To replace the wide-panel style, Fender started building its “narrow-panel” tweed cabinets, which featured less cabinet and more grille in front, in late 1954 for the 1955 model year. In the meantime, back in Fullerton, Calif., Leo Fender and his staff were hearing complaints that model 5B6 couldn’t sufficiently handle low frequencies and that its single 15” speaker tended to blow.
Fender responded in fall 1954 with a redesigned version of the amp, the narrow-panel model 5D6—the first 4×10” Bassman. It pumped 40 watts through four 10” blue Jensen® P10-R speakers. It still had only two inputs, “normal” and “bright,” indicating that Fender was well aware that the amp was being used by guitar players, too. Indeed, the amp appeared in the February 1955 price list with the notation that “While its characteristics have been designed to accommodate string bass, at the same time it makes an excellent amplifier for use with other musical instruments.”
The new narrow-panel version of 1955 also featured more controls—bass, treble and presence knobs, plus standby and ground switches—that were a significant tonal improvement over the sparse control layout of the earlier TV-front and wide-panel versions.
Listing the original 4×10” Bassman’s features, however, doesn’t really convey what a landmark in the history of instrument amplification it really was. In The Soul of Tone, Wheeler writes that:
For starters, it’s powerful, it’s loud, and it’s sensitive to the player’s touch. It sounds great, responding beautifully across the frequency spectrum. It exhibits a sparkling, harmonically rich tone at low and moderate volumes. At louder volumes it thickens with a sweet distortion that only seems to get creamier the more it’s cranked. It is particularly well matched to certain popular guitars, especially the Stratocaster.
he narrow-panel tweed 4×10” Bassman went through several periodic variations in circuitry over its five years in production, starting with model 5D6 in fall 1954, continuing through model 5D6-A (1955) and model 5E6 (1956), and culminating in model 5F6 (1957) and in what many consider to be one of the greatest guitar amplifiers of all time, model 5F6-A (1958-1960).
What is it about model 5F6-A—the last in the original tweed Bassman series—that has made it such a prized and copied amp? It and its immediate predecessor, model 5F6, had an added midrange control and four inputs (high gain/low gain “normal” and high gain/low gain “bright”). Certainly it was powerful—four 10” speakers move a lot of air, and a 1959 model could definitely fill a room with its upgraded Jensen® P10Q speakers. Once again, perhaps Wheeler put it best in The Soul of Tone when he noted that:
It was the circuitry of this amp that was copied in London in 1962 by Jim Marshall and Ken Bran as the basis for the first Marshall guitar amplifiers.