300b lovers

I am another of the lucky guys to get one of Don's 300b stereo amp.  After many years of transferring components in and out of my system, this amp simply puts everything into place.

And, of course, being matched up with the DS preamp doesn't hurt either.  Stunning sound.  Everything in its place.  Great soundstage and holographic to boot.  The only other amps I may consider in the future are the new monos when they become available.

Let’s discuss driver tubes. Back in the Nineties, my Tektronix friend Gary Pimm built a distortion analyzer that could measure each distortion harmonic, out to the 10th harmonic, down to an astounding -120 dB. Maybe even -140 dB. It was way, way down there.

So naturally Gary and I went and measured a bunch of tubes, and ran them at realistic drive levels (50 volts RMS or so). I knew from previous experience that audibility of 2nd harmonic is quite low ... I can barely hear 1% second harmonic, and audibility of 3rd harmonic is around 0.25%, if it’s mixed with somewhat more 2nd harmonic. (3rd by itself is harsh, but sounds pretty nice mixed 1:4 with 2nd harmonic, giving a richer, more fun sound.)

But the high-order harmonics are not nice sounding. Crowhurst suggested back in the Fifties weighting audibility of the order by the square of the order, or even by the cube of the order. High-order harmonics are what give electronics their nasty "electronic" coloration, and contribute very strongly with a forest of IM distortion clutter on the noise floor.

Unfortunately, unless the design is very poor, the relatively innocuous 2nd and 3rd order harmonics will dominate the THD measurements, to the point where THD is nearly useless for assessing sonics. When 2% THD is just barely audible, no, that is not a useful measurement. By that standard, all amplifiers are perfect.

But a spectral analysis is a lot more interesting, providing you pretty much discard the 2nd harmonic, and take a good, hard look at the rest, particularly the 4th on up. In a good amplifying device, you want 4th through 10th as low as possible.

We measured 300B’s from several vendors and vintage 45’s. Of all the tubes, these were closest to perfect. High-order harmonics were nearly absent, and of all the 45’s, none were visible at all. For 300B’s, they were way down, -60 dB or less, depending on the vendor.

That was one surprise. Most tubes, with a few exceptions, had comparable THD and 2nd harmonic, but the high-order spectra would vary within a given tube type by 20 dB, a huge difference. Twiddling the operating current made about 2-3 dB change ... not much ... but changing the brand would show much larger changes, 10 to 15 dB. We were plainly seeing differences in manufacturing technique ... uneven grid structure, tilted grids, etc.

The DHT’s were the clear winners in all categories, but the vintage 2A3’s were 10 to 20 dB worse than the 300B’s and 45’s. And the indirect-heated tubes were another 10 dB worse, or comparable to the 2A3’s. The worst tubes of all were the 9-pin miniatures, with the 12AU7 and 6DJ8 at the bottom of the heap. The 12AU7 had the decency to have lots of 2nd harmonic, which masked the clutter higher up, but the 6DJ8 had less 2nd harmonic and a harmonic spectra more like a transistor, with abundant high-order terms.

The 6DJ8 was a frame-grid tube designed for RF front ends in TVs and FM tuners, where linearity is of no concern at all, so you can’t really hold that against it. And the 12AU7 was designed as a compact replacement for the older 6SN7, operating at the same bias point and voltage. But ... high-order distortion is 10 to 20 dB worse than any 6SN7, even the worst. But you can’t hold that against it; 20 dB of feedback was universal when the 12AU7 was introduced. Loop feedback will reduce distortion in all tubes in the circuit, so it hardly matters.

The 6SN7 family is the tube of choice if you care about high-order distortion, and a DHT alternative is out of the question due to cost, size, practicality, microphonics, and severe filtering requirements for the filament supply. Of the 6SN7 family, the antique single triodes were the best ... 6J5, 6C5, etc. but there certainly were good 6SN7’s, both new and vintage. And differences were consistent within brands, reflecting manufacturing technique, and not always visible from the outside. Were the fancy MILSPEC ones better? Not really. More consistent, which is what MILSPEC is really about.

Don is correct that octals are (nearly always) better, unless you need a mike or phono preamp tube. That’s the 6DJ8 (or WE 417A) niche, where signal levels are very low, and noise and low microphonics are the primary concern.

