LobalWarming
Headphoneus Supremus
That's great! My 70s/80s versions are not clean - at least the famous soviet quality control worked out for your examples.I have some Melz from the 70s and 80s.
I find the 70s ones the most detailed tubes I have ever heard. Very clean and extremely extended. The 80s ones are a bit mellower. I have never found any of them bright but on my amp they are being balanced in conjunction with power tubes which will of course will make a difference. For example with WE 300B and their midrange focus they are amazing IMHO.

My 50s 1578s provide an excellent, well-balanced listen. Purchased cheaply, long before that demented despot invaded his peaceful neighbour.That said I've never heard the 50s ones.
I would certainly love to hear them but I've never seen them anywhere to purchase ever! unfortunately. Do let me know if you see any around.