Transistor Substitution

Ethan Dicks schrieb: Older transistors were generally put into a metal, and sometimes into a ceramic package, case for manufacturing reasons and better thermal distribution. Even earlier transistor cases were made of glass, painted black (you can make good photo transistors from old OCxxx devices when scratching the black paint away). Plastic packages came up around late 60s when industry found materials with both good insulation and good thermal conduction. Nowadays, putting a semiconductor chip into a casted plastic case for low power and low frequencies is mainly a factor of production costs, so if power dissipation permits there is no longer a reason to prefer a metal case over a plastic one. Same holds for old eight-legged opamp ICs which came in a round metal case. For a few high frequency applications, though, the metal case makes a Faraday cage which is connected to ground then. And still, if a lot of power has to be carried away, the thermal resistance is lower for metal obivously. For the work horses 2N2222 and 2N3904, this is no real argument though, the 2N3055 with its 15A maximum Ic there are pretty many Watts to be distributed. -- Holger