300b lovers

I have had the matching preamp running quite nicely for about 10 days and I will say the combination doesn't sound like anything I have ever heard.  First off, with my 97 dB speakers you literally have to put your ear to the woofer to know the system is on at idle (no hum).  The tube rush (hiss) varies with tubes used, but you pretty much have to have your ear to the HF driver to hear that at idle.  We are talking a Lampi Pacific DAC with DHT output stage feeding a tube preamp, which feeds the 300b amps.  All tubes and at idle it is as quiet as solid state. This gives a totally black background.   Lynn went his own way on the circuits and between the two of us we have turned them into working prototypes that are closing in on production models.   The working prototypes are what will be shown in Seattle.  Again, I hope many folks reading and participating in this lovely thread are able to come and hear them and give an honest opinion.  They do not sound like anything else I have built, or even heard.

I like to listen at the volume a live performance would be at.  Obviously, Pink Floyd concerts would be loud, but a jazz combo should sound like you are in the club at normal levels, not screaming at you.   I will try to play at various levels when we demo and I have the remote:)   June 23 is the show.  I know a few folks who say they are attending, so I am sure someone unbiased will post an honest impression.  Listening rooms at shows are often hard to tame as well, so we shall see what we can do when we get there.

I know that when I have my system "cranked" and I measure the level it is about 81-83 dB.  I rarely listen at that level.  As was stated above, the hallmark of a good system is that it has enough resolution and balance that it can be enjoyed at low to moderate volumes.  There is a minimum level for the bass to pressurize or load the room, but that isn't all that loud in any house I have lived in.  I generally listen at the level where that has happened and not much higher.

Current production Chinese 45 tubes are about $350 per pair plus shipping.  I may try a quad in my Lampi Pacific DAC.  I quite like the 46 tube there with adapters.   The current production European 45 tubes are twice that price.  That said, if run at sane operating points they may well last 30,000+ hours.  So if you like them, they are really not that expensive in the long-term.

Thanks for the positive feedback from all so far.  The room was a bit of a struggle to get things to sound good, but after a whole afternoon and evening of getting furniture moved out and putting acoustic treatment up we pretty much tamed it.  We have very good image depth, and of course the ceilings and walls limit height and width, but it is a nice sound.   Like every other team here, we work with what we have!  Hope see a few more of you today!

The older preamp is a nice, but conventional single ended tube SRPP circuit with Akido buffer (extra tube per channel).  It uses dual regulated power supplies and dual regulated filament supplies and really good signal path parts, and the wonderful Khozmo attenuator.  The Raven is a completely different approach and  circuit.  It is fully balanced and transformer coupled at both input and output with custom wound transformers from Dave Geren at Cinemag.  It will take either xlr input or rca input, and will happily provide xlr or rca, or even headphone output, and will drive even a 10K power amp impedance.   The Khozmo setup is dual mono because you have to control both halves of the xlr on each channel.  The power supply uses two damper diodes, very high quality transformer and is a true C_- L - C (cap, choke, then cap) that feeds a much higher quality regulator that is used in the previous preamp and also feeds a pair of gas regulator tubes after that.  It is dead quiet, fully balanced, and has very little sonic signature, but provides great drive for the power amp.  I really like it, and those who have been to the show have heard it driving the 300b mono amps.

The sonic differences between the old Akido circuit and the Raven are fairly dramatic. The Akido circuit sounds like one of the best darn traditional tube preamps I had ever heard, and that is why I built it for years and kept trying to squeeze another few percent out of it with every improvement. The Raven is part of the 300b project. Both the amps and the Raven will happily play with the rest of the world, either single ended RCA or XLR, but together they can form a complete balanced chain with a balanced source. The Raven can drive the input tube grids of the Blackbird amps directly via XLR because it has an output transformer. I would not do that with a solid state preamp or DAC output stage, only something with an output transformer or coupling cap to protect the amps from DC input. A solid state device would be fine for possibly many years until one instant that it isn’t, and then DC can come flooding into the amp. That would not destroy the Blackbird, but the input tube would be really unhappy, and some nasty noises could arise from the speakers. The Raven simply cannot do that because it is transformer coupled. The RCA input on the Blackbird amps is transformer coupled, so that is always safe, but the XLR inputs can bypass that input transformer. So the Raven is made to mate with the Blackbird.

