Member's recommendations for tube amplification


Your thoughts on options to consider:

- I'd prefer SET (open to DHT but not a requirement).

- I'm not looking for overtly warm, romantic or lush options.

- Minimum power in the teens to twenties, 10W being the floor.

- Open to higher power push-pull amps, but let's limit ceiling to around 60W.

- Single ended is fine though having XLR inputs would be nice (doesn't have to be true balanced)

- I'm cool with single chassis or monos.

- I have preferences for tube types, but leaving it open ended to get broad recommendations.

- I'm currently running an all solid state system, though have had tube based systems built around ARC, BAT, Ayon, Melody, Pathos, etc.

- Preamp will be a Pass XP-20 or the Metrum Adagio DAC direct to the amp.

- I'd like to stay around 3K used but can push the budget to 6K new/used.

- Speaker sensitivity is 94dB and higher.

THANKS!
david_ten

I don't know if that many SET amps will fit your profile.  While SET amps are, generally speaking, simple in design, they require really good, and expensive transformers (generally large, air-gapped transformers).  The tube type that fits the criteria you mentioned is pretty much limited to the 300B.  But, most of the 300B amps are on the warmer sounding side. 

The larger transmitter tubes (e.g., 845, 805, 211) run at quite high voltages which would make me very leery about any cheaply built amps.  Parallel output tubes in SET configuration is sometimes used to get a bit more power out of the lower-powered triodes, but, that turns out to be not that easy to implement. 

I think you will have the best luck looking at pushpull amps.  My own personal preference is amps running 6L6 tubes.  These put out less wattage than EL34s, 6550, KT-88, etc., but, to me, they sound sweet without being muddy or sluggish sounding.  A lot of lower-priced tube amps run EL84s; I like this tube too.  I generally like the amps offered by Synthesis (Italian) and Audio Note (UK). 


There are a lot of very old vintage amps that can be found in your price range, but, you would have to work with someone who knows, and can refurbish the old stuff. A refurbished RCA or Northern Electric 6L6 amp will blow away surprisingly expensive current offerings.  Other old brands, like Scott or Brooks, have really nice models too.

Most SETs employ DHT (Directly Heated Triodes) like the 300b, 845 and 2A3.

DHTs can be used in push-pull as well.

If you want more than about 10 watts, IMO/IME you are far better off with a push-pull amplifier, and in your case with your speakers you will be needing more than that unless you are listening from only a few feet in a small room. If in an average room 60 watts will be a good power rating if your speakers are 94db.

The impedance of the speaker makes a difference too; generally speaking you will get better performance out of any tube amp if the impedance of the speaker is 8 ohms or higher as opposed to 4 ohms.

Balanced operation can be very helpful! If you have monoblocks this will allow you to run shorter speaker cables which will win you greater impact and definition. You can run longer lengths of interconnect cables if they are balanced, and if the preamp supports the balanced line standard (be forewarned- most high end audio preamps do not) the length of the cable and how expensive it is will have little impact on how it sounds. BTW there are balanced line tube preamps that support the balanced standard- we make one example (which also happens to be the descendant of the first balanced line preamp made).

Good Luck with the Quest.
I agree with LarryI's comments 100%.
Coincident Frankenstein. 300B. 

I failed to mention that output transformerless amps should also be under consideration,  Atmasphere did not mention this type of amp because he makes them and is careful not to plug his own products.   
OTLs are very dynamic and lively sounding.  The Atmasphere amps also fit the OP's "not looking for overly warm, romantic or lush" criteria.  His 30 watt and 60 watt amps seem like a good candidates.
In you price range check out the 10 and 40 watt Linear Tube Audio amps (both David Berning designs?).

DeKay
+1 @noromance

I picked up a pair of the Coincident Frank mkII monoblocks last month, and these have become game-changing amps for me, after owning a multitude of other amps. Perhaps the end of the line, so to speak, for me.

I am using them with my Omega Super Alnico HO speakers (97db). They are NOT the stereotypical warm, euphonic 300b type of amp, but they are rather a dynamic, fast, open amp, that sounds a lot more powerful than the 8wpc rating. I highly recommend them for efficient speakers.
The thing about the Coincident amps is that they just don't make enough power. The speaker has an efficiency (we hope; if its a 4 ohm load the situation gets worse) of 94 db. 7-10 watts is simply not enough power, especially if you consider that with an SET, the ideal speaker for a given amp will be so efficient that there is never a demand for more than about 20% of full power.

