@BillT - I’m surprised I’m the first person responding to you on this, and I just responded to your vinyl setup post.
If you’re looking at 300B SET, chances are the power is somewhere between 8-10w/ch. While the thought of a speaker 92db might work, it will depend on the size of the room you are placing it in. Generally, I would think to pair the 300B amp with a speaker that has an enclosure or horn system that can extend to the low frequencies. This requires a rather large woofer, large cabinet, or large horn. Though the speakers are efficient, it needs the right air and reflex to get the best response. Case in point, I’ve used a few 300B SETs on a few speakers - Zu Soul Superfly, Lii Audio Crystal 10 in open baffles, and Quad 2805 (yes I’m serious) and while the gain wasn’t high enough for the Quad, they sounded best with them. Both the Zu and Lii are ~100db efficient, but the bass and mid bass were lacking as the cabinets were not sufficient enough to support.
The preamp matters a whole lot, too, in this case. You’ll want as good of a preamp as you would have in the quality of the 300B amp, if not better, and low watt amps tend to have preferences for preamps that have medium level gain.
Should you have gone this route and need thoughts on 300B tubes, I can do so - but that’s a whole different thread.