On the same "bonavolta" site, there is a 12B4 OTL circuit. Isuppose it could be tweeked for 6S19Ps.
From a lot of comments that I've read, OTL is more of a PIA than it is really worth... Mostly, OTLis simply too "tweeky" and unstable in the long run. And a lot of OTL designs take the B+ straight off the hot AC power line, not exactly the recipe for a long and healthy life :o :o :o
Unless you're a "glutton for punishment", I'd suggest sticking to transformer output tube amps Yellow_Light_Colorz_PDT_02
/ed B in NH