Thermionic valves

The war itself also drove the development of improved and miniaturised electronic components for creating oscillators and amplifiers and, ultimately, semiconductors, which made practical the electronic systems needed in portable eddy current test instruments. The refinement of those systems continues to the present day and advances continue to be triggered by performance improvements of components and systems. In the same way that today s pocket calculator outperforms the large, hot room full of intercormected thermionic valves that I first saw in the 50 s, so it is with eddy current instrumentation. Today s handheld eddy current inspection instrument is a powerful tool which has the capability needed in a crack detector, corrosion detector, metal sorter, conductivity meter, coating thickness meter and so on. 

II should noi be overlooked that platinum has played a crucial role in ihe development of many branches of science even though the amounts of metal involved may have been small. Reliable Pt crucibles were vital in classical analysis on which the foundations of chemistry were laid. It was also widely used in the development of the electric telegraph, incandescent lamps, and thermionic valves. 

There are also numerous methods depending on the measurement of the potential differences which must be applied to various parts of a thermionic valve in order to prevent, or otherwise modify, the flow of electrons from the hot filament these have been briefly summarized by Oatley6 in a recent paper this author describes a new method baaed on the measurement of the magnetic field requisite to prevent the passage of electrons from a straight hot filament, placed axially inside a cylinder, to the cylinder. 

Rubidium has been, and caesium now is, used in photo-electric cells and thermionic valves. 

COLOSSUS was not strictly a stored program machine for the program was set by wiring plug-boards. The machine contained over 1500 thermionic valves (vacuum tubes), and it surprised everyone by its reliability and speed. It did not hold its data internally either, but on a loop of paper tape that was reread as necessary. Although the secrecy, required by the state for security... 

The first electronic computer ENIAC (Electronic Numerical Integrator and Calculator) developed in 1946 at the University of Pennsylvania had about 18,000 thermionic valves and consumed about 150 kW of electrical power. It was a huge machine weighing over 25,000 kg and filled a room. Initially, it was used for calculating artillery firing tables for the US Army s Ballistic Research Laboratory. 

US engineer Lee De Forest (1873-1961) invents the triode thermionic valve. 

See COLLECTIVE excitation energy level QUASIPARTICLE. 2. The process of applying current to the winding of an electromagnet, as in an electric motor. 3. The process of applying a signal to the base of a transistor or the control electrode of a thermionic valve. 

Whereas much of the UK-based wartime work was kept secret, work progressed in the USA in parallel with the UK work, and in a more open fashion. Electronic numerical integrator and calculator (ENIAC) was conceived and designed by John Mauchly (1907-1980) and John Adam Prosper Pres Eckert (1919-1995), following a 1942 memo from Mauchly proposing a general-purpose electronic computer. A contract was received from the US Army in 1943, and the completed machine was announced to the pubhc in Eebruary 1946. It used some 17,000 thermionic valves and weighed about 27 tonnes. Vacuum tube failure rate was such that its availability was only about fifty percent. Input was via an IBM card reader. 

A final name-check in this first, pre-transistor stage of computer development is for Harry Huskey. Harry Huskey was an American who had worked on ENIAC, and then worked with Alan Turing at the UK s National Physical Laboratory on development of the ACE computer in 1947. He then moved back to the USA and worked on the EDVAC project and, later, he designed the G15 computer for the Bendix Corporation in Los Angeles. The Bendix G15 used 450 thermionic valves, weighed 950 pounds (430 kg), and was the size of a small cupboard, about 1.5 m. It cost 49500 to 60,000 and could also be rented for 1500 per month. It went on sale in 1954, and over 400 were manufactured with some remaining in use until 1970. With the Bendix G15, the computer truly entered the marketplace. 

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