WEM made a variety of slave / power amps. The best known power amp was the SL100 which was basically the 100 watt back end of the ER100/PA100 amps. Charlie used these slave amps chained together to form the first big festival PA systems and they could be seen stacked up at the side of the stage producing power in excess of 1000 watts. The design changes around 1977 although it was still basically the same amp but with a different front panel. And then between 1979 – 1981 WEM introduced the Soundman range which included the Soundman 300 power amp. These amps were a complete change from previous designs.