If you break this rule, the SET will sound a lot more 'dynamic' than it has any business being, due to distortion generated that the ear uses as loudness cues. The thing is, once you know that is the case, its hard to listen to a setup like that and not be aware of the distortion. So reading this may have wrecked it for you.

In short, while the *idea* is attractive, in practice an SET won't work very well with this speaker although it may sound fine at low volumes.
David_Ten, if an OTL may be of interest I’d suggest that you check out the following listing here for a pair of Atma-Sphere M-60s:

https://www.audiogon.com/listings/tube-mk-3-3-2017-09-01-amplifiers

The seller is Duke of Audiokinesis, and based on the many outstanding posts he’s made here over the years I’d have total confidence both in him and in any advice he may have to offer as to their suitability for use with your Tekton Double Impacts. I presume, btw, that your DI, and the DIse you have recently ordered, are in the 4 ohm configuration that is usually chosen. If so, it may be best to use an OTL in conjunction with a pair of Zero autoformers, to boost the impedance seen by the amp.

You may also want to consider a used (and no longer manufactured) VAC Renaissance 30/30 or 70/70. The 30/30 utilizes a push-pull pair of 300B output tubes per channel and is rated at about 30 watts per channel. The 70/70 utilizes two pairs per channel in a push-pull parallel configuration, and is rated at about 70 watts per channel. Both should be findable in your price range, although the 70/70 would probably be close to the upper end of that range. I use the 70/70 in my system, with 6 ohm Daedalus Ulysses speakers that like the 4 ohm DI have a very flat impedance curve, and roughly comparable efficiency. I chose that amp because I wanted one that would provide a taste of the 300B magic but without the usual power limitations, given that I listen to a lot of classical symphonic recordings that have very wide dynamic range.

Both of the VAC Renaissance amps provide three output taps, btw, including taps that are designated as being suitable for use with 2 ohm speakers!

Finally, a minor point re Larryi’s post: Larry, I think your mention of "Brooks" should have said "Brook." Brooks was a relatively minor manufacturer of FM tuners which existed in the same ca. 1950s time frame as Lincoln Walsh’s Brook Electronics Company, to which I’m sure you were referring, and which as you know manufactured very highly regarded 2A3 and 300B-based amplifiers. Although I suspect that any Brook power amps which may be findable today would go for vastly more $ than the OP’s stated price range.

David, best of luck in your search.

-- Al

@atmosphere 

For what it's worth, I filter out 70Hz (-3db) and below (-12db @35hz) from the amps and speakers (using a pair of passive filters) and I am letting my ML Depth i subwoofer handle the bottom range; IMO, this has worked wonders in driving the Omega speakers with the Franks with substantially less distortion; I don't detect any distortion, but if there is, I have no objections to it :)
For what it's worth, I filter out 70Hz (-3db) and below (-12db @35hz) from the amps and speakers (using a pair of passive filters) and I am letting my ML Depth i subwoofer handle the bottom range; IMO, this has worked wonders in driving the Omega speakers with the Franks with substantially less distortion; I don't detect any distortion, but if there is, I have no objections to it :)

The point is that unless the amp is outright clipping, the ear does not detect the distortion as such- in almost all cases, the ear converts distortion into tonality. But because the ear also uses higher ordered harmonics as a loudness cue, if there are higher ordered harmonics in the signal, the ear will hear that as louder.

In an SET, the higher orders start to show up when the amp gets to about 20-25% of full power. Since music has most of the power in the transient leading edges, if the distortion is only showing up there it will come off as 'dynamic'. Lots of people like that (often though without understanding how its happening) but it certainly isn't natural!

If you really want to hear what an SET does right you need a speaker that is efficient enough that the 20-25% of full power is not exceeded.
 Also consider these Audio Note monoblock amps for sale; 
300b parallel SET monoblock amps. 

http://www.usaudiomart.com/details/649306274-audio-note-300b-parallel-legend/

Music Reference RM 10 would also be a sweet match with your DI speakers in my estimation.  Great little stereo amp that has proven itself as a winner for decades now.  
@larryi Thank you very much. Great points.

I understand the limitation of the 300B and it happens to be one of the tubes I haven’t been a fan of in the past.

I’m open to reconsidering since I keep reading how, in some implementations, designers are getting a more ’modern’ sound from their 300B amps.

