SET amp comparable to First Watt SIT 1?

I’m currently planning to change my speakers to high efficiency horn from modern high end speakers (B&W). The speakers would be Volti horn speakers.

For amp, A friend of mine has First Watt SIT-1, which sounds great to my ears, but I have always been interested in tube SET, especially 300B. The problem is there are too many choices around, and I have read several online reviewers stated that 300B amps don’t sound as good as First Watt SIT 1, except extremely expensive ones with NOS WE300B.

Any suggestions?

My budget is around 7-15K. I don’t mind second hand ones, but I wish I could compare it with my friend’s SIT 1 before I decide to take it or not, so second hand unit is probably not an option.
Border Patrol makes a very good 300b SET (as well as 300b PP) amp. Not cheap, but they often have pre-owned units for sale. Gary Dewes is very knowledgeable. If you go this route, I strongly recommend Takatsuki 300b tubes.
I would try your current amp first and see how you like it. You really can't trust someone else's opinion on this type of thing. If you end up looking for a new amp, Shindo is a very good choice. I happen to know the importer for many years and have a lot of confidence in him and the products. When you buy expensive, specialized components like this, made in a different country, its always good to deal with reputable people that will stand behind the product. I have expensive tube amps myself, and sometimes things go wrong and you need to have them serviced. 
Tmare, there was a long thread on Audiogon a few years ago about First Watt vs SET amplifiers. Many good comments based on actual listening to both. As expected there was no consensus, some chose F.W. S.I.T.and others said their SET was preferable after comparison . Just too many variables involved to arrive at an absolute winner. You’re right about the many choices of 300b SETs available and there is a hierarchy. You don’t have to use the ultra expensive W.E. tubes to get superb sound quality Takatsuki and EML XLS are excellent choices. The Elrog 300b is excellent however only reliable in certain amplifiers, so they aren’t a universal choice.

With your price range you can get truly terrific SET amplifiers with top tier quality output transformers and power supplies. I believe the S.I.T. or a high quality SET can make you happy long term. Take some time to do some research. Gary recommend Border Patrol, other good contenders Coincident Frankenstein MK II, Triode Corp of Japan TRX series, Audion, Airtight, Audio Note, Wavelength, there are definitely good choices available. In your price range you can get truly fine 845 SET amplifiers if interested. 
I’ll also mention the Ocellia 300b mono blocks (Canadian) Thoress  Audio (German) and Raven Audio Spirit stereo chassis (American). 

While I have heard several Volti speakers (you did not specify your model), I have only heard one First Watt amp, the F2, I believe, in my own system.  I had a friend's amp for about two weeks.  I really liked the sound of the amp, certainly one of the better solid state amps I've heard.  I also heard a friend's DIY amp which is based on a First Watt amp; I don't recall which model it is based on.  Both amps are lively, natural sounding amps that don't have that dead, lifeless, quality that I hear with a lot of solid state gear when it is not cranked up to high volume levels.  As compared to my SET amp (Audio Note Kageki) and my pushpull amp running 349 output tubes, the F2 had just a touch more of an artificial "edge" to the initial attack of a note and it delivered a slightly smaller and less enveloping soundstage.  Still, it is a great sounding amp to me.

It is almost impossible to make any specific recommendations on SET or any other kind of amp.  Each specific model, tube type, specific brand of tube, etc., can dramatically affect the sound.  If you can, you should try to hear different models and tube types to develop your own sense of what you are looking for.  While 300b is a favorite tube type of many SET fans, there are others who favor types like the 45 and 2a3.  If more power is needed, the 211 and 845 and some even higher output transmitter tubes could be employed, but again, there are sonic tradeoffs with all choices you can make. 

I don't want to confuse things, but, don't overlook pushpull amps and output transformerless designs.  There are plenty of outstanding tube amps, particularly if you don't need much power, that are not SET amps.   

