in the field of bass amps. They also have a line of guitar amplifiers and a remake of the Dan Armstrong guitar and bass. Ampeg holds six U.S. patents under the Ampeg brand name. Amplifiers Ampeg Portaflex In the late-1950s Jess Oliver invented a combo amplifier with a chassis that could be inverted and tucked inside the speaker enclosure to protect the vacuum tubes. This combo bass amp was introduced in 1960 as the Portaflex, and remained a popular choice through the 1960s. Reverberocket In 1961, Ampeg became the first company to incorporate reverberation (reverb) in an amplifier with its Reverberocket, which preceded Fender's Vibroverb amp by nearly two years. Despite Hull's distaste for rock and roll and resistance to distortion, the Reverberocket employed 6V6 -type power tubes which sounded "Fendery" and did break up in a way that rock and roll players could use. Super Valve Technology During the 1960s Ampeg only produced fairly low wattage combo amplifiers. Rock concerts were becoming increasingly large affairs and bigger amplifiers were needed. In 1969, Ampeg's Chief Engineer Bill Hughes designed the Super Valve Technology circuitry for the amplifier of the same name. At , the Ampeg SVT provided 300 watts of RMS power, considerably more than most other bass amplifiers of the era. The high power rating made the SVT a candidate for use in larger venues. The SVT saw widespread use by rock acts in the 1970s and is still considered by many to be the world standard reference bass amp. The SVT-VR (Vintage Reissue) is almost identical in design and construction and the closest thing to any of the original SVT models produced by Ampeg. Recent amplifiers (after 1990s) In the mid-1990s, SLM issued several guitar amplifiers under the Ampeg name. Some of these, the "Diamond Blue Series," used the names of vintage Ampeg models (such as Jet and Reverberocket) and featured the bluish-colored diamond-checkerboard covering associated with Ampeg amps of the 1960s. The circuit designs of these amplifiers, however, were new. The Portaflex bass amp was reissued, with updates intended to make it more appealing to modern bass players. The Ampeg GVT series, introduced around 2010, is a series of tube amplifiers built in South Korea, employing the Baxandall tone circuit. Instruments and accessories Ampeg also manufactured (or had manufactured for them) lines of quirky but distinctive instruments to complement their amplifiers. Baby Bass Baby Bass, introduced around