Final tube history lecture: the dawn of a new technology
It was discovered earlier, that an electrical arc can be detected remotely by a certain crystal to metal conjunction (later becoming the Schottky-Diode) via a small capacitor and this was instantly pioneered as wide band arc transmission of morse code. To cope the degradation of the mechanical short circuit switch they were seeking for an electrical arc switch (later brought to market as the Ignitron and the Thyratron) to improve lifespan. What they found was oscillation, suddenly allowing tuned circuits enabling narrow band transmission. The Lieben tube was invented in 1906 and it had a low pressure mercury filled inner because vacuum pumps were not yet invented. With electronic theory not fully elaborated they were using primarily ionized metal conduction with heavy atoms, not lightweight electrons. The filament was made of rectangular platinum wire nickel coated for enhanced electronic emission and what was later made of thin wire wrap known as the control grid was a bored platter. The shape of the dome was inspired by falsely assumed light beam concentration, not yet aware of electromagnetic forces guiding the particle flow. For detailed information and the magical moment of ignition see Mr. Patrik Sokolls video
https://youtu.be/lWRRFi0E3a
Pictures courtesy „Vintronic“ Flensburg, Germany
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