 Today, the famous 5F8 series Fender Twin amps with their warmth of tone and rich rock & roll harmonic edge, command the highest price of any Fender amp ever built.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.