I can recommend Eric Chan (McChanson on Ebay) based in Sydney
He recently custom built me a single ended triode based on the 300B.
Using interstage transformers instead of capacitors. So a total of 8 transformers!
Max power 10 Watts but I rarely even run it at 6 Watts.
Matched with a Pair Psvane 300B-T Mark II Treasure Tubes.
I have owned a lot of tube amps over the years, EL34, KT88, KT120 etc
Ultra linear and single ended. This is by far the best I've had n heard. He does have a very minimalist website. And comes with a lifetime warranty (his lifetime...lol)
Price with valves around 3K. I have used them with full range folded horns up to complex 4 way speaker setups. And they drive all loads with ease. Plus you can specify all components you want to use, point to point wiring, ALPS pots, silver wire etc
Eric has built 4 amps for me over the years and never a problem with any of them
Eric:
https://www.mcchanson.com/
Valves:
https://grantfidelity.com/ (note, lots of tubes on Ebay are counterfeits, this is a reliable source)