In the case of one of my speakers (the Tekton Double Impacts; soon to be the SE version), based on what I’ve learned about it over the past six months, I believe a 300B amp will pair well, even a classically voiced 300B, and probably to my liking. Especially so if I’m driving it direct with the Metrum Adagio.

I like that there are many options in terms of 300B amp makers, availability, and for sale and resale.

I have a preference for 2A3, but the power output is a real concern. As you mention, a parallel design would likely meet my lower output threshold. Likely a pricier option and not as easy to get right, as you point out.

I’ll take a look at Synthesis and Audio Note as well as research the 6L6 amps.
A pair of used Cary 805s would, I think, tic every box you've specified.
+1 on Linear Tube Audio. You can't go wrong and a ZOTL10 is all you would need but I would use a MZ2 with it.
@atmasphere   Ralph, Thank you very much for your thoughts and advice and direction.

I'm taking notes. : )  

Agreed on the higher powered push-pull solutions, but am also getting feedback to stick to SET from members who I respect and who have also tried different combinations with the speakers I currently have. Obviously, this comes down to personal preference which is why I have reached out for other options. I've had good experiences with push-pull amps in the past.

Your S-30 and M-60 are on my radar.


David, we’ll see what Ralph has to say, but I would be skeptical about the suitability of the S-30 for use with a 4 ohm speaker, albeit one that apparently has a particularly flat impedance curve, given the amp’s 7 ohm output impedance and also its 50% greater power capability into 16 ohms compared to 8 ohms (with no rating specified for 4 ohms). It seems to me that you would almost certainly have to use a pair of Zero autoformers connected in a 4:1 configuration, to make the speaker appear to the amp as a nominally 16 ohm load, but even then my guess would be that neither the amp nor the speaker would be performing at its best.

On paper, at least, the M-60 seems to me to be a much safer bet.

Best regards,
-- Al

@almarg   Thank you for pointing that out. I'd rather play it safe with matching the amp to the speaker appropriately. 

Appreciate the link to the M-60s on offer by Duke / AudioKinesis. And for the information on your VAC Renaissance amp. 
First, a hearty thank you to everyone and a general shout out of appreciation and gratefulness for all of your posts and contributions. This has already been very helpful.

The multiple of choices are great but certainly overwhelming especially when I add the strong recommendations from the Tekton Double Impact thread to the mix. From that thread:

- The Triode Lab A23 amp and the Aric Audio KT88/120 amp come highly recommended by Terry London in his evaluation of two of the Tekton Design speakers.

- The M300B Frankenstein Mk2 also comes highly recommended by Charles ( @charles1dad ) as well as from those of you who recommended it above in this thread.

- and the Linear Tube Audio gear has been discussed extensively.

Just to muddy the waters...I'm in New Orleans...so muddy waters it is!

I just wrapped up an in-home demo of Volti Audio Rivals today, which are horn-loaded hybrid speakers, 6Ohm, with a listed sensitivity of 100dB (I did not measure in room). Immensely musically and emotionally engaging is an apt descriptor. At the shows they have been paired with Border Patrol gear.

I don't have immediate plans to bring something like the Rivals or a slightly higher level Volti speaker or something similar into the mix...but I can see doing so in about one year.

The Tekton Double Impacts are 4Ohm with a listed sensitivity of  98.82dB 2.83V@1m. Those who have measured, say 95dB/1W/1m, and I believe the math ~~ works out on that. I don't know for sure, but expect the SE version to come in slightly lower, therefore my 94dB figure.

When considering my amp choices, I do have an eye on both of these speakers and my reason for mentioning "94dB and higher." 

I fully realize it's probably best to optimize an amp pairing for each individual speaker, therefore focusing on what's in hand is appropriate.
david_ten-
Despite all the buzz, I have not heard the Tektons, so no idea how these amps might interact w your speakers, but I cannot say enough about the Atma and VAC Ren amps.  IME, 300b SET amps could not drive 94-95 dB speakers in my moderate sized room (18' x 14' x 8.5') w/o clipping with pretty un-demanding material (americana/singer songwriter/acoustic blues), even when the mid-low bass was handled by a separate 250 wpc ss amp.  If you listen to wide dynamic range stuff like full orchestra, you are going to run out of gas on crescendos pretty quickly.  Other advantages of those amps are variable feedback (VAC Ren) and unparalleled support from both VAC and Atma. 

