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

I’ve run 845 SET amps (Antique Sound Labs, USA) and been very satisfied with their 27watts per channel.   Very quit, lovely midrange, tight powerful bass and extended highs.   Great imagine and overall tonal quality.   They matched well with my electrostatics.   If you are concerned you need more umphf, then you might consider a SET based on the 845 tube.

Another 2a3 fan here it has a clarity and a speed that 300B doesn't have, to my ears at least.

Again don’t listen to anyone here, me included😂

With all due respect to others here, you don’t need a higher power amp, and a 2A3 amp is or is not better then a 300b, there is no such thing in this world as better. Every time you change your speakers or your amp, you’ll have to decide if you hit on the right equation. If you didn’t hit on the right equation it’s not the amps fault, it’s just that situation. I had a 45 amp that didn’t sound good with the Altec's I had, didn’t sound good with Tannoys, and I just put it aside and one day tried it with some speakers I was using at work and bingo. Again it’s a culture.  It’s a tremendous fun little corner of the high fi world. And if you get into deep enough you’ll find yourself looking for copies of Sound Practices magazine. 

Very good points yaluaka.  Every component choice involves some kind of tradeoff, and if low-powered SET is your thing, you either live with some compromise on ultimate volume capability or a MUCH more limited range of speaker choices.  The right sonic choice depends on a wide range of variables and one should not limit the candidates by the type of tube, or for that matter the topology--single ended triode is NOT inherently better sounding than pushpull or output transformereless, etc.  I own a parallel single ended 2a3 amp, a pushpull 45 amp, and a pushpull 349 amp.  The parallel single ended 2a3 is, by far, the most expensive and it is terrific sounding, but, to my taste and in my particular system, the pushpull  349 is the best overall.  If I had to pick the best amp I've ever heard, it would be a custom built OTL amp or the Western Electric 59B amp (pushpull 252 tube that is an ultra rare and expensive tube similar to a 300b).

After hearing many amps employing these tube types, I do come away with some very general observations about tendencies, although there are many exceptions.  The 2A3 tends to be leaner sounding (not as much warmth and upper bass) than the 300b, which also means it has a clearer sound and it has very good dynamics and has tighter bass as compared to a 300b.  The 45 is very nicely balanced and has tight bass, and sort of lies between the 2a3 and 300b in terms of midrange warmth.  There is something "beautiful" about the midrange for the 300b.  It has a very warm, comforting sound, but, it does not have quite the dynamics and lively sound as the other two types.  I've heard pushpull amps that are very similar, by the same builder, employing all three types, and these rough characterizations come through.  No particular sound is "better" and much depends on the speakers being use, the room acoustics, etc.  

+1 for Aric Audio

Give Aric Kimball a call, he's a great call even if you don't buy his equipment. He offers 2 different 300B amps, a 2A3 amp, an EL34 "Push Pull" amp, a KT88 "Single Ended", and a pair of KT monoblocks. I own his Motherlode XL preamp, and the EL34 "Push Pull", and they are ridiculously good with high end components.

Ralphs (Atmasphere) tube amps get great reviews (though I've not heard them), and would be a great option for OTL amps. He even suggested that you look at the below Raven monoblocks.....tells me a lot about his honesty.

The Don Sachs/Lynn Olson Raven monoblocks that Ralph suggested, are Don and Lynn's end game amps.....though end game costs $10,000 for each monoblock