Quote Originally Posted by AlexM View Post
I have three NOS Tesla E83CC in the phono stage of my CJ ET3, and they are very good indeed. I think we need to introduce a little perspective - these valves will perform very well but we are talking about a reasonably subtle improvement if you comparing NOS to NOS (or new-new). We usually think they are very much better compared new to old, tired valves plus a big slice of expectation bias. Nice dimensionalality, and clean, neutral tone, with good detail are characteristics, but I have some Ei 12AX7 which are almost as good sounding and long lived too (if they survive initial burn-in/early life failure!)
Indeed Alex and a good point about the ageing aspect.

To add a little technical meat to the bones of this thread... much is likely to depend on the exact use to which a valve is put, its biasing, and also power supply voltages. Hence a valve which gives great subjective results in one amp may be not so good in another make or a different position. As far as gain goes well the gain of a triode (mu) is one aspect that is fairly well controlled in manufacture and for a ECC83 should be 100. Actual gain depends much on surrounding circuitry and mu is the maximum theoretically achievable from the valve itself. In the case of pre amps using negative feedback (the majority) the overall gain will be set by the feedback and only slightly effected by the choice of valve... there are some variants with a bit more than standard gain, usually intended for guitar amps in order to give more distortion/overdrive.