2sc2291 Matched PNP long tailed pair 2sc1583 Matched NPN long tailed pair Many of the late 1970s Rolands. Both famously used on the TB303's filter. The 1583 was also used in Korg MS series too. Both parts are excellent, but have unfortunately fallen from the production line. Tony www.oakleysound.com Oakley Sound Systems Penrith, Cumbria, England