The sound of the Raven vs. the older Model 2...? Well, as much as I like that circuit and build, it sounds slightly slow and veiled compared to the Raven. The Model 2 is a great preamp and I have maybe 150+ of them out in the world in one form or another, but the Raven is a step up. There is just more resolution of fine detail, with what sounds like effortless and unlimited drive. It is not bright in any way at all, but it is highly detailed. The whole 300b system is like the iron fist in the velvet glove to my ear. It has all the subtle detail and shadings of a flea watt SET amp, but serious grunt and drive at the bottom and extension to 34KHz at the top end and a very subtle roll off after that. I suspect the final version of the amps may make it out to 50 KHz before the roll off begins. So HF is extended and airy, but again, never bright sounding. The Raven is definitely part of that experience because I built the amps first and used them with RCA inputs and my old preamp, and then I built the Raven. Like the amps, once I heard the Raven there was no going back. So then Lynn and I experimented with several power supply variations before deciding on the final topology. They all sounded quite good, but the final choice was clearly the best to my ear. At any rate, the Raven is a big part of the sound people heard at the show. My old preamp was good, but not in the same league. My 2 cents.....

Yes, it was fun!  As Lynn said, there were 3 or 4 outstanding rooms and we had one of them.   It was a scramble taming the room and the internet connection on setup day, well into the late evening.  But we got it!   I would say the system was very much on song except for image height and width and that was totally limited by the small room.  But depth was very good and tonality was unaffected.   Hope a few more folks that stopped by will give others an unbiased opinion on this thread as they get home.

There was a reviewer from Stereophile who came twice.  I let him play what he wanted, but I certainly did not chase anyone out of the room, so maybe that was someone else in the rear.  I assure you that Stereophile will not be getting the amps for review.  There is no free advertising as the product is not even in production yet.  Sorry you were not treated well, but it wasn't me....

Also, as Lynn said, the plan is to have Spatial Audio Lab build the preamp and matching 300b amps, which we all are currently calling the Raven pre and Blackbird amps.  They may get a final name change before launch, or they may sing together with their current monikers.  Reviews are way down the line.  Direct sales to customers is the way this will go, just as with the Spatial speakers.  There is absolutely no relationship with any publication.  We are aiming for availability late this year or first thing next.  It is our hope that a few people will have them playing in their homes for the holidays!

I second the Songer speakers as well.  Wonderful with the Whammerdyn 2A3 amp driving them.  One of my favorite rooms!

@gladmo 

I will take gossamer:)   We were trying to produce sound stage in a shoe box room, but the tonality was nice, and we could get depth.

As Thom said, and I noted about a thousand pages up, there are many paths to audio nirvana, and rarely will we all agree!

Hi Ken..

Admittedly biased, but both Lynn and I thought your room and our room were the most musical ones at the show, and we were neighbors too.  Obviously others will have other opinions, but many folks told me that our two rooms were in their top 3 or 4 in the entire show.  Great to meet you!

@pindac 

Our egos are not too bruised.  We have a pretty thick skin.  No matter what you do, there will be a certain number of people who are unhappy.  It cannot be helped.  This thread has been a wonderful discussion of amp topologies, with all points of view respected and debated.  Even a little philosophy and the nature of perception tossed in.  As was stated early on, these are prototypes that were shown in Seattle.  Most people seemed to have a favorable impression, and there are already tweaks afoot before the final versions start to be manufactured later this year.  We had great fun in Seattle meeting many other audiophools:)  We tried to accommodate most people and play tracks and volume levels they wished to hear.  Things got crazy on Saturday in our and many other rooms.  It was quite the turnout.  Again, we tried to accommodate everyone.  Friday and Sunday were much calmer.  If one person felt mistreated so be it.  We can only do the best we can,

I have enjoyed the project with Lynn for over a year now, and we are close to making them available for sale.  Like any audio product, some folks will really like them, and some folks not so much.  This is always the expectation.  The Pacific Audio Fest was a perfect example of how many different ways there are to build a stereo at different price points and levels of performance.  Some things are well worth the asking price, and others are not.  Let the customer decide.

