 However, the plate dissipation of the 6L6GC, at 30W, exceeds the KT66's 25W, and adjustment of the amplifier's bias is necessary.M-OV ceased glass vacuum tube manufacturing in 1988; their old audio tube types became valuable collectibles.In 2004 original M-OV KT66 tubes (bearing the official "Genalex" marketing brand that M-OV used outside the UK), unused in original carton, sold for US$250.