[AMRadio] Vacuum Tube centennial


John Lyles jtml at losalamos.com
Wed Nov 29 11:17:02 EST 2006


In December of 1906, Lee DeForest applied for the patent on the Audion, a three element tube. Fleming had already demonstrated the 2 element valve (diode) a few years earlier - after intense study of the 'Edison effect' of darkening lamp bulbs.  Applications of the tube (such as for amplification and oscillator) didn't really become widely known until a few years later, and have been a source of patent contention (4 people claimed discoveries). I prefer to believe that Edwin Armstrong, the young ham, first understood the actual working of the vacuum tube enough to apply feedback and make an oscillator. I just finished reading a scholarly but small book on the interactions of Marconi, Fleming, and DeForest, "From Marconi's Black Box to the Audion", by Sungook Hong. It was published by MIT Press in 2001.  

>From everything I have read, DeForest was quite the tinkerer, but he didn't really understand that electrons, not ions, were the functioning mechanism in his tubes. He also made a few missteps along the way in business with some unscrupulous partners. It took others to improve his device (with better vacuum) to really make tubes work well. And Marconi, well, he was hung up on spark transmission, ignored the Poulsen/Federal arc (close to CW) and didn't jump on HF alternators either (like GE did). Tubes became the equalizer eventually, as they became the WAY to make, detect and amplify RF. 

Happy anniversary of the patent, though. 
John K5PRO




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