Speakers that are good with tubes

Speakers' efficiency does not need to be as high as 95db. Tubes do not like big swings in impedance. I have run speakers with efficiencies as low as 88 db just fine with tubes (e.g. Fritz speakers). My Ascend towers are 92-93 db and they're great with tubes, because of the relative flatness of their impedance curves. If this fact is understood, the range of speakers opens up a lot. The hard part is finding measurements of the impedance curves. But they're out there, or you can inquire or look for a review in Stereophile.

Some good discussion, here: 

@carlsbad @charles1dad

It does seem like transformers are a bit far away from the OP’s question.

I went there because there was an assumption that a fairly narrow range of speakers are tube-amp friendly.

What I think has been established is that there is

(a) a wider range of speakers friendly to tubes than assumed.
(b) a need to understand what a specific speaker’s performance is regarding impedance
(c) a need to understand the capability of a given tube amps' performance.

My  comment about transformers relates to (c) which bears on (a).
In other words, if the OP had found a speaker with reasonable impedance performance, then the question would become how well can a given amp perform? Part of answering that question would depend on (c).

Of course, the OP may be perfectly happy or stuck with their amp, in which case they could assess the quality of the transformer on it in order to see how variable their speaker choices are.

I’ve heard from amp builders and others how important transformer size and quality are for delivering speaker performance. No one’s mentioned it yet, and I am not finding a definitive source on the web, but these two are both decent.

https://www.psaudio.com/askpaulvideo/tube-amps-and-output-transformers/

and,
https://wallofsound.ca/audioreviews/amplification/what-difference-does-an-output-transformer-make/

My QS mono blocks have great transformers; they control the bass on my speakers extremely well, and I have compared them with some very good solid state.

What this discussion seems to indicate, then, is that there are a number of commensurately important factors necessary to creating good sound. Finding "synergy" between speakers and amps is not magic; it comes down to understanding the various factors on amplifier and speaker sides, and matching them. Then, listening.

@carlsbad I have some buddies here in Denver area with that low-watt, high efficiency approach. It’s pretty magical, and I’m tempted, myself. But that’s a much more difficult path for me at the moment, as it would require getting rid of all my amps and speakers and starting over. I’m moving incrementally, and am currently pretty happy with my non-SET amps (Mono 60’s are great with the KT77s, and the Pass XA25 is really nice, too).

@charles1dad Agreed. Sometimes these threads are like rivers which develop tributaries. Perhaps that’s where I floated!

@richopp Would you say Magneplanars are the only choice -- above and beyond GR Research, Spatial, and others of a similar ilk? Curious as to how you arrived at this very exclusive conclusion.

@jond I must have missed the part where he said the amps were 350 wpc. If I had know that, I would have skipped this thread altogether.