Throughout his career Stevie Ray Vaughan used a myriad of different amps, often in different configurations with each other. His primary amps were Marshalls and Fenders, though he also used Mesa Boogies and Dumbles.
Vaughan's on-stage amplification differed from his studio set-up. Early in his career, Vaughan used a Marshall 4140 Club & Country with JBL speakers for his clean tone, and two 1964 Fender Vibroverbs for distortion when performing. He eventually traded the Club & Country in and began using Fender Super Reverbs, 200-watt Marshall Plexis and Majors, and a Howard Dumble Steel String Singer.
In the studio, Vaughan's amp use became even more intricate. Still relying on Super Reverbs, Vibroverbs and Dumbles, Vaughan incorporated Marshall and Fender Bassman bass amps, with 4x15 "refrigerator" cabinets. During the 1989 recording for In Step, Stevie Ray Vaughan and Double Trouble's final studio album, Vaughan became infatuated with a variety of amps, filling the band's rehearsal and studio spaces with 32 models.
Much like his guitars, Stevie Ray's amplifiers were often modified. Noted "amp doctor" Cesar Diaz met Vaughan in 1979 and worked as his amp technician for most of the guitarist's career. Diaz often swapped out transformers, filter caps and tubes, and occasionally reset the amp dials. Vaughan had a superstitious attraction to the number six and would set his amps to this level. Diaz would unscrew the amps and scale the knobs back so they would read six while actually at ten.
Vaughan typically played his amps in conjunction using splitter boxes. His unusual combinations matched with Diaz's modifications make emulating SRV's tone a challenge for the average guitar player, but a Super Reverb and Vibroverb split will get you closest.