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  Mala povijest triode  
  zagrijavanje za festival  
 

 

Malo "zagrijavanja" pred triode-festival...ukratko povijest triode od prvog zapažanja pojave fenomena termioničke emisije do prvog pojačanog signala... dakle, engleski znanstvenik, pisac i profesor na "Kraljevskoj rudarskoj školi", te jedan od utemeljitelja "Londonskog Društva Fizičara" Frederick Guthrie, prvi je (1873.g)  objavio članak i prijavio svoja istraživanja u kojima je primjetio da elektricitetom nabijena, vruća užarena željezna sfera "na neki način" gubi svoj naboj (ispuštajući ga u "zrak"). Također, ustanovio je da se to ne događa kad je sfera negativno nabijena. Sedam godina poslije, Thomas Alva Edison je, ispitujući razloge zašto mu se zacrnjuju njegove žarulje, također otkrio da utjecajem temperature žarne niti sa negativnog kraja ugljik sa žarne niti ostavlja sa unutarnje strane zacrnjenje na pozitivnom dijelu žarulje (u to doba još nije bilo izmjenične struje). Želeći to izbjeći, uveo je još jednu elektrodu na koju je prikačio galvanometar i mogao na taj način dokazati izbacivanje negativno nabijenih "atoma" ugljika (kako je on to tada shvaćao jer pojam elektrona još nije bio poznat). Nakon poprilično eksperimentiranja je taj svoj nalaz i patentirao 1883. g. Efekt je kasnije po njemu i nazvan. Dvadesetak godina kasnije, Owen W. Richardson je, nakon što je diplomirao na Cambridgeu, istražujući emisiju elektriciteta vezanih za zagrijavanje žice, otkrio i demonstrirao da struja sa usijane žice ovisi eksponencijalno o temperaturi žice i da se to može matematički i prikazati. Sublimirajući radove svog profesora i mentora F. Guthriea i Thomasa Edisona, te prateći rad Owena Richardsona, John Ambrose Fleming je, u to vrijeme radeći na poboljšanju kristalnih dioda koje su korištene za detekciju radio-valova, došao na ideju da bi se u te svrhe mogao iskoristiti i tzv. Edisonov efekt. Upotrijebio je lampu sličnu Edisonovoj u kojoj je metalnim prstenom okružio žarnu nit i otkrio da struja u vakumu ovisi o temperaturi žarne niti i vrijednosti napona na tom metalnom prstenu, dakle takva "elektronska dioda" propusna je samo u jednom smjeru i može poslužiti za detekciju radio valova i u višim frekvencijama di su dotadašnje kristalne diode posustajale. I on je, poput Edisona, patentirao tu, kako ju je nazvao "oscilatorsku cijev, pipu" (Oscillator Valve, Vacuum Tube) 1904 godine. Njegovo otkriće potaknut će američkog inženjera Lee de Foresta da dvije godine kasnije (1906.g), ubaci između žarne niti (filamenta, katode) i tog metalnog prstena (anode) još jednu elektrodu, koju je nazvao rešetka (grid), radi njenog izgleda i konstrukcije. Osnovna zamisao te rešetke bila je da ovisno o tome jeli pozitivnija ili negativnija prema katodi, krugom bi tekla veca ili manja struja. Obzirom da je rešetka bliže katodi nego anodi, mala promjena napona rešetke djeluje na anodnu struju kao velika promjena napona na anodi. Dakle, ukratko, došlo se do mogućnosti pojačanja signala i tako je rođena naša triodica...


Malo izvadaka sa interneta:


Frederick Guthrie (1833 - 1886)

The phenomenon was initially reported in 1873 by Frederick Guthrie in Britain. While doing work on charged objects, Guthrie discovered that a red-hot iron sphere with a positive charge would lose its charge (by somehow discharging it into air). He also found that this did not happen if the sphere had a negative charge.[1] Other early contributors included Hittorf (1869–1883), Goldstein (1885), and Elster and Geitel (1882–1889).


