300B, 2A3 experiances wanted

Bruce I've heard your amp once, at CAF a few years ago and it sounded nice with 300B tubes. That said I much prefer the 2a3 tube it's much more transparent and linear than the 300B while still maintaining a sense of naturalness to the sound. The really important question is what speakers will you be driving? Because your looking at either 3.5 or 8 watts so they better be very sensitive and easy to drive!

The sonics of the 300B are mostly limited by the power and linearity of the driver section, because it is much harder to drive than the 45 or 2A3.

IF the driver is linear and powerful enough, the 300B has a power and expanse unmatched by anything else, with transparency as good or better than a 2A3. But IF you use a 12AU7, 12AT7, or 6DJ8 driver, the 300B will be murky and congested, and the 2A3 (or 45) will sound better.

Like everything else in audio, it depends. Some power tubes are hard to drive, and the 300B is one of them.

A pentode like the 6C6 is better for driving a 300B than those small triodes. My SET45 amp uses one 6C6 per channel.

@lynn_olson @jasonbourne71  The possibility of the 2A3 is one of the reasons I got this amp and I am enough of a contrarian to go this direction first. I have heard others say the same as you , Lynn. If that were to be the case do you have any recommendations on specific makes of the 2A3 to start with? Is the 45 synonymous with the 2A3? You got to love the naming mess for tubes. It is not unlike the case with pharmaceuticals or pesticides.

Jason, speaking of contrarians I always enjoy your takes on things here at the 'gon. I am not familiar with the 6C6, is it like a 6L6? can it run in the TU-8900? If not what amps use it?

So many variables, difficult to have some overarching opinion. I run 845 and 300B amps, used to own 2a3 mono blocks. The 2a3 amps had this 'lit within' quality, read transparency the other SET's don't have quite as much of, but then 845 has massive drive the others can't match, 300B just right in my present setup, textured, so immediate, transparent, resolving, etc. IMO, transformers are most critical part in SET amps. I've also experimented with boutique caps and resistors, changes are easily heard in these minimalist circuits. My favs at this point are Duelund tin plated CAST, Texas Components TX2575 for clarity, resolving, Takman carbon film for musicality.

The 6C6 is an older pentode (early 1930's) than the 6L6. The two are not interchangeable. Will Vincent (autospec) built my SET45 on an ST70 chassis using Emcron output trannies. A C6C drives a 45 for 1.75 watts out. Rectifier tube is a 5V4. I wanted a 45 SET after reading about the Yamamoto 45 in Stereophile some years ago. Will did an excellent job for half the price of the Japanese amp!

Neglected to mention power supplies as a major variable and critical part of any audio component. Look at internal photos of 300B, 2a3, 45 amps, you'll see relatively large discrepancies in capacity, large, stiff ps will be more authoritive, greater drive.  I tend to go with mono blocks for greater real estate and non-shared power trans. Any one example of these amps may or may not reflect others, ie, some 2a3 amps may drive speakers other 2a3 struggle with.

I also have a Sanei 260A SET amp from Japan. In it I have a pair of gold-pin Electro Harmonix 2A3’s.

A good source of knowledge about offbeat tube circuits/amps is Sound Practices magazine. Joe Boyd was editor. He liked flea-power amps (45, 2A3, 300B) with horn speakers like the Altec VOTT.

Friend had, prior to his death, the Elekit 300b amp not sure if its the same model. I will say it was a stunning little amp for the money. He used it on his Cornwall (new). He had a local builder assemble the amp he also go the upgrades with it. fantastic little amp if I do say. As for 300b tubes and 2A3's I agree with another poster that the 2A3 is to me a nicer sounding tube but at half the power of the 300b. that said both are some of the best tubes made so its close.

From my experience, after owning Triode-labs 300b and 2A3 amps, the 300b has a better midrange then the 2A3 but the 2A3 has better bass and top end then the 300b.  Granted your speakers are efficient enough that the power rating of both is not a concern. 

In the end I kept the 2A3 amps and sold the 300b amp. I found the 2A3 was just a more fun tube to listen to, were the 300b was the late night jazz session tube. 

I've used both NOS tubes and new production tube, for 300b's the new production Gold lions are really excellent for the money. for 2A3's find a set of RCA black or grey plate NOS those are the ones you'll want, dam nice tube if I do say. I can't afford NOS 300b's  anymore lol. 

The 45 is from 1928. Earlier than the 2A3. It was designed for home radio receivers/consoles. It has half the output power of the 2A3. Two pairs push-pull in a console will give 8 watts.

Joe Boyd of Sound Practices liked the 45 better than the 2A3. He also liked the half-power sibling of the 45 - the 71A - good for a mere 3/4 of a watt! I have some in my tube collection.

@jasonbourne71 I think you're referring to Joe Roberts. Otherwise, all your comments about Sound Practices are right on target. A very worthwhile magazine and reference for the ages.

BTW, for those who might be reading this thread but unable or uninterested in building a kit, Alan Eaton sells beautiful sounding 45 amplifiers for a very reasonable price. I have a pair of his monoblocks, which IMHO is the way to go with his amps.

