She'll take a 5687 or a 7044 or a 6900 (should you be lucky enough to have any of those), they're similar enough to work in that spot.
It'll take most any 5v rectifier that can deliver the current. 5u4 or 5AR4 or GZ37. At the moment, the B+ is right for NOS 6B4s - when I run the Sovteks I can crank up the B+. It's also easily converted to fixed bias for up to 15wpc. It's 7wpc currently.The chassis is 10x17. The largest that would fit in my cheapo cabinet.
Speakers are old Klipsch Heresys circa 1977 - still alnico magnets then - at least on the mids and tweeters. (They're slightly modified.) Driven from the 8 ohm tap.
TC