Hi,am in the process of upgrading the valves in my stock fender drri and when I took the back off found the 12ax7s were sovtek(definitely upgradeable)the 6v6s were ehx(staying for now)and the rectifier was a ruby tubes one, I couldn't find much info on the ruby but some older posts suggested it was quite good and a mullard gz34 repro/clone,if this is true I would keep this and just upgrade the 12ax7s,cheers
