40+ watts SET, cost is not a problem

My friend just finished some 52 watt single ended triodes he will be selling 

@charles1dad I conquer with you completely. There is something so natural about the way SET present music. What it does with distortion is true and theoretical but it must be preserving something vital to make music sound so "right".

Having said that I am totally open to exploring PP amps. @atmasphere will your Novacron work well with a load like TAD CR1x ? Normally OTLs also need friendly loads. Hence I ask

Has anyone here heard the Wavac preamps?

If I go for SET, I am strongly considering AN (UK) Gaku-on but I don't like AN preamps. They are way too colored and even slow. I have owned M6 and M8. Sold them both because of their colored and slowish (too much body and tone) sound. But I absolutely love Wavac preamp. Fast and dynamic without losing harmonics

If you want something a bit less polite than Audio Note, the Atmasphere linestages and preamps are quite good--very clean, clear, and not overly warm, yet they don't sound harmonically bleached out.  

You did not specify what features you require in the linestage.  To me, remote control is not just a convenience, it is a necessity.  There tends to be a fairly small range of volume one wants to listen to music, and that setting can change even within a single recording.  It is quite hard to tell when the volume is right unless you can do it with remote control while sitting in the ideal spot.  With tube gear in particular, a balance control is essential.  The system will inevitably develop minor channel imbalances and one can go mad chasing down the cause or instantly cure the issue with judicious use of a balance control.

I liked what I heard and saw with the Backert linestages--nice sound, simple design, remote volume control, balance control, and serious people backing the product.

@larryi I dont have any particular need for the remote. Considering that we will go with a Gaku-on, what is critical is a well matched preamp which doesnt short change or create any sonic anomaly (due to character mismatch). Many people say it is best to get the pre-power from the same brand for this reason. Do you think it is okay to get a different brand of preamp without auditioning it with the power amp in question, that too when we are building it ground up? 

I have heard quite a few different brand set ups and I don't think it is necessarily a problem.  Any purchase without an audition in the particular system poses some risk.  It is not necessarily the case that a general sound of a component will carry forward into every system so any prediction on compatibility is a bit fraught.  Perhaps your best best is working with a custom builder who can "voice" the component/system after the purchase.  

I conquer with you completely. There is something so natural about the way SET present music. What it does with distortion is true and theoretical but it must be preserving something vital to make music sound so "right".

Having said that I am totally open to exploring PP amps. @atmasphere will your Novacron work well with a load like TAD CR1x ? Normally OTLs also need friendly loads. Hence I ask

@pani That speaker is not tube-friendly!! Being both 4 Ohms and sensitivity of only 86dB (meaning its efficiency of 1 Watt 1 meter is really only 83dB, which is borderline criminal), you need a lot of power! If you are only listening near field you might be alright, but if in a living room you’ll need 400 to 1000 Watts in most cases.

We discontinued the Novacron a couple of years ago- they were always limited editions. To use a set with those speakers you would need a set of ZEROs, which I think would be a good idea with any SET as well. But that won’t solve the power issue!

So I really think you need to rethink this, starting with a different speaker if you are committed to lower powered tube amps! FWIW, our class D might be alright on that speaker (I have reservations since it only makes 250 Watts into 4 Ohms at clipping); it has a distortion profile that is very similar to that of SETs although its quite a bit lower distortion overall.

And that brings me to something else you might want to understand:

The distortion characteristic of any amplifier is also the sonic quality of that amp. Put another way, distortion is far more audible than most people realize. When you compare amps (unless there is a frequency response error that might also accompany an amp of high output impedance) the differences you hear are the differences in distortion.

As a result it does not matter what the technology of the amplifier actually is; what matters a lot is how the amplifier makes distortion. The reason SETs sound the way they do is because of a quadratic non-linearity which results in a pretty prodigious 2nd harmonic, followed by a 3rd which is considerably less but also prodigious with respect to the higher orders, which, if the amp is designed properly, will fall off on an exponential curve as the order of the harmonic is increased. The 2nd and 3rd are able to mask these harmonics, resulting in a smooth sounding amp.