Thomas Alva Edison (1847-1931)

 

The effect was rediscovered by Thomas Edison on February 13, 1880, while trying to discover the reason for breakage of lamp filaments and uneven blackening (darkest near one terminal of the filament) of the bulbs in his incandescent lamps.

Edison built several experiment bulbs, some with an extra wire, a metal plate, or foil inside the bulb which was electrically separate from the filament. He connected the extra metal electrode to the lamp filament through a galvanometer. When the foil was given a more negative charge than the filament, no charge flowed between the foil and the filament. We now know that this was because the cool foil emitted few electrons. However, when the foil was given a more positive charge than the filament, negative charge apparently flowed from the filament through the vacuum to the foil. This one-way current was called the Edison effect (although the term is occasionally used to refer to thermionic emission itself). He found that the current emitted by the hot filament increased rapidly with increasing voltage, and filed a patent application for a voltage-regulating device using the effect on November 15, 1883 (U.S. patent 307,031,[2] the first US patent for an electronic device). He found that sufficient current would pass through the device to operate a telegraph sounder. This was exhibited at the International Electrical Exposition in Philadelphia in September 1884. William Preece, a British scientist took back with him several of the Edison Effect bulbs, and presented a paper on them in 1885, where he referred to thermionic emission as the "Edison Effect." [3]

http://home.frognet.net/~ejcov/edisone.html

 

Sir Owen Willans Richardson, FRS (26 April 1879 - 15 February 1959) was a British physicist who won the Nobel Prize in Physics in 1928 for his work on thermionic emission, which lead to Richardson's Law.[1]

 
Biography
Richardson was born in Dewsbury, Yorkshire, England, the only son of Joshua Henry and Charlotte Maria Richardson. He was educated at Batley Grammar School and Trinity College, Cambridge, where he gained First Class Honours in Natural Sciences.[2]

After graduating in 1900, he began researching the emission of electricity from hot bodies at the Cavendish Laboratory in Cambridge, and in 1902 he was made a fellow at Trinity. In 1901, he demonstrated that the current from a heated wire seemed to depend exponentially on the temperature of the wire with a mathematical form similar to the Arrhenius equation. This became known as Richardson's law: "If then the negative radiation is due to the corpuscles coming out of the metal, the saturation current s should obey the law ."[3]

Richardson was professor at Princeton University from 1906 to 1913, and returned to the UK in 1914 to become Wheatstone Professor of Physics at King's College London, where he was later made director of research. He retired in 1944, and died in 1959.

He also researched the photoelectric effect, the gyromagnetic effect, the emission of electrons by chemical reactions, soft X-rays, and the spectrum of hydrogen.

Richardson married Lilian Wilson, sister of his Cavendish colleague Harold Wilson, in 1906, and had two sons and a daughter. Richardson's own sister married the American physicist (and 1937 Nobel laureate) Clinton Davisson, who was Richardson's PhD student at Princeton. After Lilian's death in 1945, he was remarried in 1948 to Henriette Rupp, a physicist.


 

Sir John Ambrose Fleming

British physicist and electrical engineer (1849–1945)

 

Investigated Edison Effect

In 1899, Fleming was hired to be the scientific adviser to the Marconi Wireless Telegraph Company. The company was particularly interested in achieving greater distances in the transmission of wireless signals and Fleming became entranced by the puzzle as well. He helped design the Poldhu Power Station in Cornwall, England, the largest station in the country, and built much of the equipment that would help that facility make history. Poldu achieved fame in 1901, when it made the first successful transatlantic radio transmission. Although the groundbreaking transmission consisted of the Morse Code letter S - dot, dot, dot - Fleming inexplicably preferred the letter V - dot, dot, dot, dash - and conducted all his transmitter experiments using it. Indeed, he often became so absorbed in his work that he could be heard unconsciously humming or whistling the letter under his breath.

