In the late 1990's Stereophile ran an article about the 300B "God's tube" single ended triode. You could buy as a kit or a schematic to build your own such SET from Cary Audio in North Carolina. I built my first SET and began my journey. The modern 300B tubes had cheaper inferior cathodes to the coveted Western Electric 300B tubes so the price for scarce Western Electric 300B tubes went to hell. However, the less powerful 2A3 sounded richer, but NOS 2A3's were less available. The 45 globe triodes, or the 245 globe triodes were made the same way the Western Electric 300B was made and were affordable but they are less powerful. Eventually someone I thought was crazy built and sold 833A radio station transmitter tube SET amplifiers costing $350,000. The 833A was driven by a 300B. The circuit was simple and I was ready to change from complicated box speakers to Magnapan 0.7's which circumvented all the problems of box speakers. 0.7's could not be driven by 45 SET's but I could keep my SET sound if I used my 45's to transformer drive the grids of 833A's and Hammond made a perfect output transformer for the 833A that could insulate up to 4000 Volts the modest 1000 Volts I used for the plates of the 833A's.
I never went back to factory built amplifiers since I started my 300B journey.