Speakers that are good with tubes

It does not have so be 8 ohms or above. My speakers are 4 ohm, but they are very, very flat and very well designed. I bought them to use with an ss amp. The first time I heard them with a tube amp, I promptly sold the ss amp.

The boldened words are correct, of course. 

Using 4 ohm speakers is all good if your tube amp has a 4 ohm tap.

Otherwise not recommended if tube amp has a nominal 8 ohm tap which is probably OK for speakers rated between 6 and 10 ohms.

You can have a 4 ohm nominal speaker sound just fine running the 8 ohm tap on a tube amp. 

@tubeguy76 With full knowledge that the tube amp will have to produce twice the power that it was designed for.  This is not a risk I would consider to be prudent.

Are you prepared to name the manufacturers who said it is safe?  How about running a 2 ohm speaker from an 8 ohm tap?  That may sound just fine, too, until smoke appears.

@tubeguy76  I am still trying to figure out Ralph's paper on the issue, and other sources - I am happy to stand corrected.

When I bought my EL34 push-pull Class A tube amp from the bloke who made it he specifically asked what ohms my speakers were.  I said rated at 8, with a brief dip to 6 somewhere.

That's fine, it won't stress anything.

Because he also included a 4 ohm tap in tediously hand-winding the transformers.

In the foreseeable future I may consult with him about making a tube pre-amp, and I'll be much more prepared to ask him difficult questions and actually discuss issues.