The Svetlana 6550 vacuum tube 'S' version is available in matched pairs or quads, dispatched from Hot Rox UK in Nottingham. As a supplier of hard-to-find valves, including Russian valves, we test and match them in-house to ensure quality and consistency for use in HiFi and guitar amplifiers. Our vacuum tubes come with matched specification stickers for the Anode and Transconductance.