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Wig Wag transmitter
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Scott Dorsey wrote: Hank wrote: I've always felt that deForest's history was another exercise in alchemical strangeness. It seems fairly clear that he did not have any real understanding of why or how his tubes worked, or what they might be capable of actually doing. Nor did he ever devise any practical circuitry for using them. A much larger contributor to circuitry was Armstrong, whose patents were overturned in favor of deForest later on---generally regarded as a travesty of justice. Development of the high-vacuum triode with a scientific understanding of what the control grid was doing to the electron stream---and development of a concomitant technology for series production of the devices was more an AT&T/Bell Labs effort. Also, the first major use of these devices was as telephony repeater amplifiers. Well, one of the problems is that DeForest was convinced that electron propagation in the vacuum only took place if there was a small amount of gas left in the tube. In fact, if you do allow a little gas in there, you get much higher transconductance but much poorer linearity (the extreme case being a thyratron where all of the electrons are carried by ionized gas). Because DeForest never really got the idea of modelling the tube's transfer function, he was never able to separate out the two mechanisms and consequently was never able to make consistent devices. --scott DeForest's misunderstanding of the principles of the Edison effect and the Fleming valve seems to have been pretty basic. His first attempts to control current flow were "grids" mounted on the outside of the glass envelope. And he always seemed to think that what he was controlling was ionized gas conduction, not electrons emitted from a cathode element. There were tons of texts written around 1920 that had some pretty strange theories about what tubes did inside. As I recall, the first really good text on radio circuits I encountered was Mary Texanna Loomis's text from the late 20's. I learned EE basics from her text, Ghirardi's "Radio Physics Course" from 1932, and Terman's 1937 "Radio Engineering." One text that baffled me was Zworykin/Morton "Television," which I got as a present at the end of WWII. No wonder--the physics were much too advanced for me to understand. Looking back some years later, I think the best text on vacuum tube physics was Spangenberg's "Vacuum Tubes." It wasn't published until the dawn of the transistor era, so never got the play that Terman and some of the others did. Hank |
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