with a single 12" speaker and a rear ventilation port. In 1951, Ampeg introduced a 20-watt version with a 15-inch speaker. In 1960, they introduced the B-15 Portaflex, a flip-top 25-watt tube bass amplifier with a single 15" speaker. While the Portaflex had a pleasing bass tone, and was used by studio bassists such as James Jamerson and Carol Kaye, it was not powerful enough to be used in a stadium or arena concert. Ampeg amplifiers were widely used by electric bass guitarists in the 1950s and 1960s. Leo Fender resurrected the solid-body "bass guitar" in 1950 with the Fender Precision bass. Unlike the upright bass, a solid-body electric bass does not produce acoustic sound from a hollow body; while an upright bass player often benefits from using a bass amp, a bass amp is a necessity for an electric bass player. By the late 1960s, as electric guitarists in rock bands began using powerful amplifiers to play large venues, bassists needed to keep up. The Acoustic 360 was a "200-watt, solid state head designed to drive the 361 cabinet, a rear-firing 18” speaker enclosure". The engineers who designed the amp and cabinet in 1967, Harvey Gerst and Russ Allee, mounted the 18" speaker in a folded horn enclosure; the 360 amp had a built-in fuzz bass effects unit. The Acoustic 360 and its 361 cabinet "...got the bass world ready for the Woodstocks, Altamonts and giant festival concerts" and it was used by notable players such as funk bassist Larry Graham, Led Zeppelin's bassist John Paul Jones and jazz fusion player Jaco Pastorius. John Paul Jones used two of the amp/cabs in Led Zeppelin; Dave Brown used them with Santana; John McVie played with the amp/cab in the beginning years of Fleetwood Mac. In December 1967, the loud sound of the Acoustic 360 led to The Doors getting "...arrested for noise violations". Another 1960s-era amp and speaker that was used for loud, large venue performances was the Ampeg SVT (Super Vacuum Tube), a 300-watt amplifier head "powered by fourteen [vacuum] tubes" designed to be used with an 8x10" speaker cabinet. The Vox T-60/AC-100 bass amplifier uses two 15-inch cabinets and thirty-to-forty watts of solid-state power using "germanium transistors". The Sunn Model T was used by The Moody Blues, Kiss, Queen, The Who's John Entwistle and Rush's Geddy Lee. The Sunn used a 150-watt amp with "four 12AX7WA tubes, followed