As Lynn was saying above, I have spent the last year working on this 300b amp project and the matching "Raven" balanced preamp.  Spatial Audio will decide on final naming and pricing and I will help them get started on production.   The cosmetics will probably change a bit, but the circuits are stable and that is what will be shown in Seattle.  This thread has mentioned many fine amps and as I said, there are many paths to audio nirvana.  Lynn and I have had fun with this project and we want to see it out in the world.  It is cost no object, sort of within reason.  The gear isn't going to cost $50,000, but it also isn't going to cost what the current Kootenay amp and preamp cost either.  These are much more expensive to build and more involved.   If you can hear them in Seattle please drop by.  Honestly, I would love to hear people's opinion!

For now, Don tells me he is focusing on the Raven preamp and Statement power amp. We expect to transfer production to Spatial Audio, with product names and prices to be determined. The circuits, parts selection, and overall construction technique are pretty much done, so what you hear in your home (the first pre-production run) and at the Seattle show, will represent what's coming.

Will Don continue to make his current preamp and KT88 power amp? That's his decision, not mine. My focus right now is the Seattle show and completing the large-format high-efficiency 2-way speaker Thom Mackris (Galibier Designs) and I have been working on for the last couple of years. (This design is completely independent of Spatial Audio, and an outgrowth of the "Beyond the Ariel" thread elsewhere.)

Being a continued user and lover of Don Sachs's preamp... where & with whom do I sign up to get one of these amps?

@lynn_olson 

It’s a fully balanced circuit, with 6SN7 input, 6V6 driver, and 300B output. It’s a high current, high speed design.

Thanks for taking the time to post on this thread. I have appreciated various articles written by you over the years. Quite some very insightful participation presented here on this topic. This amplifier from you and Don is genuinely exciting and intriguing. I wish you both a terrific audio show presentation.

Charles 

Oh my, thanks for chiming in, Mr. Olson.  Don has regaled me with the story of  your joint  development of the 300b monos and my ears at the present moment, listening to your creation, leaves me just delighted with the sound of my system. It is just simply stunning, driving my Spatial Audio speakers. I am going to attend the Seattle show largely to meet both Don and you in person.  I am sure that your room with the newest Spatial Audio speakers will be spectacular!  Thanks for participating in this thread.    

Gavin,

I had a stock SP14 for a while in my bedroom system and it was a wonderful glimpse what Don has improved upon with his preamps.  I can't speak to the gain question your raised, sorry, but Don's DS2 mates perfectly with his new 300b amps.  His integrated amp will be commercial available in the near future, but none will be in the offing in kit form to my knowledge.  

Thanks for the kind thoughts, whitestix. For those who are curious, this amplifier is a more advanced, second-generation Karna amplifier, first designed around 2005, and the result of a years-long collaboration with Don Sachs. More practical, two chassis instead of four, and benefitting from Don’s decades of experience in what works and what doesn’t, especially in a production environment.

My projects are usually proof-of-concept and kind of out there. Don’s experience makes all the difference for this collaboration, getting it off the ground and into the real world. He has a lot of great ideas, taking it even further, and these will be in the pre-production amplifiers at the Seattle show.

Whitestix, don’t feel left out. The amps you are listening to now are essentially identical to the show amps, just a little earlier in the production cycle.

It’s a fully balanced circuit, with 6SN7 input, 6V6 driver, and 300B output. It’s a high current, high speed design. I tested an early 2003 prototype at 500 kHz at full power, with clean-looking sine waves on the scope, with no visible flat-topping or triangle shapes. No, I won’t repeat that test again, and I don't encourage anyone else to do it, either.

@carlsbad2  Yes the Reichert amp used 6SN7 to drive 300b and though I have not heard one, those who have said it had a sonic purity that was hard to beat.  So it was a good starting point and 6SN7 driving a 300b can sound good.  But it can be improved if you are looking for all out performance.

@atmasphere great post.  My new amp does use an interstage transformer and a larger driver tube.  The 6SN7/300B  amp I'm listening to in the mean time is darn good.  Not great, but darn good.  So lets not walk away with the understanding that all 6SN7 implementations in 300b amps are junk.  but I agree a bigger driver is a good thing.

Jerry

Thanks @donsachs - looking forward to it.

RM's minced no words in responding that 6SN7 tubes were a very poor choice of tubes -- "better employed in old TV's", because of their inherent high noise levels.  

@whitestix I encountered that with him as well- although by that time he was beefing about the 6SN7 linearity family of curves. Turned out his source was an early Tung Sol tube date manual that didn't reflect 99% of most production tubes. RCA and Sylvania of course figured things out with the 6SN7 early on and in another year or so, so did Tung Sol. RM had the bad luck to have a Tung Sol manual that was outdated. 