I hope you can see here that we really can measure what you hear and that it really is all engineering; the real issue is whether the designer of an amplifier understood this fact.

If you have a PP zero feedback tube amp that is fully balanced and differential from input to output, the even orders cancel, leaving the 3rd as the dominant harmonic (which is treated by the ear much the same as the 2nd), still able to mask higher orders. Because the even orders are cancelled, there is less distortion compounded from stage to stage in the amp so distortion is inherently lower. But you still have the exponential decay of higher orders, only now based on a cubic exponent, so they fall off at a faster rate than seen in an SET. That is why such amps are even more relaxed and also more transparent, since distortion obscures detail.

If you have a PP amp that uses single-ended input circuitry (like most PP tube amps) you combine the cubic and quadratic non-linearities, which tends to augment the 5th harmonic (and this has nothing to do with poorly applied feedback, which I touched on in an earlier post). I think this is (and understandably so) why the SET crowd disdains PP. But not all PP amps are built that way!

This is the tip of the iceberg!

In conclusion I really think what you are trying to do is a Sisyphean task. An SET simply will not work and all PP tube amps will be on shaky ground as well.

I know this isn’t what you were asking for, but your best bet here really is a class D, although you should keep in mind that class D amps vary in sound from one to another more than tube amps do- so the idea that you’ve heard one you’ve heard them all is false. The reason I say a class D amp is your best bet with that speaker is because you need the power, and some class D amps are smoother than any other kind of solid state and can be just as involving and spacious as the best SETs. I mentioned part of why this can be so in an earlier post. If you wish elucidation I can provide it.

@atmasphere , the listening distance is indeed near field (6-7 feet from the plane of the speakers). However, I do understand your point of these speakers needing a lot of power. Why do you suggest Class D and not A, AB ?

If cost really is no object, your friend might consider contacting David Berning about his push-pull ZOTL 845 amps.  These are really stunning amplifiers.  He won't miss the "SE" part, I assure you. ;-)

+1 @dogearedaudio - Berning 211 / 845 Monoblock Amplifiers

I've heard, and generally liked the Berning amps I've heard.  I don't care if they are, or are not, true output transformerless amps  (OTL).  To me, they have that immediate, exciting and vivid sound of OTL amps.  But, like ANY amp choice, it does come down to personal preferences.  For my taste, Bernings are on the slightly too lean sounding side.  But, I suspect that the OP IS looking a bit in that direction so they are certainly good candidates.  

I know the OP is looking for some fairly high end amplifier/linestage combinations.  Still, I think there are some shockingly good value amps that should at least be auditioned.  Again, Synthesis Audio makes super bargain amps that I would be perfectly happy to use in my system.  They do make some fairly pricey high-powered amps, but my personal preference is for the amps that run the KT-66 tube and the best from them is a pair of monobloc amps that cost "only" $20k or so.  

Having heard multiple Berning amps, they ultimately sound a bit sterile to me because of the switch mode power supply. If an audio designer can't even hear the basics of music and figure out what is lost with a switching PSU and just uses it for specs, I have no respect for such designers. And the industry is full of such people. Thats why high end audio is so difficult to get right, musically :-(

Reach out to Aric at Aric Audio for his take. Perhaps something bespoke is what you seek and what he can likely deliver.

the listening distance is indeed near field (6-7 feet from the plane of the speakers). However, I do understand your point of these speakers needing a lot of power. Why do you suggest Class D and not A, AB ?

@pani Most solid state amps lack the Gain Bandwidth Product to support the feedback they have. As a result, at some point in the audio band (often, only 1KHz), the feedback begins to decrease on a 6dB/octave slope, often faster as frequency increases. Distortion thus rises on a complementary curve.

This sort of thing is audible, usually as harshness (since higher ordered harmonics are unmasked in this manner) and brightness (for the same reason).

OTOH its very easy to generate enormous Gain Bandwidth Product with a class D design. That makes it possible to have feedback with no rise in distortion anywhere in the audio band, much like a zero feedback amp but with lower distortion, which results in a more musical presentation with greater detail. Some class D amps, as a result, can sound every bit as musical and involving as the best SETs, with greater transparency.

