Direct Grid Bias. The direct component of grid voltage (Note - This is commonly called grid bias.)

Dissector Tube. A camera tube having a continuous photocathode on which is formed a photoelectric-emission pattern which is scanned by moving its electron-optical image over an aperture.

Driving-Point Admittance (between the jth Terminal and the Reference Terminal of an n-Terminal Network). The quotient of the complex alternating component Ij of the current flowing to the jth terminal from its external termination by the complex alternating component Vj of the voltage applied to the jth terminal with respect to the reference point when all other terminals have arbitrary external terminations. (Note - In specifying the driving-point admittance of a given pair of terminals of a network or transducer having two or more pairs of terminals, no two pairs of which contain a common terminal, all other pairs of terminals are connected to arbitrary admittances.)

Dynode (of an Electron Tube). An electrode whose primary function is to alter by secondary-electron emission the electron current to itself or to other electrodes.

Electrode (of an Electron Tube). A conducting element that performs one or more of the functions of emitting, collecting, or controlling by an electric field the movements of electrons or ions.

Electrode Admittance (of the jthe Electrode of an n-Electrode Electron Tube. The short-circuit driving-point admittance between the jth electrode. (Note - To be able to determine the intrinsic electronic merit of an electron tube the driving-point and transfer admittances must be defined as if measured directly at the electrodes inside the tube. The definition of Electrode Admittance and Electrode Impedance are included for this reason.)

Electrode Capacitance (of an n-Terminal Electron Tube). The capacitance determined from the short-circuit driving-point admittance at that electrode.

Electrode Characteristic. A relation, usually shown by a graph, between the electrode voltage and the current of an electrode, all other electrode voltages being maintained constant.

Electrode Conductance. The real part of the electrode admittance.

Electrode Current (of an Electron Tube). The current passing to or from an electrode through the interelectrode space. (Note - The terms cathode current, grid current, anode current, plate current, etc., are used to designate electrode currents for these specific electrodes. Unless otherwise stated, an electrode current is measured at the available terminal.)

Electrode-Current Averaging Time. The time interval over which the current is averaged in defining the operating capabilities of the electrode.

Electrode Dissipation. The power dissipated in the form of heat by an electrode as a result of electron and/or ion bombardment.

Electrode Impedance. The reciprocal of the electrode admittance.

Electrode Resistance. The reciprocal of the electrode conductance. (Note - This is the effective parallel resistance and is not the real component of the electrode impedance.)

Electrode Voltage. The voltage between an electrode and the cathode or a specified point of a filamentary cathode. (Note - The terms grid voltage, anode voltage, plate voltages, etc., are used to designate the voltage between these specific electrodes and the cathode. Unless otherwise stated, electrode voltages are understood to be measured at the available terminals.)

Electrometer Tube. A high-vacuum tube having a very low control-electrode conductance to facilitate the measurement of extremely small direct current or voltage.

Electron-Beam Tube. An electron tube the performance of which depends upon the formation and control of one or more electron beams.

Electron Device. A device in which conduction by electrons takes place through a vacuum, gas, or semi-conductor.

Electron Emission. The liberation of electrons from an electrode into the surrounding space. Quantitatively, it is the rate at which electrons are emitted from an electrode.

Electron Gun. An electrode structure which produces and may control, focus, and deflect an electron beam.

Electron Tube. An electron device in which conduction of electrons takes place through a vacuum or gaseous medium within a gas-tight envelope.

Electronic. Of or pertaining to devices, circuits, or systems utilizing electron devices. Examples: Electronic control, electronic equipment, electronic instrument and electronic circuit.

Electronics. That field of science and engineering which deals with electron devices and their utilization. Electronics, used as an adjective, signifies of or pertaining to the field of electronics. Examples: Electronics engineer, electronics course, electronics laboratory and electronics committee.

Electrostatic Focusing. A method of focusing an electron beam by the action of an electric field.

Element (of an Electron Tube). Any integral part of the tube that contributes to its operation.

Emission Characteristic. A relation, usually shown by a graph, between the emission and a factor controlling the emission (such as temperature, voltage, or current of the filament or heater.)

Equivalent Diode. The imaginary diode consisting of the cathode of a triode or multigrid tube and a virtual anode to which is applied a composite controlling voltage such that the cathode current is the same as in the triode or multigrid tube.