Coincident Frankensteins? However, look into bespoke designs from boutique builders such as Simple Pleasures “Shiny Eyes” SE 45.
I recommended the Coincident Frankenstein MK II  as I've owned it for 7 years and it is superb in my opinion.  I also listed other brands of amplifiers that I believe are superb choices.  Simply impossible to say that one particular amplifier is the best.  There's a generous source of excellent sounding SET amplifiers to select from.  You only need to find one. I'd never suggest that the Frankenstein is better than any other,  I can say unequivocally that it reproduces music beautifully.
We have a number of customers with that speaker that really like the combination. They use either the S-30 or M-60.

Due to the efficiency of the speaker, low distortion at low power is really important and this is why SETs are often preferred. Because our amps don't have a dedicated separate circuit for phase inversion, they too make unmeasurable distortion at lower power levels, and at higher powers considerably less than either the basic SIT amp or an SET (the latter usually being about 10% at full power).

The advantage of the SIT semiconductor is that it has the linearity of a triode including the soft clipping characteristic. That makes it pretty attractive! The problem of course it that they aren't available- all sources now are from NOS stock or robbed from old Sony V-FET amps.

The challenge that you have is that at 99 db, its actually possible to run many SETs into a considerable percentage of full power. If you are pushing it past about 20% of full power, then you won't be really hearing the best out of the amp has it will start to take on a 'loud enough' (shouty) quality (which is why many SET users say that 7 watts is enough power (because the system starts to sound loud; a system without appreciable distortion will not sound loud), until they hear what the same speaker sounds like with more power behind it. So the SIT amp will have an advantage in that regard.

If you are getting the big Volti with the self-powered woofer, then you will be able to get along with 7 watts or so as long as you are using an active crossover. Then a 7-watt SET will make more sense as long as the room is not too big.
I agree with Charles and the other comments. My recommendation about Border Patrol was three-fold: (1) it is made in Maryland and therefore repairs are easy (my recent experience with my Ancient Audio taught me that lesson, but that is another story), (2) Gary Dewes makes only 300b amps (SET, PSET, and PP), and (3) he occasionally sells pre-owned and he might be persuaded to let you have an in-home audition. Compared to the 45 and 2a3 SET amps that I tried, I found my 300b amp to be more dependent on the specific 300b tube that is used. Takatsuki trumped Sophia RP (by a lot) that trumped Shuguang BT (also by a lot), etc.
Per atmaspere's comments- I run 95-96dB open baffle speakers in a moderate size room (14'x23'x8.5') and acoustic/american/fold/country music and found that it was very easy to drive a 7-8w 300b SET or a 10-11w EL-34 SET into that higher distortion zone that he talks about, if I ran the volume up to more than moderate levels.  If your room is not too big and you don't listen very loud, you MIGHT be OK  w a 300b.  If you are a classical music listener, the wider dynamic range will definitely run a 300b amp into clipping.  I switched to a 30 wpc OTL amp and the improvement was dramatic.  OTOH, if you want to give the SET route a try, drop me a p.m.  I have a very good one that is looking for a new home. 
If at all possible I'd strongly urge you to directly compare a high quality 300b SET to an Atma-sphere amplifier and judge for yourself.  I've done this myself. Both amplifiers were very good but certainly  with different presentations. I preferred the 300b SET sound and the obvious point is opinions/preferences will of course vary.

I believe that either choice has excellent potential with your Volti speakers.
In Linear Tube Audio amps sounded very good to me at Capital Audiofest this past summer for very reasonable cost.  These use some proprietary output transformer magic  (David BEerning ZOTL technology)  in place of a traditional output transformer.    Models I see range from just a few to 40 or so watts per channel.

I've heard a David Berning amplifier but not the Linear Tube Audio amplifiers. I believe that they utilize a high radio  frequency transformer in place of a traditional output transformer. These are more reasonably priced than the David Berning line. 

There are many good lower power amplifiers to choose from when you have a high sensitivity/efficient speaker such as the Volti. 
I've had both types in my system - in the end, its personal preference. I preferred my Quads to the SITs, but could easily see the alternative.
Thank you very much for so many comments. I read all the comments several times and added all the amp recommended here to my list. I have never heard of the most of brand name listed here, but they all look nice to me. btw, I would like to narrow my choice down to 300B SET only, because I have been already confused by way too many choices of tube amps... It would sound ridiculous for you guys, but "300B SET" has been a magic word for me for a long time.

