300B for L300 and similar
Probably you will not encounter any problem driving the L300 with an 300B amplifier regarding power and efficiency, but I think that the damping most feedbackless or low-feedback SET amps provide to heavy-weight woofers like the 2231 or 2235 (155 gr.) will not be sufficient.
I noticed that when I tried my variety of amplifiers to drive my 4430. My SET 300B amplifier (Sun-Audio) is really not able to control the 2235 woofer. The result is a boomy bass. I also tried a KT88 (triode) PP amp with low feedback (Cayin 788). This amp already works much better than the SET 300B but a really controlled bass I can only achieve with a SS amp (Hafler 9505).
According to my experience SET amps are great for high- and mid-range. For driving the bass of your L300 I guess you will have to look for another solution.
Best regards,
Norbert