Final Tech Section 1-16
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Views, Comments, Opinions 1904 – 2004 : 100 years (and more) of electronics by Dirk J Vermeulen, vice-chairman, SAIEE Historical Section Electronics is generally considered to have started with the application of the valve (vacuum tube in America). The first valve was the thermionic diode and this began to find practical use in 1904. This year has thus been widely associated with the beginning of electronics. Much relevant fundamental work had been engineer of the British Post Office, was the known devices but found that they were done before 1904. In particular in 1895 present and persuaded Edison to part with only suitable for low frequencies. JJ Thompson discovered the electron that is several of these modified lamps so that he In October 1904 he recalled that rectification the whole basis for the subject - but none of could demonstrate the phenomenon to the was associated with the Edison Effect and tried this work had yet lead to a practical outcome. Royal Society in England. one of his modified lamps. It worked and he The origins of the diode can be found in work John Ambrose Fleming, consultant to the developed a series of diodes, seeking a done on the electric lamp by Edison in 1883. Edison Electric Light Company of London, had configuration suitable for wireless telegraphy. The glass envelope of early lamps suffered visited Edison in 1884 and was probably In November 1904 Fleming applied for a from progressive blackening which obscured shown the Edison Effect. Fleming may also patent on his “oscillation valve”, as he named the light to such an extent that lamps were have been present when Preece presented it, and ceded the rights to the Marconi often discarded before the filament failed. his paper to the Royal Society in 1885. In any Company. The term valve was borrowed With DC mains one side of the hairpin-shaped case, Fleming started experimenting with from the mechanical non-return valve which carbon filament projected a clear shadow similar modified lamps and by 1890 had also permitted flow in only one direction. onto the glass. Edison believed that an came to the conclusion that “the space examination of this anomaly might throw between the metal plate and the filament was The company Ediswan produced commercial a one-way street for electricity”. some light on the cause of the problem. quantities of the Fleming valve for use in a Marconi receiver. These were installed aboard He placed an insulated metal screen between several vessels including the sister ships the two sides of the filament and found that a Titanic and Oceanic. The thermionic valve current would flow from the screen to the detector had the advantage of dependable positive terminal but that no such current performance but it was not very sensitive and flowed when it was connected to the negative never gained widespread acceptance. The two side. He also found that a minor increase in rare Fleming valves in the SAIEE collection the filament voltage caused a much greater were donated many years ago to the late rise in the current flowing through the screen. GD Walker, one of the founding members of As the screen was situated in a vacuum and our Historical Interest Group, by a naval officer completely insulated from the filament he was living in South Africa. at a loss to explain this mysterious current. Thermionic valves depended on heated The phenomena became known as the Edison cathodes to produce a supply of electrons that Effect. In October 1883 he took out a patent on were attracted to a positively charged anode. an application which magnified and displayed This resulted in a flow of current. If, however, variations in mains supply voltages. the anode was negatively charged the electrons This was the first electronic device and a unit would be repelled and no current would flow. was installed in Edison’s New York power In the beginning valve cathodes were simple station but it was probably not very successful carbon or metal filaments similar to those as it was not used again. Clearly this was not John Ambrose Fleming developed the thermionic used in light bulbs. In 1903 the German the sort of thing that would have sent Archimides diode radio detector in 1904. physicist, Arthur Wehnelt, investigated streaking through the streets crying “Eureka”. Some time later he became technical advisor thermionic emission from alkaline metal Other urgent demands on his time and to the Marconi Wireless Telegraph Company oxides. He found that these provided a rich money prevented Edison from taking this and began looking for an improved radio supply of electrons at relatively low matter further but in 1884 he asked Professor detector. Being rather deaf, Fleming wished temperatures. Plain filaments had to be raised Houston to describe it at the first meeting of to present the high frequency AC output of the to incandescence to