Power Triode Research Articles

Numerical modeling of a high power triode-based self-excited oscillator: a path forward more efficient designs and a better frequency stability of low cost high power RF sources

Triode-based circuits are still the less expensive and more reliable high power sources for industrial applications between 13.56 and 40.68 Mhz. Among them, self-excited oscillators feature the lower cost but with a frequency stability preventing them to address all ISM frequencies and applications. This article demonstrates the possibility to model numerically self-excited oscillators with power triodes using a class-C practical circuit. Advantages over existing analytical calculations and graphical derivations are shown. A method is proposed to evaluate the frequency stability in presence of internal imperfections and external perturbations. These tools offer the possibility to design and analyze more efficiently this family of oscillators especially for demanding applications regarding frequency stability.

Nonthermal Argon Plasma Generator and Some Potential Applications

Abstract A laboratory - made nonthermal plasma generator is presented. It has a diameter of 0.020 m and length of 0.155 m and contains two electrodes. The first electrode is a 2% Th-W alloy, 0.002 m in diameter bar, centred inside the generator’s body by means of a four channel teflon piece; the other three channels, 0.003 m in diameter, are used for Ar supply. The second electrode is a nozzle of 0.002 m - 0.008 m diameter and 0.005m length. A ~500 kV/m electric field is generated between the two electrodes by a high frequency source (13.56 MHz ±5%), equipped with a OT-1000 (Tungsram) power triode. For Ar flows ranging from 0.00008 m3/s to 0.00056 m3/s, a plasma jet of length not exceeding 0.015 m and temperature below 315 K is obtained. Anthurium andraeanumis sample , blood matrix, human hair and textile fibers may be introduced in the plasma jet. For time periods of 30 s and 60 s, various effects like, cell detexturization, fast blood coagulation or textile fiber or hair cleaning and smoothing are obtained. These effects are presented and discussed in the paper.

Measuring system for the determination of nonlinear elastic and electromechanical properties in solids

An arbitrary waveform generator was introduced to produce pulse bursts with improved time jitter for the generation of ultrasound pulses. The problem of pulse amplification was solved using a ceramic power triode driven by a power FET amplifier. The construction of these special amplifier stages is mainly considered in this paper.

Conceptual design of a novel instrument far producing intense pulses of 10 ps X-rays for ultra-fast fluorescence measurements

We report a conceptual design of a novel bench-top device for producing intense, fast pulses of X-rays with 10 ps fwhm (full-width at half-maximum) X-ray pulse width, 120 keV maximum energy, 100 kHz repetition rate, and 1 A peak current onto the X-ray anode. The device includes three sections: (1) an electron gun that generates 5 ns wide pulses of electrons; (2) solenoidal magnetic lenses and rectangular deflection plates that focus the electrons onto an aperture plate and sweep the pulsed beam past the slit aperture, respectively; and (3) a tungsten anode onto which the post-aperture electrons are focused, producing X-ray pulses. Solenoidal magnetic lenses with a current density of 150 A/spl middot/turns/cm/sup 2/ focus the 120 keV electron beam to a spot diameter of 0.32 mm such that a deflection plate dV/dt of 10/sup 13/ V/s (achieved with power triode circuitry) will yield X-ray pulse widths of about 10 ps. We used EGUN, an electron optics and gun design program, to simulate the electron trajectories throughout the instrument.

Optimal Design of the High-Power Plate and Grid Modulated HF Amplifier by High Modulation Levels

The optimal design of the high power plate and grid modulated selective amplifier is examined in this paper. For the analysis purposes, the linear model of constant plate current characteristics for HF power triode is applied. The carrier wave state of the unmodulated amplifier is chosen so to enable the realization of the high levels of modulation. The results are obtained immediateZy, and the estimated error is acceptable. The estimated characteristic values of this high power and high efficiency HF amplifier are shown in the corresponding diagrams.

An electron accelerator for irradiation: “CASSITRON”

The “CASSITRON” actually under development is an accelerator operating at 166 MHz using a high power triode TH 116 operated at 4 MV peak 50 kW average, and a resonator made of three cavities working in π- mode, similar to the lines used on the electron and positron stockage rings.

Evaluation of arc damage to power triode grid wires

Experiments involving aluminium foil damage tests and a simulated grid structure were performed in order to relate such tests to the minimum energy required to damage the grid structure of a type A-15186C tube. In the case of foil tests conducted in air, it was shown that the energy in a particular fault is related to the foil hole size and is in close agreement with engineering calculations and published data. In a vacuum arc gap the damage is much less than indicated by the air foil test. The arc becomes mobile and the energy dissipation appears widespread over the surface area rather than being concentrated or anchored in a spot. (The damage or hole size was much smaller than obtained from engineering calculations.) With energies up to 100 joules and charges up to 0.25 coulombs, more than 100 pulses were required to damage simulated grid wires to the extent where breakage occurred. On a single shot basis, energies in excess of 3000 joules were required to produce damage.

High-performance experimental power triodes

The plate current, transconductance, gain-bandwidth product, and power output capabilities of small planar triodes have been increased nearly tenfold over that obtained from present day commercial tubes of comparable size and weight. In the new experimental triodes, the cathode can supply a CW current density of 1.6 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . A closely spaced, rigidly supported grid structure can provide a transconductance of 0.7 mho. The output capacitance is low enough to render a gain-bandwidth product of 22 Gc/s at 1.3 Gc/s. In this frequency range, the CW power output capability is 1 kW, and the pulsed power output capability in a 10-percent bandwidth circuit is 5 kW with 500 μs pulses at a duty factor of 0.07.

