I also have a 300b amp (Woo Audio WA-5). I did massive research on speakers for 300b amps and came across Tonian Labs TLD-1 speakers. They are no longer available new, but you can look for used ones. I have a pair and they are amazing! They won't sound super for hard rock, but for lighter, quicker music, even orchestra they sound great. They're a little light on the bottom end, but you don't really miss it unless you're listening to music made to highlight low notes (e.g. organ music). Do a google search on them for grins.
Speaker Suggestions for 300b SET Amp
I built an Elekit 8600 300b set amp recently. It's amazing. I maxed out upgrades (all Takman resistors, Mundorf top end caps, solder/wiring, etc.). It's a wonderful amp. It cost me $2k to build it and it's glorious.
My issue hasn't been the amp, but finding speakers that I want to use with it.
I started with Omega XRS 8 Juniors (~$2k). I broke them in for 300 hours and, while they did get better, they largely sounded like the top and bottom ends were just truncated off at both ends the sound spectrum. They sounded more akin to a transistor radio speaker. I feel terrible to say that and I hope others really love them and hear them differently, as the company is great and the owner is wonderful. They just weren't for me.
So, I just paired the 300b up with some inefficient speakers (both KEF LS50s and Wharfedale 80th anniversary Dentons). Both speakers were part of other systems I have. Both sets, and especially the cheaper Wharfedales, just sing with the 300b. They do not play particularly loud given their efficiency ratings, yet they sound wonderful for very close nearfield listening.
But what I'd like to do is go a bit more into the full range speaker category without buying a massive product. Or, I consider a smaller bookshelf/monitor if it were more efficient.
What speakers do folks like with their 300bs?