Yamaha Merken Yamaha Srx 6 reduced effect Yamaha Srx 6 reduced effect generaties Yamaha Srx 6 reduced effect 1987 Yamaha Srx 6 reduced effect 1988 Yamaha Srx 6 reduced effect 1989 Yamaha Srx 6 reduced effect 1990 Yamaha Srx 6 reduced effect 1998