Simms-Watts was a British amplifier brand founded in 1968 by David Simms and Richard Watts. David Simms ran a music shop in Ealing where Richard Watts also worked as technical director. Terry Marshall (son of Jim Marshall) also joined Simms-Watts in 1968. Simms-Watts launched a range of high quality instrument and PA amplifiers in 1969 and these were used by the likes of Mick Ronson and John Entwistle. In 1972 the company was bought by EMI Sound and Vision and produced amplifiers for a few more years during the 1970s - moving to solid state circuits to save production costs.

Source: Voodoo Guitar -  Oddball British Hi-Fi: Sound City & Simms-Watts Amps  (15 September 2020)