What I still would like to know is, how I choose the right one from this list for the purpose of comparison with First Watt SIT. Do they all share the same 300B SET character enough for this purpose? And is it OK that I just (rather blindly) pick up one of them for demo?
You may see what Volti Audio has to say. I have listed the owners contact info below; also there web site has a dialogue box for contacting them.
It also seems helpful to use this platform to reach out to others that own your Brand/model of speaker (Need Help From Volti Users) and ask them what they have tried with there speakers and what and why they selected there amp/integrated of choice.

By the way Volti Audio used a BorderPatrol S20 single-ended 300B amp the RMAF in 2012

Greg Roberts
Volti Audio
6100 Nashville Highway
Baxter, TN 38544
I fully understand your predicament in trying to narrow down the field of worthy amplifiers. It is frustrating in the sense that it is not really  realistic to be able to hear these various 300b SET ampliifiers and particularly in your own system. It is by nature very subjective (just look at the responses thus far) and all of us have our own bias and preferences.

Then there’s the question of what is 300b sound? You can generalize in only a broad and somewhat vague sense as different 300b amplifiers have their own sound. Circuit, part quality, transformers and power supply are significant factors of sonic influence. Then factor in the variable of different brands of the 300b tube itself.

Even the same country of origin there’s ample variety. Japan for instance offers many choices, each with its own musical character. Some offer more grunt and drive than others,some more warmth, others more neutral and transparent. You get the point I’m sure.

Volti has mated with the Border Patrol at a number of shows, that list I posted yesterday consists of high quality alternatives. Tmare I don’t blame you for wanting to experience a 300b SET amplifier. A good one has the capacity to thoroughly connect you on a deep emotional level with your music.
I really appreciate the suggestions that I find them very helpful. I put the Border Patrol at the top of the list. I just read 6 moons review about their SE 300B. Should be an excellent amp.
If the Volti model you are buying is the Vittora, you may be able to use a lower power SET amp using a 2A3 or 45, which opens the door to lots of options other than the 300B.  I have heard the Vittora at several of the Capital Audio Fest shows, and the very best sound in my opinion was with Greg Roberts' own 2A3 SET amps.  At one of the shows, when a room visitor asked Greg to play a particular CD he turned the volume up and said he would have to switch amps because he could hear some compression on peaks.  He then hooked up a borrowed pair of Border Patrol 300B amps with 18 watts.  For what it's worth, I didn't hear the compression with the 2A3 amps and this was a very loud volume, louder than I would normally find comfortable.  Also, to my ears the Vittoras did not have the same magical sound with the BP amps that they had with the 2A3 amps.  This wasn't just due to the BP amps being cold when I first heard them; Greg left the BP amps running for the remainder of the day so I had a chance to hear them after they were fully warmed up as well.  I am not saying this to put down the BP amps but rather to emphasize that for many listeners, such as myself, the 2A3 amps would have had plenty of power on the Vittoras.
Sal is right in that the very high sensitivity of the Volti Vittoria makes all of the low power DHT tubes viable options. The problem is which one? There are countless threads on numerous audio forums regarding this genre of tubes,. Everyone has their favorite, some say that the 45 is better than both the 2A3 and 300b,. Others insist the rarer 50 is superior, another person would be an advocate for the PX 25, it never ends. You could spend half a lifetime sampling the vast world of SET amplifiers given the plethora of choices in the marketplace.

Say that an 2A3 SET were chosen, which particular one? They all do not sound the same. Tmare has specifically on two occasions expressed a desire to go with the 300b. I would try to hear the Border Patrol (top of his own current list) and use that SET amplifier as a point of reference and go from there.  Honestly any of the DHT  tubes mentioned above in the hands of a talented builder and high level implementation will yield an excellent SET amplifier. 
Good luck,
That's right.  All amps sound different.  All tube types sound different.  Choosing a particular amp is very much a personal choice, and there are no absolutes here about one specific tube or topology being best.  One has to listen to a variety of different amps before making a final choice.  In my case, if I had bought the Vittoras and I came close to doing so, I would have used my 46 SE amps which have even less power than the 2A3.  I am pretty sure the 46 amps would have sounded great and would have had more than enough power for my needs, but I suppose I will never know that for certain.

