Power Vacuum Tubes. Handbook

Transcription

1 Power Vacuum Tubes Handbook

2 Power Vacuum Thbes Handbook Jerry c. Whitaker ~ Springer Science+Business Media, LLC

3 Copyright 1994 by Springer Science+Business Media New York Originally published by Multiscience Press, Inc in Softcover reprint ofthe hardcover 1st edition 1994 Library of Congress Catalog Card Number ISBN ISBN (ebook) DOI / All rights reserved. No part ofthis work covered by the copyright hereon may be reproduced or used in any forrn or by any means-graphic, electronic, or mechanical, including photocopying, recording, taping, or inforrnation storage and retrieval systems-without perrnission of the publisher

4 This book is dedicated to my daughter Alexis Ann Whitaker Enjoy the wonder of life

5 Acknowledgment This handbook was developed with assistance from the technical staff of Varian Associates (Palo Alto, CA). Varian provided background information and technical guidance on the project. Cover photograph courtesy of Broadcast Engineering magazine and Thomson Tubes. Information contained in this work has been obtained by Van Nostrand Reinhold from sources believed to be reliable. However, neither Van Nostrand Reinhold nor its authors guarantee the accuracy or completeness of any information published therein and neither Van Nostrand Reinhold nor its authors shall be responsible for any errors, omissions, or damages arising out of use of this information. This work is published with the understanding that Van Nostrand Reinhold and its authors are supplying information but are not attempting to render engineering or other professional services. If such services are required, the assistance of an appropriate professional should be sought.

6 Contents About the Author Preface Chapter 1 Power Vacuum Tube Applications Vacuum Tube Development Standardization Transmission Systems VACUUM TUBE APPLICATIONS Market Overview AM Radio Broadcasting Shortwave Broadcasting FM Radio Broadcasting TV Broadcasting Satellite Transmission Radar Electronic Navigation Microwave Radio Induction Heating Electromagnetic Radiation Spectrum Chapter 2 Modulation Systems and Characteristics Modulation Systems Principles of Resonance Frequency Source xv xvii 1 1 I vii

7 Operating Class 46 Broadband Amplifier Design 48 AMPLITUDE MODULATION 50 High-Level AM Modulation 54 Vestigial-Sideband Amplitude Modulation 56 Single-Sideband Amplitude Modulation 56 FREQUENCY MODULATION 57 Modulation Index 57 Phase Modulation 62 Modifying FM Waves 63 Preemphasis and Deemphasis 63 Modulation Circuits 64 PULSE MODULATION 67 Digital Modulation Systems 67 Pulse Amplitude Modulation 68 Pulse Time Modulation (PTM) 68 Pulse Code Modulation 71 Delta Modulation 72 Digital Coding Systems 72 Spread Spectrum Systems Chapter 3 Vacuum Tube Basics CHARACTERISTICS OF ELECTRONS 77 Electron Optics 78 Thermal Emission From Metals 80 Secondary Emission 81 Diode 83 Triode 84 Tetrode 90 Pentode 93 High-Frequency Operating Limits 97 VACUUM TUBE DESIGN 103 Device Cooling 103 Cathode Assembly 108 Grid Structures 113 Plate Assembly 121 Ceramic Elements 122 Tube Construction 124 Connection Points 125 Tube Sockets 126 viii

8 NEUTRALIZA TION Circuit Analysis Circuit Design Grounded-Grid Amplifier Neutralization Self-Neutralizing Frequency Neutralization Adjustment Chapter 4 Designing Vacuum Tube Circuits Class A Amplifier Class Band AB Amplifiers Class C Amplifiers PRINCIPLES OF RF POWER AMPLIFICATION Drive Power Requirements Mechanical and Electrical Considerations Bypassing Tube Elements Parasitic Oscillations Shielding Protection Measures CAVITY AMPLIFIER SYSTEMS Bandwidth and Efficiency Current Paths 1/4-Wavelength Cavity 1/2-Wavelength Cavity Folded 1/2-Wave Cavity Wideband Cavity Output Coupling Mechanical Design HIGH-VOLTAGE POWER SUPPLIES Silicon Rectifiers Operating Rectifiers in Series Operating Rectifiers in Parallel Silicon Avalanche Rectifiers Thyristor Servo Systems Polyphase Rectifier Circuits Power Supply Filter Circuits ix

