With a single ended tube amp it is easy to build your own. But to keep it linear you can't push a tube very hard. You need heavy duty transmitter tubes. There is a WAVAC SET that sold for $350,000 that you can build with under $2000 in retail parts. It runs 833A triodes at about 1000 Volts which will make these tubes last for many years. Hammond makes a transformer more than robust enough and more robust than any bigger name or vintage transformers and Lindahl makes an input transformer for the grid suitable for a 45 SET to drive the 833A.
This gets you SET purity you can use for less sensitive speakers such as planar magnetic speakers which have a purity that is difficult to approach with cabinet speakers.