(!!!!) (Good Value Pair) 6X4 SER = LM Ericsson Sweden "D" getter NOS 1950's 1-2% matched - slightly faded top getters (54-55/40 x 2 tubes)1 pair) 6X4 SER = LM Ericsson Sweden NOS "D" getter 1950's 1% matched in white boxes slightly faded top getters 1 tube) 54 40 and 55 40 1 tube) 54 40 and 55 40 Aktiebolaget Svenska Elektronror = Limited Company Swedish Electron Tubes Recommended for Audio Note DAC 1. 2 LAMM LP2 phono KONDO KSL M7 preamp Kondo M77 preamp Eastern Electric Minimax Phono Pultec EQ Wright WPP200C Audio Note M7