9 Chapter 5 Applying Vacuum Tube Devices AM POWER AMPLIFIER SYSTEMS Control Grid Modulation Suppressor Grid Modulation Cathode Modulation High-Level AM Amplification Pulse Width Modulation LINEAR AMPLIFICATION Device Selection Grid-Driven Linear Amplifier Cathode-Driven Linear Amplifier Intermodulation Distortion HIGH-EFFICIENCY LINEAR AMPLIFICATION Chireix Outphasing Modulated Amplifier Doherty Amplifier Screen-Modulated Doherty -Type Amplifier Terman-Woodyard Modulated Amplifier Dome Modulated Amplifier TV POWER AMPLIFIER SYSTEMS System Considerations Power Amplifier FM POWER AMPLIFIER SYSTEMS Cathode-Driven Triode Amplifier Grounded-Grid vs. Grid-Driven Tetrode Grid-Driven TetrodelPentode Amplifiers Impedance Matching into the Grid Neutralization SPECIAL-APPLICA TION AMPLIFIERS Distributed Amplification Radar Chapter 6 Microwave Power Tubes Linear-Beam Tubes Crossed-Field Tubes GRID VACUUM TUBES Planar Triode High-Power UHF Tetrode KLYSTRON x

10 Reflex Klystron 268 The Two-Cavity Klystron 271 The Multicavity Klystron 274 Beam Pulsing 288 Integral vs. External Cavity 291 MSDC Klystron 294 KL YSTRODE (lot) 306 Theory of Operation 307 Electron Gun 309 Grid Structure 310 Input Cavity 311 Output Cavity 311 Application Considerations 314 Continuing Research Efforts 315 TRAVELING WAVE TUBE 315 Theory of Operation 316 Operating Efficiency 319 Operational Considerations 321 CROSSED-FIELD TUBES 322 Magnetron 323 Gyrotron 328 MICROWAVE TUBE LIFE 328 Life-Support System 328 Protection Measures 329 Filament Voltage Control 332 Cooling System 332 Reliability Statistics Chapter 7 RF Interconnection and Switching Skin Effect 337 COAXIAL TRANSMISSION LINE 339 Electrical Parameters 339 Electrical Considerations 344 Coaxial Cable Ratings 345 Mechanical Parameters 354 WAVEGUIDE 356 Propagation Modes 356 Ridged Waveguide 359 Circular Waveguide 359 Doubly Truncated Waveguide 361 xi

11 Impedance Matching Installation Considerations Cavity Resonators RF COMBINER AND DIPLEXER SYSTEMS 4-Port Hybrid Combiner Non-Constant-Impedance Diplexer Constant-Impedance Diplexer Microwave Combiners Hot Switching Combiners Phased-Array Antenna Systems HIGH-POWER ISOLATORS Theory of Operation Applications Chapter 8 Cooling Considerations Heat-Transfer Mechanisms The Physics of Boiling Water APPLICATION OF COOLING PRINCIPLES Forced-Air Cooling Systems Water Cooling Vapor-Phase Cooling Temperature Measurements Air-Flow System OPERA TING ENVIRONMENT Air-Handling System Air Cooling System Design Site Design Guidelines WaterNapor Cooling System Maintenance Chapter 9 Reliability Considerations Terminology QUALITY ASSURANCE Inspection Process Reliability Evaluation Failure Analysis Standardization RELIABILITY ANALYSIS xii

12 Statistical Reliability Environmental Stress Screening Latent Defects Operating Environment Failure Modes Maintenance Considerations VACUUM TUBE RELIABILITY Thermal Cycling Tube-Changing Procedure Power Tube Conditioning Filament Voltage Filament Voltage Management PA Stage Tuning Fault Protection Vacuum Tube Life Examining Tube Performance Shipping and Handling Vacuum Tubes KLYSTRON RELIABILITY Cleaning and Flushing the Cooling System Cleaning Ceramic Elements Reconditioning Klystron Gun Elements Focusing Electromagnet Maintenance Power Control Considerations Chapter 10 Device Performance Criteria MEASUREMENT PARAMETERS Power Measurement Decibel Measurement Noise Measurement Phase Measurement Nonlinear Distortion VACUUM TUBE OPERATING PARAMETERS Stage Tuning Amplifier Balance Parallel Tube Amplifiers Harmonic Energy Klystron Tuning Considerations Intermodulation Distortion VSWR RF SYSTEM PERFORMANCE xiii

13 Key System Measurements Synchronous AM in PM Systems Incidental Phase Modulation Video Parameters Site-Related Intermodulation Products Chapter 11 Safe Handling of Vacuum Tube Devices ELECTRIC SHOCK Effects on the Human Body Circuit Protection Hardware Working with High Voltage First Aid Procedures OPERA TING HAZARDS OSHA Safety Considerations Beryllium Oxide Ceramics Corrosive and Poisonous Compounds FC-75 Toxic Vapor Nonionizing Radiation X-Ray Radiation Hazard Implosion Hazard Hot Coolant and Surfaces Polychlorinated Biphenyls Chapter 12 Reference Data Index xiv

