Some years ago I used American Amperex 7308s a lot in the CSP3. As an input, it stayed in a really long time. As outputs, I also liked them depending on what else was in the amp. I think to balance the tube's particular signature, especially its warm/rich and complex mids, and slight upper end roll-off, I used some nice, spacious and fast PCC88s with the Amperex.
But as I progressively got other areas of my system smoothed and refined, balancing edge with very fine detail became a revelation, and these 7308s started having too much signature for me...
Having done a number of modifications over the last few months to the CSP3, musically refining the signal, and many on the forum loving them, I thought I should try the 7308 again. I cleaned up the pins put it in the input.
I left in my latest standard outputs, parasol getter 60's Mullard ECC88s that are warm in the way I like, without sacrificing really good detail, while being extra good at very fine detail. With a fast/revealing/open/spacious yet sweet Mullard GZ32 (this tube has been in my system a really long time for me!), the sound is great. Fine detail and spacious ambient information were quite good, the abundant micro detail of the other tubes supporting the American Amperex's textured, open and revealing midrange emphasis.
These are clearly really good tubes, doing what they do in a beautiful, open, and mellow way. Very quiet, revealing, warm, rich and spacious mids especially, with a refined and musical bass...they seem mellow and revealing at the same time.
Probably because of the mods I have done to the amp, making it more quiet and revealing without edge, the balance has shifted enough for me to really like the American Amperex again. Generally though, I have preferred tubes that are more transparent and neutral....also without edginess, but with less signature.
Now, oddly for me, I am using all Mullard tubes in the CSP3. An A-frame getter 60s ECC88 in front, the parasol getter 60s E88CC in the middle, and a early 60s GZ32 rectifier. This is unusual, being used to getting my favorite sound mixing types and makers.
Like usual, for me, if it is good stuff to begin with, it is more about balancing parts than one tube or another being a good one