View source for 6L6

{{Short description|Vacuum tube}}
{{Infobox vacuum tube
|image = [[File:Tube 6L6 Sylvania.jpg|190x502px]]
|caption = A 6L6 tube manufactured by Sylvania
|classification = [[Beam tetrode|Beam power tetrode]] <!-- Mandatory -->
|service = [[Class-A amplifier]], [[class-B amplifier]], [[class-AB amplifier]], (audio amplifiers)
|height_in = 4.25 <!-- inches -->
|diameter_in = 1.438 <!-- inches -->
|weight_lbs =  <!-- pounds -->

<!-- Cathode -->
|cathode_type = Indirectly heated <!-- Mandatory -->
|heater_voltage = 6.3
|heater_current = 900 mA
|filament_voltage =
|filament_current =

<!-- Anode -->
|max_dissipation = 30 <!-- Mandatory -->
|max_voltage = 500 <br /> Specification listed is for type 6L6-GC

<!-- Socket Connections -->
|pinout = [[File:BPT Pinout.png|thumb|left|125px|The 6L6 Pinout, metal versions had the shell connected to pin 1]]
Pin 1 – [[not connected|n.c]] <br />
Pin 2 – Heater <br />
Pin 3 – Anode (Plate) <br />
Pin 4 – Grid 2 (Screen) <br />
Pin 5 – Grid 1 (control) <br />
Pin 6 – n.c <br />
Pin 7 – Heater <br />
Pin 8 – Cathode & beam-forming plates

<!-- Class A amplifier ops -->
|class_a_amplification_factor = 
|class_a_anode_voltage = 350 V
|class_a_anode_current = 54 mA
|class_a_screen_voltage = 250 V
|class_a_bias_voltage = −18 V
|class_a_anode_resistance = 5 kOhms

<!-- Class C amplifier ops -->
<!-- Recommend the use of highest rated CCS specification -->
|class_c_power_output =
|class_c_anode_voltage =
|class_c_anode_current =
|class_c_screen_voltage =
|class_c_bias_voltage =

<!-- Class AB amplifier ops -->
<!-- Recommend the use of highest rated CCS specification -->
|class_ab_power_output = 55 W
|class_ab_anode_resistance = 5.6 kOhms
|class_ab_anode_voltage = 450 V
|class_ab_anode_current = 2*54 mA
|class_ab_screen_voltage = 400 V
|class_ab_bias_voltage = −37 V
|reference = Essential Characteristics, General Electric, 1973
}}
'''6L6''' is the designator for a [[vacuum tube#Beam power tubes|beam power tube]] introduced by [[Radio Corporation of America]] in April 1936 and marketed for application as a power amplifier for audio frequencies.<ref name=dreyer>J. F. Dreyer Jr., [https://worldradiohistory.com/Archive-Electronics/30s/Electronics-1936-04.pdf "The Beam Power Output Tube"], New York: McGraw-Hill, ''Electronics'', April 1936, pp. 18 - 21, 35</ref><ref>RCA Manufacturing Co. Inc., [https://worldradiohistory.com/Archive-Electronics/30s/Electronics-1936-05.pdf "Here is the New RCA 6L6 Beam Power Amplifier"], New York: McGraw-Hill, ''Electronics'', May 1936, back cover</ref> The 6L6 is a [[beam tetrode]] that utilizes formation of a low potential [[space charge]] region between the anode and screen grid to return anode [[secondary emission]] electrons to the anode and offers significant performance improvements over power pentodes.<ref name=dreyer/> The 6L6 was the first successful beam power tube marketed. In the 21st century, variants of the 6L6 are manufactured and used in some high fidelity audio amplifiers and musical instrument amplifiers. 

== 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 Corporation|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]].

== Variations ==
The voltage and power ratings of the 6L6 series were gradually pushed upwards by such features as thicker plates, grids of larger diameter wire, grid cooling fins, ultra-black plate coatings and low loss materials for the base. Variants of the 6L6 included the 6L6G, 6L6GX, 6L6GA, 6L6GAY, 6L6GB, 5932/6L6WGA and the 6L6GC. All variants after the original 6L6 utilized glass envelopes.  A "W" in the descriptor identified the tube as designed to withstand greater vibration and impact. A "Y" in the descriptor indicated that the insulating material of the base was [https://web.archive.org/web/20110819185840/http://www.antiquewireless.org/otb/vt0108.htm Micanol].
==Application==
The high transconductance and high plate resistance of the 6L6 requires circuit design that incorporates topologies and components that smooth out the frequency response, suppress voltage transients and prevent spurious oscillation.<ref>L. C. Hollands, [https://worldradiohistory.com/Archive-Electronics/30s/Electronics-1939-03.pdf "Circuit Design Related to Tube Performance"], New York: McGraw-Hill, ''Electronics'', Mar. 1939, pp. 18 - 20 </ref><ref>Editors, [https://worldradiohistory.com/Archive-Electronics/40s/Electronics-1940-01.pdf "The Electron Art" "Ultra-High Frequency Oscillation with the Beam Tube"], New York: McGraw-Hill, ''Electronics'', Jan. 1940, p. 69 </ref>

== Characteristics ==
[[File:6L6 Beam Tetrode anode characteristics.jpg|thumb|Anode characteristics with screen grid (grid 2) voltage as parameter]]
[[File:6L6 triode anode characteristics.jpg|thumb|Anode characteristics with the screen grid (grid 2) connected to the anode (i.e. used as a triode)]]

== Improved substitute ==
* [[5881]]

== Similar tubes ==
* [[6P3S]] (6П3С)
* [[6P3S-E]] (6П3С-E)
* [[7027a]]
* 6BG6

== See also ==
* [[6V6]]
* [[KT66]]
* [[KT88]]
* [[6550]]
* [[6CA7]]
* [[EL34]]
* [[List of vacuum tubes]]

==References==
{{reflist}}
== External links ==
* [http://tdsl.duncanamps.com/show.php?des=6L6 TDSL Tube data <nowiki>[6L6]</nowiki>]
* [http://tubedata.milbert.com/sheets67.html Electron Tube Data sheets]: Several 6L6 datasheets from various manufacturers
* {{cite web |url=http://www.amplifiedparts.com/sites/all/modules/custom/tech_corner/files/6l6gc_comparison_of_current_made_tubes.pdf |title=6L6GC Comparison of Current Made Tubes |type=PDF |author=Kurt Prange |access-date=2014-02-16 |archive-url=https://web.archive.org/web/20140221181448/http://www.amplifiedparts.com/sites/all/modules/custom/tech_corner/files/6l6gc_comparison_of_current_made_tubes.pdf |archive-date=2014-02-21 |url-status=dead }}
* [https://tubemaze.info/tag/6l6/ Reviews of 6L6 tubes]
* Barbour, Eric. "6L6 Forever (1936-1996): 60 Years of Amplifier Service." Vacuum Tube Valley 4:1 (Spring/Summer 1996), 3-10.

[[Category:Vacuum tubes]]
[[Category:Guitar amplification tubes]]
[[Category:Telecommunications-related introductions in 1936]]