Good Tube Selection for Atma Sphere S30?

Russian power tubes are fine! The only Russian 6SN7s worth looking into are vintage made in or before the 1960s.

Pubul57, there are now Russian made, newly manufactured tubes marked 'Tung Sol' and 'Mullard" as the US importer has acquired the rights to those names here in the US.

What we have been finding with these tubes is very similar to what we find with the Electro Harmonix brand, as well as the generic Sovtek; if you put the tube on a tester it seems very likely that it will show leakage on the leakage test of the tube tester.

In practice, tubes with leakage can buzz if used in our amps. An additional issue has been that the life expectancy of these tubes seem to us to be really variable, some lasting only a few weeks. OTOH, we've seen US and Chinese tubes go over 50,000 hours.

I did inform the importer about these problems a good ten years ago. I was told that the 'next batch' would be different but so far that has not manifested, as far as I can tell.

That's correct. The 6SN7 is the tube where we've seen problems. The Russian power tubes work just fine :)

Hello Al, We reject the tube if we see less than about 10M. On some speakers its not such a big deal, but if the amp is used on horns tubes with such leakage are trouble makers.

Its not really that hard to find tubes without leakage (+50 Mohms) if you stay away from the Russians (BTW we *have* seen vintage Russian tubes that work great). So far IME if the tube tests with leakage, that is not going to change over time.