Turn-on Transient of p-n-p-n Triode †

ABSTRACT The turn-on transient of the p-n-p-n switch is analysed with simplifying assumptions. Experiments on the silicon p-n-p-n power triode show that the two mechanisms determine the current waveform during the transient. Before the centre junction becomes forward biased (switches on), the current increases nearly (or faster than) exponentially. After switch-on, the p-n-p-n switch behaves as an inductive impedance and the increase rate of current decreases. This is ascribed to the gradual modulation of conductivity of a base region of high resistance. Analytical expression is derived for the relation between base current and delay time when the step current is applied to the base.

A Silicon p-n-p-n Power Triode†

ABSTRACT Under the approximation of equal ionization rate for electron and hole a simplified theory of a p-n-p-n switching triode is presented. This theory enables us to understand in a straightforward way the effect of controlling base current on the current voltage characteristics of the triode. Observations are made on a developmental silicon p-n-p-n power triode. The developmental unit is fabricated by the solid state diffusion technique and can block a few hundred volts in the ‘ off ’ state and pass several amperes with tho internal drop of about ono volt in the ‘ on ’ state. Both turn-off current in diode operation and base current necessary to trigger the triode into tho ‘ on ’ state aro in the vicinity of 10 mA. In order to explain the observed control characteristics of base current, it was found that we must take into account the transverse flow of base current. The decreases in turn-off current and breakdown voltage by the applied base current are caused mainly by apparent increase in saturatio...

Large-signal theory of UHF power triodes

Using a parallel plane model, an analysis is made of the UHF electronics of triodes operating under Class B conditions. The theory, in its most general form, includes the effects of space charge in both the grid-cathode region and the plate-grid region. However, most of the solutions contained in this paper were obtained by neglecting space-charge effects in the plate-grid region. Over the wide range of UHF operating conditions investigated, it is found that the reduction of a triode's power output due to transit times is accounted for almost entirely by transit-time effects in the plate-grid region only. The principle effect of transit times in the grid-cathode region is to introduce a phase shift. This phase shift is quite important, however, for it contributes to a mechanism of regenerative feedback from output to input. The reduction of transit-time effects for a fixed operating frequency is limited by four factors: temperature-limited saturation of the cathode emission current, reliable mechanical spacing considerations, electrode dissipation capabilities, and amplifier bandwidth requirements. It is shown that there exists an optimum plate-grid spacing which leads to the highest possible RF output power consistent with the required bandwidth of the amplifier.

"Large signal theory of UHF power triodes"

Universal curves are presented which give the theoretical performance of triodes as Class B power amplifiers at ultra-high frequencies under a wide range of operating conditions. The curves may be used to determine the rf power output, plate efficiency, electronic driving power, power gain, and emission requirements of the cathode. The curves are the result of a large signal analysis of the parallel plane triode, with space charge effects taken into account. Touching only briefly upon the analysis itself, the present paper is concerned primarily with the presentation and interpretation of the results of the analysis so as to be of practical use to the tube designer. Two factors-the emission capabilities of the cathode consistent with long tube life, and the bandwidth requirement of the amplifier -are shown to play a major role in determining how nearly the uhf performance of a Class B triode can be made to approach its corresponding low frequency performance. Taking these factors into account, curves are presented which enable one to determine the optimum choice of interelectrode spacings for any given uhf triode application.

An automatic output regulator for power oscillators

The paper describes a new system of automatic output regulation for induction heating oscillators. With the use of a power triode as part of the oscillator grid-resistor an oscillator is made to block whenever a negative voltage is applied to the triode grid. This grid voltage is applied for a controlled portion of each half-cycle by means of two small thyratrons whose firing angle is determined by the phase of an error signal. The error signal is derived from a tungsten lamp bridge in which the lamp is heated by part of the high-frequency output of the oscillator. This system enables an existing oscillator to be regulated without alteration of its power supply. An automatic regulator unit using the system is described. It is interchangeable between a number of oscillators of different designs installed in the exhaust section of a tube plant.

A Coaxial Power Triode for 50-KW Output up to 110 MC

The introduction of all coaxial ring-seal terminals, a thoriated cathode, a re-entrant anode with integral coolant jacket, and a novel assembling technique has facilitated the development of a new power triode for 50-kw rf output up to 110-mc frequency. Increased power output ratings are available at lower frequencies. The bandwidth is suitable for television broadcasting. Design requirements are reviewed for optimum electrode geometry, heat-dissipating ability, minmum lead inductance, high rf conductivity of the vacuum seals, and other desiderata for high-power, high-frequency service. Mechanical features are described, and the circuit performance of the tube is discussed for lower frequencies as well as the vhf region.

The Characteristic Curves of the Triode

A method is described by which the entire static characteristic curves for the plate current of a power triode can be deduced from one experimentally determined curve. This experimental curve can be obtained at low power without danger of overheating the tube. Using the same procedure, the grid-current curves and the total space-current curves can be determined. A new log-log chart is described on which the static characteristic curves of a triode are presented by means of straight lines, and two curves giving the division of space current between the grid and plate.

Parasitic Electronic Oscillations and Coupling Frequencies in a Power Tube

The frequency spectrum of electronic oscillations in a large power triode having cylindrical plate and grid, and a filament consisting of four wires arranged at the corners of a square has been investigated. Experimental curves are displayed showing that two distinct primary frequencies may be generated at the same time, and that each of these may be replaced by two coupling frequencies, which also may be observed simultaneously, when the secondary circuit is near resonance with the primary clouds of electrons. The curves are interpreted in terms of a doubly resonant space-charge region, and in terms of coupled-circuit theory. Wave-lengths extending from 50 to 250 cm have been recorded.