Hello Sal,
I agree. That’s the fun and (potential) frustration, there  are many good choices/paths available 😊.
If you're going to stick to a 300b you do have several options. normally a 300b can only make about 7 watts. You will need more power unless your room is a small one, or if you only listen to light chamber music or solo guitar. Musical peaks take real power! My speakers are 98 db (and don't use a subwoofer but are good to 20 Hz) and I find that 30 watts isn't enough; 60 watts works a lot better. I don't play the system particularly loud either- I just like it to sound as real as possible.

You might consider an Electra Fidelity
It operates class A3, a class of operation invented by Jack Elliano (who makes the Electra-Print transformers). It offers a few more watts, all of which will be precious when working with a speaker at this level of efficiency. The Class A3 operation also offers lower distortion.
The Electra Fidelity 300b SET ìs very good sounding.
I listened to it driving the Cessaro horn speakers in the High Water Sound room for an extended session during CES a few years ago. No doubt that it’s very natural and convincing. It filled a pretty large space with realistic beautiful and engaging music reproduction. Many good SET choices.
Thank you for more replies. I heard the 2 different types of Volti at different audio shows, and both sounded great to my ears. I have not decided which Volti I would choose. And I’m actually still researching the other horn speaker possibility.

I walked in high end audio world only a few years ago with a rather conventional system (B&W 800D and Classe, etc. ), which I chose based on the store recommendation and the magazine reviews. I still think they are not a horrible choice, but more I listen to the other system, I’m less happy with mine. So this time, I decided to follow my instinct and I’m trying to choose things by my ears as much as possible. The problem is, there are so many interesting equipments on the net, but I have almost no chance to hear them. More I research, I find myself more confused...
You are correct to follow your instincts and simply trusting what you hear. You've discovered the world of lower power  (but high quality) amplifiers and higher efficiency speakers.  This is a very rewarding pathway. In this genre there's a lot of worthy choices and you'll never hear them all. It will all come together in time. Keep reading, learning and listening. 
Charles, thank you for your encouragement words.

tmare, if considering 300B the Sophia Electric amps are ridiculously good for the money.  There are some terrific options like those at realistic price points below your stated range.  I learned the hard way it's not biggest $$ = Best amps when it comes to SET.  Happy to discuss offline if you'd like.  Shoot me a PM.


P.S.  Charles is wise  :-)

arthursmuck, thank you for the recommendation. I'll put Sophia Electric to my list.
If you want the clarity, quietness, speed of the SIT-1 with superior tonality and spatial presentation in SET, an Audion amp is perfect, and I have to say best.

In your price range you can choose from a simple 300B stereo power amp at $5.5K, up through $18K and any choice would best the SIT-1, by varying degrees. Since you are interested in 300B and alternatives, the DUO is interesting for you at $6K as it can run 2a3, 45 and 300B at your discretion. But you can trust you'll get excellent sound from a 300B, so given your price range, stepping up to the Golden Night monoblocks at $10K/pair is the sweet spot. 10w each amp, all silver wiring, wide-band OPTs. These amps ship with JJ 300B tubes. Put them aside as spares and spring for a pair of KR 300B balloon glass. That will give you high integrity in the bass region where so many 300B amps fail. Midrange tonality, dimensioning and detail are beyond reproach. Top end is extended, spacious, harmonically legitimate and top-to-bottom speed and dynamics are consistent (and *fast*).

There are PSET alternatives, PX25 variants in the line, and 845 monoblocks. If you want plenty of dynamic headroom, the $14K/pr. Black Shadow II 845 SET monoblocks and the $18K/pr Golden Dream 300B PSET monoblocks each output 24 watts. The 845 has a ton of shove but you don't absolutely need it with the Voltis. The 300B PSET Golden Dreams have more power than you need but that amp is musically gorgeous, harmonically complete and full of realistic nuance, so the circuit is worth the overkill.