I'm having really good results from Finale Audio's stuff I currently using their F-3008 SET 300b based integrated (8wch) driving 94db 6ohm nominal speakers that are a fairly easy load for tube amps. I don't think more power would significantly improve my overall sound quality. I am in a large by volume space (18ft ceilings) and get more then enough spl for my loft. They have mono  amps now on audiogon that may fill your tube needs. Finale Audio is the sister company to Triode labs based out of Toronto. all built in north America no Chinese stuff there. build quality is excellent with many options to upgrade. Good people to deal with as well.  


I don't post much here anymore but sometimes follow a thread or two. This one piqued my interest because it mentioned a couple of my favorite amps. It also piqued my interest because I think there are a few points by other posters that should be reinforced.


First, I have experience with SET amps having worked with someone for several years well known for manufacturing transformers and designing several SET amp circuits for our own manufacturing and sales. I can say from his perspective, the designs were best put to use on speakers whose efficiency was 98 dB or higher. However, we found one interesting exception to that rule. Pairing a 12 watt 300B with a pair of Fritz Carbon 7 speakers (88 dB, 6 ohm) at a very popular audio show. That matching came about by accident, as a 50 watt PP amp failed on us and while it was being repaired we played around with the 300B. We didn't go back. Anyone who heard that combination was amazed it could work. We played it as loud as we could and it continued to perform flawlessly. Sometimes you get lucky, but as Ralph pointed out, the norm will have different results.

The M-60 OTLs will drive your speakers quite well. I have used them for several years now with a variety of speakers ranging from 88 dB to 94 dB, with both smooth and somewhat bumpy impedance curves. In fact I used them with AudioKinesis Jazz Modules for a majority of that time and now with Quad ESL 57, using autoformers to better match the impedance. The autoformers add nothing to the sound in my opinion.

Bill's (grannyring) suggestion of the Music Reference RM-10 is spot on. This amp has balls and puts out 35 watts per channel (double what most EL-84 designs can muster). I have owned mine for 12 years now and used it on many speakers. It just recently powered speakers I am playing around with that go down to a 2 ohm load in the 15 - 20k range. No problem whatsoever. It works great on the ESL-57s as well.

One thing I've learned over the years is there are other factors that can determine how an amp matches up with speakers. I believe Ralph mentioned the size of the listening room and how loud you like to listen.  Another is damping factor, or the amps ability to control the woofer. Lately a question I've been asking speaker manufacturers is what amps did you use to test your speakers. Generally that will give you a good idea of the damping requirements. Some speakers were designed with solid state in mind, others tube amps. You can learn a lot talking to the speaker designer.

I suppose you should take what I say with a grain of salt:

1. Jack Elliano is my business partner.

2. I am an Atma-Sphere dealer.

3. I work with Roger Modjeski


If you'd like to go with a SET amplifier with some power, then the 805 based amps should be high on your list.  The Cary gets lots of praise though I haven't heard it.  I do own the JAS Array 2.1 which has a built-in passive line stage than can be bypassed.  I usually run the amp directly with a Consonance Droplet 5.0 and am quite pleased with the transparency and detail.  It's certainly not a warm or lush sound but it has a directness, a palpability that makes most other amps seem opaque and under-involving in comparison.  It also uses a pair of 300B so they are in there affecting the sound as well.  JAS also makes a pair of monoblocks using 805s with 2a3s.  And Antique Sound Lab has the Explorer 805 which Stereophile reviewed some years ago.  The Psvane 805 are pretty good and affordable at about $250/pr and a big step up from the stock Shuguangs but are bettered a bit by the vintage RCA/GE 805s.  Be aware though that 805 tubes get very hot and would be dangerous to kids and/or pets.  Best of luck with your choice!
David, please let us know how the Volti speaker compared to the DI.  Which one would be your keeper if only one could be kept? I assume the DI, since you did not purchase the Volti? 
What Atmasphere is saying. 

GO to eBay and but the Lafayette KT-550 PP amp and convert to EL tubes and be done with your search.

Happy Listening.
@grannyring   These two speakers make me feel like talking about light.
 

The Rivals remind me of that late afternoon glow from the sun that’s warm, soft, golden hued and alluring. A wonderful time of the day. Existential happiness.

The Double Impacts remind me of daytime sun on a tropical island in the middle of the Pacific, an hour after that mid-afternoon shower has passed through. The atmosphere has been cleansed, the wetness glistens, the sunlight is direct and clear, shadows are short. Realization of a living, breathing and vibrant planet.