External Termination (of the jth Terminal of an n-Terminal Network). That passive or active two-terminal network which is attached externally between the jth terminal and the reference point.

Fault Electrode Current (Surge Electrode Current). The peak current that flows through an electrode under fault conditions, such as arc backs and load short circuits.

Field-Free Emission Current (of a Cathode). The electron current drawn from the cathode when the electric gradient at the surface of the cathode is zero.

Filament. A cathode of a thermionic tube, usually in the form of a wire or ribbon, to which heat may be supplied by passing current through it. This is also known as a filamentary cathode.

Filament Current. Current Supplied to a filament to heat it.

Filament Voltage. The voltage between the terminals of a filament.

Flexion-Point Emission Current. That value of current on the diode characteristic for which the second derivative of the current with respect to the voltage has its maximum negative value. This current corresponds to the upper flexion point of the diode characteristic and is an approximate measure of the temperature-limited emission current.

Focusing. The process of controlling the convergence and divergence of an electron beam.

Focusing Coil or Focusing Magnet. An assembly producing a magnetic field for focusing an electron beam.

Focusing Electrode. An electrode to which a potential is applied to control the cross-sectional area of the electron beam.

Gas (Ionization) Current (in a Vacuum Tube). Current flowing to a negatively biased electrode and composed of positive ions which are produced by an electron current flowing between other electrodes. Positive ions are a result of collision between electrons and molecules of the residual gas.

Gas Focusing. A method of concentrating an electron beam by the action of ionized gas.

Gas Ratio. The ratio of the ion current in a tube to the electron current that produces it.

Gas Tube. An electron tube in which the pressure of the contained gas or vapor is such as to affect substantially the electrical characteristics of the tube.

Gas Discharge. A discharge of electricity through a gas, characterized by a space potential in the vicinity of the cathode that is much higher than the ionization potential of the gas.

Glow-Discharge Cold-Cathode Tube. A gas tube that depends for its operation on the properties of a glow discharge.

Grid. An electrode having one or more openings for the passage of electrons or ions.

Grid-Drive Characteristic. A relation, usually shown by a graph, between electrical or light output and control-electrode voltage measured from cutoff.

Grid Driving Power. The average product of the instantaneous values of the grid current and of the alternating component of the grid voltage over a complete cycle. (Note - This comprises the power supplied to the biasing device and to the grid.)

Grid Emission. Electron or ion emission from a grid of an electron tube.

Harmonic Conversion Transducer (Frequency Multiplier, Frequency Divider). A conversion transducer in which the output signal frequency is a multiple or sub-multiple of the input frequency. (Note - In general, the output signal amplitude is a nonlinear function of the input signal amplitude.)

Heater. An electric heating element for supplying heat to an indirectly heated cathode.

Heater Current. The current flowing through a heater.

Heater Voltage. The voltage between the terminals of a heater.

Heptode. A seven-electrode electron tube containing an anode, a cathode, a control electrode, and four additional electrodes that are ordinary grids.

Heterodyne Conversion Transducer (Converter). A conversion transducer in which the output frequency is the sum or difference of the input frequency and an integral multiple of a local oscillator frequency. (Note - The frequency and voltage or power of the local oscillator are parameters of the conversion transducer. Ordinarily, the output signal amplitude is a linear function of the input signal amplitude over its useful operating range.)

Hexode. A six-electrode electron tube containing an anode, a cathode, a control electrode, and three additional electrodes that are ordinary grids.

Hot Cathode (Thermionic Cathode). A cathode that functions primarily by the process of thermionic emission.

Hot-Cathode Tube. An electron tube containing a cathode.

Iconoscope. A camera tube in which a high-velocity electron beam scans a photoactive mosaic that has electrical storage capability.

Image Orthicon. A camera tube in which an electronic image is produced by a photoemitting surface and focused on a separate storage target, which is scanned on its opposite side by a low-velocity electron beam.

Indicator Tube. An electron-beam tube in which useful information is conveyed by the variation in cross section of the beam at a luminescent target.

Indirectly Heated Cathode (Equipotential Cathode, Unipotential Cathode). A cathode of a thermionic tube to which heat is supplied by an independent heater element.

