Glennewdick mentioned the Finale amplifiers. I have not heard them but they have a very solid reputation for sound and built quality. The SET/SEP amps are very simple circuits with few parts, this why they're capable of such pure and natural sound .
The key to their success is a serious effort to build them right, meaning quality transformers and power supplies. The "junk" versions always cut corners in these crucial areas as George noted in his comments about winding transformers.
The better brands mentioned above won't do this as they know the result will be a crap/junk amplifier. My advice is to go in the direction of the serious intentioned amp builders and you will achieve very high sound quality.
Charles

