Stereophile published an article on the Westinghouse 300B, which, unlike cheap modern 300B triodes, had a triple coated cathode which lasted longer and was the secret to the better sound. If you can tolerate less power the NOS 45 globe tubes were made the same way and many people find them richer sounding than the cheap modern 300B.
Around 2005 there was a Japanese 833A SET amplifier driven by 300B transformer coupled to the grid of the 833A and rumor had it the 833A was run on only 1000 Volts with a positive grid bias to force it to draw more plate current. It sold for $350,000, but the parts and labor could scarcely cost a percent or two to manufacture it. You would not need high sensitivity speakers for it, you can use planar magnetic speakers if you want. Lundahl has probably the best coupling transformer there is for coupling a globe 45 to the 833A grid which can run on zero or ground bias for eliminating a bias supply capacitor from the signal path and this is more than enough power for driving less sensitive speakers. Either a globe 45 or a WE 300B will work for this. Hammond makes a more robust air-gapped output transformer rated at higher DC current than smaller more expensive big-name brands and it is perfect for the 833A.
This is relatively easy to build yourself for less than $2000 retail in parts if you know how to be careful with the 1000 Volt power supplies it needs.