I'm going to get around to doing a passive transformer M-S matrix someday (schematics at Jensen Transformers).
The V72 interested me as an easier project than the V76, and I believe Chris had mentioned at the old place that it shouldn't be too hard to do a modern version with the more available EF-86 pentodes. (Are the transfomers 1:20 and 20:1 on that one? Likely candidates?) I wonder how they'd sound as the makeup gain to a Pultec or other passive eq . . .
On the Helios, I'd want to build the whole channel. Well, 16 of them, with a couple mix buses and some ADR 760's. (Anyone got a picture of Mike Tholen's console handy to get me drooling?) The pre is supposed to be a chunk of the beauty there, so I wouldn't want to stop at just the eq, and besides, they were using Beyer transformers - that should still be available, right?
Bear