low power tube amp

It's a serious problem, don't do it. A good chance you will damage the speakers when you clip the amp. If you absolutely love the speakers, then get a more powerful amp, but I'd suggest finding speakers that are made to mate with your lower powered amp. Cheers,
Spencer

A tube amp will clip "softly" by rounding off the wave, as opposed to the much more dangerous hard clipping produced by a transistor amp that's pushed too hard.  My speakers are recommended for 150-800W, and I've driven them for years with a 38-watt tube amp.  If I can remember not to be greedy by chasing slam and impact by turning up the volume knob, I'm rewarded with stellar imaging, tone, and texture.  Going too loud flattens the imaging and transient incisiveness.

You won't get pants-flapping bass and room pressurization out of your SET, but if that's not the highest priority you may still be pleased with it.  Hook 'em up and listen.

Soft clipping tube amp is less likely to damage speakers when clipping. 

Cymbop,
Your 38 watt amplifier is able to do what it does no doubt based on high quality power supply design and transformers. Another (lesser quality) 38 watt amplifier could fail miserably with these same speakers. As you said, hook them up and just listen.
Charles

Klee123,
A minor correction the KT 88 is a tetrode/pentode not a DHT (directly heated triode) so it would be a (SEP) single ended pentode )rather than a SET (single ended triode. Regardless,  if it is of good design, built and implementation it will sound very good. Good luck to you.
Charles