Tube Amplifier Research Articles

Design of class f reconfigurable power amplifiers

With the rapid development of mobile communication technology, RF amplifier requirements becoming higher, miniaturization, high efficiency and multi-band have gradually become a research hotspot. Based on these hot research directions, this paper designs a dual-band reconfigurable power amplifier. The input of the amplifier adopts a stepped impedance matching network, which has a good matching effect in the 1.6 - 2.8 GHz band. The output is switched by a single-knife double-throw switch to the corresponding band output matching network to achieve the fast switching of different frequency bands. The RF amplifier tube is designed by using Cree’s GaN chip CGH40010F, which has an additional power efficiency of more than 60% in the frequency range of 1.7 - 1.9 GHz and 2.5 - 2.7 GHz bands, a gain of about 12 - 14 dB and a saturated output power of more than 40 dBm. This design has the features of high efficiency, high gain, miniaturization and multi-band, which is applicable to the mobile communication system.

Design of an ultrashort H‐plane coupler without transition structure for sheet beam traveling‐wave tube amplifier at W‐band

AbstractAn ultrashort H‐plane sheet beam traveling‐wave tube (SB‐TWT) coupler without transition structure is proposed. The coupler adopts a new idea of directly coupling the microwave from H‐plane of the slow‐wave circuit (SWC) and optimizes the matching by introducing an asymmetric circular ridge on the E‐plane of the coupled waveguide. As a result, the length of the SB‐TWT coupler is reduced from more than 3λ to 1λ. At the same time, the beam tunnel area is enlarged to twice that of the SWC beam tunnel. In the working band (90–100 GHz) of the SWC, the simulation results show that the reflection is less than −25 dB, the isolation is greater than −22 dB. And the influence of the dimensions and locations of ridge on the performance of the coupler is studied. Particle‐in‐cell simulation results also show that the new coupler can not only complete the microwave coupling well but also reduce the number of SWC periods.

Development of a single-ended magnetic alloy loaded cavity in the Japan Proton Accelerator Research Complex rapid cycling synchrotron

Abstract The Japan Proton Accelerator Research Complex (J-PARC) Rapid Cycling Synchrotron (RCS) employs magnetic alloy (MA) loaded cavities. We realize multi-harmonic rf driving and beam-loading compensation owing to the broadband characteristics of the MA. The currently installed cavity is the conventional type, which is designed to be driven by tube amplifiers in a push–pull operation. The push–pull operation has some advantages, i.e., suppressing a higher harmonic distortion without the beam acceleration and shortening the cavity length. However, a disadvantage arises at the high intensity beam acceleration where the multi-harmonic rf driving causes a severe imbalance of the anode voltage swing and restricts the tube operation. Although we have achieved an acceleration for the design beam power of 1 MW, the imbalance becomes an issue in increasing the beam power further. We have developed a single-ended MA cavity to avoid such difficulty. The cavity has no tube imbalance intrinsically and it is found that the power consumption to drive the cavity can be reduced compared with the conventional one.

Deep learning-based wave digital modeling of rate-dependent hysteretic nonlinearities for virtual analog applications

Electromagnetic components greatly contribute to the peculiar timbre of analog audio gear. Indeed, distortion effects due to the nonlinear behavior of magnetic materials are known to play an important role in enriching the harmonic content of an audio signal. However, despite the abundant research that has been devoted to the characterization of nonlinearities in the context of virtual analog modeling over the years, the discrete-time simulation of circuits exhibiting rate-dependent hysteretic phenomena remains an open challenge. In this article, we present a novel data-driven approach for the wave digital modeling of rate-dependent hysteresis using recurrent neural networks (RNNs). Thanks to the modularity of wave digital filters, we are able to locally characterize the wave scattering relations of a hysteretic reluctance by encapsulating an RNN-based model into a single one-port wave digital block. Hence, we successfully apply the proposed methodology to the emulation of the output stage of a vacuum-tube guitar amplifier featuring a nonlinear transformer.

Microphones: A bit of history

The earliest commercially successful microphone design was the carbon microphone, whose original patent was filed by Emile Berliner in 1877. An interesting variant of the basic carbon microphone was a dual diaphragm microphone patented by Granville Woods in 1883. The basic carbon microphone provided adequate performance at low cost and remained in service in the telephone system for at least the next century. Other microphone technologies can also be found in the early patent literature, though their commercial acceptance was delayed until electronic amplification was possible. The eventual development of vacuum tube amplifiers enabled the development of the condenser microphone, whose initial patent was filed in 1916. Condenser microphones provide the improvement of wide bandwidth and flat response compared to carbon microphones. The invention in the 1960s of high quality electret materials enabled the manufacture of low cost electret microphones that quickly displaced carbon mics in telephones and most commercial devices for at least the next 40 years. Then, in the early years of the 21st century, condenser microphones implemented in silicon, also known as MEMS microphones, took over in high all volume applications. This paper will discuss this history and the current state of the art.