Inflection-Point Emission Current. That value of current on the diode characteristic for which the second derivative of the current with respect to the voltage is zero. This current corresponds to the inflection point of the diode characteristic and is an approximate measure of the maximum space-charge-limited emission current.

Input Capacitance (of an n-Terminal Electron Tube). The short-circuit transfer capacitance between the input terminal and all other terminals, except the output terminal, connected together. (Note - This quantity is equivalent to the sum of the interelectrode capacitances between the input electrode and all other electrodes except the output electrode.)

Insertion Power Gain (of an Electric Transducer). The ratio of (1) the power developed in the external termination of the output with the transducer inserted between generator and output termination to (2) the power developed in the external termination of the output with the generator connected directly to the output termination.

Insertion Voltage Gain (of an Electric Transducer). The complex ratio of (1) the alternating component of voltage across the external termination of the output with the transducer inserted between the generator and the output termination to (2) the voltage across the external termination of the output when the generator is connected directly to the output termination.

Intensifier Electrode. A post-accelerating electrode.

Interelectrode Capacitance (j-lth Interelectrode Capacitance Cjl of an n-Terminal Electron Tube). The capacitance determined from the short-circuit transfer admittance between the jth and the lth terminals. (Note - This quantity is often referred to as direct interelectrode capacitance.)

Interelectrode Transadmittance (j-l Interelectrode Transadmittance of an n-Electrode Electron Tube). The short-circuit transfer admittance from the jth electrode to the lth electrode.

Interelectrode Transconductance (j-l Interelectrode Transconductance). The real part of the j-l interelectrode transadmittance.

Internal Correction Voltage (of an Electron Tube). The voltage that is added to the composite controlling voltage and is the voltage equivalent of such effects as those produced by initial electron velocity and contact potential.

Inverse Electrode Current. The current flowing through an electrode in the direction opposite to that for which the tube is designed.

Ion Spot (on a Cathode-Ray-Tube Screen). An area of localized deterioration of luminescence caused by bombardment with negative ions.

Ionic-Heated Cathode. A hot cathode that is heated primarily by ionic bombardment of the emitting surface.

Ionic-Heated Cathode Tube. An electron tube containing an ionic-heated cathode.

Ionization Time (of a Gas Tube). The time interval between the initiation of conditions for and the establishment of conduction at some stated value of tube voltage drop.

Line or Trace. The path of a moving spot.

Load (Dynamic) Characteristic (of an Electron Tube Connected in a Specified Operating Circuit, at a Specified Frequency). A relation, usually represented by a graph, between the instantaneous values of a pair of variables such as electrode voltage and current, when all direct electrode supply voltages are maintained constant.

Local Oscillator Tube. An electron tube in a heterodyne conversion transducer to provide the local heterodyning frequency for a mixer tube.

Magnetic Focusing. A method of focusing an electron beam by the action of a magnetic field.

Main Gap (of a Glow-Discharge Cold-Cathode Tube). The conduction path between a principle cathode and a principle anode.

Mercury-Vapor Tube. A gas tube in which the active gas is mercury vapor.

Microphonism (Microphonics) (in an Electron Tube). The modulation of one or more of the electrode currents resulting from the mechanical vibration of a tube element.

Mixer Tube. An electron tube that performs only the frequency-conversion function of a heterodyne conversion transducer when it is supplied with voltage or power from an external oscillator.

Modulating Electrode. An electrode to which a potential is applied to control the magnitude of the beam current.

Monoscope. A signal generating electron-beam tube in which a picture signal is produced by scanning an electrode, parts of which have different secondary-emission characteristics.

μ-Factor (of an n-Terminal Electron Tube). The ratio of the magnitude of infinitesimal change in the voltage at the jth electrode to the magnitude of an infinitesimal change in the voltage at an lth electrode under the conditions that the current to the mth electrode remains unchanged, and the voltages of all other electrodes be maintained constant.

Multielectrode Tube. An electron tube containing more than three electrodes associated with a single electron stream.

Multiple-Unit Tube. An electron tube containing within one envelope two or more groups of electrodes associated with independent electron streams. (Note - A multiple-unit tube may be so indicated; for example, duodiode, duotriode, diode-pentode, duodiode-triode, duodiode-pentode, and triode-pentode.)

