Is there any 50W 300B SET monoblock out there?

The tubes used in the application of a SET design are the limiting factor not the engineering. There is only so much power a 2A3, 300B, 845 triode can produce. What you need is a tube manufacture to manufacture a more powerful triode tube.

As Brf indicated, there is only so much power a given tube type can produce. Using two or more power tubes in parallel, in a single-ended configuration, would allow more power to be generated, and is sometimes done. That would be referred to as a PSET (parallel SET) configuration. Alternatively, the VAC Renaissance 70/70 MkIII amplifier I have uses four 300B's per channel, configured as two push-pull pairs in parallel with each other. It is rated at 65 watts per channel. But of course it is not a SET (single-ended triode), because it is push-pull rather than single-ended.

Regards,
-- Al

Check out the Emission Labs website. They have several 300b variants that can put out around 20 watts.

I built an SET with 200WPC. It uses the 833C Directly Heated Triode tube. It sounds like an enormous 300B amp, with better bass, IMO.

Not commercially available, but it can be done.

The Midlife Crisis

Ait, that image blows my mind!