SET for 88 dB 4 ohm loadspeaker

88db's not very efficient. Are you married to the SET topology? Have you considered triode tubes wired in PP configuration or pentode tubes wired triode mode? This might be an acceptable compromise for you if your speakers are a constraint.

I had used Antique Sound Labs Explorer monoblocks (about 45 watts SET based on the 805 triode) to good effect with Spendor SP 1/2E's in a small room (156 sq ft). The Spendor's are 88 dB sensitivity. I never ran out of volume with that combo. I play mostly classical including large orchestras at realistic volumes. This amp was given a very positive review by Art Dudley some time ago in Stereophile. A good and relatively inexpensive way to try out SET. Good luck.
Mark

I doubt this is a good idea.

Won't work. You need push/pull tube. Either KT90 or 6550. Just curious, the speakers are they Theils, Vandersteens, Von Schwikert or Tyler?

speakers dali helicon 400