Single tube, Single ended, 20W, impossible?

[revival56]

I guess the guy who built that power amp with the 211 was driving it with a preamp using the same transformer in reverse mode: 100K:150R.
Only practical side of this is that you can put them in separate cases....
Otherwise it looks more like a tube amp that needs a strong SS preamp. Maybe even using some specilized OP-amp...

the SEP 211 amplifier was built by Sakuma

 

[revival56]

interesting : look here :
https://jandkaudiodesign.blogspot.com/2017/09/tamura-stu-001-input-transformer.html