’Nearfield’ is usually about 3-4 feet FWIW. If you really are limited to that distance you might find a tube amp that can do the job. The reason the Sensitivity spec (2.83 Volts/1 meter) is used is because solid state amps can double power as impedance is halved. Being able to do that defines the amp as a Voltage source and that is what the speaker is designed for. Tube amps can behave as a Voltage source too, but do it by cutting power in half as impedance is doubled. So tubes tend to be a lot more expensive on that account. Since tubes don’t double power as impedance is halved, the Efficiency spec (1 Watt/1 meter) is more useful with tubes because it tells you at a glance if you have enough power. 83dB in my room would require 800 Watts(!) and I really don’t know of anyone making an amp that is that powerful and also sounds like real music.

Consider that if you had a speaker of 93dB you would not need to take a hit on resolution or bandwidth, but the amp needed would be a 10th of the power. So you could do the same sound pressure with 80 Watts instead of 800 in my example just above. Now its easy. If nearfield you really could use an SET (although not to its best advantage).

Right now its simply out of the question. If you want to do your friend right, really think about a different speaker.

Having heard multiple Berning amps, they ultimately sound a bit sterile to me because of the switch mode power supply.

Its highly unlikely the switch mode supply has anything to do with what you heard! When you hear differences in amplifiers, again its the distortion of that amp that is its sonic signature. The SMPS is operating at 250KHz in that design; you’re not going to hear it. IOW I get that you might not like the sound of the amp but the SMPS isn’t why it sounds that way.

The biggest I know of are the NAT Audio Magma's.  Those things are monsters.

@paradisecom, yes, the Magma’s are monsters! The transformers are about twice as big as the ones on the NAT Audio Generators. The chassis is 26" long. The Magma M’s transformers are almost one foot tall!

The sonics are much more pleasing than the push/pull 805 Generators. Currently these high powered SET arms may offer the most value of high current/watts SET amps on the market.

My amp is a Shishido 805, which is the basis of the Wavac 805 (effectively the same).  I find it a truly stunning amp - I think there is an early review that pretty much sums it up.  What is wrong with it??  You would have to hear it, and then maybe you could figure out something wrong with it - I can't think of anything,  The amp is driving a pair of Altec 604 drivers in 9 cu ft cabinets.  Tons of power, and the amp has the drivers in a vice grip with regards to control and presentation.

The Wavac secret sauce is likely the Tango transformers, custom wound by extraordinarily skilled craftsmen in Japan for the Shishido design.  Hirata Tango for mine, ISO Tango and apparently Wavac for the later variants.  You can likely find response curves for the special transformers on the web - my book shows the output transformer flat from 30 to 40K Hz (0db down).  Also there is an interstage transformer, so no caps in the signal path.  A simple, yet highly competent amp using stunning parts.

Seems like nobody else has actually heard a higher power set amp like the Wavac, and yet they are fine saying they don't sound good, or it cannot be done.  Not sure how they feel comfortable doing that.  If you have a chance to hear one, then do so.  It might well change your perspective.

Pani, I powerful single ended tube amp design could work out fine but you will need to find the one that gives you the sound you’re looking for.  Some can be very musical and full sounding while others can be very neutral. Me and my friend both own different 45-50 watt single ended 805 tube type mono block amplifiers. Mine sounds very full, large and musical. His, very neutral and accurate. Mr and my friend have been into audio for 35 years. I own about 12 amps and he has probably about the same. We been through tons of stuff. I agree that a properly designed PP tube amplifier can sound absolutely fantastic. I have 3 amplifiers setup in my living room now in 3 different systems. A pair of VTL EL34 mono amps 178 watts triode modified. The single ended amp, a 805 tube working with a 300b tube to get 45 watts power.  And last amplifier is a CJ 100 watt PP EL34 amplifier.  I can honestly say, neither one of these amplifiers is better than the other. They are just different in what they do and how they present the music. I also own a Canary 300b amplifier that is wired with silver and do not hear anything negative about its sound. In fact, it sounds absolutely fabulous. My point is, I own a lot of stuff. Me and my buddy have owned ton of gear and still do.  I thought as you did about single ended designs, and yes, they can be excellent but so can other tube designs.  

informative discussion, thx

Couple of questions:

re p/p- see lots of offerings with auto bias, not sure how much to trust this feature-anyone with experience pls share

Re atma sphere--are the m60 still available in kit form?