@pindac 

There are only a few things one can do to keep someone from pirating a design.   Point to point wiring and manufacture avoids circuit boards.  When someone sends a PCB design for manufacturing, there have been cases when designs have been stolen.  That said, there is little that can be done to eliminate someone tracing out the circuit.  I used to restore vintage tube gear years ago and one major American manufacturer would actually use regulator and other chips whose labels had been erased so you couldn't tell what part they used.  They guarded the schematics of course, so you simply could not repair their gear unless the problem was obvious.  

One just has to hope that owners are honest.  I have never had a problem with the issue.  I suppose should this design become wildly successful, someone may wish to steal it.  The power supply is non-standard and would be a little more difficult to copy, but the possibility exists.  So be it.

I might add that these preamps and amps will be produced by Spatial Audio Lab in Salt Lake City, UT.  The builders are young and will be around for a long time.  Should they ever need repair it will be easy shipping.  They should be quite reliable though.

@alexberger Fantastic!  I love success stories!   I came around to really good ITs on this project.  LC coupling was next best, but once I got the custom wound Cinemag IT, designed specifically for the circuit it was no contest.  Enjoy your amp.   You have installed a top shelf IT and now you know why:)  There is no going back to coupling caps.....

@antigrunge2 Yes, IT is known as an excellent way of coupling, but it is expensive for very good ITs, and also they take far more physical space than your typical coupling cap.  So most vintage tube amps use RC coupling due to cost and size considerations.   Bad ITs don't sound very good, they can oscillate, or have very poor frequency response.  Done correctly with top shelf ITs and with a plan for the layout, then IT coupling walks all over RC coupling.   Medium ground is LC coupling with a high quality anode choke and good capacitor.  Also, there are circuits and tubes that are very difficult loads for ITs, so it is process of using the right method for the right circuit.  It is not one size fits all....  But in the right spot, I prefer IT coupling....

@alexberger 

I don't use tube rectifiers in power amps, but I do use them in preamps.  In your amp, if you wish to keep the 5u4g, I would consider using it for the input and driver section and using good quality diodes to drive a separate power supply for the 300b.   I use only regulated supplies, and I have my way of doing it that I don't wish to get into here.  But, yes, it is a good idea to have separate supplies for the input/driver section and the power tube sections.  What sort of supplies is up to  you, but a DHT will echo your power supply AND your filament supply very clearly so make sure they are very good.  

Good luck!

Don

@lewinskih01 I have experimented for years with tube preamps.   When I built the Raven preamp it was after I had sent the 300b monos down to Spatial Audio for the Seattle show.  Then I built the matching preamp.  They were able to run the mono amps directly from the tube output stage of the Lampizator Pacific DAC, and they had one with a volume control.  I wanted to test it so I took used my Pacific DAC (no volume control) and implemented digital volume control in ROON.  It worked fine and sounded good.  I built the Raven preamp and inserted it in the system between the DAC and my 300b amps and the improvement was obvious.   I have done this experiment before with other preamps and DACs and every time I have preferred the sound of my good custom tube preamps to a direct connection from a DAC to the amp.  I have built passive preamps with the Khozmo volume controls.  I always preferred the active tube preamp and it was never close.  That is just my experience and others will undoubtedly have different opinions, but I have experimented off and on for years and always preferred a very high quality active tube preamp in the system.  That said, I have never owned active crossovers, nor will I, nor have I ever bi or tri amped a system, nor will I.  So my experience is not really applicable to your case.  I prefer the simplest system with passive crossover and one amp per speaker.   My 2 cents and of course your mileage may vary:)  This is why I build high quality active tube preamps for people with fairly simple systems.  Just my preference.   