There is a group who prefers this approach and there is a group who prefers the more simple way - using half or the 6SN7 in parallel as one triode and interstage coupled with the next stage, or alternatively using a more capable driver, including a DHT such as 300B itself, 4P1L, 10y, 801, EML’s 20 or 30, etc. 

@ffzz I've found that implementation plays an enormous role in zero feedback amplifiers: grounding, component quality, power supply design and of course getting the operating points right in the circuit design. I challenge the idea that using an interstage transformer is actually a simpler approach- it is once you have a suitable transformer, but a good transformer design is the tricky bit; on that account direct-coupling is IMO easier. It has the same advantage of being able to support class A2 operation as well as instantaneous overload recovery, plus wider bandwidth and lower distortion.

The lower distortion may well be why it sounds less 'dynamic'! The use of that word when associated with SETs is always tricky, since most of the 'dynamic' nature of SETs has to do with how they make distortion. IOW its normal for a lower distortion circuit to sound less 'dynamic'. 

These amps do PP a different way and limit the phase split issue and avoid some SE distortion.   Again, there are many fine examples of all sorts of amp topologies, but these don't sound at all like other PP amps you have heard.  They sound like a great SE amp with the drive of a PP amp.  That is the design goal....

@donsachs +1

I've been harping on this very issue for years. Our amps do not have a dedicated 'phase splitter', relying instead on good CMRR in the differential voltage amplifier.

@ffzz ​​​​@donsachs 

Thanks for your very informed feedback and perspectives. The builder of my 300b (Israel Blume) Coincident SET mono blocks decided to go with an interstage transformer and 6EM7 driver tube. As has been openly acknowledged, numerous paths to success. In my case I can happily say that the sonic outcome is superb.

Charles

@charles1dad 

I used the 6SN7 to drive both KT66/6L6 and KT88 in two different amps and they are great for that.  They are marginal to drive a 300b.  As @atmasphere said, there are many approaches and schools of thought about drivers.  Many paths to audio nirvana as it were.   There are also many power supply approaches.  As for SE vs PP, well, traditional PP has issues with phase splitter circuits right in the middle of them, and SE amps do have certain types of distortion.  These amps do PP a different way and limit the phase split issue and avoid some SE distortion.   Again, there are many fine examples of all sorts of amp topologies, but these don't sound at all like other PP amps you have heard.  They sound like a great SE amp with the drive of a PP amp.  That is the design goal....

@charles1dad

I belong to the camp that prefers simple triode circuit with interstage coupling in DHT SET. It sounds more dynamic and transparent to my ears.

I don’t think it’s just an implementation issue though. DHT output tubes such as 300B are not that easy to drive and will not sound at its full potential if driver circuit is inadequate. The coupling method affects driver tube’s ability to swing voltage/drive the output tube, hence has direct impact to the final sound.

Interstage coupling allows more voltage swing to be squeezed out from the driver tube in theory and practice. In addition, the output tube can recover from overload very quickly with interstage coupling as the grid current can easily go through secondary winding of the interstage transformer to ground - an unique benefit of interstage transformer. These benefits are not insignificant in DHT SET.

I suspect that interstage coupling is less important for IDHT output tubes since IDHT output tubes are often easier to drive compared with DHT output tubes.

Also, it’s easy for me to advocate for interstage coupling in DHT SET as that’s not difficult to do in DIY - where cost, weight, and space are often less important (in fact, interstage transformers are often cheaper than high-end coupling caps). But if a manufacturer needs to fit everything in a single box, then the choice is very limited.

@gavin1977 

No, I am not going to do kits... I am retiring and letting a partner build the 300b project and matching preamp.  That should be going before the end of the year.  If you make kits you have no control over how they are built and you get LOTs of questions so customer service is a big issue.  Just because most folks are competent and can build a kit, even if only 5-10% of people are in over their heads you get a support problem.  It is far easier to build a product, test it, and then warrant it.  Plus, these amps use multiple regulated supplies per amp, and it took a while to work it out and get it right.  They are very stable when built correctly, but not trivial to do the build.  They are designed to be easy to service as well, but kits... no.   The amps need about 1.5 volts for full output so any preamp can do that.  They also feature XLR inputs, which are very easy to drive.

I a quite smitten with this design and think they sound great, and of course I have not heard all the other great amps discussed in this thread.   Hopefully someone who comes to Seattle has and can tell me their opinion!  

