The NOS tubes are about twice the price, still about the third of NOS Mullards though. I'm using the SEDs now in my Guytron (4xEL34), and I'm wondering if the Siemens are worth the extra $$. The thing about the Guytron is most of the OD comes from the EL84s in the first stage, so it mostly a question of the clean sound of these NOS tubes. Noticeably better then the Winged Cs? Anyone have any opinions? Also the amp is run at least an avereage of four hours a day, so tube life is an issue too. Thanks in advance.