Good history lesson !
I'm swapping to these russians tubes this morning. 6C15P (6S15P) the predecessor of 6S45P. Sovtek 6H30Pi but it's labelled as 6H6P-N. This is 6H30Pi that Eric call the Supertube.
6C15P - typical russian old boxes but these are rare now. I'm privilege to have sampled it. It is much better than 6S45P. It's so much more clearer.
6H6P-N - I wasn't so impressed with the EH 6H30Pi yesterday because the soundstage is narrower but this soundstage is as wide as the 6C15P and also super clear and vibrant. It's going to be a few more hours before I can decide whether I like this more or the 6C15P. Notice the box symbol and the tube symbol are not the same?