• Erregi Elettronica

The thermionic valve: the Origin of the myth



November 16, 1904, London. Apparently a day of daily routine for Londoners of the time. But you know, appearances can be deceiving. Our story - yes, because it affects us all - begins at University College London where John Ambrose Fleming, a renowned professor passionate about electrical engineering, develops the first active electronic component in history: the thermionic valve. It consists of a heatable metal wire and two terminals, a cathode and an anode, the first coinciding (more or less) with the wire itself and the second outermost immersed in high vacuum. The principle of operation? Relatively simple: exploit a heated metal to make it emit electrons to another region with a higher potential, namely the other terminal; on the contrary, an opposite polarization, that is, with the anode having a lower potential than the cathode, would not cause any currents to flow because the anode would reject the charges.


About a couple of years later, the American Lee De Forest, an individual with decidedly varied interests, added another metal terminal, called a grid, to modulate the charge passage between cathode and anode. Thus was born the device called triode. The more experienced will be able to read between the lines an ancestor of the modern transistor and for the novices one can think of a sort of "tap for electrons".


And what happened then? It all started, or rather it continued in a different way. Tesla, Marconi and Hertz (to name the best known) had already laid the foundations of the work with studies and applications on long-distance transmission systems by radio waves, but none of them had ever distanced themselves so markedly from 'electrical engineering, as Fleming had done instead. And the repercussions were not long in coming, indeed Marconi himself was among the first to recognize the great potential of the invention of English.


In short, already from this brief summary it is evident that electronics is a relatively young science if compared to physics or analysis, nevertheless its growth in the immediate future compared to where we have just left it will be rapid as guided by a good star. But for the rest, dear readers, I refer you to the next articles.


We owe a lot to our British and American "colleagues", if only for having opened the doors to electronics that today make their importance felt even more than yesterday. But basically we know and it shouldn't be surprising, Anglo-Saxon art has been able to make people talk about it many times and widely. Yes, because basically this is what it is. Art. A practical science that tries to move something so small that it cannot be seen between two different points, the bizarre embrace of geometries in the schematics and the pervasiveness in everyday life: all elements capable of making the fibers of scientists, engineers and even simple people resonate. passionate. Electronics.


P.S. I leave an interesting anecdote about thermionic tubes to the willing reader who has gone to the end of this short but very dear article to me. Does the name ENIAC mean anything to you? No? ENIAC (Electronic Numerical Integrator and Computer) is the first example of a general purpose computer dating back to the period of the Second World War. The project was most likely financed for war purposes starting from the 40s and was then completed in 1946. Well this "gem" could boast 5000 operations per second with an mtbf (Mean time between failures) of only 8 hours, a trifle if compared to today's one of several years, compared to 19000 valves, 1500 relays with a consumption of 200KW to operate and a consequent ambient temperature of 50̊.


article by Gabriele Magni


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