For some time now I've used a Tesla E83CC in my Croft preamp as my NOS ECC83-type tube of choice (along with the main output NOS 6SL7 tubes I've mentioned before on another thread, RCA5691s and Tung Sol 6SU7GTYs), as they are to my ears, along with the Telefunken 803S, unquestionably the finest sounding ECC83/12AX7s ever produced.

The filigree detailing, sheer midrange 'presence' and huge soundstage these tubes give has to be heard to be believed!!

To that end, I bought a matched quad of NOS ones from 1982 from Tubemonger in the US before they were discontinued to do me for years (these are exactly the ones I bought). Btw, this is the 'proper' Tesla from Czechoslovakia, not the inferior 'JJ' of today:





Telefunken 803S:





However, there are TONS of fakes around, and people claiming that grossly inferior tubes are 803s or E83CC, which makes it a bit of a minefield for people trying to distinguish between them.....

So, I found a couple of interesting articles which describes exactly what to observe when looking for GENUINE 803s or E83CC frame-grid tubes:


http://www.jacmusic.com/nos/ECC83-part-numbering1.html


http://www.jacmusic.com/nos/images/Fakes/index.htm


Therefore, if you're in the market for buying these very special tubes which have such unique and desirable sonic characteristics, you'll no longer be fooled by inferior sounding imitations!

Marco.