Complementary vs NPN / NPN

Some time during 1972 - 1977 nearly all amps went from having NPN / NPN output stages (like 2x 2N3055s) to PNP / NPN complementary configuration. I assume this had a lot to do with availability of new, high power PNP transistors (like 2N2955) but what are the benefits of this newer set up? I presume Popular Electronics and similar magazines ran articles on this subject but I have been unable to find any.

I will appreciate any insight on this matter!


2007-09-21 6:28 am
When PNP devices with characteristics similar to NPN power devices became available, it was possible to build complementary symmetry push-pull output stages - both the devices could be operated as emitter-followers in Class-B (the most common topology) or both could be operated common-emitter with drivers of the opposite polarity (CFP/Sziklai). In either case, symmetric operation helped to bring certain kinds of distortion under control, and also simplified the driver stage topology in certain cases.