(!!!) (Recommended Pair) 311B Amperex made in Russia NOS 1977 (37.2ma and 38.5ma) (Highest mA and Gm)

1 pair) 311B Amperex made in Russia NOS 1977 large getters

1 tube) 37.2mA Gm=3100 3/16″” taller

1 tube) 38.5mA Gm=3200

Tested on Amplitrex

Vplate=180V

Vscreen=135V

Vgrid=-15V

Good Ma = 30ma

Good Gm = 2900