Original pear shaped 6550 tube was introduced by Tung-Sol back in 1955 as an answer to European KT88 tube. Other US manufacturers such as GE and Sylvania followed and produced 6550 tubes also, but with a straight bottle.
All American Tube Sound
6550 tube has been the output tube of choice in high power audio amplifiers in the USA. 6550 tube was found in legendary Ampeg SVT, Harmon-Kardon Citation II, and Audio Research VT200 to name just a few. 6550 tube was even used in imported Marshall JMP amps. 6550 tube represents the all American high output tube sound.