I have a good amount of transistors without any marking or still with marks that I do not know or that I do not find reference in the internet, nor consulting the source of datasheets of the site. How can I know what they are and when to use them?
This is a problem for mainly repair technicians, Many equipment manufacturers order the transistors for their products with a proprietary marking with a code that only they know. To prevent unauthorized repair work ... So, by dismantling old appliances or even by packing up inventory of factory components or finding them in scrap metal, it is difficult to know what they are and how to use them. By size we can know if they are power types or not, but the rest is difficult. The terminals can be identified according to the procedure that will be taught soon in an article in our section "How to Test Components", to know if they are NPN or PNP and to know which is the base, emitter and collector. These transistors can be used in general applications in less critical assemblies such as source circuits, audio oscillators, amplifiers, relay drives, etc.