achieve sufficient the American Institute of Electrical Engineers receiver visually using a DC galvanometer. emission and this limited their life and in Philadelphia. William Preece, chief This required a suitable rectifier. He tried all required a lot of power. Elektron Nov/Dec 2004 9 Wehnelt-coated cathodes diminished both Arnold persuaded the company to take the defects and were widely used after the mid- matter further and Western Electric paid de 1920s. Forest $50 000 for the rights to use the audion in telephone applications. This was fortunate In January 1904, Wehnelt patented thermionic as the vacuum tube had now reached the rectifiers with oxide-coated cathodes to hands of a well-motivated company with the produce DC from AC mains. Fleming claimed means to develop its capabilities. They that he had anticipated this use before 1890 assembled a group of competent physicists but neither could claim royalties as there was and engineers to elevate the audion from a little demand for such devices before the 1930s. crude prototype into a practical device. In 1905 the American Lee de Forest A young South African physicist, Dr. Hendrik acquired a Fleming oscillation valve and van der Bijl was included in this team. His had copies made to explore their suitability job was to find out how the audion functioned as radio detectors. He seemed to be and to determine the mathematical impressed with his findings and tried to relationship between its parameters. Van der modify the device sufficiently to circumvent Bijl soon developed a procedure for designing the Marconi/Fleming patent. He audions that remained current throughout the subsequently took out patents on several life of the vacuum tube. variations calling them audions. In later years during protracted legal disputes de In 1914 he conceived the tube used on the Fig. 1: Marconi/Fleming “Oscillation valve” Forest firmly denied that his audions were first successful telephone link between New (diode radio detector). derived from the Fleming valve. York and San Francisco. This was initially designated type M, for mounted, as it was the Eventually de Forest’s work led him to place first tube to be fitted with a plug-in base to a wire grid between the anode and the facilitate replacement. The tube illustrated cathode of a diode. This new three-element (Fig.3) is in our collection and is one of van device functioned particularly well as a radio der Bijl’s prototypes – these were hand-made, detector and was sufficiently novel to justify including the base. The type M was later de Forest’s patent application of January 1907. redesignated 101A. He subsequently The main reason for the success of the grid designed a number of important tubes audion was its ability to amplify but initially including the VT1, VT2 and VT3 for military de Forest was happy to exploit his new audion use during WWI. as a superior wireless detector. In 1920 McGraw-Hill published van der Bijl’s In a large country like the USA long-distance book - this must surely be the first textbook telephone connections were limited by line on electronics. losses. By 1910 the greatest attainable range Soon after this General Smuts invited van using 4 mm diameter copper wires on an der Bijl to return to South Africa to become open wire route was about 1500 km. This scientific advisor to the government. In 1925 was barely a third of the distance from New van der Bijl founded the Electricity Supply York to San Francisco. To stretch this further Commission, or Eskom as it is now known. would require amplifiers and the American Fig. 2: Special de Forest grid audion He also originated several other important (triode). Telephone and Telegraph Company (AT & T) industrial enterprises including Iscor and were looking for a suitable device to do just the Industrial Development Corporation. this. When de Forest heard of this application Van der Bijl is acknowledged as a pioneer he tried, unsuccessfully, to produce an audio of electronics in the USA but his amplifier using his audion. achievements are rarely recognised here, Eventually he had a few tubes made with in his own country. special larger anodes to deliver more power I believe that the word electronics must have and, with help, produced a unit that looked been coined in the mid-1920s because in 1927 promising for telephone use. He sealed it in a a monthly periodical known as Electronics box and demonstrated it to the Western Engineering appeared in the UK. In April 1930 Electric Company, the manufacturing arm of McGraw-Hill also began publishing a AT & T. Unfortunately he was not able to monthly journal called Electronics. convince them that he had a suitable solution. In retrospect it has become clear that the In 1912, with the help of a telephone engineer, diodes which emerged quite humbly in 1904 he gave a second demonstration revealing, started a progression which led to the birth of this time, the amplifying tube.