I have Klipsch Cornwall IV’s

What you are looking for does exist and can sound superb with your speakers.  

KR Kronzilla's would be an interesting choice.  The tube is esoteric but it sounds really good and delivers a lot of power.  Not exactly like a 300B but 300Bish. KR also makes a 40w 300B push pull.  

Alternative options that would be intriguing would be the Art Audio Quartets (845 push pull) and Opus 4 (Kt88 push pull) that deliver a very engaging experience.  They both use a small amount of negative feedback.   These are both 45w in triode.  Michael Bump did a review of the Quartets a few years ago.  Bob Grossman recently did a review of the Opus 4s.  Both for Enjoy the Music.  

The CANOR Virtus M1 monos are a KT150 based amp that is switchable between 0dB of negative feedback and 6dB.  They also allow for switching to Ultralinear and are 110w in that mode.  Several reviews have been done in Europe on these amps.  

Aries Cerat makes a few amps that are higher power and deliver what you are looking for.  The Concero 65 is parallel SET running the 813 tube.  The Essentia is a SS Amp that sounds very much like a SET and could do a nice job.   

None of these are inexpensive but all are stunningly good amps and will do okay with your speakers in that smallish room.  They either have 4ohm taps or in the case of the Essentia are stable to 1 Ohm.  

Full disclosure, I am a dealer for all these brands.  That said, it also means I have tested these amps in the real world.  I have publicly shown speakers as low as 84dB sensitivity in rooms about your size with the Art Audio and Canor amps and have heard the Kronzilla and ACs in similar spaces.  

You could also go with a more traditional design like VAC or a hybrid design from a brand like Riviera.  Any of these will shine like the sun with those speakers.  

 CAT JL5. Convergent Audio Technology 

This is so easy. The CAT JL5 can drive the smallest speakers with all of the detail and sound stage you could ever want. I just saw them at Axpona driving the new baby Clarysis Piccolo speakers. Also, my friend has olderCAT equipment driving his Tekton tower speakers which are pretty efficient. You did say cost is not a problem. The CAT JL5 was also used in the Aretai speaker room driving their book shelf speakers. Which are not hard to drive at all. The JL5 can work with anything.

The one thing I was surprised about is the run very cool for a tube amp even while driving huge speakers. 
 

Thats a nice problem to have, really superb equipment.

Already the predecessor R1 was outstanding however also demanding on the upfront chain but truly world class.

I may have a soulution for sale.

My thoughts are that there is one pair of Single ended that easily can feed the TADs

The older Siltech single ended power ampilifiers SEPA are giving out 80w/8 ohm real class A from a single nuvistor tube. 
A group compared them and the Kagura monoes mk1 and the Siltechs were clearly better and with an extreme lifespan from the nuvistor tubes also winns there.

They are however rare and were only produced in 15 limited pairs and actually not even set up for public sales but only for Silteck picked out distributors around the world at the sum of 130.000. Which with a normal profit factor would have had a retail price of around the double and in the Kagura area.

They weighted almost 60 kg each and all wire included transformers were the G5 silver/gold aloy from Siltech.

Only a few have be up for sale until now but soon I may put up a set and they can be testet in AB against a set of Robert Koda K70 mk2 which also are a outstanding poweramp.

Happy listening.

If I have to go push pull, my first choice would be a CJ sa108 monoblocks with Art88 preamp. But I am so keen and smitten by SET that I will first explore it well. 

@pani

But I am so keen and smitten by SET that I will first explore it well!

