They're Svetlana Russian tubes - I found them to be a bit more "open" than the STR-420's and STR-430's. I liked them alot, and depending on how much they are, you might want to try them out!
They are the real deal Svetlana. The ones that are called SED =C= presently. They are made by Sveltlana in St Petersberg, Russia. Not the ones made by New Sensor (Sovtek). It's too bad Mesa no longer offers the STR-454 (as well as the STR-442 EL34 which was also made by SED). They are great sounding, long lasting power tubes.
I went from STR430's to 440's and finally STR454's in my MKIII. They sound awesome. I finally have lost the temptation to experiment with other power tubes I like them so much. I certainly recommend trying them out. I got three pairs of them off ebay for $66. Don't know if that's a good price or not. But I like them alot so it's worth it for me. Hope this helps.
