KT-77S Beam Pentode. This is a direct replacement for an EL34 or E34LS tube. It is a matched duet of two tubes. This tube has a different design than an EL34 tube and a higher vacuum. This tube will have mids and lows that sound somewhat deeper and bigger than most EL34 types. Similar to an EL34 but with the low end authority of many 6L6 types. This tube has a very long service life when compared to most EL34 tube types. This is also a very rugged tube with a wonderful thick glass bottle is is less prone to physical microphonics.