Very insightful comments and again another excellent recommendation regarding the Audion line of SET amplification . What do you think of the suggestion above for lncreaed watts via higher power OTL as a perhaps better alternative for the Volti speakers? I believe either path can be sucessful. I’m admittedly personally drawn to the full harmonic qualities and nuance  of well executed SET that you referenced. Many roads lead to Rome.
Still regret selling my BP amp, his power supply is what really makes them shine. 
We don't have enough info from the OP wrt room size/characteristics and which model Volti he's considering, to answer definitively. Also, I can't find an impedance spec on the Volti site. Nevertheless, I have owned OTL amps and like many of their characteristics, but I've never heard one, especially using massed output tubes, that has the sheer transparency, speed, holistic tone and spatial precision of Audion SET overall, and especially the Golden Dream monoblocks, which would only require a little stretching of the OP's stated budget. I think at ~100db efficiency, 24w with smooth clipping should be plenty, unless the room is cavernous.

I also think at a step-down price of $10K/pair, the Audion Golden Night @10w has most of the qualitative character of the Golden Dream, minus some of the shove. With KR tubes, the bass will gain some discipline. Having recently gotten some experience with the Takatsuki 300B, which is very good, I'll still take the KR balloon glass full range, and it's half the price. Equally well made.

Charles, you know I use Zu speakers at 101db/w/m, and that I've written elsewhere that while such a speaker can clearly be paired with some of the beautiful low-watt 2a3 and 45 offerings, I think they give up too much shove and dynamic fidelity. When 300B is done as well as Audion implements it, and there's a PSET option, why cramp yourself? For shove over ultimate nuance and transparency, the 845 Black Shadow is squarely in the OP's stated economics too, and would put a firmer grip on the very bottom end. But overall, for what the OP seems to be after, he can pretty much index his preferred price to the Audion SET offerings and go, knowing that for the dollar level chosen the march to the Volti will be sublime.

A bit different recommendation: Audiopax Model 88.

I am coming from an Audio Note Quest Silver and it has everything the Note had plus more. It is capable to show the same midrange magic but has much more versatility because of its power reserves. I am using it with Avantgarde horns where it shouldn't matter, but it does.

It is however a rare find these days (sadly).
I've used the Takatsuki, KR and EML XLS 300b in my Coincident SET amplifier and all three are of premium quality level. I have a slight preference of the EML XLS  over the KR but could reflect amplifier differences as well as listener.  Border Patrol vs Audition is an  interesting contrast as their approach is quite  different.  The BP utilize large external power supplies whereas Audions are smaller, more compact and noticeably lighter in weight. Both have earned esteemed reputations and offer upgraded models in their lines. As said before, there are numerous top quality choices among the 300b SET amplifiers.
Audiopax Model 88 utilize the KT 88 tubes and is an exotic and more complicated design than the very simple circuit of a 300b SET amplifier. The Audiopax was very well regarded but its talented Brazilian designer/builder died several years ago. This would be a rare find on the used market.
Is an SET design really necessary? I have a VAC amp that uses 2 300b's per channel, and it drives just about anything. I had it on a pair of ESL's for over 2 years and had absolutely no problems. 
You can also get a Wyetech Labs SET Sapphire 300B monoblocks with plenty of power to drive your speakers [ 18 watts RMS ] It's also on sale now at $7800 a pair

Thank you so much for the precious comments again.

Regarding the rooms size, my rooms size is 15ft x 30ft, ceiling is 8-10 ft (room is a bit irregular), and listening position is about 10-12 ft (3m) from the speakers. I mostly listen to jazz, classical (piano, chamber) and vocal. I usually do not listen to orchestral or rock, but I’m afraid that my current normal listening level would probably be a bit louder than the other SET people, considering the level that the SET exhibitors play at the audio show. It is definitely louder than Audio Note demos, but not loud as those loud solid state demo rooms. I start wondering if 300B SET is really powerful enough for my propose, since several people mentioned it... I also wonder if 100dB or 105dB speakers make a big difference.
Hi tmare,
You have a generous size listening room. You’re beginning to express some concerns. Why don’t you call Volti and talk with the builder himself? Parallel SET 300b, 845 or 211 SETs are options. Ask the builder his thoughts regarding OTL amplifiers as well. Discussion with him is a good starting point in my opinion.  Man oh man,  you have wonderful options. 
Hi Charles, thank you for another great advice. I really wanted to try 300B SET, so I know I should just go for it, at least for my first SET amp.

