I picked up one of these TS-4Js a while ago that had been converted entirely to filament transformers. But the wiring of it was a bad mess, which I eventually sorted out, I got it to work with the transformers, but never that well, although I don't recall ac coupling being a problem. Here's a pic of where the transformers were mounted:
http://www.audiokarma.org/forums/att...8&d=1134020896
I have since picked up 1 empty suitcase cabinet, and 2 other TS-4Js, both in cabinets that need work, 1 with a good 7JP4 and a complete original chassis, which I plan to restore and put in the suitcase cabinet. And 1 with a bright 7JP4 which arcs in the base, and is missing the flyback, but otherwise has an unmodified chassis, I was going to part out the chassis modified for filament transformers to restore this one, and put it in the already refinished cabinet the modified chassis came in. I also have that 7JP4 that originally came in that modifed set that me and jpdylon rejuvinated yesterday on his beltron, which I'll use in that set, if I can't fix the arcing in the other tube.
I was just planning on replacing the ballast tubes with resistors on both chassis, using that method I saw posted here before mounting them on a piece of metal atop the chassis. I would think you would have to add an extra dropping resistor to replace the 7JP4 in the filament string, have you figured out what value yet? If using a transformer for just the 7JP4 works well, I might try it on my sets when I get to restoring them.