2a3 ?

I had a wonderful Tektron amp that used 45, 2A3, and 300b.  I think the 2A3 might have been best but it depended a lot on the tubes.  Jerry

I own the Coincident 300b stereo and am very happy and impressed with it. I did upgrade the tubes on my own.

There are fans of the romantic sounding midrange of the 300b, who will not listen to anything else, while there are people like me, who like the tube, but not as much.  You simply must listen to a variety of amps using the various tube types to make up your own mind.  

All of these simple triodes are most often employed in single-ended amps, but they work well in pushpull; the sound is different for the two topologies.  Pushpull tends to have tighter, punchier bass and a better sense of drive, but, single ended amps tend to sound more natural, relaxed and less "mechanical" sounding (the bass punch of pushpull can sound the same all of the time, hence mechanical, while single ended amp bass seems more subtly variable).  I like both types of amps.  As I mentioned above my favorite is a very low-powered pushpull amp, but my all time favorite amps (that I don't own) include an output transformerless amp and an extremely vintage pushpull amp that runs a 252 tube (variant of a 300b).

I am a huge fan of the SET vs the push pull.  Push pull is your only option if your speakers are not sensitive enough but my speakers are and i've tried several different amps.  SET for the win.

Jerry

SETs have a limitation of the greater the power, the less bandwidth is obtained from the output transformer. 7 Watts (300b) is a practical upper limit to what can be considered 'hifi' bandwidth. The 2A3, being good for about 4 Watts, allows the designer to have a wider bandwidth and therefore less phase shift (which can be heard in how the sound stage is presented). The reason the type 45 has ascended the throne in the last 20 years is for this very same reason.

A pair of 2A3s in push pull can produce about 16 Watts, making for a more practical amount of power. If the circuit design is good, it will not cede anything to an SET; quite the reverse.