Dating a twin
The exact plight of the Twin-Amp during the months between January and May 1960, however, remains open to considerable speculation, debate and study.The prevailing explanation is that production was temporarily interrupted during these months as they coincide with the debut of Fender's new "flagship" or top of the line amplifier, the Fender Vibrasonic-Amp. kept the image of the Twin-Amp before potential consumers during this short period.The brown one still had the harmonic tremolo and early Vibroverb reverb circuitry with an extra tube and rear dwell control.The blonde Twin Reverb Leo gave to steel player Red Rhodes for testing purposes at the famous Palomino Club (North Hollywood).By 1961, the Bandmaster, the Bassman and the newly debuted Showman were all covered in the new look exemplified by the late 1960 Twin-Amp: blonde tolex and maroon or "oxblood" grille cloth.The Twin-Amp of this period (late 1960–1963) was manufactured with a variety of speakers including Jensen, Oxford and JBL designs.It was modified in 1957 for more volume, switching to four 5881 power tubes with the more efficient long-tailed pair phase inverter for a power increase to 80W.This "hi-powered," tweed-covered design continued into early 1960, after the other Professional Series of Fender amplifiers had made the transition to the modern brownface design.
After a slight change in appearance, from the rough blonde tolex and maroon grille appearance to a smooth blonde tolex with a gold grille cloth, the Twin-Amp was replaced with the Twin Reverb-Amp in 1963.
During the blackface era of Fender amplifiers from 1963 to 1967, the amps had black faceplates, black tolex covering on the cabinet, and neutral to slightly amber tinted silver sparkle grill cloth with a small ribbed rectangular pattern.
The Twin now had an onboard spring reverb tank and was renamed the Twin Reverb.
The upgraded 5F8 Twin-amp of 1957 with its complement of four military grade 5881's was briefly rectified with a tall mercury vapor 83 tube and special tube socket.
Due to its volatile nature if broken, it was quickly superseded with a GZ34 rectifier but not duly noted on the tube chart until the second production.
Like its predecessors, the narrow panel tweed Fender amplifiers used Jensen Alnico V Concert Series Speakers, for the most part.