In 1946 Clarence Leo Fender began building guitar amplifiers in Fullerton, California. He first targeted country players, and spenta lot of time in consultation with musicians to improve his designs. He initially trained as an electrical engineer, and was never much of a musician, so this process of consultation was his main guide through the years to development of his designs. As we shall see, it often lead to truly significant improvements to amplifier design, although it occasionally lead him down the wrong path. All of Leo's designs were based on the research developed and released to the public domain by Western Electric in the 30s, and used vacuum tubes for amplification. A much more detailed description of the individual amplifiers is available atThe Fender Amp Field Guide.

After a few prototype amps, he began building his first big series of amplifiers in 1948. These were known as tweed amps because they were covered in the same kind of cloth used for luggage at the time. These amps varied in output from 3 watts (the Champion or Champ) to 75 watts (the high power Tweed Twin). They were characterized by a warm clean tone-with more harmonic complexity than the input signal, and a gradual onset of a sweet to raunchy distorted tone. They introduced Fender's first use of Tremolo-a rhythmic variation in the volume of the amp. This is often mislabelled Vibrato by Fender.

In the interests of more clean headroom (volume before distortion) to please his country players, Fender moved to the brown and blond amps in 1960. These were named for their harder plastic covering (DuPont Tolex) colored off-white, pinkish or darker brown. There is often a lot of overlap between series of amps. You'll see brown amps with tweed internals and tweed amps with some of the innovations that went into brown amps. These amps were higher powered than their tweed counterparts. In general, they have a cleaner clean tone with slightly less harmonic complexity, and a similar overdrive tone. To achieve more volume, Fender also started using JBL speakers at this point-much more efficient and louder than the original Jensens. JBLs were usually available on most higher-powered models on custom order. Fender also began using Oxford, Utah and CTS speakers interchangeably with the Jensens; generally the speaker that could be supplied most economically would be used. Jensens and Oxfords remained the most common during this period by far, however. The Jensens offer a more traditional Fender sound and are preferred by most collectors. The Brown/Blond amps also introduced an effect sometimes known as "harmonic vibrato," a phase-shifting tremolo system that required two and one half 12AX7/7025 tubes but had a sweet swirl that has been imitated but not improved on in 40 years. Much of this tremolo's character results from the fact that it separates the low and high frequencies and applies the tremolo effect to each separately and out of phase.

By 1963 Fender wanted more power, less distortion and less cost, so the amps changed to what is commonly known as "blackface" cosmetics. These amplifiers had a black Tolex covering, silver grille cloth, and black forward-facing control panel. By reducing the amount of midrange frequencies in the signal, Fender was able to increase volume without increasing distortion. This resulted in the classic Fender "sparkle"-a bright clean tone most beloved by Fender's favorite country players. The blackface era also brought the widespread use of reverb, which uses springs to bring a sense of space (or in the case of surf music, a crashing wash of echos) to the sound. The tremolo was changed to a simpler circuit based on an optical coupler and requiring only one tube. The amps still spanned the spectrum from 4 watts to 85, but the difference in volume was even larger due to the improved clean tone of the 85w Twin. One of these, with JBL speakers, can be absolutely deafening, even in a big room.

In 1965 Fender was tired and ill, he sold the Fender musical company to CBS. As a large conglomerate, their management seemed more interested in making money than in making the best amplifiers money could buy, so over the next 18 years the quality of Fender amplifiers gradually went downhill. These are the Silverface Fenders, and can vary from almost identical to the Blackface version (prior to 69) to completely different (in the late 70s). Some of the "innovations" that were tried include pull knobs for increased volume, master volume controls, ultralinear transformers for more clean output, increased power outputs-to 100 watts for the twin and 135 watts for the Bassman 135, the Super Six Reverb and the Quad Reverb, and other circuit changes to reduce distortion. The cosmetics of these amps are similar to the blackface amplifiers, but the forward facing control panel is silver with blue block lettering instead of black with white script lettering.

In the early 80s, under the supervision of Paul Rivera and others, there was a resurgence in R&D at Fender, resulting in a short run of very desirable amps. These range from the two channel Superchamp, putting out 18w, through a channel switching version of the Twin. They are the last amps Fender made in which discrete components were connected by point to point wiring, a method now replaced by use of printed circuit boards.

After this brief period, Fender began building amps similar names to the older versions, but without a lot in common. They are not of much interest to vintage amp lovers, although there are certainly still people playing with 80s model Fenders, particularly the "red knob Twin" of 1987 onwards. In the early 90s Fender reissued some of its most beloved amps-the Twin, the Deluxe Reverb and the Super Reverb-these tended to sound brighter than the originals but have met with some success. More recently, they've come out with Fender Custom Shop handwired amps which more closely match the tweed and blackface amps for their sound and specifications.