Sonic qualities of SET output tubes?

I've returned to using my Silverline Preludes (allegedly 91 db) as they sound astonishingly good with the Fire Bottle HO (the HO…it's a HO)…along with 2 REL subs. I understand completely about the obvious benefits of higher efficiency speakers with lower power amps, so I was surprised at how well the Preludes are working…absolute clarity at the levels I choose to listen, and I'm very picky about noise and distortion. You can simply turn the amp up to test the limits (at a certain point it just loses it's mind), and at my normal listening levels which are plenty loud at times, the little amp works splendidly with surprisingly clean dynamic punch . Note that I've been using the Preludes for years, and with this amp listening at low levels (late at night generally) is far more detailed and enjoyable than before the HO was installed. Dennis Had claims that pretty much any great speaker will work with this amp, the only limiting factor being ultimate level constraint due to efficiency. 

I guess in the golden days of audio weren't most speakers 16 ohm to be more tube friendly in that respect.

Of course!

1 4 ohm load impedance speakers are easier to design/build.
2  An assumption that the majority of buyers plan to use solid state amplification.
3  The designers/builders simply believe that the speakers sound better with the lower 4 ohm impedance.

My SET and 2 push pull amplifiers all mate beautifully with my 14  ohm speakers. I do believe Ralph's assertion that higher speaker impedance is beneficial to all amplifier topologies.  It seems many speaker builders would disagree with him given the predominance of 4 ohm speakers in the marketplace.

The vast majority of amplifiers are solid state. These days most of them are safe with 4 ohms, and further many of them can double power into 4 ohms. In this regard, many speaker manufacturers are seeking to make (under a false impression) to make their speakers more compatible with solid state and thus secure a greater market. Its a good example of dollars being the goal rather than the ultimate in sound reproduction.

If they were to simply raise the speaker's impedance and keep all other things the same (which in many cases would be a bit of a trick) they would find that their speaker is sounding smoother and more transparent, regardless of the amp they use.

There really isn't any point in making a speaker that is 'difficult to drive' as the result will be more distortion, of a type that will cause the amp to be harsher and less detailed. You can see it in the specs.

Blindjim- I found the same exact thing as Grannyring when I was using SETs (no surprise, one was the same exact amp, and neither of us has ultra-high eff speakers):

The music was wonderful at lower volumes, and they did drive my
speakers to go very " loud " I was initially impressed, only to find the sound not to my overall liking longer term.

It was this whole issue of sounding "loud" when a system should not sound loud when turned up. Rather, the performance should simply swell and grow with greater impact etc....

My mistake was not the particular SET amp, but pairing the amp with a 4-8 ohm speakers with sensitivities ranging from 89-93db.  My 8-20 watt SET amps, while playing these speakers loud, always fell a little short of greatness. 

I have zero and I mean zero technical knowledge but everything that Atmasphere has posted has turned out to be true in my experience.  If you do not want to be confined to ultra-high efficiency speakers I think this means you can rule out the 2A3 and 45 amps.  If you want to go SET, you will probably want something 6C33C, 211 or 845 amps with a moderately high eff speaker (95--96 dB).  I found that 300b and EL-34 SETs did not cut it in my 14 x 23 x 8.5' room, driving 95-96 dB speakers, listening mostly to the same type of music as you do.  Great sound at low-moderate volume, but when you get grooving and want to go a little bit louder, the sound starts to get less enjoyable and fatiguing.  OTOH, my 300b push pull that makes 27 wpc (VAC Ren 30/30) or my 6AS7G OTL that makes 30 wpc (Atma S-30) sound fantastic. 

I think it should be obvious by now that if your speaker or your amp selection is priority one, then you have to get a "matching" amp or speaker.  If you go moderate efficiency, or 4 ohm on the speaker, you are going to want a reasonably large, SS amp, of which there are many.  OTOH, if you decide first on a 45 SET, you are going to be restricted to a fairly small group of very high eff speakers (>100 dB/w/m).  Those are the two extremes.  If a tube amp is your first criterion, and you don't want to be restricted to the v high eff speakers, IMO, you will want something in the 25-30 wpc range (or greater) paired with moderately high eff, 8-16 ohm speakers.  To get that, you can go OTL or you can go push-pull.  The very high output transmitter tube SETs are, I believe, out of your (very generous) budget. 

To get back to your original question, I am persuaded by my limited experience and the technical explanations of others, that the differences between the "voice" of different output tubes is outweighed by the requirements of your amp/speaker combo.  Particularly with SETs, the power requirements dictate the tube choice.  As you go to push-pull or OTL designs, you have more flexibility in terms of both output tube and speaker efficiency.  Both Berning/LTA and Atma-sphere offer a range of power output options in OTL designs and some variation in tube types.  Push-pull designs offer the widest range in tube types and power output, giving you the widest range of tube-friendly speakers to choose from. 

Hi Swampwalker,
Nice comments, I also suggested the VAC Renaissance 30/30 or a high quality moderate power class A push pull tube amplifier. As you note they do offer increased speaker choice flexibility and are easier to build a system around for most people as well. 

SET will frustrate some people and will require more of a thought out plan of action. It’s worked out very well for me but I knew what was needed and was prepared for it. By the way I am not saying that you weren't prepared for SET,  it just didn't meet your particular needs. 

In addition to the VAC REN amplifier, believe that the Atma-Sphere S-30 , M-60 and the Linear Tube Audio ZOTL 40 would serve Blindjim well. Wolf Garcia seems to be getting results/outcome quite similar to mine.
Charles

@swampwalker, +1 big time!

I have been talking to Ralph at Atma recently as I do want a second amp and want for it to be tubes. SET amps will not work with my current speakers. 6 ohm, 89db sensitivity in a very large room.

In order for a SET amp to work for me, it would need to put out 100 watts. Some amazing SET amp! An OTL or PP tube amp could do the job at 60 watts. Especially OTL with the Zero autoformers by Paul Speltz. 

@swampwalker I remember the amp! I purchased a set of 300b monos from you also! I think we have sold each other gear several times over the years.