The 6550 is a high power tetrodevacuum tube used mainly as an audio power amlifier. It was developed byTung-Sol in 1955[citation needed], originally for use as a servo amplifier. It came to be used in audio equipment before semiconductor power amplifiers came into use, and continues in production and is often used in valve-driven bass amplifiers because it does not distort even at extreme volume levels and is considered to have a very crisp low and high end sound[citation needed]. In particular it is used in Marshall and Ampegguitar amplifiers and the Leslie speaker.
The 6550 was based on the 6L6 vacuum tube and was designed to have higher output power and better stability. It operated with a plate voltage of 600VDC, a screen voltage of 400VDC, and plate dissipation of 35 watts.[1] The KT88, KT90, and 6550, although not identical, are interchangeable. The 6550 was originally wider in the middle than at the top and bottom, but a straight-sided design was later introduced by GE and Phillips.[2]
