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The 6550 is the output tube used in Leslie model 122, 147 and various other amplifiers. (Actually, they're used in pairs.)

For pictures of the guts of one, see

The 6550 tube was developed by Tung-Sol Electric, Inc. as a high-output audio tube in the mid-1950's. 6550's might be found in Leslie amps with the Leslie private-label brand applied but they can be identified as Tung Sols by the EIA (Electronic Industries Association) manufacturer's code "322." NewOldStock ("NOS") Tung-Sol 6550s are widely sought-after and command high prices.

A variant of the tube, the 6550A, was developed by G-E. The G-E tubes can be differentiated from the Tung Sol tubes by shape: The G-E tubes have a straight-sided glass envelope; Tung-Sols have the cooler-looking "shouldered" or "Coke-bottle" envelope.

6550 tubes are no longer manufactured in the US, but are still being produced in Russian factories.

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