The reason why I have not contacted any manufactures on the list is I feel my candidates should be narrowed, and I don’t want to bother those people with my ignorant questions, also I don’t want to be biased by them. I’m planning to contact all manufactures when my candidates are finalized. and I’ll do it very soon. I have learned a lot from this thread already, and I’m much more confident what I was trying to do!

PSET (Parallel Single-Ended Triode) topology with 300B tubes will do fine at the Volti- efficiency level, your listening habits and your room size. On nominal 100db/w/m speakers using for example 24w Audion PSET 300B Golden Dreams, at 1m you'll yield 112db at the 16th watt, and be quite usable into soft clipping by 115db. Now, you'll be sitting 3m away, and room surfaces, contents, etc. will reduce those actual and apparent levels at your listening position. If you routinely listened to full orchestral music at symphony hall crescendo live levels, you'd probably want a little more dynamic headroom in that listening space. But what you outlined indicates PSET 300B will be more than sufficient on a ~100db/w/m speaker.

You can drive keep most aspects of the 300B SET sound with a push-pull configuration. You'll gain some bass discipline but lose some nuance and tonal purity. Still good. But unless you find a four-tubes/ch p-p amp, the actual dynamic gain over PSET will be only about 3db.

A ~24w 845 SET amp will have the same measurable dynamics but will sound subjectively as having more "shove." For your stated preferences, I don't think the trade-off of 845 SET muscle for 300B PSET nuance and transparency is necessary.

For reference, on one of my systems, I use 24w on 101db/w/m speakers in a 21x14x 8.5 room, unbounded in two walls so he acoustic pressure dissipates into an open plan house. Seating position is 11.5' from the centerpoint between speakers.  I can cave my skull in with full on rock or symphonic music. You'll do fine.

I suggest against 211 amps. Tube choices are narrower, and you don't get the 845's shove nor the 300Bs nuance, tone and delicacy.


The XLS variant of the 300B can be used in a straight 300B circuit, with normal 300B power output. Used in an amp configured to leverage the XLS tube's higher power potential, it takes on slightly different character but sounds impressive nevertheless. ~18w of premium 300B sound is nice. I'm right now able to compare Takatsuki, the EML 300B XLS and the KR 300B balloon in both Audion Golden Dream and the Luxman Anniversary MQ300 SET amp. The three tubes have roughly the same influences on both amps, but each amp imposes its signature on all three tubes as well. For me, the KR 300B prevails as the most objective and the most dynamic of the three tubes. The Takatsuki is very nice and is the most euphonic of the three but without bloat. The EML is the noisiest and the least consistent in octave-to-octave consistency, but these are not vast differences. Actionable but not vast.

I abandoned the EML tubes for chronic noise and reliability troubles. Perhaps you got better samples than me. The KRs take a licking and keep on ticking. I haven't enough time with Takasuki to judge but their build quality suggests great long-term stability and durability.

I owned the Audiopax 88 before I fully committed to Audion SET and PSET in my systems. The 88 is a beautiful sounding amp, though it is hardest to get deep bass to sound right. If you have speakers that have nothing usable below 40Hz or so, this isn't any problem.

The main contemporary problem with going Audiopax 88 is the sound quality of current production KT88 tubes. I was fortunate at the time to have an ample quantity of NOS British Gold Lion (Genelex) KT88s, as well as 1990s KR KT88s, ultra-screened from the old Tesla Vrovosic factory and relabeled KR. Both seriously improved the sound of the Apax 88 compared with any Russian production tetrodes. I let the Apaxes hang around awhile and pulled them out from time to time to try new tubes. They were pretty good with the Shuguang Treasure KT88, but still not up to NOS sonics.

So, that's what you have to consider going that route. Look at the price of remaining NOS Genelex/Gold Lion KT88s from the 1960s/70s or KRs from the 1990s, before making that commitment.

