Electus Distribution has published a short article on how to choose a substitute transistor. According to the article, you need to consider the application and the transistor’s basic characteristics, including:
- whether it’s germanium (Ge) or silicon (Si);
- NPN or PNP;
- high power or low power;
- designed for linear amplification or switching; and
- low noise or not.
Also, note its main performance parameters, including:
- voltage breakdown rating (usually Vcemax or BVceo);
- current gain (beta or hFE) at the likely collector current; and
- upper frequency limit (fT or Fmax).