Vintage Pioneer SX 550 receiver after full restoration - Pioneer SX-550 is one of the smaller receivers produced by Pioneer. It is the successor of the SX-535 and produces as much as 20 watts per channel. It was introduced in 1977 and was discontinued in 1977. It features the standard styling of the late 1970s Pioneer SX line with a silver dial and faceted knobs. It had wooden side panels, but the top panel was metal. In the beginning, its list price was almost $250, but dropped to around $200.00 in 1977. This made the SX-550 very affordable for someone on an audio budget.