This is where my good friend Lynn and I disagree:)   I have heard my Lampi Pacific in the same system as the May (which Lynn doesn't favor).  I have heard various tube based DACs, the Schiit Yggy and a few others for SS, and the Pacific is in a different universe to my ear than any of the others.  I have not heard the Bruno Putzey DAC except briefly in the Songer/Whammerdyne room.  I liked the sound, but I need to hear things in a known system.  That DAC was over $10K though.  I will bet money that in a blindfold test I will prefer the Pacific or perhaps the expensive SS DAC over the $1000 Chinese dac du jour on ASR.   Of course the rest of the system has to be totally transparent for such differences to be heard.  My 2 cents and others will disagree.  Of course the law of diminishing returns kicks in very hard somewhere about $1000-2000.  The Pacific and others of that class live and breathe in a way that even the May cannot (to my ear).

The above, in a nutshell, is why tube amps behave very differently at clipping than SS amps. It is why, with the right speaker of course, that a 60 watt tube amp can sound like it has the drive of a 200 watt SS amp, and especially why these 300b monos with a mere 27 watts each can sound like a 200 watt SS amp. Those of you who heard them at the show when the system was cranked up could hear their drive capability on an open baffle speaker of approx. 88-89 dB efficiency with a stable 4 ohm that is very well behaved. You cannot clip the amps at any sane volume level, and they can deliver large amounts of instantaneous current, while maintaining their sound quality.

There are certainly speaker designs that require 200 watts of SS amp power to wake them up. These amps are not for those speakers. But any reasonably "tube amp friendly" speaker is no problem.   If you have a speaker that presents a difficult load for the amp, then certainly one of the class D amps may be a very good choice for you.  

@atmasphere 

Yes we agree.  If you cannot drive a loudspeaker in a normal room to adequate levels with 60 watts/ch, then you really need to reconsider your speaker choice!

The least efficient speaker I ever owned was a pair of Joseph Audio RM25si Mk2, which were 89 dB and a true 8 ohm easy load.   With the 60 watt amp I could play them to FAR higher levels than I would ever listen to in a very big living room.  Now my speakers are generally in the 95-97 dB range so I could do the same with 10 watts.   The 27 watt 300b monos hardly know the speakers are connected.....

There are so many just brilliant speaker designs out there that are 89-90 dB+ and easy loads.   Why on Earth people get huge 84 dB poorly behaved speakers that require 200 watts/ch or more is beyond me.....

@atmasphere Please don't think I was implying that "tube watts" are somehow louder than "SS watts".  Just that I have heard both driving speakers and straining and I know which I would prefer to listen to when driven hard.   When I was building the 60 watt push pull Kootenay amps I had numerous customers sell 120-200 watt SS amps after getting one.  Many of them described the amp as easily playing as loud as their big SS amps on 87-88 dB speakers and sounding better to their ear.  That of course means nothing since obviously 60 watts was plenty to drive their speakers to levels they liked in their rooms, but they were shocked what a "mere" 60 watts could do.  I am not implying that my 60 watt tube amp was the world's greatest, just that a competent 60 watt tube amp can do a heck of lot more than many people think.

As an aside, I have an old customer who has the stereo prototype of the 300b mono project amps.  He hooked it up to a small pair of Maggies that is a difficult load and told me that was the first amp (27 watts/ch) that drove those speakers that well and he had tried some large SS amps before.   So it is quite amazing what a reasonably well made tube amp can actually drive.

