These are the sockets for the 3-400, 3-500Z tubes. Ceramic. need a pair. Lane Ku7i San Diegto 92139 -- FAQ on WWW: http://www.contesting.com/ampsfaq.html Submissions: amps@contesting.com Administrative requests: amps-REQUEST@contesting.com Problems: owner-amps@contesting.com Search: http://www.contesting.com/km9p/search.htm