Editing Audion (section)

===Kenotron and Pliotron===
[[Image:Early triode vacuum tubes.jpg|thumb|upright=1.4|Audions and early triodes developed from them, 1918
<ul>
<li>''Bottom row (D):'' De Forest Audions and oscillaudions</li>
<li>''Third row (C):'' Pliotrons, developed at [[General Electric]] by Langmuir</li>
<li>''Second row (B):'' triodes developed at [[Western Electric]] which bought the rights from de Forest in 1913.</li>
<li>''Top row (A):'' French triodes. The French government gained the right to manufacture Audions in 1912 when de Forest failed to renew his French patents for lack of $125.</li>
</ul>]]

Langmuir had long suspected that certain assumed  limitations on the performance of various low-pressure and vacuum electrical devices, might not be fundamental physical limitations at all, but simply due to contamination and impurities in the manufacturing process.   His first success was in demonstrating that, contrary to what Edison and others had long asserted, incandescent lamps could function more efficiently and with longer life if the glass envelope was filled with low-pressure inert gas rather than a complete vacuum. However, this only worked if the gas used was meticulously 'scrubbed" of all traces of oxygen and water vapor.
He then applied the same approach to producing a rectifier for the newly developed "Coolidge" X-ray tubes. Again contrary to what had been widely believed to be possible, by virtue of meticulous cleanliness and attention to detail, he was able to produce versions of the Fleming Diode that could rectify hundreds of thousands of volts. His rectifiers were called "Kenotrons" from the Greek ''keno'' (empty, contains nothing, as in a vacuum) and ''tron'' (device, instrument).

He then turned his attention to the Audion tube, again suspecting that its notoriously unpredictable behaviour might be tamed with more care in the manufacturing process.

However he took a somewhat unorthodox approach. Instead of trying to stabilize the partial vacuum, he wondered if it was possible to make the Audion function with the total vacuum of a Kenotron, since that was somewhat easier to stabilize.

He soon realized that his "vacuum" Audion had markedly different characteristics from the de Forest version, and was really a quite different device, capable of linear amplification and at much higher frequencies.  To distinguish his device from the Audion he named it the "Pliotron", from the Greek ''plio'' (more or extra, in this sense meaning [[gain (electronics)|gain]], more signal coming out than went in).

Essentially, he referred to all his vacuum tube designs as Kenotrons, the Pliotron basically being a specialized type of Kenotron. However, because Pliotron and Kenotron were registered trademarks, technical writers tended to use the more generic term "vacuum tube". By the mid-1920s, the term "Kenotron" had come to exclusively refer to vacuum tube rectifiers, while the term "Pliotron" had fallen into disuse. Ironically, in popular usage, the sound-alike brands "Radiotron" and "Ken-Rad" outlasted the original names.