Yes we all have different tastes.  I would say the Lynn and I overlap considerably.  When we discussed our favourite rooms at the PAF we were in general agreement.  I stand by what I said a million pages back in this thread.  If I were to magically create a straight wire with gain that could drive any speaker load with infinite power and had no sonic signature at all, my guess is that half the people wouldn't like it.   Heck, maybe I wouldn't like it.   If I were to characterize what I favour it would be lush, not mush, an ethereal high end where cymbals and triangles hang in the air and decay, and tons of detail without brightness.  I hate artificial, in-your-face detail created by bright sounding systems.   I am an imaging freak as well.  If I build an amp or preamp and the sound stage doesn't extend at least a few feet outside the speaker boundary and the vocal doesn't appear at the floor to ceiling interface, then something is wrong.   I was a little dismayed at the show when our system could give great depth, but we had a shoe box of a room and the sound stage was constricted in height and width by the room boundaries.  Same system in my room threw the sound stage I just described.  I voice things with acoustic instruments and vocals.  If you can get a piano right you can pretty much play anything else with correct tonality.   If you can follow individual voices in a choir or instruments in an ensemble of some type, then your system can handle complex passages without breaking down.

Oh, and I love a good horn system.  Not the cheap ones that are popular, built with junk parts and cabinets, but a good horn system.  

So that is what I like.  Lynn and I agree more than we disagree!

@bcurtis1 I looked that piece up.  It has absolutely no tubes of any sort in it at all.  Can you enlighten me?  Did I miss something?

@alexberger Consider using the tube rectifier for the front half of the amp and good diodes for the 300b.   Do a C-L-C for each and use a good film cap as the last one after the choke.   Separate power supplies allow the input and driver tubes to basically not know the 300b is clipping.  When you push the 300b the power supply for the whole amp sags a bit.   With separate supplies the input and driver sections are isolated from the 300b.   You will hear a certain ease and clarity to the sound that you don't have now.  The Blackbird uses a similar approach, but much more sophisticated power supplies, which I will not get into.

Actually, I have already improved the preamp considerably with a few subtle changes, and the power amps will get improvements to the power supply with the larger case, as well as higher quality and physically larger film caps in what we now know are 3 really important places.  I could not fit some things in the previous case that Lynn and I agree should be added.  I would expect the whole system to sound noticeably better than what was at the show.  Same tonality, but a bit faster, with even better imaging and separation of elements in the sound stage, and tighter and deeper bass.  Experiments are already showing these improvements.  Production by the end of the year is the goal.  When we have production models there will be photos posted on the Spatial Audio Lab site.   I really appreciated meeting people at the show and getting their opinions!

Yes, it is quite surprising how sensitive these two circuits are to parts choices.  Much more so than any I have ever worked with.  I am used to coupling cap differences, and I have my favourite types, but there are several film caps in here that make as much or more difference.  Also, I have been through several versions of anode loading, and it is clear in this circuit that a custom designed interstage transformer walked all over the other choices in the amps.  We developed a new twist on the regulated supplies for the preamp, and now we will extend that idea to the power amp and then we are done.  As Lynn said, I think we are reaching the limits of what the circuits can do.  Also, I am trying the excellent Monolith Magnetics transformers as soon as they arrive.  I will see if this pushes the amps over the top!  As I believe I said earlier in the thread, this is pretty much a cost no object project to see what is possible with these circuits.   They sound unlike anything I have ever heard or worked with.   The better you make them, the less they sound like anything at all, which is about the highest compliment I can give an amp or preamp.

Much appreciated.  I will investigate further.  Vinnie is a well respected designer of note.

cheers,

don

Yes, you do star grounding, and you always do "sub" stars for each stage.  At least that is how I do it.....

nice wish list....   unfortunately, the power race is on to build even more powerful KT88 to get KT120 and now KT150.   They generate more watts if the amp can be biased to run them, but they don't sound as good as a good KT88.  I think it is the watts race that is driving development though.  What Lynn suggests would be really interesting and I would certainly try working with such a tube.

