I have a pair of Von Schweikert VR-7 tower speakers. Their forte is a fantastic open, airy sound. I conducted a comparison of about 20 6SN7s and the surprise winner to my ears in terms of maximizing the open, natural sound of my speakers were Westinghouse 6SN7GTB tall copper rod. These edged out several variations of Sylvania chrome domes, Ken Rad, Sylvania VT-231, RCA, Tung Sol (but not the ones which are highly sought after). The Westinghouse can be had for $10-$20 each. I now have 4 of them and they all sound identical to my ears. Nearly all of the ones I've seen were manufactured in the 1960s.
The worst one I tested was the new production Tung Sol. I wanted to like it, as they are plentiful and inexpensive, but it produced such a flat image.
The worst one I tested was the new production Tung Sol. I wanted to like it, as they are plentiful and inexpensive, but it produced such a flat image.