The history of the Fender Twin Amp stretches all the way back to 1952 when it was first released. The model has received numerous circuit and cosmetic changes over the years. For example, the early amps were covered in tweed "airline linen" cloth that was similar to what was commonly found on luggage in that era, while later amps use a vinyl covering called Tolex. Electronically, the earlier Twins were much simpler than the revised models that would follow, with two 12" Alnico speakers and a dual 6L6 power tube configuration that put out only 25 watts -- which was considered quite powerful in its day, although it is only a fraction of what later Twin models would be capable of generating. By 1957, the Twin Amp was using the 5E8A circuit, and the power amp section had been beefed up and was putting out 40 watts. It also used a relatively rare dual rectifier design and two 5U4 rectifier tubes. This unusual arrangement resulted in lower power amp "sag" or compression on hard note transients than the previous "tweed" Twins had.
In 1960, the design was changed, and the amp, which had its power increased to 80 watts in 1958, received the new "blonde" cosmetics, with a rough textured blonde vinyl Tolex covering and oxblood (dark maroon) grille cloth. These Twins were so high powered for their time that the speakers of the era generally couldn't hold up when the amp was turned up loud on a regular basis. Various speakers were tried, including models from JBL, Jensen and Oxford. Within a few years, speaker performance and power handling capabilities increased enough to make this a non-issue, but finding an all-original amp with stock speakers from this era is fairly rare today.
By 1965, the Fender Twin had reverb and "vibrato" added to the amp. The "vibrato" was actually misnamed -- instead of producing pitch fluctuation like a true vibrato, the effect can be more accurately described as tremolo, which is cyclic volume fluctuation. The power level of the 1965 Twin Reverb Amp was also increased and it was rated at 85 watts. The cosmetics were well into the "blackface" era by this point, with a black control panel, black vinyl Tolex covering and a silver sparkle grille cloth. Later Twins used "silverface" front panels, and added master volume controls and increased output to 100W and beyond. Prized for their exceptional clean tones, Fender Twin amplifiers have been used for practically every musical genre. Their ability to get very loud and yet stay clean is legendary. They are also known as being very "pedal-friendly" amplifiers, and many players use distortion and overdrive stomp boxes with Twins for when they want to play dirty, and switch them off and let the Twin do what it does best for their clean tones.