I'll post more on the Audiogon thread related to the Volti Vittora. 

I thoroughly enjoy both speakers.

David,

Well your writing is wonderful. Beautifully communicated and so enticing. Well said sir.   
Hello David,
I find your sunlight analogy for the Double Impacts effective and accurate based on my recent extensive listening session with them. Mated to my amplifier(Coincident Frankenstein MK II) the combination was exceptionally open, transparent, lively/vivid yet at the same time natural and without stress. High resolution nuanced sound but devoid of an analytical character, overall very clear and natural "sunlight" 😊. You captured the Double Impact character well, I certainly heard the same. 
Charles
David,
You’ve received some terrific suggestions and replies. In my humble opinion I don’t believe you’ll find one "best" amplifier choice. Some of the amplifiers mentioned I’ve had the pleasure of actually hearing.
VAC Renaissance 300b push pull
Jack Elliano Electra 300b SET
Atma-Sphere MA -1 and M-60

Any of these (and others) would sound excellent with your Double Impacts. I can’t think of a reason why they would not. Each will bring their individual beauty to your system. Really impossible to say that these or my Frankenstein is "the right choice ". You simply have numerous superb options, that’s good 😊.
Charles
@atmosphere

You got me thinking Ralph, so I wanted to check the output of my Coincident amps with my 97db, 4-6 ohm Omegas.  This is a very crude test since I don't have any engineering test equipment other than a multimeter, so some assumptions had to be made, but here is my summary:
- I played a 1Khz test tone (sinewave) at 90db in my listening spot (damn that was ear piercing, so I put some plugs in my ears, lol)
- My meter read 2.26 Vrms at the speaker terminals
- My calcs show that I was using between .85 and 1.3w to output the 1kHz wave, which places my amp's power output (out of 8wpc) usage somewhere in the 11% to 16% range, which is inline (actually less) than your 20% spec for SET amps.

Does this hold water and put me in the ballpark, or did I miscalc somewhere? What am I missing?

Obviously real world audio is way different from a simple sinewave, but then, I don't listen at a steady 90db either, and I do filter off the low bass from my amp/speakers, which helps immensely.

All in all, these amps really work wonders in my situation.



^^ a 1KHz tone really isn't anything like an actual musical signal, which is a bit harder to reproduce, but the sound pressure meter isn't going to care about that.

The speaker is measured in sensitivity, not efficiency, so to correct for that your actual efficiency is more like 94 db. I'm sure your use of the subwoofer is helping a lot!

I often listen at higher levels (95-100db), but the trick is that at those levels the system does not sound loud. My speakers are 98db 1 watt/1 meter and they are 16 ohms at the same time Classic Audio Loudspeakers model T-3). Plus I am usually using amps with 60 watts output and at that power the distortion is quite a bit lower (about 0.5% THD at full power despite no feedback). So the result is less loudness cues generated by the system, which allows for higher volume levels without it sounding loud. Instead it sounds relaxed and effortless.
^^ a 1KHz tone really isn't anything like an actual musical signal, which is a bit harder to reproduce, but the sound pressure meter isn't going to care about that.

The speaker is measured in sensitivity, not efficiency, so to correct for that your actual efficiency is more like 94 db. I'm sure your use of the subwoofer is helping a lot!

I often listen at higher levels (95-100db), but the trick is that at those levels the system does not sound loud. My speakers are 98db 1 watt/1 meter and they are 16 ohms at the same time Classic Audio Loudspeakers model T-3). Plus I am usually using amps with 60 watts output and at that power the distortion is quite a bit lower (about 0.5% THD at full power despite no feedback). So the result is less loudness cues generated by the system, which allows for higher volume levels without it sounding loud. Instead it sounds relaxed and effortless.
@clio09   
However, we found one interesting exception to that rule. Pairing a 12 watt 300B with a pair of Fritz Carbon 7 speakers (88 dB, 6 ohm) at a very popular audio show.

I believe @glennewdick  is reporting the same with his Finale amp.

I'm bringing this up because @teajay Terry London has brought up how a 1W output from the LTA MZ2S pre/amp was able to drive the Tekton Double Impact. His favorite combination is the LTA MZ2S as pre and a Triode Lab 2A3 (3.5W) for power amp. He finds that's all he needs to drive the speakers effectively and is loving this pairing/system.