@ffzz 

Based on your listening experiences have you found one approach to provide better sound quality or is it simply an implementation issue? 

Charles

@atmasphere 

The approach you described is used in DIY world for DHT SET, particularly 300B SET. There is a group who prefers this approach and there is a group who prefers the more simple way - using half or the 6SN7 in parallel as one triode and interstage coupled with the next stage, or alternatively using a more capable driver, including a DHT such as 300B itself, 4P1L, 10y, 801, EML’s 20 or 30, etc. 

Charles, 

Evidently more use this splendid octal tube than I was aware of.   There are lots of ways to get to sonic splendor and Don advocates one particular approach that is clearly favorable to my ears.  Owners of Ralph or Rogers' gear might say the very same thing and they would be right.  SQ is such a a subjective notion that there are plenty of paths to pure listening pleasure for all of us music lovers, because the gear is just that which yields the SQ with which our ears most happy.  

@whitestix

I believe that the 6SN7 is actually a pretty popular tube for input/drivers of power amplifiers and In preamplifiers. I think that the degree of success is overwhelmingly dependent upon the talent, knowledge and skill of the particular designer/builder.For example, Atma-Sphere and VAC utilize them quite effectively.

Charles

Gavin,

Don is licensing the production of his Valhalla integrated amp that owners on this forum have praised.  I recall that the Valhalla amp is one of several that Clayton Shaw uses to demonstrate the best aspects of his speakers.  

I am the least knowledgeable guy on this forum about electronics. I clearly admit it.  I remember listening to Roger Modjeski explaining the design of one of his preamps at Burning Amp a few years ago where an attendee asked about worthy driver tubes.  RM's minced no words in responding that 6SN7 tubes were a very poor choice of tubes -- "better employed in old TV's", because of their inherent high noise levels.  Well, I had had Don's first preamp with 6SN7 tubes (derivative of the Roy Mottram's SP14 design and with Roy's full approval), and his Kootenai amp with the same driver tubes, and wondered how to square away RM's comment with the dead quiet sound from my system.  When I shared RM's comment with Don after the show, oh boy, it was an interesting conversation.  It is true that few audio designers use this tube in their designs (Modwright and Supratek come to mind), but Don does and is doing so with his new 300b monos and my ears tell me that Don is correct in his use of the octal tubes in all of his designs.  Hearing in believing.

@atmasphere 

I do not understand why this approach hasn't been used in SETs since the design consideration is similar. It might be because a negative power supply would be needed. 

Ahh, I see. The usage of the 6SN7 with your preferred utilization mandates a negative power supply. Does this add noticeable complexity and cost to accomplish successfully? This could be the explanation for its lack of popular use.

Charles 

Ralph has written in the past that the 6SN7 is a sufficient driver tube “dependent “ on its implementation in a given circuit. I have been told that the 6EM7 provides much more current, power and drive capability compared with the 6SN7.

I will say that I’ve heard an excellent sounding PSET 845 amplifier that utilized the 6SN7. I could certainly be wrong, but isn’t the 845 a more difficult tube to drive than the 300b?

@charles1dad The issue is always how much voltage swing will drive the tube to full output and how much grid capacitance is there. The more grid capacitance, the harder the tube is to drive.

You can get a 6SN7 to drive a single 300b no sweat. But doing it the way is traditionally done in SETs will likely but the tube at a disadvantage.

The 6EM7 does have one section that is considerably more gutsy than a 6SN7 has. But you will always be looking on the collector's market for replacements.

The way to get a 6SN7 to really do the job is to have it wired as a cathode follower direct-coupled to the grid of the power tube. In this way the coupling cap used in the amp stays rather small since its driving the 6SN7 rather than the output tube. Smaller caps are more transparent...

This is the technique we've used in our OTLs for several decades now. Its very reliable. One 6SN7 section is thus able to drive a number of highly capacitive triode grids with the voltage swing needed. I do not understand why this approach hasn't been used in SETs since the design consideration is similar. It might be because a negative power supply would be needed. But from what I've seen, SET users are not particularly worried about cost if the amp gets the job done for them.

Great news - I own a fully tricked out one of Dons SP14 builds.  Fantastic preamp.

Will this new 300b push-pull require that much gain from a preamp (6SN7), or will it have normal input sensitivity?

I'd also be very interested in an integrated version... don't know if that's on the cards. 

