tube watts vs transistor watts?

Just because a speaker says "200 watts power handling" doesn't mean that it requires 200 watts to function. The 200 is a maximum, not a minimum and only a very loose maximum at that. Ratings in watts tell you very little about how any amp, tube or transistor , will drive any particular speaker load. Many lesser rated amps of either type will drive speakers that amps of higher rating have trouble with. The output transformer of tube amps smooths out difficult loads in many cases. Conversely the early Classe SS amps were rated at about 25 watts but would drive one ohm loads that would blow up many amps of 200 watts or more. The moral, all watts are not created equal, tube or transistor.

That is not correct, it depends on the amplifier. My Musical Fidelity NuVista M3 is rated 275 at 8 ohms, my tech friend measured 325 with extremely low distortion. It will pulse over 800 watts at 2 ohms. Any good amp will deliver much more than its rated power for very short bursts, that was the basis of the late , unlamented "peak" power or "music" power ratings. Any amp that behaves as you describe is a bad amp and should be avoided.

I was over to my tech friends house this morning, he has over 30 years experience and has had published articles in DIY mags on the design of TUBE equipment. I told him about your statement that a 200 watt amp would give 10% distortion at 210 watts. After a loud burst of laughter he said "he sounds like a real expert". I can't add anything to that.