Telefunkens
I also rolled some Telefunkens into the C2300 both MM and line stages. I did not find the difference to be "night and day" but a worthwhile improvement none the less with a 'sweetening' of the sound - improved musicality. Of course, there are likely differences in the sound of various NOS, match tubes which could account for the end results. I purchased mine from Brent Jesse tubes. they were around 100 a piece a year or so ago. Well worth the effort. I will eventually pick up another couple of matched pairs to have in reserve.
Jason