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6550 / KT88 / KT90 / KT120 tubes
The most common types of 6550 tubes and their European equivalents used today include:
6550 - Tung-Sol developed the first 6550 tube in 1955. The design was based on the 6L6GC tube with higher power ratings, and featured a coke bottle shaped envelope like the European KT66 tubes. GE and Sylvania later developed uprated 6550A tubes with straight-sided glass. The 6550 can be used interchangeably with its European rival, the KT88.
KT88 - Marconi-Osram Valve Co. introduced the KT88 in 1957, and its Genalex Gold Lion KT88 became known as "King of Power Tubes." The KT88 is a larger version of the KT66 that features higher power and very low distortion. The KT88 can be used interchangeably with its American rival, the 6550.
KT120 - In the spirit of Tung-Sol’s creation of the 5881 and 6550 power tubes, New Sensor Corporation released the KT120 under its Tung-Sol label in 2010. With a plate dissipation of 60 watts, the Tung-Sol KT120 is the most powerful tube in the 6550/KT88/KT90 family. Please see our notes about substituting KT120 tubes for 6550 and KT88 tubes.
Comparison of design maximum values for 6550 tube types (pentode connection)
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6550 |
KT88 |
KT120 |
| Max. Plate Dissipation |
42 Watts |
42 Watts |
60 Watts |
| Max. Plate Voltage |
660 Volts |
800 Volts |
850 Volts |
| Max. Screen Voltage |
440 Volts |
600 Volts |
650 Volts |
6550 / KT88 / KT120 tubes in stock now
Scroll down to browse our current selection of vintage 6550 tubes and burned in, tested, and precision matched new production 6550 power tubes. Click "more info" for pricing, availability, and matching options.
The 1987 Gold Aero 6550A tubes in this precisely matched quad have coke bottle shaped glass, black plates with extra support rods, and metal collar bases. Click "more info" for test results.
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The Svetlana / SED 6550C tubes in this matched octet (8) were made in St. Petersburg, Russia in 2008. The etched print on the glass has the Svetlana logo and OTK factory mark. All eight tubes are matched for current draw (47.0 mA) and Gm (6400 = 100%).
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The Valve Art 6550A tubes in this matched pair have top and side getters with lots of flashing, with a similar look as the vintage GE 6550A tubes. The gold print on the glass has the Valve Art logo and reads "6550A O & J CHINA."
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TC Tubes specializes in precision testing and matching of vintage and new production vacuum tubes for guitar & bass players, audiophiles, and DIY tube audio enthusiasts. Our website features secure payment options and fast, convenient shipping around the world.
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