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(Bruce J. Richman) said:

I'll second the quacking . Many users don't think that, for example,
Svetlana 6550C or EI KT-90 Type III output tubes are inferior to some of the
older GE or other historic brands at all. (Chinese output tubes, granted, are
not all that well received by many users).

The problem with many Chinese brand tubes is their reliability.
I've had many 6550s from Chinese descent that sounded wonderful, but
lasted very short in a standard application.
It is said their quality has gone upwards the last few years, but I've
never since tried any Chinese tubes.
I've heard similar reportings from tube-related friends of mine.

I can live very happily with modern production Svetlanas, Sovteks and
JJ Teslas though.

--
Sander deWaal
Vacuum Audio Consultancy