14 About the Author Jerry Whitaker is a technical writer based in Beaverton, OR, where he operates the consulting firm Technical Press. Mr. Whitaker has been involved in various aspects of the communications industry for more than 20 years. He is a Fellow of the Society of Broadcast Engineers and an SBE-certified senior AM-PM engineer. He is also a member of the following professional organizations: International Society for Optical Engineering Society of Motion Picture and Television Engineers Audio Engineering Society International Television Association Institute of Electrical and Electronics Engineers (Broadcast Society, Power Electronics Society, and Reliability and Maintainability Society) Mr. Whitaker has written and lectured extensively on the topic of electronic systems installation and maintenance. Mr. Whitaker is the former editorial director and associate publisher of Broadcast Engineering and Video Systems magazines. He is also a former radio station chief engineer and TV news producer. Mr. Whitaker is the author of a number of books, including: Radio Frequency Transmission Systems: Design and Operation, McGraw Hill Television and Audio Handbook/or Technicians and Engineers (coauthor), McGraw-Hill Television Engineering Handbook, revised edition (coeditor), McGraw Hill Electronic Displays: Technology, Design, and Applications, McGraw-Hill xv

15 Maintaining Electronic Systems, ere Press AC Power Systems Handbook, ere Press Interconnecting Electronic Systems (coauthor), ere Press Information Age Dictionary (coeditor), Intertec/Bellcore Mr. Whitaker is a contributor to the ere Press Electrical Engineering Handbook, the McGraw-Hill Audio Engineering Handbook, and the National Association of Broadcasters' NAB Engineering Handbook, 7th and 8th editions. Mr. Whitaker has twice received a Jesse H. Neal Award Certificate of Merit from the Association of Business Publishers for editorial excellence. He also has been recognized as Educator of the Year by the Society of Broadcast Engineers (1992). xvi

16 Preface The phrase "high technology" is perhaps one of the more overused descriptions in our technical vocabulary. It is a phrase generally reserved for discussion of integrated circuits, fiber optics, satellite systems, and computers. Few people would associate high technology with vacuum tubes. The notion that vacuum tube construction is more art than science may have been true 10 or 20 years ago, but today it's a different story. The demand on the part of industry for tubes capable of higher operating power and frequency, and the economic necessity for tubes that provide greater efficiency and reliability, have moved power tube manufacturers into the high-tech arena. Advancements in tube design and construction have given end users new transmitters and RF generators that allow industry to grow and prosper. If you bring up the subject of vacuum tubes to someone who has never worked on a transmitter, you are likely to get a blank stare and a question: "Do they make those anymore?" Although receiving tubes have disappeared from the scene, power tubes are alive and well and are performing vital functions in thousands of divergent applications. Solid-state and tube technologies each have their place, each with its strengths and weaknesses. Tube design and development, although accompanied by less fanfare, is advancing as are developments in solid-state technology. Power tubes today are designed with an eye toward high operating efficiency and high gain/bandwidth properties. Above all, a tube must be reliable and provide long operating life. The design of a new power tube is a lengthy process that involves computer-aided calculations and advanced modeling. Despite the inroads made by solid-state technology, the power vacuum tube occupies-and will continue to occupy-an important role in the generation of high-power RF in the HF regions and above. No other device can do the job as well. Certainly, solid-state cannot, especially if cost, size, and weight are important considerations. xvii

17 The field of science encompassed by power vacuum tubes is broad and exciting. It is an area of growing importance to military and industrial customers, and a discipline in which significant research is now being conducted. Power vacuum tubes include a wide range of devices, each for specific applications. Devices include power grid tubes (triodes, tetrodes, and pentodes) and microwave power tubes (klystrons, traveling wave tubes, gyrotrons, and numerous other high-frequency devices). Research is being conducted for both tube classes to extend output power and maximum frequency, and to improve operating efficiency. This handbook examines the underlying technology of each type of power vacuum tube device in common use today and provides examples of typical applications. New development efforts also are reported, and the benefits of the work explained. This book is directed toward engineering personnel involved in the design, specification, installation, and maintenance of high-power equipment utilizing vacuum tubes. Basic principles are discussed, with emphasis on how the underlying technology dictates the applications to which each device is dedicated. Supporting mathematics are included where appropriate to explain the material being discussed. Extensive use of technical illustrations and schematic diagrams aid the reader in understanding the fundamental principles of the subject. This handbook is not intended for the designer of power vacuum tube devices. This specialized discipline requires, and deserves, a handbook of its own. It is unfortunate that most publications on the topic are many years old. New books in this area are needed. Such efforts, however, must be left for another day. Furthermore, this handbook does not address the question of which device, a power vacuum tube or a semiconductor, is better for a given application. This question has been examined in other publications, including one by the author (Radio Frequency Transmission Systems: Design and Operation, McGraw-HilI, 1990). Today's modern power tube is unlike the power tubes in use a decade ago. And with the trend in industry toward operation at higher power levels and higher frequencies, the vacuum tube is certain to remain on the scene for a long time to come. Jerry C. Whitaker xviii