Fleming realized that the main impediment to further improvements in the development of radio signals was the inability to effectively detect the signals themselves, especially at higher frequencies. Crystal rectifiers could be used to convert alternating current into direct current in order to achieve amplification of weak radio waves, but were only efficient at lower frequencies. As he cast about for ideas about how to solve the problem, Fleming had an inspiration. He recalled an 1883 discovery by American scientist Thomas Alva Edison, one that Fleming had also investigated himself over the years, but that no one had found a particular use for. Known as the Edison Effect, the phenomenon was briefly explained by a contributor to the IEEE History Center Web site: "When he [Edison] introduced an extra electrode into the [incandescent] bulb, he realized that, even though the electrode wasn't part of the bulb's circuit, it could carry a current when it was of a positive potential relative to the filament. This so-called Edison Effect was later interpreted to be a flow of electrons from the hot filament to the extra electrode." Because electrons had been discovered in 1896 by Joseph J. Thompson (1856-1940), the Edison Effect showed more potential when Fleming took another look at it in 1904. He saw that a tube, or cylinder, could accomplish the work of crystal rectifiers more effectively.

Specifically, Fleming used a metal cylinder surrounding a filament, and a high vacuum. He then constructed a diode by attaching the cylinder plate and the filament through a second current circuit, using a battery to increase the electron flow and permitting the current to flow in only one direction. Able to detect high-frequency radio waves, this filament and plate apparatus was connected to an antenna circuit through which Fleming applied fluctuating voltages generated by radio signals. The changing voltages caused the plate current to vary in strength, creating changes that could be registered by a receiving apparatus. In essence, Fleming created a tube that controlled the flow of electricity in the same way that a fluid valve worked. He patented the device on November 16, 1904.

The Fleming Valve

Fleming initially called his invention the oscillation valve, but it eventually became known by such alternate names as the Fleming valve, vacuum tube, and thermionic valve. While its immediate impact was felt, the invention proved much more important as a foundation for the field of electronics overall. One indication of its huge impact was the introduction of the Audion vacuum tube by American engineer Lee DeForest in 1906. DeForest took Fleming's idea and added a third electrode, which was called a grid because of the way in which it was constructed. The device caused a great uproar in the scientific community, as many saw it as an infringement on Fleming's invention. Fleming's own suit for patent infringement as to the Audion tube's thermionic technology failed. Nonetheless, his mark on the world was firmly in place.

The ramifications of the Fleming valve were myriad and far-reaching. It was a key component of radios for nearly three decades, until it was replaced by the transistor, and was integral to the development of television, telephones, and even early computers. Just as he had inaugurated the department of electrical engineering at University College, London, Fleming also established the basis for the field of electronics itself. As Orrin E. Dunlap, Jr., quoted Fleming as modestly commenting in Radio's One Hundred Men of Science, "The little things of today may develop into the great things of tomorrow."


 

Lee de Forest

1873 - 1961

http://www.leedeforest.org/

http://www.leedeforest.org/inventor.html

 
 
 
Audion, prva trioda:
 
 
 
 
 

Možda će biti zanimljiv i podatak da su se i neki Nijemci, napr. Wehnelt i Von Lieben, navodno istovremeno, ako ne čak i malo ranije bavili gotovo identičnim istraživanjima, čak su i patentirali slične izume ponešto ranije:

 
Arthur Wehnelt

A Wehnelt cylinder is an electrode in the electron gun assembly of some thermionic devices, used for focusing and control of the electron beam. It is named after Arthur Rudolph Berthold Wehnelt, a German physicist, who invented it during the years 1902 and 1903. A Wehnelt cylinder is also known as a grid cap, and plays the role of a control grid. It is held biased to slight negative voltage relative to the cathode (usually a hot cathode). It has a shape of a hollow barrel with no top side (oriented towards the cathode) and a hole in the center of its bottom side (through which the focused electron beam escapes towards the anode).

