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Tung-Sol was founded as Tung-Sol Lamp Works Inc. in Newark, New Jersey in 1907. Their early products were mainly geared towards the automotive market and included headlamps, pilot lights, and flash-light bulbs.
The trade name was formed from the first syllable of 'tungsten' and the Latin word 'sol' meaning sun.
The company entered the electronics field in the 1920s. In time they established themselves as leaders in the development and production of vacuum tubes, with their main competition including RCA and Sylvania.
By 1951, they began doing business as Tung-Sol Electric Inc. Soon after, they were acquired by Wagner Electric, which itself merged into Studebaker-Worthington in 1967.
Tung-Sol was privately held and run like a laboratory. This gave Tung-Sol valves a reputation of having some of the best metallurgy and chemistry in actual production.
The Tung-Sol brand name is now (2020) owned by the New Sensor Corporation, the same company that owns the brands Sovtek and Electro-Harmonix.
Introduced by Tung-Sol in 1954 for application as an audio frequency power amplifier was the beam tetrode 6550. It was based on the 6L6, the 6550 was designed to have higher output power and better stability. It operates with a maximum anode voltage of 600 VDC, a screen voltage of 400 VDC, and anode dissipation of 35 Watts. The KT88, KT90, and 6550, although not identical, are often interchangeable, dependent on external circuit parameters. The 6550's glass envelope was originally wider in the middle than at the top and bottom, but a straight-sided design was later introduced by General Electric and Philips.
Reference: Wikipedia.
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