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MASTERTONE
Instruments previously produced in Kalamazoo, MI by Gibson between the 1920s and 1940s. See chapter on House Brands.
While the Mastertone designation was applied to high end Gibson banjos in the 1920s, the Mastertone trademark was used on a Gibson-produced budget line of electric guitars beginning in 1941. Some acoustic "Hawaiian" guitars from the 1930s by Gibson also carried the Mastertone label. While built to the same standards as other Gibson guitars, they lack the one "true" Gibson touch: an adjustable truss rod. House Brand Gibsons were available to musical instrument distributors in the late 1930s and early 1940s. Source: Walter Carter, Gibson Guitars: 100 Years of an American Icon.