As well you at the very least should do. I recall sharing numerous interesting threads with you in past years. You have extensive experience With a wide variety of  Audio components. At this stage it is fair to say that you know what you like and what and what you are seeking.

@verdantaudio gave you some promising SET options, Aries Cerat and KR Kronzilla. Also VIVA Audio PSET 845 I’d mentioned previously. There’s an excellent PSET 845 made in Japan by Triode Corporation. These are big 50 watt per channel mono blocks. I’ve heard them personally and they are splendid! I believe that a top notch SET, PSET or DHT class A push pull amplifier will deliver what you are searching for sonically and musically.

Charles

Thanks @charles1dad i am exploring all the SET suggestions you and other fellow audiophiles have suggested. Audio Note (UK) ANKORU or even Gaku-On is looking very interesting

@pani The following suggestion will possibly be difficult for yourself to consider, but I will put it out on this forum once more.

The Pass Korg B1 Pre Amp, i its basic build Guise is very good in terms of the perception of Transparency it can produce when used with a Valve Power Amp.

The same designs using some of the well known schematic tweaks are exceptional Amps and quite able to fend of £Multi Thousand Pre Amp's which I know the have done.

There is not much monies required to experience this design as a Basic Model. 

@pani 

I am not very familiar with the Audio Note Ankoru. Given its pedigree I’m sure that it is quite worthy. Best wishes for this endeavor.

Charles

Give David Berning a call

Pani I don’t know if my tsakadiris apollon tube monoblock are triode. They use KT 120 tubes.I stop by an audio store pre pandemic.While Iam listening Iam so impressed.i asked the store owner If they will be ok to power up my Eggleston Andra? These are I think 150 w per channel. I was surprised to hear that they are good with Andra , Iam guessing my Andra are between 86 to 87db.i brought them not expecting anything, I am almost sure they will run of gas powering the Andra . I end up keeping them, I tried , Krell, Mark levinson, Pass , BaT. This are the perfect amps for ANDRA THEY MADE THIS SPEAKERS THE WAY WES Philips gave them stellar reviews.They brought the best of Andra musically.Andra loves tubes. Iam not sure if you can still find them. Brand new 4 k.

My only regret I did not buy the tsakadiris preamp.The store owner kept increasing the price.I got turned off and did not make a deal. Still I thank the store for carrying this brand.TVAD heard my system using ss . It sounds not good. That is  20yrs ago when he visited Chicago it was the time . I don’t have listening skills. And knowledge. Grant stop by listen to my system I will treat you good delicious pizza.

By the Way TVAD is a very nice guy. Like Davidten.Who both visited my place. Skhong was scheduled to visit but unable due to food poisoning. He miss Axpona 2024 as well.

Have you considered an OTL amp?  Atma-Sphere makes some excellent product that may open up the sound of that system.

@tvad 

the symbiosis with Audio Note amplification and loudspeakers cannot be replicated. One without the other is handcuffing the possibilities, and those amps are very expensive

Interesting. I wasn't aware that the Audio Note components were so specifically tied (Synergistic ) to their siblings in order to extract the very best sound quality they're capable of.

Charles

@charles1dad If you or anyone else is interested here is some writing on the Ankoru but Andy Grove the designer, interesting stuff.

@jond 

Thank you! I will read it. I have  held Andy Grove in high regard for some time now.

Charles

@jond 

As usual a very descriptive and informative article by Andy Grove. In addition to audio/electrical engineering talent, he is a very adept writer.. Appreciate his distinctions between the 845 and 211 DHT tubes and why he decided upon the former in the Ankoru amplifier.

Charles

@charles1dad Very much agreed and glad you enjoyed it!

Most audiophiles who have heard tube amps have listened to "Golden Age" push-pull circuits that date from the Fifties, with a few modern tweaks like regulated supplies or a current source or two sprinkled through the design. A smaller number have heard low-power SETs in the 2 to 20-watt range.

Looking back, the "Golden Age" circuits were optimized for power above all else; there were no 100-watt transistor amps back then, so it had to be tubes, and high-voltage transmitter types were never sold as consumer products. So the tubes used then were 6L6, EL34, KT88, 6550 and other similar types. If you optimize for power, you can squeeze 60 watts out of a pair of 6550’s, or more if you’re really willing to hammer on them.

