Riverstone Audio Matched Pair (2 Tubes) 6N3 Vacuum Tubes Fully-Tested Matched Pair (2 PCS) 6N3 Vacuum Tubes Direct Replacement for 6N3 vacuum tube Used in headphone amps & other preamplifiers and amplifiers Mil. Spec. Tubes - Higher Durability and Life Each tube carefully checked for shorts and gas, and matched for Gm within 250 micro-mho.