Power Vacuum Tubes Handbook

Jerry Whitaker

• Publisher: CRC Press
• Year: 2017
• Print ISBN: 9781138077485
• eBook ISBN: 9781351833271
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Providing examples of applications, Power Vacuum Tubes Handbook, Third Edition examines the underlying technology of each type of power vacuum tube device in common use today. The author presents basic principles, reports on new development efforts, and discusses implementation and maintenance considerations. Supporting mathematical equations and extensive technical illustrations and schematic diagrams help readers understand the material.

Translate Principles into Specific Applications

This one-stop reference is a hands-on guide for engineering personnel involved in the design, specification, installation, and maintenance of high-power equipment utilizing vacuum tubes. It offers a comprehensive look at the important area of high-frequency/high-power applications of microwave power devices, making it possible for general principles to be translated into specific applications. Coverage includes power grid tubes—triodes, tetrodes, and pentodes—as well as microwave power tubes such as klystrons, traveling wave tubes, gyrotrons, and other high-frequency devices. These vacuum tubes are used in applications from radio broadcasting to television, radar, satellite communications, and more.

Explore a Wide Variety of Methods in Power Vacuum Tube Design

This third edition includes updates on vacuum tube technology, devices, applications, design methods, and modulation methods. It also expands its scope to cover properties of materials and RF system maintenance and troubleshooting. Explaining difficult concepts and processes clearly, this handbook guides readers in the design and selection of a power vacuum tube-based system.

What's New in This Edition

• Includes two new chapters on properties of materials and RF system maintenance and troubleshooting
• Contains updates and additions in most chapters
• Identifies key applications for commercial and scientific research
• Examines the frontiers of materials science directly impacting construction, reliability, and performance
• Reviews methods of power tube design for more efficient, longer-lasting tubes
• Features updated illustrations throughout to clarify and explain fundamental principles and implementation considerations

1
Power Vacuum Tube Applications

1.1 Introduction

The continuing demand for energy control devices capable of higher operating power, higher maximum frequency, greater efficiency, and extended reliability has pushed power vacuum tube manufacturers to break established performance barriers. Advancements in tube design and construction have given engineers new radio frequency (RF) generating systems that allow industry to grow and prosper. Power grid vacuum tubes have been the mainstay of high-power transmitters and other RF generation systems since the beginning of radio. Today, the need for new gridded and microwave power tubes is being met with new processes and materials.

Although low-power vacuum tubes have been largely replaced by solid-state devices, vacuum tubes continue to perform valuable service at high-power levels and, particularly, at high frequencies. The high-power capability of a vacuum device results from the ability of electron/vacuum systems to support high-power densities. Values run typically at several kilowatts per square centimeter, but may exceed 10 MW/cm². No known dielectric material can equal these values. For the foreseeable future, if high power is required, electron/vacuum devices will remain the best solution.

1.2 Vacuum Tube Development

Receiving tubes have more or less disappeared from the scene (high-end audio applications notwithstanding) because of the development of transistors and integrated circuits. Power grid and microwave tubes, however, continue to push the limits of technology. Power tubes are an important part of RF technology today.

From 1887—when Heinrich Hertz first sent and received radio waves—to the present, an amazing amount of progress has been made by engineers and scientists. The public takes for granted today what was considered science fiction just a decade or two ago. The route from the primitive spark-gap transmitters to the present state of the art has been charted by the pioneering efforts of many. It is appropriate to review some of the milestones in electron tube development. Much of the fundamental work on power vacuum devices can be traced to early radio broadcasting, which—along with telephone technology—has brought the nations of the world closer together than the early pioneers of the art could have imagined. More than 100 years have passed since Charles D. (Doc) Herrold founded a voice station (as it then was known) at San Jose, CA. Developments since have been the result of many inspired breakthroughs and years of plain hard work.

1.2.1 Pioneer Developers

In 1895, 21-year-old Guglielmo Marconi and his brother Alfonso first transmitted radio signals across the hills behind their home in Bologna, Italy. Born in 1874 to an Italian merchant and a Scotch-Irish mother, young Marconi had learned of Hertzian waves from August Righi, a professor at the University of Bologna. Convinced that such waves could be used for wireless communication, Marconi conducted preliminary experiments using a spark-gap source and a coherer detector. Unable to interest the Italian government in his invention, Marconi took his crude transmitter and receiver to England, where he demonstrated his wireless system to officials of the British Post Office. Marconi received a patent for the device in July 1897. With the financial support of his mother's relatives, Marconi organized the Wireless Telegraph and Signal Company that same year to develop the system commercially. Regular transatlantic communications commenced in 1903 when a Marconi station at Cape Cod, MA, sent a short message from President Theodore Roosevelt to King Edward VII in England.

The invention of the vacuum tube diode by J. Ambrose Fleming in 1904 and the triode vacuum tube amplifier by Lee De Forest in 1906 launched the electronics industry as we know it. The De Forest invention was pivotal. It marked the transition of the vacuum tube from a passive to an active device. The new “control” electrode took the form of a perforated metal plate of the same size and shape as the existing anode, positioned between the filament and the anode. Encouraged by the early test results, De Forest worked to perfect his invention, trying various mechanical arrangements for the new grid. Additional refinements and innovative circuit applications were subsequently developed by Edwin Armstrong.