Funny you talk about filament sag.  I used to restore tons of vintage tube amps when I collaborated with Jim McShane.  So I worked on many amps that used the EL84 type tubes.   There is a Russian variant that is quite a good sounding tube and you could get them for peanuts.  The only thing was that for a series of years they made that tube, they suffered from filament sag.  They were tough as nails and worked for years, but it you tipped an amp on its side to work on something while it was running.... bbzzzzt.  Fried output tube and usually the cathode resistor as well.  You could run any other EL84 type in any direction, but not those Russian ones of that decade or so!  You could run them upside down without an issue, but not on their sides.

@eddie138 Thanks so much for chiming in.  Really interesting post and the economics are of course as you stated.   It is not like getting a custom capacitor made where you only have to have 100 of them for an order.   I guess that explains why manufactures stick with the known tube types where there will be a market.   Now if someone would start cranking out moderately priced 45 tubes......:)  But you would have to sell a lot of them to make it worthwhile.

Basically what Lynn just said.  Once you hear it you cannot go back.  Even the best caps cannot touch it.  Now, that said, you will not hear this if the rest of your system is not up to the task.  You put a $500 DAC in front and a mediocre preamp that uses small signal tubes, and a mediocre pair of speakers behind and you will mask all of this.  You are not going to get this with cheapo ITs either.   The Lundahls I played around with last year sounded good, but rang at 15KHz.  That doesn't mean Lundahls are bad, just that they were not designed specifically for this circuit.  So if you get really good quality ITs that are designed for your circuit, then you will hear what Lynn described.  These replaced VCap ODAM, and I also tried top shelf Miflex and Duelund JDM copper foils.  All are very good caps.  None has the realism of the custom wound Cinemag transformer.  I have no doubt the Monolith iron is superb and I am about to try their OPTs whenever they arrive.   But you need iron of this quality.  You wouldn't judge all coupling caps based on a cheapo Solen, nor would you judge all ITs based on something like a Hammond or Edcor.

There are levels and to my ear in our circuit (important caveats), the top quality IT is better than the top quality coupling cap used in the LC with a very good anode choke.   My 2 cents and feel free to disagree, but it is what I hear.

What you will hear in your circuit .... I don't know, and it doesn't make me right and you wrong or vice versa.

Again, basically what Lynn said.   At each stage of the project whether in the preamp or amps I discussed the exact parameters and even shared the relevant part of the circuit with Dave Geren at Cinemag, who is a very experienced master winder of small transformers.  He models everything and makes a prototype and then I build with it and listen. Then I give my impression and measurements of the frequency response to him and we do round two where he tweaks the design and that is that.  Dave is also a maestro of core materials and interleaving.  The result is that all coupling caps are now gone from the input to the preamp to the output of the amplifiers.  Certainly you can accomplish this with direct coupling in places.  Every approach has strengths and potential pitfalls.  One advantage of transformer coupling is the complete isolation of every stage and the banishment of hum, and also far greater immunity to ambient RF.   Also, if a tube goes south, or a customer does something odd like put the wrong tube in the wrong place (yes I have repaired things where people did this), or pulls a hot running tube, any potential damage is limited to a very small portion of the amp.  Direct coupling can lead to a daisy chain of failures, cascading through your amp.   These are considerations for commercial gear, where numerous units will go to many environments over which you have no control.  I can build whatever I want for my living room because I know how it works, and I can fix it.  But if a commercial product I want reliability.  Transformers are very reliable.

I will say that I have had the luxury of semi-retirement to spend a over a year with these preamp and amp circuits.  That has allowed me to try pretty much every permutation and combination of power supply and coupling topologies.  We have finally settled on everything and the final tweaking is about done.  When you are trying to make a living selling gear you generally get something that works and sounds quite good, and is reliable and then you make them.  When you are semi-retired you can go down every rabbit hole until you find the exact sound you seek.  Good enough isn't good enough.....

