Speaking of TubeDepot - just came here to chime in that I got a pair of their Sovtek 6N1P's ($25.95 ea/$32~ with options) that they have listed delivered today. I haven't seen these mentioned.
They're shockingly good, I was about 4 songs in before I ordered another pair to have on deck. Very resolving, clean, natural, and controlled presentation. I was expecting to plug em in, give em a listen, and be like, meh another spare set to the pile, but instead I am very pleasantly surprised by how much I like them.
Edit: Just to throw out a somewhat comparable reference, I have the Genalex Gold Lion 6922's and they fell into that "meh another spare set to the pile" category.
For what I typically like in this amp - I primarily listen to USA Amperex 7308's (have a pair of orange and white label, prefer the orange).