Hello Phil,
I'm inclined to believe my EMLs were from a better batch than yours based on your comments.  I've alternated between my Takatsuki and EML XLS the past few years.  In my amplifier the EML have been simply stellar,  workhorse reliable and as quiet as any 300b I've used. There were subtle distinctions between the the KR and EML with the latter a bit more vibrant, open, alive and engaging. I certainly trust your judgement and listening impressions,  but again different set of ears,amplifier, system and room environment. IMO both are top tier choices. 

I was actually suggesting you talk with the builder of  the  Volti and see what he may suggest in terms of Your room and musical tastes. I'm sure that he would provide worthwhile insight regarding his two speakers and your objectives.
You may have already considered a Line Magnetic  product, if not here is a couple for your consideration.
There are many reviews on line, that you should be able to get an idea of the characteristics of each amp.
Phil, Charles, et al.

I am a fan of the Takatsukis, but have not heard the Balloon KR 300b. That said, I can attest to the longevity of the Takatsukis. I have been using the same pair for about 5 years without any issues. I was fortunate to source a couple of pairs from Japan at a reasonable cost when they were first released. I have also found the dealers in Japan to be very accommodating - but the current price is steep and not negotiable.

While we tend to talk about output tubes and their variations, recently I have been trying different 6922/7308/etc. driver tubes and have been impressed by the impact - at least in my amplifier (custom made Ancient Audio 300b SET). I am currently using a carefully matched pair of Amperex white label, PQ shield 6922s. The difference is not subtle.

You and I go back quite far with our mutual admiration of the superb Takatsuki. I have come to suspect my amplifier may be a little tough on some 300b tubes. In the past 4 1/2 years I had to replaced 2 individual Takasuki tubes (done without any hassle per my Japanese source AMS Tram). The EML XLS is a heavy duty constructed 300b and seems very well suited in my amplifier. Reports say this durable 300b has a life span capacity of 40,000 hours ( similar to the discontinued AVVT SL 32).

A friend of mine has a very upscale and accurate tube tester. He tested my EMLs when they were brand new 3 1/2 years ago. He recently tested them and they measure "exactly" the same and they are used frequently in my system. This is a very rugged tube that also sounds superb in my amplifier. The Elrog 300b is sublime in sound quality but too fragile for my particular amplifier.
I don’t want to bother those people with my ignorant questions,
@tmare, ignorant questions are the best ones! Never, ever worry if you are bothering the manufacturer by asking them; that should be part of why they are there!! Otherwise you might want to rethink how much support you're going to get.

I have owned OTL amps and like many of their characteristics, but I've never heard one, especially using massed output tubes, that has the sheer transparency, speed, holistic tone and spatial precision of Audion SET overall, and especially the Golden Dream monoblocks
Funny- my experience has been the opposite. Our amps have a risetime in the output section of 600V/mS, where the typical SET might be about 10V/mS. So its not only audible but measurable. Usually that's a pretty good indication that its actually real. In addition to the speed, our amps have more bandwidth as well.

Now what is going on with a specific amp on a specific speaker might really affect the outcome of your perceptions (for example a low impedance at high frequencies that one amp can drive while the other can't might make that latter seem slower even though its not). So its a good idea when doing comparisons to make sure that both amps, whatever they are, are in proper operating condition and are also a reasonable match for the speaker being used (that is, if you really want to find out what the differences are between the amps being compared).
Yup, true. I've used OTL and SET on a very wide variety of speakers under optimal conditions for both amps. I'll put my statement cited in further perspective:

40, 30, 20 years ago, I would have (and did) recommend and own OTL tube amps for maximum transparency, speed and musicality, used with appropriate speakers, including over all the SET amps I'd gotten my hands on up to 1999. That's when I first happened upon an Audion SET 300B amp. And then further put original KR Enterprises 300Bs and well-chosen NOS input and driver tubes in it. With the emergence of objective high efficiency speakers (ala Zu) in the 2000s, the higher power of OTL became less necessary.

The Atmasphere amps are certainly transparent and fast, and I don't dispute the rise time measurements you site for them. But Audion SET amps are uniquely fast and transparent examples of that topology and I hear them as a notch above OTL.