With the addition of the control grid, De Forest and Armstrong had set in motion a chain of events that led the vacuum tube to become the key element in the emerging discipline of electronics. Early experimenters and radio stations took this new technology and began developing their own tubes using in-house capabilities, including glassblowing. As the young electronics industry began to grow, vacuum tubes were produced in great quantity and standardized (to a point), making it possible to share new developments and applications. A major impetus for standardization was the U.S. military, which required vacuum tubes in large numbers during World War I. Pushed by the navy, a standardized design, including base pins and operating parameters, was forged. The economic benefits to both the tube producers and tube consumers were quickly realized.

Most radio stations from 1910 through 1920 built their own gear. For example, at the University of Wisconsin, Madison, WI, special transmitting tubes were built by hand as needed to keep radio station 9XM, which later became WHA, on the air. The tubes were designed, constructed, and tested by Professor E. M. Terry and a group of his students in the university laboratories. Some of the tubes also were used in wireless telephonic experiments carried on with the Great Lakes Naval Training Station during 1918, when a wartime ban was imposed on wireless broadcasts.

It took many hours to make each tube. The air was extracted by means of a mercury vapor vacuum pump while the filaments were lighted and the plate voltage was on. As the vacuum increased, the plate current was raised until the plate became red hot. This out-gassing process was primitive, but it worked. The students frequently worked through the night to get a tube ready for the next day's broadcast. When completed, the device might last only a few hours before burning out.

Plate dissipation on Professor Terry's early tubes, designated #1, #2, and so on, was about 25 W. Tube #5 had a power output of about 50 W. Tubes #6–#8 were capable of approximately 75 W. Tube #8 was one of the earliest handmade commercial products.

The addition of a “screen” grid marked the next major advancement for the vacuum tube. First patented in 1916 by Dr. Walter Schottky of the Siemens & Halske Company (Germany), the device garnered only limited interest until after World War I when the Dutch firm, Philips, produced a commercial product. The “double-grid” Philips type Q was introduced in May 1923. Later variations on the initial design were made by Philips and other manufacturers.

Early in the use of the tetrode it was determined that the tube was unsuited for use as an audio frequency power amplifier. Under certain operating conditions encountered in this class of service, the tetrode exhibited a negative-resistance characteristic caused by secondary emission from the anode being attracted to the positively charged screen. Although this peculiarity did not affect the performance of the tetrode as an RF amplifier, it did prevent use of the device for AF power amplification. The pentode tube, utilizing a third (“suppressor”) grid was designed to overcome this problem. The suppressor grid provided a means to prevent the secondary emissions from reaching the screen grid. This allowed the full capabilities of the tube to be realized.

Philips researchers Drs. G. Holst and B. Tellegen are credited for the invention, receiving a patent for the new device in 1926.

1.2.1.1 Radio Central

The first major project that the young Radio Corporation of America (RCA) tackled was the construction of a huge radio transmitting station at Rocky Point, NY. The facility, completed in 1921, was hailed by President Harding as a milestone in wireless progress. The president, in fact, put the station into operation by throwing a switch that had been rigged up at the White House. Wireless stations around the globe had been alerted to tune in for a congratulatory statement by the president.

For a decade, this station—known as Radio Central—was the primary means of direct communications with Europe. It was also the “hopping off” point for messages transmitted by RCA to Central and South America.

The Rocky Point site was famous not only for its role in communications, but also for the pioneers of the radio age who regularly visited there. The guest book lists such pioneers as Guglielmo Marconi, Lee De Forest, Charles Steinmetz, and Nikola Tesla. Radio Central was a milestone in transatlantic communications.

Originally, two antenna structures stood at the Rocky Point site, each with six 410 ft towers. The towers stretched over a 3 mile area on the eastern end of Long Island.

The facility long outlived its usefulness. RCA demolished a group of six towers in the 1950s; five more were destroyed in early 1960. The last tower of the once mighty Radio Central was taken down on December 13, 1977.

1.2.1.2 WLW: The Nation's Station

Radio station WLW has a history as colorful and varied as any in the United States. It is unique in that it was the only station ever granted authority to broadcast with 500 kW. This accomplishment pushed further the limits of vacuum tube technology.

The station actually began with 20 W of power as a hobby of Powell Crosley, Jr. The first license for WLW was granted by the Department of Commerce in 1922. Crosley was authorized to broadcast on a wavelength of 360...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Table of Contents
• Preface
• Acknowledgment
• Author
• 1 Power Vacuum Tube Applications
• 2 Modulation Systems and Characteristics
• 3 Vacuum Tube Principles
• 4 Designing Vacuum Tube Systems
• 5 Applying Vacuum Tube Devices
• 6 Microwave Power Tubes
• 7 RF Interconnection and Switching
• 8 Properties of Materials
• 9 Cooling Considerations
• 10 Reliability Considerations
• 11 Device Performance Criteria
• 12 RF System Maintenance and Troubleshooting
• 13 Safe Handling of Vacuum Tube Devices
• Appendix: Mathematics, Symbols, and Physical Constants
• Index