The electrical characteristics of the two transistors are the same, however, by its casing, the metal 2N3055 has a slightly greater ability to dissipate heat. Thus, an assembly in which the transistor will work at the limit, the metallic type is also as indicated. Also note that there are 2N3055 in lightweight aluminum housings and heavy metal casing. Heavy envelope are better because dissipate more heat as well. In an application such as power supplies, the metal are the most recommended.
