6SN7's a dual triode vacuum tube, on an 8 pin octal base. Although the 6S-- series tubes are often metal cased, the 6SN7's generally found only in a glass GT size envelope. The 6SN7's basically two 6J5 triodes in one glass envelope. History Originally released in 1939 it was officially registered in 1941 as the glass-cased 6SN7GT. During World War II a 6SN7A was developed as a slightly improved version, then also a more rugged 6SN7W for military use. With the advent of television the 6SN7 was… (More on 6sn7)