So my comments above are based on this approach.  I cannot tell you whether you will like all transformer coupling vs. RC or LC using your favourite capacitors.  I much prefer IT coupling, but I had everything custom wound by a very experienced winder, and we did a prototype and final version in each case.  I can do this because I have time and am willing to devote some money to the project.  For your one off amp you are forced to buy off the shelf transformers, but there are some very good winders out there and if you communicate what Lynn discussed with them, you may well get a very good solution.  Just don't expect to pick a transformer off some web site and have it work perfectly.  You will have to communicate with the winder.  I wish you all success.  If you persist, then you can probably get a great transformer for your circuit.

 I will also say that if you heard the gear at the Pacific Audio Fest in June, you heard prototypes and the set in my living room is considerably better, both preamp and amps.  Now they are about done.  The cases will be redesigned by the folks at Spatial Audio and the amps are getting physically larger so we can fit one more mod under the hood, which I expect to bring the sound up yet another notch.   Then they will be commercially available, probably late Q4 or early Q1.  There are already 4 or 5 folks on the wait list at Spatial and I would expect them to have gear very late this year or early next.  So if you are on that list, your patience will be rewarded with gear that is considerably better than what was shown in Seattle.

Lastly, I will say that internet forums are both a blessing and a curse.  There are people who tout one amp topology over another, or whether they prefer SS or tubes, or interstage transformer coupling over LC or RC, etc...   When you read these things consider the source.  There are lots of people who have strong opinions about what sort of coupling to use between tube amp stages, or even whether they should be direct coupled.   We all have our biases.  You need to figure out whether that poster has actually tried custom transformers for example or whether the opinion is based on some off the shelf midrange transformer.  Or the person who states that coupling cap quality doesn't matter much, or they love this or that cap.  The question is what have they heard before, what circuit is it going in, etc.... I have had several cherished notions overturned by this project, simply because I experimented thoroughly with different approaches and let my ear by the final arbiter.  I started out with the silicon assisted tube amp approach and ended up with all IT coupling, like the original Karna amp.  So my point is that you have to keep an open mind.   I am definitely a tube guy and solid state makes me unhappy when I listen for long periods of time, but that said, if a pair of Ralph's latest and greatest Class D amps appeared in my living room I would give them a serious audition and chance to shine.  I hope to hear them at a show some day.   As I said way up above many pages ago, there are many paths to audio nirvana, and we all may have our own.

I rebuilt a number of classic mac tube amps when I was restoring vintage gear.  They all sound very nice, but the mac house sound is a bit soft to my ear.  Sort of on the warm side.  Pleasant sounding, but not the absolute last word in detail.  The preamps sounded like that too.  Very good gear if you like that sound and very reliable, but warm....  CJ gear was also a warm sound.

The HK Citation gear was the most razor flat sounding, and the Fisher receivers were actually quite good.   The Scott gear was also quite good, and my favorite small integrateds were the Sherwoods.   Their little EL84 based integrated was quite good if rebuilt.  None of these are as good as the really good modern tube amps, but only the really good gear.  The transformers in the much of the old gear were really good, but they didn't have the quality signal path parts we have today.  Also, they had all sorts of features that robbed signal quality, like miles of wire in the signal path to support things like stereo/mono and phase reverse switches, and of course tone control circuitry.   Very long signal paths in many of the old integrated amps and preamps.

The Dynaco ST 70 had good transformers, but the driver section was barely adequate and if you replace it with one of the more modern boards, especially the all octal tube ones, the amp is greatly improved.  The small chassis limited the quality of the power supply you could fit in there though.  Still, if modded, the ST70 is a great little amp for the money.

@atmasphere Actually, I have rebuilt a few ST-70.   I agree, the rectifier is inadequate, but so is the driver section, which is at clipping at or just before the output section clips.   I have heard a couple of drop in boards and the octal version was by far the best.  Much better amp with 6sn7 input tube and 6sn7 drivers.   Still, the small case keeps you from installing a really nice C-L-C supply built with only film caps rather than lytics.  When modded it is a cute little amp, but hardly worth the trouble compared to other designs in my book.  I recall another vintage amp or two that used 6GH8 or similar for driver section, probably Scott, but too long ago.  Yes, we re-wired the sockets to take more common variants of the triode/pentode combo tubes.  They are all nice little amps, but not in the same universe as the topologies we are discussing in this thread.   However, would make nice little systems though with good speakers.  

