@atmasphere Actually, I have rebuilt a few ST-70. I agree, the rectifier is inadequate, but so is the driver section, which is at clipping at or just before the output section clips. I have heard a couple of drop in boards and the octal version was by far the best. Much better amp with 6sn7 input tube and 6sn7 drivers. Still, the small case keeps you from installing a really nice C-L-C supply built with only film caps rather than lytics. When modded it is a cute little amp, but hardly worth the trouble compared to other designs in my book. I recall another vintage amp or two that used 6GH8 or similar for driver section, probably Scott, but too long ago. Yes, we re-wired the sockets to take more common variants of the triode/pentode combo tubes. They are all nice little amps, but not in the same universe as the topologies we are discussing in this thread. However, would make nice little systems though with good speakers.
I recall a Fisher flagship el34 amp that was really rare that actually sounded quite good when restored as well. So long ago I forget all the model numbers! When I was doing all the vintage work I could probably have rattled off the model...