This requires Class AB operation with a relatively small Class A region (to increase efficiency) and using 20 dB or more of feedback to both linearize the pentodes and smooth out the crossover region. This is the real reason a Golden Age amp, or a modern copy, sounds quite different than a zero-feedback SET. The SET relies on the inherent linearity of the triode power tube, while the Golden Age amp relies on feedback to do the heavy lifting.

For most of the history of audio, high power and the highest quality sonics have been in opposition to each other, although the marketers always want to sell the most expensive amp ... which these days means an amp with banks of power pentodes sizzling away in the chassis.

Rest assured, any amp with arrays of devices operating in Class AB will NOT be the most linear amplifier, since every device will have a slightly different AB transition point. Perfect matches are impossible to maintain, even if they come out of the factory that way. Tubes drift as they age.

There’s a rule of thumb that if linearity is important, minimize the number of output devices. One device is obviously the lowest number, but SET output transformers have serious design challenges once the power gets much beyond 20 watts. A useful compromise are two devices running in push-pull, but biased into Class A, like SET amplifiers.

Unfortunately, our 60 to 100 watt Class AB amplifier now shrinks to 15 to 20 watts if re-biased and re-designed to run in Class A. Yes, you can build really big PP amps using transmitter tubes, but these are notoriously hard to drive, and safety considerations become very serious with B+ voltages of 1000 volts or more ... audiophile construction technique is NOT appropriate at these voltages.

To be blunt, if your speakers need more than 20 to 30 watts to fill the room with full dynamic sound, your choices for amplifiers narrow quite a bit. If tube amps are a must, there are Class AB PP pentode amps with 4, 6, or 8 output tubes. This is expensive and no fun to keep in balance. There’s good old Class AB transistor, using either bipolar or MOSFET output transistors. Or modern Class D amps, preferably with the latest ultrafast GANfet output devices.

@lynn_olson

but SET output transformers have serious design challenges once the power gets much beyond 20 watts.

In the link provided above, Andy Grove (Audio Note) acknowledged that in his article and explains his remedy. By many listener accounts he was successful with the 845 tube amplifier output transformers dilemma.

I wish the OP could sample your Black bird designed 300b push-pull with the TAD speakers he wants to drive with tube amplifier. 17x13 ft room, pretty much near field environment.

Charles

Hmm, well the Blackbird puts out an honest 22 watts, with half-second transient peaks probably around 60 watts. They power highly reactive electrostats with no issues, because of deep Class A biasing and zero feedback ... the load-lines for the PP 300B’s are nearly perfectly straight, which is ideal for reactive loads. With zero feedback and power supply isolation between drivers and outputs, the amplifier behaves like a limiter/compressor as it is pushed beyond 22 watts. (The power supplies are good for 200 watts per channel, plenty of reserves there. The voltage and current limiting is in the 300B’s.)

But for inefficient speakers with high-order (18 or 24 dB/octave) crossovers ... probably not. Speakers like that need an amp with a high damping factor and at least 200 watts of clean power. High damping factor typically requires high feedback, and high feedback also means hard clipping. Hard clipping sounds terrible and can destroy tweeters, so the amp should never be operated in the clipping region. So lots and lots of power, enough to never approach clipping.

Modern Class D amplifiers, particularly with GANfet switching transistors and well-designed PWM modulators, are probably optimal for these kinds of speakers. This class of amplifiers avoid those annoying Class AB colorations, and don’t have problems with bias drift as they warm up. And power reserves are large enough to avoid the clipping region.

Note there are two approaches with not that much in-between. Either moderate to low power (2 to 20 watts) with very gentle clipping and modest damping factor (between 3 and 4), accepting that clipping will happen but will have low audibility, OR 200 to 500 watts of power and clipping never happening. There’s also a handful of low-feedback low-power Class A transistor amps, which I guess are sort of a halfway house between the two.