Lol, I was reading Joe Boyd and thinking he was the producer of the incredible string band and a bunch of other British folk rock type bands. Thanks for the clarification, of course there could’ve been more than one Joe Boyd, I suppose :-)

I apologize! It was Joe Roberts who was editor of Sound Practices. Joe Boyd was indeed a record producer. Blame it on my old brain which is not getting any younger!

I have had a 300B amplifier with a 6f6 driver for many years.

I upgraded and rebuilt it many times.

What was an essential upgrade is adding an interstage transformer between driver 300B instead of RC coupling.

My experience shows that monoblocks are not essential for good soundstage and imaging. It is enough to isolate right and left channel power supplies by LC or even by RC filter. It gives enough channel separation except sub bass that is not important for imaging. But sub bass isolation is super important for the driver to output power supply. Otherwise we get PS feedback between output and driver and as result motorboating that leads to loose bass. As a result, it is better to separate driver and output power supplies.

Another important subject is power supply capacitors quantity and quality. The same thing is important for cathode bypass capacitors.

Good point: the 300B driven by an interstage transformer is a completely different animal than a 300B driven by RC coupling. From that perspective, an IT is almost mandatory to hear the full potential of the 300B tube. By contrast, the 45 and 2A3 are much easier to drive, and RC coupling works a lot better.

(RC coupling typically throws away 1/3 of the power of the driver tube, while transformer coupling is about 95% efficient. Big difference.)

Great input @glennewdick  on your tube experiences, I will be saving it for reference. The interstage transformer idea is a new one to me. I will be looking for examples of that implementation down the road if I fall under the 300B spell, but I have to be honest and say the cost of 300Bs is a deterrent, so I am liking what I am hearing about the 2A3.

Can I pose a broader question to you gentlemen of experiance with tubes? When considering the difference among different brands of a given tube such as the 300B or the 2A3 or Even the EL-84 would one reasonably expect to hear sonic differences closer to changing one's speakers or one's cables? In other words is the design of the tube more controlling of the sound produced or is it the execution represented by particular brands or models within a brand?

I will chime in since you have already bought the piece of gear you are going to assemble.  I have 45’s, 2a3 and 300b amps-Triode Labs, 2a2, Yamamoto 45 and 300b and Coincident Frankenstein 300b and preferred the 2a3 over the 300b amps, better bass and treble and not far off a 300b on mids.  I used NOS RCA 2a3 and preferred them over any modern tube with better dynamics and better across the whole frequency band.  My favorite is the 45 but believe you can’t use that on your kit you will be assembling.   Congrats and good luck on the build!

Audio Note has IT 300B looks very nice.

Check out the Bottlehead Stereomour 2A3 parafeed amp. There is quite a bit on diyAudio about this circuit topology.

I used a simple transistor-MOSFET "Shunt regulator" to replace the RC (self-bias) in my 45, 2A3, and 300B SE amps. The sound quality improved significantly. All my audiophile buddies were amazed.

The very nice thing is that I can set the right amount of idle current of the power tubes. 

I share the same preferences as cfarrow.  I like the 45 too, but, as a tube for a SET amp, it can be used for only very efficient speakers.   A dealer who builds his own house brand amps used to build his pushpull amps to run 2a3 tubes quite conservatively; those same amps were used by some customers to run 45 tubes.  The 45 were being pushed hard—high B+ voltage—so they did not last long (about a year or so), but the amps did sound good.

I have a TU-8900 with the Lundahl transformers and Gold Lion 300B's driving my AG Trios and am very happy with this combination, having had many amplifiers in the chain.  At the price point of the TU-8900, nothing comes close. 

Despite the high efficiency of many horns, I have found (IMHO) that you really need more than 3 or 4 watts to drive them full range, hence the advantage of the 300B over the other tubes mentioned in this thread.

Good luck with your project.

Agreed on power needed for what would be a true full range sound(lubachl).

I recently parted ways with a pair of Zu Druids V that were rated I believe at 101 db efficiency that I just didn’t get the sound I was looking for with my amps.  I replaced them with a pair of hORNS Mummy’s rated at 93db and the sound opened up quite a bit for me in my listening room which is 18x14.  It’s a fine line between having enough power with any of the tubes we are talking about and what speakers you use.  I prefer a full range sound with in room dynamics of 65-80db.  300b’s will give you that extra power you need unless you sit in a more near field position. 

The TU-8900 is an excellent choice.  I think I heard a stock version.  Your plan to do subsequent upgrades if the basic amp sounds good to you is the right approach.  The parts that the distributor--Victor Kung--offers and suggests are very good choices.  I would start with a transformer upgrade--this, more than anything else determines the sound of an amplifier.  The option of silver foil Audio Note caps is also enticing--these caps deliver a clear sound without sounding thin or harsh.  

@alexberger so you added an interstage transformer into a 300 B amp that originally did not come with it, if I understand correctly. What amp was it and what kind or what model transformer? Did you determine the specs for this or did someone else? I would like to learn more.

