Both of my US-Amperex 6922s, 1961 and 1964, sound very similar, as one would expect. However, the 61s are just a bit warmer and more forward, reminding me of my 1967 OGs, whereas, the 64s are a bit leaner and drier, with a tad bit more bass punch. Given my ears and gear, I personally prefer the sound of the 61s, but of course, I can easily see that others might prefer the 64s. Both are excellent tubes.
And I was surprised to read about the different Voskhod getter posts in your review above, as in your July post, you differentiated the 75s only by shield color. So there are three different 1975 Voskhods! Anyway, I managed to purchase three of these, two from one vendor and a third from another, but won't know what I have until they get here.