Octode. An eight-electrode electron tube containing an anode, a cathode, a control electrode, and five additional electrodes that are ordinary grids.

Orthicon. A camera tube in which a low-velocity electron beam scans a photoactive mosaic that has electrical storage capacity.

Oscillograph Tube (Oscilloscope Tube). A cathode-ray tube used to produce a visible pattern, which is the graphical representation of electrical signals, by variations of the position of the focused spot or spots in accordance with these signals.

Output Capacitance (of an n-Terminal Electron Tube). The short-circuit transfer capacitance between the output terminal and all other terminals, except the input terminal, connected together.

Peak Cathode Current (Steady-State). The maximum instantaneous value of a periodically recurring cathode current.

Peak Electrode Current. The maximum instantaneous current that flows through an electrode.

Peak Forward Anode Voltage. The maximum instantaneous anode voltage in the direction in which the tube is designed to pass current.

Peak Inverse Anode Voltage. The maximum instantaneous anode voltage in the direction opposite to that in which the tube is designed to pass current.

Pentode. A five-electrode electron tube containing an anode, a cathode, a control electrode, and two additional electrodes that are ordinary grids.

Persistence Characteristic (Decay Characteristic) (of a Luminescent Screen). A relation, usually shown by a graph, between emitted radiant power and time after excitation.

Perveance. The quotient of the space-charge-limited cathode current by the three-halves power of the anode voltage in a diode. (Note - Perveance is the constant G appearing in the Child-Langmuir-Schottky equation

ik = Geb3/2

When the term perveance is applied to a triode or multigrid tube, the anode voltage eb is replaced by the composite controlling voltage e' of the equivalent diode.)

Phosphor. A substance capable of luminescence.

Phototube. An electron tube in which one of the electrodes is irradiated for the purpose of causing electron emission.

Picture Tube (Kinescope). A cathode-ray tube used to produce an image by variation of the beam intensity as the beam scans a raster.

Plate. A common name for the principle anode in an electronic tube.

Post-Acceleration (in an Electron-Beam Tube). Acceleration of the beam electrons after deflection.

Raster. A predetermined pattern of scanning lines which provides substantially uniform coverage of an area.

Rectification Factor. The quotient of the change in average current of an electrode by the change in amplitude of the alternating sinusoidal voltage applied to the same electrode, the direct voltages of this and other electrodes being maintained constant.

Regulation (of a Glow-Discharge Cold-Cathode Tube). The difference between the maximum and minimum anode voltage drop over a range of anode currents.

Screen (of a Cathode-Ray Tube). The surface of a tube upon which the visible pattern is produced.

Screen Grid. A grid placed between a control grid and an anode, and usually maintained at a fixed positive potential, for the purpose of reducing the electrostatic influence of the anode in the space between the screen grid and the cathode.

Secondary Emission. Electron emission from solids or liquids resulting directly from bombardment of the surfaces by electrons or ions.

Secondary Grid Emission. Electron emission from a grid resulting directly from bombardment of its surface by electrons or other charged particles.

Sensitivity (of a Camera Tube). The signal current developed per unit incident radiation density, (i.e. watt per unit area). Unless otherwise specified the radiation is understood to be that of an unfiltered incandescent source of 2870 degrees Kelvin, and its density, which is generally measured in watts per unit area, may be expressed in foot-candles.

Short-Circuit Driving-Point Admittance (of the jth Terminal of an n-Terminal Network). The driving-point admittance between that terminal and the reference terminal when all other terminals have zero alternating components of voltage with respect to the reference point.

Short-Circuit Feedback Admittance (of an Electron-Tube Transducer). The short-circuit transfer admittance from the physically available output terminals to the physically available input terminals of a specified socket, associated filters, and tube.

Short-Circuit Forward Admittance (of an Electron-Tube Transducer). The short-circuit transfer admittance from the physically available input terminals to the physically available output terminals of a specified socket, associated filters, and tube.

Short-Circuit Input Admittance (of an Electron-Tube Transducer). The short-circuit driving-point admittance at the physically available input terminals of a specified socket, associated filters, and electron tube.

Short-Circuit Input Capacitance (of an n-Terminal Electron Tube). The effective capacitance determined from the short-circuit input admittance.

