I love my SX-28A. Of all the receivers I have, it's one of my favorites overall. Not for being the best performer or the best at anything really, but doing a lot of things really well for a late 30's design. And I can't think of a better looking receiver. Art Deco influences mixed with excellent symmetry.... wonderful soundstage and excellent tessa...ooops!
We're fortunate today to be able to enjoy so many fine receivers that were unreachable for most back in the day. The 75A-4 certainly runs circles around the SX-28 and any other receiver of that era and it should, being nearly 2 decades newer in design. But its audio ain't nothin' to write home about. Why would it be? It was designed as a communications receiver. The SX-28 was as much entertainment receiver as anything.
I cannot hate it. It is one of the most beautiful sets there is, and I have the huge bass-reflex speaker cabinet for it as well. It's always been a wish to have that combo on one side of a comfy chair and a lamp table with some good books on the other.
You'll love it in that service - if you can find anything worth listening to. Mine sat on a marble shelf over a large EV speaker for years in the VT house. There was a station out of western NY that played Big Band classics and swing music before being taken over and turned into a Disney station. The SX-28A would shake the windows. But it needs a good going through, so it was replaced with it's younger cousin, the SX-62B in much the same configuration you mention, Pat. In this case, it sat atop a large Collins lobby speaker until Christmas 2018 when the audio transformer and whatever else went up in smoke. Probably bad caps in the receiver, though I'm not sure the Jensen JHP-15 speaker was the correct impedance for it. Sure sounded great playing the old Christmas tunes, though!
Good luck with yours. It's worth the effort to chase down those few gremlins and get it squared away. So long as you don't expect it to perform like a Yaecomwood sand state rig, you'll never be disappointed. A reasonable warm up period and decent line regulation will go a long way to taking care of drift once you replace any faulty parts.
Would love to find the big R-12 floor speaker for my -28. It
will get rebuilt someday, hopefully sooner than later.