I know very little about this, but I have been keeping half an eye out for circuits. There tend to be one or two recommended, but I know one good one is the Mullard Circuit. The 5 10 is the most often mentioned, 5 tubes, 10 watts. Bigger versions too. Lots of stuff online including this: http://www.r-type.org/articles/art-003e.htm Google it and you'll also find a booklet on Mullar, available on the Primary Windings site. Their blog features some Mullard builds and they also do a number of the necessary transformers. https://primarywindings.com/product-category/mullard/ There might be better versions, but the Mullard circuits are well documented, and there are a good number of Brit companies that supply transformers, including Primary Windings, Sowter and Majestic. I suspect Edcor do too. In short, the 5 10 seems almost to be the 5E3 of audio amps. Would be very interested to see your progress on this.