These were part of the standard G12 range from the early 80's to late 90's. They used a 27oz ceramic magnet with a 1.5" voice coil on kapton, were always built in Ipswich, England in the traditional celestion style. 50W RMS power handling, about 95-96dB sensitivity with a nice, fairly neutral balance. Not as bassy or loud as a g12T-75 or vintage 30, a bit brighter and more aggressive than either of those too, but a good all rounder for most styles. Can bet a bit fizzy and bite a little too much with high gain, and aren't as tight and defined in the bass as the classic models. These were a mid range, cost effective but good sounding speaker, and quite widely used.
The full range consisted of the L-35, S-50, T-75, K-85 and H-100. variants of the S-50 were made for many different companies, but usually under their own name.the closest current speaker is the G12E-50/Rocket 50, which has a smaller magnet and is built differently.
Not an all time classic, but certainly a good speaker.