Ruby is not a brand of tube. It is a marketer's logo.....just as GT is not a manufacturer but a 'brander'. I have good experiences with JJ's. The Ruby EL-84CZ is a JJ tube. The Cz is the indicator of the manufacturer. GT uses 'S' for JJ tubes, iirc.....R for Russian, C for Chinese???? I don't pay for screened logos.