The BC107, BC108 and BC109 are general purpose low power Silicon NPN bipolar junction transistors found very often in equipment and electronics books/articles from Europe, Australia and other countries.
Vahid alpha at English Wikipedia / CC BY
These transistors were created by Philips and Mullard in 1963 and introduced in April 1966. Initially in metal (TO-18) packages, the range expanded over time to include other package types, higher voltage ratings, and a better selection of gain (hFE and hfe) groupings, as well as complementary PNP types. Some manufacturers have specified their parts with a higher power dissipation rating (Ptot) than others.
The BC548 is an example of the modern low-cost member of this family, still in a through-hole package, while the BC848 is the Surface-mount version.
The BC108 was, for the 1970s constructor, one of the most popular transistors in the UK and the rest of Europe.1 One of the reasons for this was the fact that most of the electronics magazines of the day described circuits with these transistors included. It is interesting to not that while the BC108 family of transistors were used in offerings by magazines and kit manufacturers - there were many other alternatives available at that time.
The prime directive dictates the absolute necessity to at least mention the BC108 and a little of its historical importance. ↩