(!!) (recommended Single) 6SU7GTY=6188 Tungsol 1950's rebranded "5691 NATIONAL" in 1980's black ribbed plates "D" getter halo triple mica (2.3/2.5ma)
(!!) (Recommended Single) 6SU7GTY=6188 Tungsol round black plates coated glass NOS 1950's rebranded "5691 National" in 1987 aged 48-hours (1.8/2.1ma)