@lynn_olson 

But for inefficient speakers with high-order (18 or 24 dB/octave) crossovers ... probably not. Speakers like that need an amp with a high damping factor and at least 200 watts of clean power. High damping factor typically requires high feedback, and high feedback also means hard clipping.

Okay got it..I'll defer to your assessment. No one knows more the capabilities and suitability of this amplifier than you (And Don Sachs).

Charles

Low-order passive crossovers (6 or 12 dB/octave) are less sensitive to amplifier output impedance (damping factor) than high-order crossovers (18 or 24 dB/octave). High feedback is the most direct method of reducing output impedance for both tube and transistor amplifiers.

Which in turn affects how an amplifier clips. Unless a "soft-clip" diode array is used in the feedback loop, but those have other, unwanted side effects, such as increased distortion in the top 3 to 6 dB of the amplifier’s power curve.

It’s considered good practice to let the output devices define clipping. At that point, they are giving all they have, forward gain collapses, and feedback loses effectiveness. The transition zone from linearity to clipping might involve charge storage if solid-state devices are used, or the power supply for the driver stage could sag, and let the drivers clip at the same time. This extends the recovery time from clipping, with power supply rails fluctuating up and down as the circuit recovers.

The SET amplifiers without feedback do not hard-clip, but if the driver and output section have a common B+ supply, that supply will sag when the amp clips, and if the driver and output section are RC-coupled, then the coupling cap must re-charge before normal bias appears on the grids of the power tubes.

If regulators are used, they must tolerate overload conditions and recover quickly, preferably within milliseconds. As you can see, a lot can go wrong if the speaker demands more current or voltage than the amplifier can deliver.

I should mention speakers not only consume energy, but they reflect it back to the amplifier as well. This is what a reactive load does. The most severe condition is a pure reactance with a phase angle of 90 degrees. That reflects ALL the power back to the amplifier, which can create an overcurrent condition in the power transistors. Tubes tolerate this better than transistors because it takes a gross overload lasting several minutes to overheat the plate of the tube, while a transistor can fail in milliseconds.

It’s kind of sad how low speaker efficiency really is. We think of a 92 dB/meter/watt speaker as "efficient", but it’s only 1% conversion efficiency. (A more typical 86 dB/meter/watt speaker is 0.25% efficient.) The 1% efficient speaker needs 100 electrical watts to create 1 acoustic watt (which is very loud).

What makes it worse is the other 99 watts (which are quite expensive) do nothing but heat the voice coil, which is undesirable because it is in a very small space and is not easy to cool. A more efficient speaker has the advantage of cooler voice coils for a given playback SPL, which gives it greater headroom.

Kondo or AN UK are some (or the) of the finest SETs you can find, but I can't comment on the silver used in the Kondo, although silver is the best conductor. However, as other people stated, the TAD speakers are low sensitivity so even if you have 40W, they are probably not the right amplifiers. I would suggests to look at push pull like the EAR 509, which is 100W per channel or the EAR 890 which is also bridgeable to 140W per channel. Otherwise you better change speakers if you want to use a SET.

EAR509 amplifier is a good amplifier but it sounds completely different compared to any SET amplifier.

It has a number of feedbacks and is designed and sounds more like a transistor amplifier. It is also completely balanced from input to output.

https://www.turneraudio.com.au/EAR509-reformed.html 

Pani,

You have two of the best circuit designers I am aware of (Ralph and Lynn) tell you that tubes are not going to deliver what you are looking for with your hard to drive speakers. I'd believe them.

Class D GnFETs are one very good option (that I have no experience with), but I'd also make a phone call to Doug Dale at CODA regarding his Class A solid state high current amplifiers. He has the newest version of the System 150 WPC (100 WPC Class A) and System 250 WPC (200 WPC Class A) coming into production soon....his contact information can be found on the CODA website.

Since they are new products I of course have not heard them. I do own their baby brother the S5.5, and it is an absolutely brilliant amplifier with performance I never thought I'd be able to achieve in a "mid/hi fi" system.

@vthokie83 +1