Thanks for all the replies. Yes, they are indeed different shapes, that's what I noticed right off the bat. It is the first model, but I've never heard of it having auto bias, you sure about that? I know the YBA 300 has autobias, with tons of glowing light on the back panel. Oh well, I'm probably gonna retube it sooner or later. One pair is TungSol, so I might use those to replace the stock tubes in my EBS Classic T90 head before selling it (if they still have juice in them). Ooor would someone advice against that?