Could it even be a DIY kit (Elekit style 😁)... unlikely perhaps, but at least Don wouldn't need to build them anymore.  VK Music seems to do well enough from this business model.

Where do I sign up?

@carlsbad2 

I hope that you have a wonderful time at the Pacific audio show. I’m interested in your listening impressions.

Charles 

@charles1dad Not sure what speakers yet.  While my new amp is AD1 based, I think its strong points are more the design and power supply than the tubes used.  I'm sure it would sound great in 300b too.

Wish you were going to be there.  I will be there several days and plan to fully appreciate Don's stuff.

Jerry

@carlsbad2

No doubt that your AD1 amplifier will acquit itself well. What speakers will it be paired with? If I were attending that show I would make it a point to hear that system and the Don Sachs amplifier room for sure.

Charles

I like the Viva Solista too.  I own a very odd ball Viva 300b component.  It is the Viva Fono phonostage that utilizes two 300b tubes as RECTIFIERS.  The power supply to this component is massive in size (about the size and shape of the Solista).   

@charles1dad @donsachs I will be at the Pacific Audio Fest Thurs thru Sunday.  While I am currently listening to an Italian 300b with Sophia mesh tubes, my new custom AD1 based amp will be on display there before I bring it home. 

Jerry

@ffzz

RE: the Viva Solista 845 integrated amplifier,

I had the amp for 6-7 years. Out of curiosity, I tried tube push-pull amps from very reputable brands during those years and found that I much prefer Viva each time!

I completely understand. There are just certain audio components that can somehow get the listener emotionally deeper into the pure heart/soul of the music. It’s definitely an art to accomplish this.

Charles

The Nenuphar is an interesting speaker.  The Nenuphar Basis is a great speaker (full range driver plus powered woofer).  The Basis has more weight and midbass fulness than the Nenuphar that makes the speaker very good with large scale classical music.  The Nenuphar is, like many full-range speakers, is slightly rough and peaky sounding while the Basis is smoother sounding (full-range drivers used in multi-way system often sound smoother).

One of the best single driver system I’ve heard are the Charney Companion with the AER driver option.  I heard this speaker, which is about 100 db/watt efficient, driven by a 300b SET.  I also liked a Songer fullrange system that utilized a field coil driver. I believe it is quite high in efficiency.  These two single driver systems are rare in that they sound smooth while retaining the liveliness of such systems.

@ffzz

I understand. One of the most intriguing systems I have ever heard was powered by the Viva. Oddly a set of Millennium electrostatic. A ridiculous combination. But, it’s incredible emotional connection brought tears to my eyes. I never forgot it.

Nearly thirty years later I have a 300B headphone system and an all ARC Reference main system that captures the magic and emotional connection that the Viva did, but with warm and realistic details. Wow, it took so long to get here.

@charles1dad 

My first tube amp was a Viva Solista Lt - a 845 SET with 6SN7 driver. The Viva Solista Lt produces more than 8 watts that many 300B amps advertise for, but only marginally more.

I had the amp for 6-7 years. Out of curiosity, I tried tube push-pull amps from very reputable brands during those years and found that I much prefer Viva each time!

@whitestix 

I don’t believe that you could possibly go wrong with either of those 2 speakers. I expect your pairing to be truly excellent!

Charles 

Charles, 

My friend in Italy got the Nenuphars and has been been overwhelmed with the sound of them. I got their little brothers, the Jazzon, after hearing them at Axpona. 

I heard that Sakuma used 300b driver tube for 300b. He always used transformer for coupling.

To get 27 watts from the 300b push-pull it should be class AB.

@ffzz 

Just look at Viva, their flagship model uses 211 as driver of 845. Thomas Mayer does the same. It’s not a show and dealing with filament for 211 (845 too) is no fun - it’s simply because 211 can share the same B+ and drive 845 well.

Good examples . I really like the Viva 845 amplifiers I’ve heard. Here’s what is interesting to me. A friend owned the Absolare Passion PSET 845 mono blocks for several years. They sound simply fantastic! The 845 was driven by the 6SN7. How ever they accomplished this, it worked.

Charles

@oddiofyl 

I sincerely hope that you receive the same tube longevity from your new production Western Electric 300b as I’ve gotten from the EML. 

Charles

@whitestix 

I didn’t know that you are getting Cube Audio speakers. Which model?

