Editing 6L6 (section)

== History ==
In the UK, three engineers at [[EMI]] ([[Isaac Shoenberg]], [[Cabot Bull]] and [[Sidney Rodda]]) had developed and filed patents in 1933 and 1934 on an output tetrode that utilized novel electrode structures to form electron beams to create a dense space charge region between the anode and screen grid to return anode secondary electrons to the anode.<ref>Schoenberg, Rodda, Bull, [https://patents.google.com/patent/GB423932A/en?oq=gb423932a ''Improvements in and relating to thermionic valves''], GB patent 423,932, published Feb. 1935</ref><ref>Schoenberg, Rodda, Bull, [https://patents.google.com/patent/US2113801A/ ''Electron discharge device and circuits therefor''], US patent 2,113,801 published Apr. 1938</ref> The new tube offered improved performance compared to a similar power pentode and was introduced at the Physical and Optical Societies' Exhibition in January 1935 as the Marconi N40.<ref name="editors">Editors, [https://worldradiohistory.com/Archive-Electronics/30s/Electronics-1935-02.pdf "New Output Tetrode"], New York: McGraw-Hill, ''Electronics'', Feb. 1935, p. 65 </ref> Around one thousand of the N40 output tetrodes were produced, but MOV ([[Marconi-Osram Valve]]) company, under the joint ownership of [[EMI]] and [[General Electric Company|GEC]], considered the design too difficult to manufacture due to the need for good alignment of the grid wires.<ref name="Thrower">K. R. Thrower, ''British Radio Valves The Classic Years: 1926-1946'', Reading, UK: Speedwell, 2009, pp. 125 - 126</ref> As MOV had a design-share agreement with [[RCA]] of America, the design was passed to that company.<ref name="Thrower"/><ref>O.H. Schade, [https://worldradiohistory.com/Archive-IRE/30s/IRE-1938-02.pdf "Beam Power Tubes"] ''Proc. I.R.E.'', Vol. 26, No. 2, Feb. 1938, p. 153</ref>

[[File:Beam Pentode Cross Section-en.svg|thumb|350px|left|Top view cross-section showing typical 6L6 type electrode structures and beam formation]]The metal tube technology utilized for the 6L6 had been developed by General Electric and introduced in April 1935, with RCA manufacturing the metal envelope tubes for GE at that time.<ref>Editors, [https://worldradiohistory.com/Archive-Radio-Engineering/30s/1935/Radio-Engineering-1935-04.pdf "Metal Tubes for Receivers"], ''Radio Engineering'', April 1935, pp. 18 - 19</ref> Some of the advantages of metal tube construction over glass envelope tubes were smaller size, ruggedness, electromagnetic shielding and smaller interelectrode capacitance.<ref>Metcalf, Beggs, [https://worldradiohistory.com/Archive-Electronics/30s/Electronics-1935-05.pdf "All-metal receiving tubes, the manufacturing technique"], New York: McGraw-Hill, ''Electronics'', May 1935, pp. 149 - 151</ref> The 6L6 incorporated an [[Tube socket#Octal|octal]] base, which had been introduced with the GE metal tubes. The 6L6 was rated for 3.5 watts screen power dissipation and 24 watts combined plate and screen dissipation.<ref>RCA, [https://frank.pocnet.net/sheets/021/6/6L6.pdf RCA 6L6 Beam Power Amplifier], RCA Manufacturing Co., Inc.</ref> The 6L6 and variants of it became popular for use in public address amplifiers, musical instrument amplifiers, radio frequency applications and audio stages of radio transmitters.<ref>Wholesale Radio Service Co., [https://worldradiohistory.com/Archive-Catalogs/Lafayette-Catalogs/Lafayette-1939-76.pdf Lafayette catalog no. 76], New York: Lafayette Radio Corp., 1939, pp. 38, 90, 96</ref> The 6L6 family has had one of the longest active lifetimes of any electronic component, more than 80 years. As of 2021, variants of the 6L6 are manufactured in [[Russia]], [[China]], and [[Slovakia]].