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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 Type I Ei KT90 power tubes in this precision matched pair were made in the former Yugoslavia. They have welded gray plates and dual O getters. Type I KT90 tubes can be used as substitutes for 6550 / KT88 tubes in amps that have enough bias range.
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The Type I Ei KT90 power tubes in this precision matched quad were made in the former Yugoslavia. They have welded gray plates and dual O getters. Type I KT90 tubes can be used as substitutes for 6550 / KT88 tubes in amps that have enough bias range.
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The Type II Ei KT90 power tubes in this precision matched quad were made in the former Yugoslavia. They have welded gray plates and dual O getters. Tubes test as new and are precisely matched for both current draw (mA) and transconductance (Gm).
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The Type II Ei KT90 / KT99A power tubes in this precisely matched octet were made in the former Yugoslavia. They have welded gray plates and dual O getters. Tubes test as new and are matched for both current draw (mA) and transconductance (Gm).
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Price: From $197.00 to $214.00
The late 1970s GE 6550A power tubes in this premium matched pair have gray plates, 3 getters, metal collar bases, and 188-5 factory code (Owensboro, Ky). Tubes test as new and are precisely matched. While supplies last!
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The GE 6550A power tubes in this premium matched quad have welded gray plates, 3 getters, metal collar bases and 188-5 factory code (Owensboro, Ky). Tubes are precisely matched for both current draw (51.0-52.0 mA) and transconductance (96%-100% Gm).
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The SED Winged C 6550C power tubes are made exclusively at the SED SPb factory in St. Petersburg and they bear the "Winged C" logo. Price includes extended burn-in and precision matching.
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The Sovtek 6550WE features thicker plates, improved heat dissipation, higher transconductance, and increased linearity. The result is higher output power, greater headroom, and superior tone. Price includes extended burn-in and precision matching.
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With a plate dissipation of 60 watts, the Tung-Sol KT120 is the most powerful tube in the 6550/KT88/KT90 family. A matched pair in push-pull configuration can deliver 150 watts of power. Price includes extended burn-in and precision matching.
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This new old stock 6550B power tube is the predecessor to the highly regarded current production SED Winged C 6550C tube made in St. Petersburg, Russia. Same great quality at a much lower price! Price includes extended burn-in and precision matching.
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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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