A good friend has had their Nenuphars for about 4 years and he absolutely loves them. He’s driven them with a Pass Labs  XA 30.8 as well as a T+A amplifier to very good effect.  However, his favorite choice and main amplifier is a custom built (Found Music) 2A3 SET mono blocks.

Cube Audio speakers will unequivocally sing with your 300b amplifier. Excellent move by you.

Charles

As I mentioned, I am going to attend the Seattle Audio show to hear Don and Clayton's latest gear and will be booking a room at the venue on Saturday night, June 24.  If anyone of you AGer's are interesting in attending solo, I'd be up for sharing the room and splitting the cost between us, about $100 each.   I did the same with a long-time internet audio pal at Axpona and we had a great time together, during and after the show, comparing our recollection of what heard at the show.  Let me know if you are interested.  

Oddiofyl,

I did the same when I bought the inexpensive Willsenton 300b integrated amp, having never heard a 300b amp, but was aware of their sonic attributes and it opened my ears to the joy of this tube type.  I have the Willsenton amp in my bedroom system, driving my Gallo Stradas and it is just a joy.  A properly built 300b amp like Don's, is in a different realm, but the inherent magic of these tubes is revealed even with the modest Willsenton amp.  I was a gateway amp that lead me to Don's creations. 

I took a leap of faith and had a 300b built without ever hearing one.   It has none of the “cons” often associated with generic descriptions of the tube type. 
 

No mushy lows, rolled off highs.   It all has to do with the design and parts used..  I can’t count how many times I have been surprised at the information I was missing with other amps that pours out of this amp.    The detail and holographic image is spooky.   Using WE 300b. produced in Dec 2021. , hopefully I get the kind of life that  Charles Dad got out of his 300b 

Good gosh, were I to get 11 years out of 300b tubes, I'd be extremely happy as would my pocketbook.  ;-)  I added some fans in my audio rack to ally some of the heat generated by the tubes.  As I say, I am willing to play to play for this degree of sonic splendor.   How Don got 27 wpc out of these monos is a mystery to me, but they sure drive my Spatials with alacrity and I am sure they'll do the same with my new Cube Audio speakers.  

@whitestix

Thank you for your very kind words. I don’t have any experience with the Lanlai but hope that they are durable and trouble free. Yes, the EMLs are pricey, but fortunately utterly robust and reliable. I got over 11 years with my first pair with very frequent (Many long listening sessions) amplifier usage.

Charles

Charles,

Thanks as always for your positive comments; you set the high mark for thoughtful and erudite comments on this forum, once and always the most generous and civil gentleman on all audio matters.  It would be a delight to meet you one day. 

I got a quad of the Linlai 300b tubes recommended by Don from his Chinese supplier for $800, which is ~40% of the cost of the Emission Labs quads, yet Don admits that your tubes are even more revealing than the Linlai tubes.  You have to pay to play with these tubes, but if Don is using these Linlai tubes in his own 300b monos, that is good enough for me.  I sure hope they are long lived.  ;-)

@whitestix

It is so good and refreshing to read how much you are enjoying your Don Sachs 300b amplifier. I’m on my 2nd pair of the EML XLS 300b tubes. They are superb! However, I’d trust the Lanlai 300b recommendation from Don. I am lucky in that I only need one pair of tubes for my SET amplifier. Your PP amplifier obviously requires 2 pair of 300b. Things can become expensive quickly.😊

If he said the sound quality further improves, I believe it based on my experience with various 300b tubes. Keep us posted.

Charles

The sound of these amps continues to blossom by the day, providing the most realistic sound presentation I have ever heard in my room.  The images are palpably real with a pure tonal correctness to the music.  I forgot what Don sourced for the stock tubes, but he recommended much better, but yet still afforable, 300b Linlai tubes, which is tells me will be even more revealing.  I have rolled a boatload of input tubes in gear over the years, but will be happy to rely on Don's recommendations for affordable 300b tubes.  By all accounts, Emission Labs also makes excellent 300b tubes, but they are nearly twice the cost of the Linlai tubes I ordered.  Honestly, I could easily live with these stock 300b tubes, but Don assures me the Linlai WE300b tubes will provide a significant SQ improvement.

@alexberger 

You make salient and pertinent points. This is why there’s such a price discrepancy/spectrum for 300b amplifiers. They range from 500.00 to 50,000.00 USD. Implementation and quality of the power supply/driver stage and output transformer has so much do with what you get and hear.

@donsachs 

I wish you much success with your new 300b PP amplifier at the Seattle audio show. It sure seems it is a winner.

Charles