6L6s

6L6s are a family of beam-power tetrode vacuum tubes used as audio power amplifiers. They were developed by RCA and introduced in the late 1930s. The family includes several variants such as 6L6G, 6L6GA, 6L6GB, 6L6GT, and 6L6GC. The G-series generally uses a glass envelope, and the 6L6GC is a higher-power version introduced in the 1950s with higher plate voltage ratings and transconductance, making it the most common version in later equipment. The 6L6 family is widely associated with guitar and hi-fi amplifiers of the 1950s–60s, notably in many Fender Bassman and other push-pull configurations, as well as early guitar amplifiers from other manufacturers.

The 6L6 is a beam tetrode that operates with a 6.3 V heater typically drawing about 0.9 A, and it requires a high positive plate voltage, commonly several hundred volts, to deliver tens of watts of output. In audio use, it can produce clean power and, when driven into distortion, a smooth overdrive characteristic favored by players.

Variants and equivalents: 5881 is a military variant similar to the 6L6GC, widely used as a substitute in some circuits. The 6L6GC remains in production and is the standard replacement in many classic designs. Substitution depends on heater, plate voltage, and pin compatibility, so datasheets should be consulted.