I was told that NPN transistors are faster than the PNP equivalents in RF circuits. It is true?
Yes. What occurs is that the charge carriers are faster in N materials (electrons) than in P materials (gaps). Thus, while in an NPN transistor the current must cross two regions N and a P, in the PNP transistors are two regions P and an N, which makes them slower. Thus, an oscillator using a BC548 (NPN) achieves higher frequencies than the same oscillator using the PNP equivalent, BC558.
