Newbee is spot on with his advice. The stock tubes that come with the Prima Lunas are pretty decent and will serve you well. If you can identify in what direction you want the improvement, then the next step is to call Kevin Deal at Upscale and ask for his advice.
For my Prima Luna 2, I wanted to smooth the bass out a bit and went with Svetlana SED Winged KT88's. Good move. I read in a post Newbee (? or maybe Tobias) had ultimately gone with 6550's. I tried those, just to try them, and felt that they bridged the El34 sound and KT 88 sound nicely.
As for my Prima Luna 5, I have kept the stock tubes in place without looking for anything else.
Regards, Rich
For my Prima Luna 2, I wanted to smooth the bass out a bit and went with Svetlana SED Winged KT88's. Good move. I read in a post Newbee (? or maybe Tobias) had ultimately gone with 6550's. I tried those, just to try them, and felt that they bridged the El34 sound and KT 88 sound nicely.
As for my Prima Luna 5, I have kept the stock tubes in place without looking for anything else.
Regards, Rich