Short-Circuit Output Admittance (of an Electron-Tube Transducer). The short-circuit driving-point admittance at the physically available output terminals of a specified socket, associated filters, and tube.

Short-Circuit Output Capacitance (of an n-Terminal Electron Tube). The effective capacitance determined from the short-circuit output admittance.

Short-Circuit Transfer Admittance (from the jth Terminal to the lth Terminal of an n-Terminal Network). The transfer admittance from terminal j to terminal l when all terminals except j have zero complex alternating components of voltage with respect to the reference point.

Short-Circuit Transfer Capacitance (of an Electron Tube). The effective capacitance determined from the short-circuit transfer admittance.

Signal Electrode (of a Camera Tube). An electrode from which the signal output is obtained.

Space-Charge Grid. A grid, usually positive, that controls the position, area, and magnitude of a potential minimum or of a virtual cathode in a region adjacent to the grid.

Spectral Characteristic (of a Camera Tube). A relation, usually shown by a graph, between wavelength and sensitivity per unit wavelength interval.

Spot. The area instantaneously affected by the impact of an electron beam.

Starter (of a Glow-Discharge Cold-Cathode Tube). An auxiliary electrode used to initiate conduction.

Starter Breakdown Voltage (of a Glow-Discharge Cold-Cathode Tube). The starter voltage required to cause conduction across the starter gap with all other tube elements held at cathode potential before breakdown.

Starter Gap (of a Glow-Discharge Cold-Cathode Tube). The conduction path between a starter and the other electrode to which starting voltage is applied.

Starter Voltage Drop (of a Glow-Discharge Cold-Cathode Tube). The starter-gap voltage drop after conduction is established in the starter gap.

Static Characteristic (of an Electron Tube). A relation usually represented by a graph, between a pair of variables such as electrode voltage and electrode current, with all other voltages maintained constant.

Suppressor Grid. A grid that is interposed between two positive electrodes (usually the screen grid and the plate), primarily to reduce the flow of secondary electrons from one electrode to the other.

Surge Electrode Current. The recommended term is Fault Electrode Current.

Tetrode. A four-electrode electron tube containing an anode, a cathode, a control electrode, and one additional electrode that is ordinarily a grid.

Thermionic Grid Emission (Primary Grid Emission). Current produced by electrons thermionically emitted from a grid.

Thermionic Tube. An electron tube in which one of the electrodes is heated for the purpose of causing electron or ion emission from that electrode.

Thyratron. A hot-cathode gas tube in which one or more control electrodes initiate, but do not limit, the anode current except under certain operating conditions.

Transconductance. As most commonly used, the interelectrode transconductance between the control grid and the plate. At low frequencies, transconductance is the slope of the control-grid-to-plate transfer characteristic.

Transfer Admittance (from the jth Terminal to the lth Terminal of an n-Terminal Network). The quotient of the complex alternating component Il of the current flowing to the lth terminal from the lth external termination by the complex alternating component Vj of the voltage applied to the jth terminal with respect to the reference point when all other terminals have arbitrary external terminations.

Transfer Characteristic. A relation, usually shown by a graph, between the voltage of one electrode and the current to another electrode, all other electrode voltages being maintained constant.

Transfer Current (of a Glow-Discharge Cold-Cathode Tube). The starter-gap current required to cause conduction across the main gap. (Note - The transfer current is a function of the anode voltage.)

Transrectification Factor. The quotient of the change in average current of an electrode by the change in the amplitude of the alternating sinusoidal voltage applied to another electrode, the direct voltages of this and other electrodes being maintained constant. (Note - Unless otherwise stated, the term refers to cases in which the alternating sinusoidal voltage is of infinitesimal magnitude.)

Triode. A three-electrode electron tube containing an anode, a cathode, and a control electrode.

Tube Heating Time (in a Mercury-Vapor Tube). The time required for the coolest portion of the tube to attain operating temperature.

Tube Voltage Drop. The anode voltage during the conducting period.

Vacuum Tube. An electron tube evacuated to such a degree that its electrical characteristics are essentially unaffected by the presence of residual gas or vapor.

Variable-mu Tube. An electron tube in which the amplification factor varies in a predetermined way with the control-grid voltage.


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