Sorry - I went on and on about Russian stuff - but the point I was trying to make was the Cyrillic transliteration of "Nuvistor" is "Нувистор" and there is a Russian-branded product of that name with the logo you showed. What looks like an "H" in that logo is actually the Russian letter "N."
Н у в и с т о р
N u v i s t o r
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Нувистор 6П37Н-В
(Nuvistor 6P37N-V)