Planar Triode Research Articles

Design Considerations for a 5-Watt 4-GHz Microwave Planar Triode

The 416C Planar Triode has been designed to provide 5-watt broad-band RF output at 4.2 GHz. Emphasis is placed on low cathode temperature and beryllia envelope to reduce tube operating temperatures for long life.

Microwave planar triodes in preamplifiers of nuclear magnetic resonance spectrometers

Microwave planar triodes are investigated as low-noise devices for preamplifiers of high-resolution nuclear magnetic resonance spectrometers in the frequency band from 10 to 100 MHz. Noise sources, noise figures and a preamplifier circuit for planar triodes are considered. Planar triode noise performance is realistically evaluated by measurements under actual operating conditions. Comparison with other competitive low-noise devices in the frequency band from 10 to 100 MHz are given. A microwave planar triode preamplifier with high amplification stability has been designed; when operated with the optimum value of source conductance, it has a minimum noise figure of 0.35 dB at 24.3 MHz.

Planar Triode as the Logarithmic Element†

ABSTRACT The logarithmic region of the planar triode with a Maxwellian distribution of initial velocities of electrons is considered, The equations are derived which give the dependence between normalized grid and anode current of the triode in the logarithmic region and the limits of this region.

The effect of statistical variations in grid winding pitch upon the performance of a planar triode

The effect of statistical variations in the pitch of the grid winding of a triode valve is to produce an apparent increase in the `variable-mu' constant. Formulae are developed by which the magnitude of this effect may be calculated.

A new potential function for a planar triode

A new potential function has been developed for a planar triode. The function is accurate for a wide range of valve geometries and sufficiently simple to be suitable for iterative calculations of valve performance.

Spark-Gap-Trigger Amplifier

Short over-all time delay, low time jitter, and excellent long-term reliability are among the desirable features designed into a pulse generator that produces a 2-MW output pulse 30 nsec after the application of a 1-V signal at its 50-ohm input connector. The 10-kV output pulse can be used to trigger simultaneously several spark gaps of the type used in spark-chamber pulse modulators. The 10 power gain of the spark-gaptrigger amplifier is achieved by four stages of amplification packaged in a 5-1/4 in. rack-mount chassis that operates directly from a 117-V line. The individual stages, each selected to give minimum time delay for a given power gain at their respective power levels are: avalanche transistors, planar triode, grounded-grid planar triode, and a triggered-spark gap. The techniques used for the last stage, a spark gap triggered by a corona light, are of particular interest since the same techniques are applicable to obtaining short time delays and long-term reliability from the larger spark gaps that the amplifier was designed to trigger. During 10 months of operation, there have been no failures and no adjustments necessary in any of the seven spark-gap trigger amplifiers used in various spark-chamber experiments at the Lawrence Radiation Laboratory of the University of California (UCLRL) in Berkeley.

Noise transport in the crossed-field diode

The present work treats the transport of noise, originating at a thermionic cathode, across a planar crossed-field diode. A multivelocity Monte Carlo analysis is used to simulate thermionic emission by using random numbers to generate electron emission times and velocities. Trajectories for many charges are followed through the diode space by means of a high-speed digital computer. Measurements performed on a planar triode model for the crossed-field diode show that the anode noise current increases rapidly near the critical magnetic field, at which the stream just grazes the anode. The theory agrees well with these experimental findings. The Monte Carlo study predicts the increase of both the normal anode velocity fluctuations and the spread of the velocity distribution with magnetic field. This is caused mainly by the "geometrical" spreading of the initial velocity distribution. The crossed-field potential minimum exhibits no instabilities in the planar model. The noise current smoothing at low frequencies in ordinary streams is predicted for moderate fields but disappears near the critical field.

Rf Gate with 109 Carrier Suppression

A 10.7-Mc cw reference oscillator drives the cathode of a planar triode grounded-grid amplifier, which is normally cut off by −20 v on its plate. The grounded planar grid forms a perforated region in the wall of a copper can which otherwise totally shields both the cw oscillator and the planar cathode. Radio-frequency energy, which leaks capacitively from that cathode through the grounded grid to the negative plate, is bypassed to ground at the plate through a conducting diode. A positive gate voltage applied to the plate switches off the bypass diode and causes the grounded grid stage to amplify the rf voltage on its cathode. The following power amplifier stage, whose input is dc coupled, develops about 100-v rf output during the positive gate. When the gate is off, the output of the power amplifier is ≤10−7 v. The carrier suppression ratio is therefore ≥109, or 180 db. The ungated cw signal is continuously available. Circuitry, leakage measurement, and shielding are described in detail.

Studies on grid emission

This paper is concerned only with the study of primary grid emission of various types of grid materials resulting from the evaporation products of L, impregnated, oxide-coated, and thoriated tungsten cathodes. The factors contributing to grid emission are analyzed. A detailed discussion of the performance of titanium, which exhibits excellent grid emission inhibiting properties, is included. In our investigation a planar triode construction was used, the grids of which consisted of a two-terminal loop of 0.010 inch diameter wire. In the assembly and processing utmost precautions were taken to insure minimum contamination of the various elements. The methods of assembly and processing are fully described in the paper. These tubes were tested using pulsed and dc techniques, and a discussion of the testing methods is included. The work function of a tungsten grid exposed to the evaporation products of the L, impregnated, and oxide-coated cathodes varies from 1.2 to 2.0 ev, the final value depending upon the past history of the cathodes, namely, the nature of the surface of the grid and the temperature and length of exposure to the cathodes.

The small signal performance of the 416B planar triode between 60 and 4000 MC

The small signal performance of the 416B planar triode between 60 and 4000 MC

A Disc-Seal Triode as a UHF Amplifier

A disc-seal planar triode and its performance as a UHF amplifier are discussed. The description of mechanical features is followed by calculations of available power gain, and the measured gain is shown to be close to that computed by theory. The noise figure is calculated by conventional means, but the measured value is found to be higher. Reasons for the discrepancy are pointed out. The four pole admittances, y ij , and their influence on practical circuit design, are discussed.

Microphonism in the Dynamically Operated Planar Triode

The theory of microphonism in planar triodes is extended to cover the practical case of simultaneous electrical and mechanical excitation. It is shown that, in addition to other components, microphonic plate current components result at the sum and difference frequencies of the two types of excitation for transverse motion of any of the three electrodes. Experiments providing verification of the theory, with a tube especially designed and constructed for this purpose are described. On the basis of the theory, (1) an electrical nondestructive method for determining which electrode of the tube is set into vibration at a given mechanical frequency is outlined, and (2) a method for considerably reducing the microphonic output of certain high-gain amplifiers of practical interest is described.

The Reduction of Microphonics in Triodes

An analysis is presented showing the effect of grid displacement on the plate current of a planar triode. This is defined in terms of a new parameter called the motional transconductance. The analysis indicates that a useful mechanical displacement indicator may be constructed by moving the grid and noting the change in plate current. The analysis also indicates that the effect of certain modes of grid displacement on the plate current may be eliminated under conditions which are stipulated. Since microphonic effects are, in great part, caused by the mechanical motion of grid structures, the analysis indicates how microphonism may be reduced. It is shown that the electrical transconductance is large under these conditions, for the case investigated, so that the tube functions normally as an amplifier. Preliminary experimental results for comparison with the theory are presented.