I am not familiar with your amp and maybe this is tossing an unnecessary hang grenade into the debate for you but there are other, somewhat esoteric tubes that are in the middle and may work for you.  

Have you looked at something like the Emission Labs 300B Mesh 2.5v or PX4 or PX25.  In the case of the 300B 2.5v it is a drop in replacement for a 2A3 and is a middle ground between the two tubes.  It is more detailed and linear than a 300B but not to the extreme of a 2A3.  PX4 and PX25 are in the middle with the PX4 closer to a 2A3 and PX25 closer to a 300B.  

Years ago Dick Olsher reviewed a PX25 amp and referred to it as the closet thing to "velvet in a bottle" he had ever heard.  Tubes that have characteristics of both could present and ideal compromise.  

Full disclosure, I am one of the two importers of Emission Labs tubes.  Not just trying to sell you tubes (I make nothing on them).  Just think it was an interesting provocation.  

Hi @bruce19

My amp is DIY. The set of tubes was always the same 6sn7, 6f6 in triode and 300B.

But for 15 years I did different upgrades of this amplifier. A year ago I added IT between driver and output. Then I made a separate PS for the driver. After that I added IT between input and driver. And In the end I disassembled the amplifier and assembled it in the new chassis.

https://photos.app.goo.gl/isJsvYM3x7hDaput9

Here is the old version of my DIY amplifier

https://goo.gl/photos/S25aReL5jyTuAF1G9

@cfarrow 

What is your favorite 45 tube?

I also love the 45 and have a Yamamoto A-08s with Emission Labs tubes. Big improvement over stock tubes, at a big premium. But always interested in learning about great tubes from experienced users.

I use Sylvania or RCA, have the Emissions Labs tubs as well but prefer NOS.

Thank you @cfarrow 

How do you find the Sylvania and RCA different from the Emissions Labs? Who do you buy Sylvania/RCA NOS from?

I think I'll try another driver for 300B - 6v6 instead of 6f6. I already bought new cathode resistors to adjust the circuit for 6v6.

The question is what 6v6 can you recommend? Which NOS and modern 6v6 do sound best?

Hi Alex,

I would prefer using those NOS 6V6's. They are available from Ebay and https://www.usaudiomart.com/.

Hi @kmtang 

The link you gave doesn't point to any 6v6 tubes.

Which 6v6 did you mean?

Hi Alex, 

The link is just for the US Audio Mart. You may search for 6V6 tube from there.

There are a lot of vintage 6v6 tubes. Which of them sound good?

The new 6v6 I see Psvane. I have Pasvane 5u4g and 12ax7 and they do sound good. On the level of good (but not the best) vintage tubes.

There is a new JJ 6v6. But I have a JJ ECC803S and I hate the sound of this tube. They have such a bad midrange. They sound like a bad SS amplifier. So JJ tubes are not my cup of tea.

I'm currently running Linlai E-Series 2A3 tubes in my Yamamoto A011. So far, I like them the best of the handful I've tried.

@bruce19 That ’magic’ you’re looking for in an SET might be mostly distortion- they make quite a lot of it, mostly the 2nd harmonic which gives ’warmth’ to the sound.

I’d give your ST-35 another chance. Here are the considerations that will help it out:

1) driver/input tube- the NOS ones are better.

2) coupling caps. This is a bit tricky in the SCA-35 but in the ST35 I think you have the room to install something similar to what you see in a lot of SETs.

The 2A3 assumed the mantle of King from the 300b sometime in the late 1990s and the type 45 in the early 2000s succeeded it. Its not because any of these tubes sound any better than any of the others- its because the smaller tubes are easier to drive and its much easier to make an SET output transformer with bandwidth if you make it for lower power. So the 300b doesn’t stand a chance if you equalize all the other variables like power supply, transformer quality, parts quality and drive concerns.

But I’ve found that if you put a PP amp against an SET, the PP amp is obviously wider bandwidth and more transparent (easier to make out vocals and the like; because the higher distortion of SETs obscures detail).

So I think you’ll want to think this one through very carefully. Do lots of audition, but if you do so try to limit the variables! For example, most of the time PP amps are considerably higher power, use feedback and may not be class A (I think the ST35 is BTW...). If you really want to hear what the difference there is about its best done with a PP amp of the same power and build quality as the SET...

SETs tend to sound ’dynamic’ because of the way they make distortion; for this reason they really don’t have much more than about 20-25% usable power before distortion causes them to sound ’dynamic’. On this account you really need an efficient speaker so you never have to ask greater power! By comparison almost any PP tube amp has more like 90-95% usable power, even if its zero feedback.

I’d give your existing amp another chance before you change it out!

I upgraded my 300b SET amplifier. I replaced 6f6g Torvac driver tube to 6v6 Psvane. 6f6 worked with idle current 26ma. 6v6 withe the same cathode resistors gave 24ma. I changed cathode resistor to get 29ma. In result much better bass control and dynamics, better instruments separation. 

Conclusion, the more powerful driver is better for 300b. I know some folks (including Sacuma) end by 300b driver for 300b.