Pruning Deep Neural Network Models of Guitar Distortion Effects

Deep neural networks have been successfully used in the task of black-box modeling of analog audio effects such as distortion. Improving the processing speed and memory requirements of the inference step is desirable to allow such models to be used on a wide range of hardware and concurrently with other software. In this paper, we propose a new application of recent advancements in neural network pruning methods to recurrent black-box models of distortion effects using a Long Short-Term Memory architecture. We compare the efficacy of the method on four different datasets; one distortion pedal and three vacuum tube amplifiers. Iterative magnitude pruning allows us to remove over 99% of parameters from some models without a loss of accuracy. We evaluate the real-time performance of the pruned models and find that a 3x-4x speedup can be achieved, compared to an unpruned baseline. We show that training a larger model and then pruning it outperforms an unpruned model of equivalent hidden size. A listening test confirms that pruning does not degrade the perceived sound quality, but may even slightly improve it. The proposed techniques can be used to design computationally efficient deep neural networks for processing the sound of the electric guitar in real time.

High Performance Broadcast Receiver Based on Obsolete Technology.

Since its inception, the electronics industry has mass-produced equipment. The fast evolution of electronic technologies made obsolete the entire generation of products and even technologies. Until the government issued regulations and guidelines on how to address the issue of reuse of obsolete electronic equipment, with special regard to the ones still operating (e.g., give it to family/friends, donate to charity, or sell to individuals or recycling companies), most of it was thrown out with usual rubbish, with a destructive effect on the environment. This paper presents the design techniques and methods for revaluation of obsolete vacuum tube analog receivers, with a focus on the manufacturing steps of a high-performance receiver. The choice of receiver type is not accidental at all, since tube technology is still a real success among audiophiles many providers offer vacuum tube amplifiers at considerably high prices. The redesign implied the original FM unit replacement with a DSP-based AM/FM tuner while the AM RF vacuum tube section has been preserved with the original architecture to allow the reception of the broadcast stations for the long-wave band and the alternative operation with the silicon tuner for the medium-wave and short-wave bands. The electrical performances of the modified receiver in terms of reliability, sensitivity, selectivity, and distortions on the reception chain are clearly superior to the original one, while the power consumption of the RF section is reduced more than 10 times from 11.5 W–15.5 W to 1 W. Last, but not least important, the proposed solution implied the use of few additional parts and resources and extended significantly the lifetime of the original vacuum tubes receiver. The work has been developed to serve as an example of how obsolete electronic equipment can be redesigned and reused avoiding its complete recycling or even worse, its disposal with usual rubbish. It has been imagined and performed as the initial step in launching a professional student contest on the reuse/redesign of obsolete equipment aimed at raising awareness regarding the issue of pollution with e-waste amongst students from the electronic departments of Romanian technical universities.

A Review of Neural Network-Based Emulation of Guitar Amplifiers

Vacuum tube amplifiers present sonic characteristics frequently coveted by musicians, that are often due to the distinct nonlinearities of their circuits, and accurately modelling such effects can be a challenging task. A recent rise in machine learning methods has lead to the ubiquity of neural networks in all fields of study including virtual analog modelling. This has lead to the appearance of a variety of architectures tailored to this task. This article aims to provide an overview of the current state of the research in neural emulation of analog distortion circuits by first presenting preceding methods in the field and then focusing on a complete review of the deep learning landscape that has appeared in recent years, detailing each subclass of available architectures. This is done in order to bring to light future possible avenues of work in this field.

The evolution and maturation of the electric guitar as a system

The electric guitar came to its initial prominence in the 1940s when its volume allowed jazz guitarists like Charlie Christian to step out in front of the rhythm section like other soloists, competing with the brass, wind, and piano. Further changes in the playing and design of the instrument came with exploitation of the interaction of the electric guitar, tube amplifiers, and analog effects as a larger system. Especially in the rock and funk idioms, the playing and construction of the overall instrument evolved and expanded rapidly with the mainstream embrace of digital technology. This talk will consider the evolution of the electric guitar as a system up through today and consider why it seems the instrument has fully evolved and is unlikely to experience further seismic shifts, especially as the overall thrust of music has shifted to digitally-manipulated sound that is often entirely independent of the physical playing of any instrument.

