Photo by Tom Moberly.
- NOS electrical specs (GE essential characteristics)
- Classification by construction: “beam power amplifier”
- Filament volts: 6.3 V
- Filament current: 0.9 A
- Max plate volts and watts: 500 V, 30 W
- Max screen volts and watts: 450 V, 5 W
The 6L6 was introduced in the 1930s and made in the United States. Early on it was primarily used in radio sets, with a metal envelope to prevent breakage. Revisions to the original 6L6, such as glass envelopes and increased power handling, yielded new designations such as 6L6G, 6L6GA, 6L6GB, and finally the 6L6GC (introduced in the late 1950s). Because of its superior power handling and efficiency over the earlier 6L6 versions, modern tube manufacturers only make the 6L6GC. As a result, most guitarists and some manufacturers simply refer to the 6L6GC as “6L6.” If you plan on buying a new-old-stock (NOS) 6L6GC, be careful not to order the original, metal-tube 6L6—which will likely sound bad and won’t be able to take the heat from your guitar amp.
1960s Fender Blackface Twin Reverb. Photo courtesy of Tim Mullally and Dave's Guitar Shop.
The 6L6GC is commonly associated with classic American rock ’n’ roll and the sound of vintage Fender amps. It was Fender’s tube of choice in the ’60s for such higher-powered amps as the Bassman, Showman, and Twin Reverb. For a great demo of the 6L6GC sound from back in the day, check out Dick Dale and the Del-Tones’ 1963 performance of “Miserlou.” (See the “YouTube It” sidebar for links.) The lows come through fat, punchy, and strong. Mids are tight, articulate, and warm, accented by top-end chime. The 6L6GC does not break up easily—and when it does, the overdrive sound is thick and tight.
The KT66 and 5881 are common substitutes for the 6L6GC. Developed in the late 1930s as Great Britain’s rival to the American 6L6, the KT66 was used in many Marshall amps from the early to mid 1960s. Most believe that Eric Clapton recorded “Hideaway” with John Mayall’s Bluesbreakers in 1966 using a Marshall JTM45 with KT66s. Clapton found his sound during this era using a Les Paul’s bridge pickup, maxing-out the volume on the guitar and the volume and bass on the amp for a uniquely fat overdrive sound with much bite and sustain. Try a KT66 in place of the 6L6GC for a slightly cleaner sound.
The 6L6GC is commonly associated with classic American rock ’n’ roll and the sound of vintage Fender amps. It was Fender’s tube of choice in the ’60s for such higher-powered amps as the Bassman, Showman, and Twin Reverb. Photo courtesy of Tim Mullally of Dave's Guitar Shop.
The 5881 predates the 6L6GC. It was introduced in the early 1950s as a smaller, more rugged version of the 6L6G for military use. The 5881 was used in Fender’s famous tweed Bassman, whose circuit was copied for the earliest Marshall amps. (These are probably the tubes Buddy Holly had in his Bassman.) Try the 5881 in place of a 6L6GC to reduce low-end frequency response and get easier breakup into overdrive.