Do you and others have thoughts about and an explanation for this? Thanks.
Very subjective for sure with 1 - 3.5 watts. I have talked to DI owners who experience did not match Terry’s with the ZOTL combo or good flee watt amps. Terry and others love it, others will not. No right or wrong here, just differing sonic pleasures. Very subjective for sure. We all hear differently and have differing expectations and sensitivities. This is one reason David, but a smart guy like you knows this 😊

Some are more sensitive to "underpowered" or "little headroom" in an audio system. Others hear the same system with no sensitivity to this and hear all the good. What is a black dot on a white piece of paper for some is not seen by others. We are fascinating creatures.
I used to own the original Micro ZOTL and used it on high efficiency speakers and it did quite well, were talking 98 - 104 dB. Again, I think a lot has to do with how large your room is and how loud you listen.

The ESL panels I am using now have adjustable sensitivity, from 70 - 80 dB. The impedance is pretty acceptable from 100 Hz to about 10K Hz whereupon it begins to drop down to 2 ohm pretty quickly (note the speakers do not go below 100 Hz and I bi-amp them).

Understanding the designers goal was to make a panel with a very small footprint that can provide extensive detail at low volume, he had to make significant comprises. So he said the heck with the rest of it and made a set of panels that are better than my ESL-57s, but not as flexible with amplification. While the recommendation was to use a 100 watt amp (ss or tube) I was able to use a tube amp that is 35 watts per channel to drive them cleanly getting SPL levels up to 90 dB, which is a good 10 dB more than my preferred listening level. The level of detail and clarity in the music is fantastic.

In addition to room size and listening levels, if an amps damping factor is synergistic with a speaker, a lot can be done with a little power. There is too much emphasis placed on headroom in 2-channel. although in home theater I think it's important. Less is more in many cases. Mind you I'm talking about the ability of an amp to drive a speaker cleanly to reasonable listening levels. Just because it can be done doesn't mean the listener will like how it sounds.


Coming too close to a SET amp’s maximum power output with little "headroom" left is an important consideration clio09... especially with SET amps. Ralph at Atmasphere has shared the Tech reasons behind this several times in these threads. Can you share why you think differently @clio09?

BTW....,Good to hear from you here on the Gon! I love the speaker and amp combo you have put together. What are you using for a preamp and source now?

Thanks

Try to audition Mastersound from Italy. 
I recently followed an advice and I bought the compact 845. Then the Monos PF100.
I had owned many desirable pieces under 50k. Nothing can't be compare with mastersound.  
Regards 
+1 Mastersound.  

I also urge the OP to check out Ayon Audio amps. 

@mountainsong  and @lalitk 

Can you expand on why Mastersound?  Thanks.

I've had Ayon in system before and liked what they did. 
I'm not disputing Ralph's observation. I'm just saying there's too much emphasis placed on headroom in a 2-channel system. I have used low power SET amps with a variety of speakers and with the ability to measure output while music is playing could clearly see no more than 2 watts being used to achieve reasonable listening levels, without compromising sound. This using 8 - 12 watt SET amps, zero feedback.

Again, size of room, SPL level you listen to, damping factor all play a part in how much power you need to effectively drive a speaker. As per my previous example, 12 watts of SET power, zero feedback, and 6 ohm 88 dB speakers on paper would make anyone think "huge mismatch." Not the case from mine and others perspectives, include a reviewer who wrote up the system, and another reviewer who took the amps home on the spot to do a review.

Feel free to disagree. Better yet get the equipment, learn how to use it, and measure it for yourself.

I should have stayed in hibernation. Enjoy.
Dennis Had Inspire Fire Bottle HO (High Output) SEP (single ended pentode)…a bit hard to find (Ebay for new ones) but utterly worth it…bought a lightly used one some months ago and it's sort of astonishingly good, and for a point to point wired little piece of audio artwork they're relatively inexpensive ($1500 or so new). I use it with allegedly 91db speakers and rant often about it. A great amp.
"I should have stayed in hibernation "
Well clio09, as far as I am concerned you made a very good point. You correctly acknowledged the variables involved that will make each situation have possibly different outcomes.

I own speakers that are 94 dB sensitivity and 14 ohm nominal load. I have driven them with 4 different power amplifiers
100 watt PP tube amplifier 6550/KT 88.
40 watt PP tube amplifier el 34.
40 watt class A solid state amplifier (First Watt S,I,T. 2, PP version)
8 watt 300b SET amplifier .

