I saw this on Primaluna's Facebook page today:Tung-Sol KT170
Due to the success of the KT120 and KT150 tubes and the popularity of these tubes with High-End Audio manufacturers, the Tung-Sol KT170 tube has been developed to provide a beam tetrode with even more power capability. The Tung-Sol KT170 has a power dissipation of 85 watts allowing amplifiers using a pair of these tubes to reach power output levels in excess of 300 watts.
The Tung-Sol KT170 has an original shape glass bulb that was designed specifically to maintain the highest vacuum and dissipate heat when the tube is operated at high power levels. The Tung-Sol KT170 also has an equipotential cathode for increased reliability and to effectively amplify audio frequencies in the output stages of High-End Audio equipment.
The Tung-Sol KT170 is the largest and most powerful tube in the 6550, KT88, KT90, KT120, and KT150 series of audio tubes.