For quite a few years, I was wondering the phones on the attached pictures were a clone or the original design - until recently I came across phones featured in this thread. Well, as you see, they do have a striking resemblance to the Yamaha!
I bought two pairs of those Soviet-made 'phones new in the early '80s; they were called "isodynamic" and back then were likely the best ones produced over there and were most expensive. The sound quality was quite good (or appeared so) back then, but deteriorated over the years. Last year the first pair has developed destortions, and I disposed it; the second pair (pictured) is still alive, althouth barely. The cushions are completely gone, but my daughter still uses it on her Technics digital piano; in fact, she prefers them to Sens' 600 she has.