Brimar EL84's if you can find them, Sylvania Black Plate are very good, The amp was originally voiced with Tesla 6BQ5 tubes and will sound good with them too, if slightly cooler sounding.
Ndoshi, many thanks for your reponse. I thought I might not get any responses, which is understandable given the small numbers of these amps in the U. S. I will have to look for some Brimars. Currently I'm burning in some new Ei's and some new Valve Arts to replace the well used Sovtek EL84Ms that came to me with the amp (but which still sound nice to me).
Again, a big thanks for helping me out on this one.