Even if you can't get by on 1.5 watts, you might find the Transcendent 300B single ended OTL interesting.
http://transcendentsound.com/Tubes_and_Circuits_by_Bruce_Rozenblit.htmlI heard a pair of these monoblocks at a DIY meet in England earlier this year. Even though they struggled in a large unforgiving room, their treble was amazing. The filaments are heated by a DC supply developed by this UK group that they reckon sound better than the Rod Coleman boards. You can read more about the amps at
http://tubehifi.websitetoolbox.com/post/300b-otl-with-dc-7525758Within this Transcendent forum, ray p is the buider of the amps I heard. He also gave me a ride to the meet and it was fun to talk to him about the hobby. He uses Lowther drivers.
For more about the meet and plenty of my photos, take a look at
http://ratbagp.blogspot.com/2017/06/owston-visit-to-diy-audio-land.htmlray