I have an OLD ST-70 that may have been upgraded some by the guy I bought it from. IIRC he said he upgraded the storage caps, and the six orange caps on the input board look newer than everything else there. I rolled in a matched quad of the Svetlana winged C EL34 tubes maybe as much as 10 or more years ago. They still sound fine.
I've always biased them at 1.56V because that's what it says on the test points. A few years ago the amp started blowing fuses, so I set it aside. I dug it back out the other day and haven't had any trouble (yet!) and it sounds fine.
I see here that the VTA ST-70s want to see 0.4V bias. And I think I read that lowering the bias can be advantageous on a stock ST-70 as well. So lately I've been running 1.35 - 1.4V and it sounds great. QUESTION: Should I go lower on the bias? Go back to 1.56V? Or...?
I have a Genelex GL GZ34 arriving any day just because I thought my rectifier tube might be going soft, thus the fuse blowing issue. Maybe it was just me not keeping close enough tabs on the bias, I dunno.
My line voltage varies 122 - 123 VAC.