They seem to be ARC's tube of choice right now, so you are not the only one who likes them. But , that said, as I mentioned before they have much higher current requirements in terms of both output and operating currents (bias and filament) so even though they are pin compatible with other EL34/KT-88 tubes, there are not a lot a amps that can use them as a plug in replacement for the tubes they came out of the factory with.