I recall a Fisher flagship el34 amp that was really rare that actually sounded quite good when restored as well.  So long ago I forget all the model numbers!  When I was doing all the vintage work I could probably have rattled off the model...

@atmasphere Hi.. you are only running 3 6sn7 tubes.   Input tube and then a long tailed pair driver on each side using a single 6sn7....

@atmasphere the ST70 power transformer spec was allegedly 2 x 6.3 V windings @5A each.   Pair of el34 is 3 A, even a pair of 6sn7 is only 1.2A, so that should be only 4.2A.  Should be safe 

@charles1dad

I am sure it is a great amp.   Looks like my usual sources have 6EM7 for $15 a tube or so.  If you love the amp, you probably already have bought a few for the drawer.  If run conservatively I would expect them to last a long time, so a few spares will set you up for many years of listening.   As Lynn said, I just cannot design an amp around extinct tubes.   The exception are the various damper diodes and gas VR tubes.   But there are tons of these out there for under $10 each and they last many years.   When we ramp things up we will source a mass buy.   It is always risky to design gear around extinct tubes... a delicate dance.  You certainly don't use rare tubes.   I think your 6EM7 is reasonably available so you should be good for years. 

Yes there are current production 45 tubes, but they are ridiculously expensive.   As soon as Linlai decides to make one it will be much more reasonable and quite good I am sure.  You can still get some of the TJ full music ones at about $350 a pair if you know where to look.  I am sure they sound pretty good.  There is no reason you cannot buy a quad of modern production for $700 or less if there was another source.   Even so, if a 6V6 will sound pretty much as good for $50-100 per quad as a driver, then I would probably stay there.   For a preamp tube... then maybe I would run a quad of 45 tubes, but I hesitate to design a preamp around tubes that are $700+ per set.  

I would do a full wave bridge if you have the choice 

Rolling your own is always cheaper and can be fun!  I would highly recommend that people build good quality kits if they can do so.  It is a great way to start.

I use the Linlai E-6SN7 pretty much exclusively.  A very well balanced tube that rivals any of my NOS ones and I can buy all of them I want.  The PSVane tennis ball shaped ones are also quite good, but I prefer the Linlai in my gear.  Point is that there are some very good modern production 6SN7 tubes.

The treasure globes are most likely just hand selected psvane tennis ball tubes.  They are indeed also a very good 6sn7 if they will physically fit in your application.  The Shuguang WE6sn7 series was wonderful as well, but sadly all things Shuguang are out of production......   The Linlai WE300b copy is superb and what we will provide with these amps....

@1markr  I have not heard the original WE300b, but I have heard many of the $400-500 per quad 300b tubes and then I heard the Gold Lion 300b, which was a definite step up.   Then I got the Linlai WE300b copy and it is a far better tube than the Gold Lion to my ear.  I am not looking for other 300b tubes now.... not when I can buy the Linlai WE300b copy for a rational price per quad.

I have only had 3 or 4 pairs of the tennis ball psvane 6sn7 tubes come through here and I have yet to see a microphonic pair.  I still prefer the sound of the Linlai E-6SN7 though.   @1markr  I think you will love the Linlai WE300b.  They take maybe 50-100 hours to really come into their own, so be patient.  Just put them in and forget about it and listen.  In a week or two or three they will really open up.   I am sure the super expensive original WE300b, or some of the pricier other 300b types may be slightly better, but these are so good I really don't care.  There are far greater returns from changes to amplifier topology than switching 300b types after you hit a certain level of quality of 300b.   Also, I am listening to them in my push pull 300b amp that is the original subject of this thread.  I cannot say what they sound like in a SE amp or preamp or wherever else you may be trying them.  They are very good in my Lampi Pacific DAC as well, but I prefer my 46 tubes with adapters to any 300b there.  So application matters a lot.