H- ion source operational performance and latest development at the Spallation Neutron Source

The U.S. Spallation Neutron Source (SNS) at Oak Ridge National Laboratory is the world’s most powerful accelerator-driven pulsed neutron source. An H- injector feeds the accelerator with high current (>50 mA), time structured (1ms, 60 Hz) H- beam. The injector consists of an RF-driven, Cs-enhanced H- ion source and an electrostatic low energy beam transport section. In the recent three run cycles, an H- ion source operated ∼4 months for each run with excellent availability near 99.9%. The presently ongoing run is also on track to finish another ∼4 months run with similar high availability. Lately, we have tested a solid-state RF system for the ion source to replace the existing vacuum-tube type RF amplifier for the sake of improving the ease of operation and maintenance. Progress has also been made on the continued development of an external antenna RF H- ion source with a focus on improvement to its plasma ignition scheme.

Design and Experiment of a 200-kW Q-Band Gyro-TWT

In this article, the design and experimental verification of a 200-kW ${Q}$ -band gyrotron traveling wave tube (gyro-TWT) amplifier are presented. A low-velocity spread magnetic injection electron gun (MIG), a new type of multichannel TE01 mode input coupler, and a broadband double-disk output window are adopted in the design to improve the performance of the gyro-TWT. At the same time, the lossy ceramic ring-loaded high-frequency interaction circuit is constructed to provide the required loss for stable operation, and the potential oscillations are effectively suppressed. Saturated peak power of 208 kW and 12.5-kW average output power are measured at 47 GHz by hot test, corresponding to a saturated gain of 50.2 dB, an efficiency of 29.4%, and a −3-dB bandwidth of 5.5 GHz.

Design of Electron Tube and Semiconductor-Based and Voltage Stabilised Amplifier Circuits

Abstract In this project, an electron tube circuit consisting of a voltage stabiliser, preamplifier, and final stage amplifier circuit was designed. One of the main aims was to reuse as many components and materials as possible, thereby decreasing the project’s ecological footprint. The result is a hybrid electron tube amplifier. The function of the circuits was subsequently measured and analysed using various tests.

Gain radial distribution of copper bromide lasers

The paper presents the experimental results on how the tube bore of copper bromide laser influence the gain radial distribution. A pair of copper bromide lasers in an oscillator- amplifier configuration was operated to measure and compare the small-signal gains of different laser tube bores. The gain radial distributions were measured in different size of amplifier tube bores. It was shown that, by changing the amplifier tube bore, the gain radial distribution was changed, similar to that of the temperature profile, but the average of radial gains through cross-section are the same in different laser tube bores.

Results on FPGA-Based High-Power Tube Amplifier Linearization at DESY

Vacuum-tube amplifiers are the most widespread type of radio frequency (RF) sources used to produce high-power signals needed for beam acceleration in superconducting cavities. At Deutsches Elektronen-Synchrotron (DESY), megawatt-rated klystrons are used to produce millisecond-long RF shots for pulsed operation in particle accelerators. In contrast, inductive output tubes (IOTs) are used to provide a continuous RF signal for continuous-wave (CW) operation. In both cases, the amplifiers suffer from amplitude-dependent nonlinearity between the driving and generated signals. This nonlinearity complicates the setup operations of the low-level RF (LLRF) system and makes it harder to regulate the accelerating field. Therefore, a way to linearize the amplifier is highly valuable. This article covers the design, implementation, and test of a field-programmable gate array (FPGA)-based predistortion linearization unit. The first results on the performance of this component in linearizing the amplifiers of running CW and pulsed superconducting accelerators are presented. Such a component uses programmable interpolating lookup tables (LUT) that are addressed using the squared value of the requested signal amplitude. This component only adds 64-ns latency to the RF control system without relying on any vendor-dependent FPGA component. Other benefits of using programmable interpolating LUT are low usage of FPGA resources and flexibility in terms of the type of amplifier to be corrected. The benefits of using this linearizer for klystrons and IOTs are presented and quantified.

Design, Beam-Wave Interaction, and Efficiency Enhancement Studies of Millimeter Wave Gyro-TWT With a Three-Stage Depressed Collector

In this article, a $W$ -band gyrotron traveling wave tube (gyro-TWT) amplifier that uses periodically dielectric-loaded (PDL) waveguide and operates in TE01 mode is designed and studied for its stability against backward wave oscillations and beam wave interaction behavior. The subassemblies including a magnetron injection gun using E-GUN code, RF output window, and electron collector using “MAGIC 3-D” are investigated. The present particle-in-cell (PIC) simulation of millimeter-wave gyro-TWT results in a peak RF power ~195 kW in TE01 mode with an electronic efficiency of ~28% and a saturated gain of ~63 dB. Further, the overall efficiency of the device is enhanced by using a three-stage depressed collector, which is designed and simulated using “MAGIC 3-D. ” The collection efficiency of the present collector is calculated as ~74% and the overall efficiency of the gyro-TWT is improved to ~60%.