Wehnelt cylinders are found in the electron guns of cathode ray tubes and electron microscopes, and in other applications where a thin, well-focused electron beam is required.

Robert Von Lieben

The results of the discovery of an electro-chemical phonograph and the polarization of X-rays in 1903, as well as the purchase of a telephone factory in Olomouc (Moravia) in 1904, provoked Lieben to develop a telephone amplifier via a cathode beam (electron beam) known as the telephone-relay.

In 1906 von Lieben applied for a patent for his cathode-beam relay: he patented the ability of a magnetic field to deflect an electron ray.

In 1910 he improved the design by adding a control-grid, with which the current density could be varied and consequently amplification attained. Lieben patented this effect. Electrostatic control also underlies the operation of Lee de Forest's Audion (vacuum tube triode), patented in 1907 (U.S. patent 879, 532).

 

Nakon de Forestovog otkrića i dodavanja treće elektrode, rešetke između katode i anode jedan dio priče o triodi završava jer je ipak došlo do kakve-takve mogućnosti pojačavanja signala, no onaj drugi dio, kad je trebalo napraviti samu implementaciju takvog izuma u stvari tek počinje. Razlog tomu je vjerojatno u tome da sam de Forest zapravo nije mogao pravilno objasniti što se zapravo zbiva među elektrodama, nije vjerovao u elektrone i elektronski oblak koji nastaje zagrijavanjem katode već je mislio da se tu zapravo radi o ioniziranim rezidualnim plinovima koji su ostali u tom nepotpunom vacuumu. Tako da su mu se događale pomalo apsurdne situacije, jer je sprava prvenstveno zamišljena kao detektor radio signala i njegov pojačavač, već u zavisnosti o količini prisustva tih rezidualnih plinova bila ili jedno ili drugo, dok je bilo dovoljno "zraka" u tom tzv. niskom vacuumu, Audion je mogao ponešto detektirati radio signal, a kad bi se "potrošio" taj zrak oksidacijom na površini metala, audion je postajao pravo pojačalo signala, i to su bile u to doba de Forestu nerazrješive zagonetke. Tada se, kako to već biva u znanstvenom svijetu, pojavio novi lik, izvjesni kemičar Irving Langmuir, koji je eksperimentirajući sa Audionom, uspio usavršiti živinu vacuumsku pumpu i napraviti uvjete tzv. visokog vacuuma, u kojem se audion ponašao isključivo kao pojačalo signala i izgubio ona svoja "detektorska" svojstva. Langmuir je inspirirao slijedećeg znanstvenika, Edwina H. Armstronga koji se također dulje vremena bavio pokušajima teoretskog objašnjenja rada Audiona i koji je 1914.g. u svom čuvenom djelu "Operating features of the Audion" prvi znanstveno obrazložio i prikazao osnovne principe rada tog stroja. U međuvremenu je još jedan znanstvenik, finac Eric Tigerstedt, opsjednut idejom pokušaja ubacivanja zvuka u tadašnje nijeme filmove i njegovom amplifikacijom, poboljšao samu konstrukciju triode, katode, rešetke i anode i u mnogočemu je zaslužan za njen daljni razvoj. Naravno, tadašne velike američke firme koje su se bavile tom vrstom tehnologije poput Westinghousea, Western Electrica (1915 patentirao indirektno grijanu katodu) General Electrica (napravio Langmuirov Pliotron, prvu potpuno funkcionalnu triodu), RCA, Marconija i ostalih, kao i njemački Siemens and Halske, nešto kasnije i Telefunken, snažno su krenuli u utrku i proizvodnju, te usavršavanje i poboljšavanje svojstva triode.


Irving Langmuir (1881-1957)

 

 
 
 
 
 
 

Edwin Howard Armstrong (1890-1954)

 

 


2011.01.31 - 15:31
 
 
 
 
     
 
 
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