I kind of missed that detail, didn't I ? Not very sharp these days. The tubes are the 5670/2C51/6N3P/396a types. There's actually a bunch of equivalents. This acts as just a buffer, and no need for balanced triodes according to the manufacturer.
Apparently with an adapter one can use a 6922 type, but since I have none of those in the stash, the 5670 types are more economical to acquire. (none of those in the stash either until recent shopping)
I've been trying out Sylvania (stock), GE, RCA, Raytheon, and Tung-Sol.