Mike Matthews of New Sensor has just announced that they will soon be carrying the new Tungsol KT120 tube. The tube is not as yet on their web site but a description of the tube sent to me by New Sensor is below. This tube is plug compatible with a KT88 or 6550 tube. They released some dealer prices to me but figure a retail price in the $45 price range per tube. (Retail prices are now posted on the New Sensor web site with a mid May delivery date)
"March 25, 2010
In September of 1950 Tung-Sol introduced the 5881, an uprated and industrial version of the 6L6GA with a 23.5 watt plate dissipation, opening the doors to the hi-fi movement of the 1950s. This rugged tube also found a home in the '59 Fender Bassman and servo amplifiers used in B-52 bombers. In 1955 Tung-Sol raised the bar of high fidelity with the introduction of the 35 watt 6550, which could deliver 100 watts with a pair in push-pull configuration. This tube was used in the Dynaco Mark III and Sunn amplifers.
New Sensor now announces the Tung-Sol KT120, which has a plate dissipation of 60 watts, making it the most powerful tube in the 6550/KT88/KT90 family. A pair of these tubes in push-pull configuration can deliver power levels of 150 or more watts. When used at the parameters found in existing 6550/KT88/KT90 circuits, the Tung-Sol KT120 is impervious to overload, delivering peak power with extreme reliability and long tube life. However, taking advantage of the higher current handling capacity of these tubes, a very unique and super powerful and stable amp can be designed using the Tung-Sol KT-120."
This tube should work fine in any Dynaco Mark III or VTA ST-120. It could also be used with any Dynaco ST-70 or Mark IV as long as you have an upgraded power transformer.
Specifications for this tube > http://www.newsensor.com/releases/KT120TungSol.pdf
Curves for this tube > http://www.newsensor.com/releases/KT120TungSol-Curves.pdf
Last edited by Bob Latino on Tue Nov 27, 2012 6:36 pm; edited 3 times in total