The Age of Electroacoustics [Book Review

This book is an fascinating read. The author does a good job of putting the study of acoustics in context within social, political, academic, and industrial environments through time. He concentrates primarily on the U.K. and Europe, with a few references to the U.S. and other countries. The Weimar Republic chapter of course deals almost exclusively with Germany during that era but that focus is acceptable as Germany was then also addressing questions as to what physics was in a broader context. When WWI began, a major shift occurred regarding the definitions of noise and sound, and the recognition of the value of studying more than musical notes as sound. The sound made by an enemy airplane was a signal to be detected, so that the bearing, elevation, and range could be determined for defensive purposes. Valuable data could also be obtained through studying the sounds produced by U-boats or long-range cannons. Suddenly what was previously ignored as irrelevant became of great interest. Noise was redefined as that which is not the intended signal. Noise abatement also moved to the forefront — making ships and airplanes quieter became very important. The implementation of electroacoustics changed the interpretation of signal characteristics, with the introduction of microphones, vacuum tube amplifiers, and visual displays. The technology of these devices was greatly advanced during WWI. The author points out a number of technical solutions to problems in electroacoustics and how they influenced the field. For example, since electronic filtering was not well developed, and microphones did not have a large dynamic range, the frequency selective Tucker’s Hot Wire Microphone was developed. Tucker’s Hot Wire Microphone, a resonant cavity with a hot wire stretched over one end whose resistance changes when vibrated by sounds at the cavity’s resonant frequency, can be made to detect sounds below 500 Hz without interference from other frequencies.

Stability and Multimode Simulation Studies of ${W}$ -Band Uniformly Dielectric-Loaded Gyrotron Traveling-Wave Tube Amplifier

In this article, a nonlinear self-consistent, multimode analysis, and particle-in-cell (PIC) simulation of a uniformly dielectric-loaded (UDL) millimeter-wave gyrotron traveling-wave tube (gyro-TWT) amplifier has been discussed. A single-anode magnetron injection electron gun is designed to produce a relativistic electron beam of 100 kV and 5 A with a unity velocity ratio and 5% of axial velocity spread. The desired operating mode TE01 is fed by converting the TE10 rectangular waveguide mode through the Y-shaped power transducer. Both the multimode theory and PIC simulation results are agreed and predicted the saturated RF power of ~140 and ~145 kW at 92 GHz, respectively. A saturated gain of ~51 dB, a 3-dB bandwidth of ~5%, and a power conversion efficiency of ~28% are obtained. To collect the spent electrons, a collector is designed by using electron optics, E-GUN. The maximum heat wall loading at the collector surface due to a spent beam is calculated as 0.255 kW/cm2.

Simulations of beam loading compensation in a wideband accelerating cavity using a circuit simulator including a LLRF feedback control

Magnetic alloy cavities are employed in the J-PARC RCS to generate high accelerating voltages. The cavity, which is driven by a vacuum tube amplifier, has a wideband frequency response and the beam loading in the cavity is multiharmonic. Therefore, the tube must generate a multiharmonic output current. An LTspice circuit model is developed to analyze the vacuum tube operation and the compensation of the multiharmonic beam loading. The model includes the cavity, tube amplifier, beam current, and LLRF feedback control. The feedback control consists of the I/Q demodulator including low pass filters, PI control, and I/Q modulator. In this article, we present the implementation of the LLRF functions in the LTspice simulations. The preliminary simulation results are also presented. The simulations fairly agree with the beam test results.

Multiharmonic vector rf voltage control for wideband cavities driven by vacuum tube amplifiers in a rapid cycling synchrotron

Multiharmonic vector rf voltage control for wideband cavities driven by vacuum tube amplifiers in a rapid cycling synchrotron

Amplifying characteristics of small-bore copper bromide lasers

A pair of copper bromide lasers in an oscillator–amplifier configuration was operated to measure and compare the small-signal gains and saturation intensities, as amplifying parameters of different laser tube lengths. The independencies of these amplifying parameters on the different amplifier tubes length with identical diameter were investigated, individually. Therefore, the output powers of the system were measured in different tubes lengths of amplifier and the optimum conditions were obtained. It was shown that, by changing the amplifier tube length, the amplifying parameters remain nearly constant without any remarkably changing, but the output power of the system was increased linearly due to increase of tube length. The experimental results were in good agreement with the theory. Moreover, the radial gain distribution was studied.