I went ahead and checked every single one of the G12H30s that had come out of the 73 cab. With a multimeter, and I also did the 9 volt battery trick, just to make sure nothing was actually reverse polarity and just labeled wrong. These speakers check out perfect. I also went ahead and checked the Scumback M75-LDs that I had put in that cab. Not that I had any reason to suspect something was wrong with Jim's speakers...just wanted to be thorough. No surprise, they are absolutely fine as well. The G12H30 cones move a bit more than the Scumbacks, which I suppose is to be expected since they are almost 50 years old. But otherwise, nothing weird with any of my ohm readings, nothing funky going on with polarity.
I hate to say it, but I'm at a loss here. 2 different quads of speakers sounded dreadful in that 73 straight cab. On paper, both quads should have sounded killer, even at mouse fart volumes (and I've been doing loud TV volumes anyway).
I was willing to believe the G12H30s were pummeled into submission. I'm just not willing to believe the Scumbacks are somehow also no good.
I've tried 5 different guitars, and something is weird no matter which one I use.
I've tested my speakers cables, and swapped them around. I've tested and tried 3 different guitar cables.
I've tried a 68 Plexi / Hopkins Pandora, I've tried my Ceriatone King Kong, I've tried the Syn-2 with the SLO module into a Fryette 2502, and I've even tried going right into some pedals, and then into the 2502. And there is something weird about both cabs.
So, that leaves:
• Somehow the wiring is still wrong, even though I followed that diagram from the Scumback site exactly for both cabs
• There is something magically, disastrously wrong with the room acoustics, and it's fighting 4x12s like I've never encountered before, ever
• The 73 cab is cursed, and the 82 G12-65 cab is just super dark and muffled
I'm not really sure at this point which is more likely.
I think my next move here is the big loud testing day I have booked at a rehearsal studio, on the 6th. I'm bringing literally every piece of gear I have, EXCEPT for the two cabs (logistically it would be a nightmare). The room I booked has 2 newer Marshall slant cabs w/ G12T-75s, 2 Mesa 4x12s with V30s, two Fender combo amps, and even a JC-120. I can test all my gear at volumes ranging from mouse fart to RUN AWAY!!!! and see what's what.
After that, maybe I just go ahead and order a 2x12, and before I buy any more speakers, try the Scumbacks in there, and see what I get.