6DN7 RCA Mexco coin-base same internals as Sylvania NOS 1970's (40ma and 8.5ma)1 tube) 6DN7 RCA Mexco coin base same internals as Sylvania NOS 1970's 40ma Gm=12,500 8. 5ma Gm=2600 Tested on Amplitrex 1 section) Good NOS Ma=35 40ma and Gm=7000 7700 1 section) Good NOS Ma=8ma and Gm=2500 Bottlehead S. E. X. amp (Headphone amp) Bottlehead SMACK CONN organ console amp 1970's 2 channel MFA Luminence preamp 1990