You forgot to write ^2, but you compute it well Rtr = 7,5*(130/117)^2 + 3 = 12,26 Ohms It isn`t "mine", but it is well known formula...you have it elsewere, in some tube rectifiers data, for example. The problem is - only 130V of sec. voltage means max. 130*1,4=182V (probably less in practice) - too low...except by using voltage doubler?! Is it 130-0-130V or just 0-130V secondary? And another thing I didn`t quite understand from your description: "It also has a 6v leg on the pri tied to the 6v leg on the sec with a wire to both ends. On the pri. there is a tab E also." Is it some form of "boost/buck" voltage, or...? Any chance that you can post a picture/diagram or a better description?