Some of the technical aspects of SET amps that many people appreciate, are pure class A operation, simple signal path, very linear amplification devices(triodes), and almost totally 2nd order harmonic distortion profile.
This typically leads to a very pleasant, coherent, and lifelike presentation, as long as the speakers are a good match. It is very difficult to match the purity of this type of amp, with anything else.
As with most things, the cheaper SET amps will suffer compared to the higher priced ones, primarily because of the cost of good output transformers is quite high. The output transformer characteristics will significantly influence the sound that you get from the amp, and cheap ones give the "rolloff and bloat" that many people associate with SET amps, because they have not heard the better ones. If you are serious, make sure that the SET amp you get has very good output transformers, as well as having a good circuit design.
Regarding tube choices, 300B is very popular, but I prefer the lower power choices, especially the 45. It limits the choices of speakers to quite a narrow range, but if you can get the right speakers, the sound is quite amazing. Alot of people are finding the 845 to be a great sounding tube in a SET amp, and this gives much more power and opens up the range of speaker choices.
This typically leads to a very pleasant, coherent, and lifelike presentation, as long as the speakers are a good match. It is very difficult to match the purity of this type of amp, with anything else.
As with most things, the cheaper SET amps will suffer compared to the higher priced ones, primarily because of the cost of good output transformers is quite high. The output transformer characteristics will significantly influence the sound that you get from the amp, and cheap ones give the "rolloff and bloat" that many people associate with SET amps, because they have not heard the better ones. If you are serious, make sure that the SET amp you get has very good output transformers, as well as having a good circuit design.
Regarding tube choices, 300B is very popular, but I prefer the lower power choices, especially the 45. It limits the choices of speakers to quite a narrow range, but if you can get the right speakers, the sound is quite amazing. Alot of people are finding the 845 to be a great sounding tube in a SET amp, and this gives much more power and opens up the range of speaker choices.