McIntosh MC275 VI preamp tubes

The Black Diamond Telefunken tubes are are made by JJ in Slovakia:

"TELEFUNKEN vacuum tubes have been the benchmark of excellence in all audio applications, both production and reproduction, for many decades. This rich history continues with the introduction of new production tubes from TELEFUNKEN Elektroakustik, in partnership with JJ Tubes from the Carpathian Mountains of Cadca in Slovakia."

JJ tubes in general do not have a reputation for good sound, but the black diamonds may work for you, who knows? The one thing to be aware of is that new production tubes have nothing in common with the vintage tubes whose names they use. These new production tubes license the names from whoever owns the rights and that’s it.

Some of the classic tube makers sold their equipment to others when they shut down production. I think Telefunken sold some equipment to Tungsram and some Mullard equipment went to Japan, IIRC, but even then the tubes produced were not identical to the originals. They could be very good tubes though.

I should have known I couldn’t recall correctly. It was Ei in Yugoslavia that bought the Telefunken equipment according to this web page:
12AX7 Tube Gems - Tubes for Amps

Which is kind of odd, in a tube nerd kind of way, because Ei was owned by Phillips who owned many brands like Mullard, Amperex, Siemens, Valvo, etc. but not Telefunken. Maybe Phillips cut Ei loose when demand for tubes began to drop. Anyway here’s a quote from the link above:

"Ei was a tube factory that operated in Yugoslavia. Ei had close ties with Dutch Phillips. They even coded their tubes just like Phillips did.

Ei also supplied OEM tubes to companies such as Telefunken when they shifted their focus away from vacuum tubes. In fact, Ei built their small tubes on tooling supplied by Telefunken.

Now, although Ei got their tooling from Telefunken and tutelage from Phillips, their quality control tended to be minimal. So Ei screened their small signal tubes and labeled the good ones as Elites and sold at a higher price. They also offered gold plated pin version as Elite Gold."