Well, after nearly a week of listening to the Mullard ECC35s with the EL38 & 274b I’m really enjoying them now. I guess there has been some burn in but also a case of getting used to the different presentation.
It's definitely added more weight and texture to the bass when used with the EL38s. Very spherical stage with lovely lush mids a d smooth highs. The lad I bought them from had another 2 1950s tall boy versions with the skinny base so I have a backup on its way. I guess at some point I’ll see how they sound with other pairings but if you need to loose a bit of that clinical feel from EL38s, it’s certainly a good option.
Still prefer the 5691s for electronic, EDM etc.