The speakers/system sounds exceptionally well with any of the 4 amplifiers. The best sounding match "overall" of the group is when using the 8 watt SET. So Clio 09 my experiences are similar to yours and yet this won’t be the case for everyone for the various reasons you’ve already covered.

Any of the 4 power amplifiers I used would I’m sure sound very good driving the Double Impacts. Although these 4 amplifiers vary in power quantity all of them are high quality in design and implementation.  
BTW Clio09 I heard the Jack Elliano 300b SET driving the 4 ohm Horning Eufrodite speakers in the High Water Audio room at CES several years ago.  This combination filled a good sized room with beautiful sound. One of the best sounding systems of the entire show. Elliano knows how to build a superb sounding amplifier 😊. 
Charles 
Just asked a question? Really just wanted to hear your response?  Yes I have done the SET amp speaker combo numerous times with and without success. All your points are true @clio09 

Your hibernation comment seems way over the top and you did not answer my other questions? My post is quite benign and I truly wanted your perspective.  What just happened here? 
I owned two of Jacks amps. Loved his 15 watt 34 SET. In the end I needed more power for some 90db, 8 ohm speakers.

I have owned other SET amps that worked well with 92 - 95db speakers. I certainly have posted the exact additional considerations you posted over and over on this site. I simply wanted your deeper thoughts on headroom.

Not sure how you became upset, but I am genuinely sorry for that.
@charles1dad

Why did you repeat the hybernation comment in agreement? You should know better and have read me stating the very same points as @clio09

I just had a sincere question on headroom. It was specific. Not sure why you are pouncing on me in your professional and slightly concealed manner of late. Seems your view and understading of all things Audio is fixed and sensitive to more open minded considerations. I feel this is a fair assessment of late. 
Hi Bill,
I believe that you are misinterpreting my response. I included clio09’s " hibernation" reply to express that his comments are insightful and that he "shouldn’t " consider returning to a state of hibernation i.e.. Forum inactivity. Sorry for the confusion but I thought that the body of my post implied that sentiment. 
Charles
@clio09

I am truly sorry if I upset you. I respect your experience greatly and miss your posts here. My question was a sincere probing into your thoughts on headroom and its impact on speaker/amp synergy.
Bill,
I believe that I'm as opened minded as you or anyone else.  At the end of the day we all have our unique listening preferences and know what we like.  I have in fact encouraged others on this forum to seriously consider the Lyngdorf 2170 for their audio systems.  

Why would I suggest a product that I have not personally heard? I did it strictly out of respect for your high opinion of it based on your happy ownership and nothing more. Having an open mind means that I can appreciate the positive experiences of other audiogon members and make others aware of them.

Yes I am very fond of lower power SET amplifiers for meeting "my" musical needs.  I have also stated clearly on numerous occasions that these types of amplifiers won't satisfy every listener.  Numerous times I've written this acknowledgement. 

Having an open mind doesn't necessitate having to always agree and have the same outcomes. 
Charles 
Agreed Charles. I do think my comment has some truth. It is for you to decide if there is a modicum of truth. We all have certain biases and bents. Goodness I have my quirks. Just good to see them sometimes. 

While I have, in this thread, cautioned against using the really low-powered triodes in single-ended topology, I am sort of in agreement with clio09 about the possibility that someone may be satisfied with the result; it all depends on the specifics, such as how easy a load the speaker is, type of music, how loud one listens, how large is the room, and most importantly, what compromises one is willing to make.  There is always compromises involved, no matter the budget or any other consideration.  If one does not highly prize extremely deep and tight bass, or if one listens mostly at modest volume levels, a SET amp might work even with speakers not designed to work well with this type of amplification.  Unless one listens to head-banging music most of the time, the average listening level will be such that one would be using less than a watt with even inefficient speakers.  So, the question is: how important to you is it that the sound system performs well for the comparatively shorter time it is asked to deliver higher volume?

When I listen to large choral works with my 6.5 watt parallel 2a3 SET (Audio Note Kageki) driving 99 db/w 8 ohm speakers, I can tell that on peaks, the sound is becoming a little bit muddled and is sounding compressed (not really getting much louder even though it should be).  But, for almost all other types of music, the amps deliver all the power I need, and given my priorities (I demand good dynamics and a full and lively sound at LOWER volume levels), the compromise is worthwhile.  The same holds with my other low-powered tube amps.