300B or 2a3 SET Class A for Heretic Model A?

All good amplifier possibilities by the OP. I'd like to suggest another possibility that would let you have your cake and eat it too -- Why not consider building an Ele-kit TU-8900 from Victor Kung at VKmusic.ca?

I have one and really love it with Avantgarde Duo SD G3 horns. The Ele-kit is an easy build and with the carefully curated upgraded parts that can be bought from Victor with the amp kit, it is a very high performing, lovely sounding amplifier. It is auto-biasing and auto-sensing between 300B and 2A3. Herb Reichert at Stereophile loves his (Gramophone Dreams #74 

For not much more money you could add a Sunvalley SV-S1645D, also from Victor Kung, that uses the 45 tube or with an inexpensive plug-in adapter socket, the the 46 for outputs. Less power than the 2A3 typically produces as a SET, but Oh My! the 45 sound is seductive.

I've both of these amplifiers, having moved way to the other end of the spectrum from my previous D'Agostino Momentum M400 monoblocks, and I am completely happy with the flea powered amps. 

Anyway, just another couple alternatives out many fine amplifiers. Aric is also an excellent possibility and he will build you an amplifier that can switch between 2A3, 45 and 46 if you approach him about it.

Good luck with your journey!

Steve Z

PS: @yaluaka -- Best posts I've read in years. What I want is My-fi, not some else's idea of hi-fi.

Stev eZ

To me this is also a specious point, the idea of accuracy in recorded reproduction. I’m looking for something I like. I don’t want a stereo limited by only sounding good with any particular music or record label. It’s not about accuracy, to me accuracy is anti musical. I want the music I listen to- to be engaging. Accurate is irrelevant, in fact I don’t think it exists. Perhaps an extreme view point. You get into set amps because you want to experience the music not judge the recording.

@yaluaka It appears to me that you are conflating ’accurate’ with ’anti musical’ as emphasized above. That isn’t how its supposed to work; if the amp isn’t musical its also isn’t accurate. IOW if you want the most engaging presentation, the amp will be both musical and accurate. That exists. When the amp is musical but not accurate (as is the case with most SETs) then while it might be engaging, its not as engaging as it could be, because you’re really not hearing the music properly.

For some decades now the solid state community has beat up on tubes by saying that solid state is more accurate. But most of the time those amps were not musical because they made distortion to which the ear is keenly attuned. So those amps had ’low distortion’ but sounded harsh and bright- not at all engaging.

As a designer, once you understand how the ear perceives sound and how that relates to distortion amps make, you can design an amplifier that is both accurate and musically engaging. If you really understand how this works, it doesn’t even have to be a tube amp; the ’sonic signature’ of any amplifier is also its distortion signature. So if you can get a solid state amp to have the same sort of distortion as a tube amp, it will sound like a tube amp. That’s only one of the implications of understanding how this all works.

Put yet another way, there are tube amps that are more engaging than the best SETs, with wider bandwidth (read: more and deeper bass impact) and greater power at the same time.

Its not about judging the recording so much as it is enjoying the music. We’re on the same page with that. It sounds to me as if you’ve been exposed to too many amusical amps that were purported as ’accurate’ when they were not. Harsh and bright to me a far more egregious coloration than the ever-lovin’ 2nd harmonic of tube amps. But if you can get that 2nd harmonic down, you can get more detail, since distortion obscures detail. And you can do this without it being bright.

Again I feel you are missing my point. I am assuming you make amps, funnily enough I make records. So what I care about is musical engagement, this really has nothing to do with accuracy. Why I feel accuracy is anti musical is because you are focused on accuracy. That is not where I am focused. If the amp is accurate and I like the way it sounds great. If it's not accurate (I still really do not believe in this term but I'll use it for this discussion) and I like the way it sounds great as well. The accuracy part is the least of my worries, and for me doesn't enter into the discussion. Just the fact you posit - most single ended triode amps (SET) are not accurate - right then then and there tells me you are not focused on what is important to me, which is how the music sounds. I've learned through making records that distortion is often a musical attribute. I know people don't feel that is the case in the hifi world, but try to get an Al Jackson on Hi Records drum sound without it.

And as for me being exposed to to many amusical amps, I have actually instead been exposed to too many amusical audio fans 😂

@yaluaka I am very focused on the sound; if its right then the music is processed by the limbic portions of the brain which increases body movement and emotional response. Increased engagement.

I run a recording studio as well as manufacture amps and preamps. When the system is accurate it is also musical and engaging. IOW 'accurate' and 'musical' are not two different things. They are the same thing.

If you think otherwise it is because you've only encountered equipment that was claimed to be 'accurate' but was not (and was amusical; far too much of that out there) similarly the 'musical' equipment you've heard apparently was not as musical as is possible because it could not also be true to the music (accurate) at the same time.

Now I get that you can use R2R tape to warm up a digital recording (because it adds a 3rd harmonic) or run it through a single-ended tube circuit to add a 2nd harmonic; I understand how distortion affects our perception of musical (keeping in mind that understanding that is important for the design side of my work).

What I'm saying here is the distortion signature of any amp is paramount to how it sounds- the distortion signature is its sonic signature. So obviously the distortion signature must be as benign as possible (lower ordered harmonics dominant as seen in an SET or our class D or our OTLs) but also as low as possible so the equipment can reproduce low level detail properly.