Speaker for 300b amp?

PS this amplifier also works nicely with my Klipsch heresy ones.

DeVore Fidelity O96’s and 300 Bs are a wonderful match .

I'd suggest Zu speakers as well.  Pretty efficient, but maybe not as efficient as their specs indicate.  I have one of those high watt resistors across the speaker terminals to tame the impedance down to ~8 ohms.  The 8 wpc of my 300B amp is plenty of power for my Soul Supremes.  Never any breakup or saturation distortion.

Second vote for Charney Audio.  I have the Maestro II with AER-BD3 drivers and they match well with my 300b Tube Audio Lab amp. A little pricey though. I’ve rolled Sophia and Western Electric tubes and there is a difference.

I have a 300 B Audio Note amp (Meishu Tonmeister Silver) that sounds amazing with both Audio Note AN-E speakers and Pure Audio Project Duet 15 speakers.  Both speakers have high 90s sensitivity.  You need sensitive speakers for 300b amp.