Newb Tube question

With vintage small-signal tubes, long plate variants are usually considered more desirable. Long plates and short plates are not specific to a manufacturer, but they are generally used in reference to 12ax7 or 12au7 type tubes. "Long" is generally around 19 mm, and "short" about 16 - 17 mm. In most cases, a manufacturer produced long plates in their early-year runs of that type, and then later switched to exclusively short plates (late 1950s - 60s). In general, earlier vintages from any given manufacturer contain features that are considered more desirable (but it can be hard to decouple this from the fact that earlier vintages themselves are almost ALWAYS more desirable in vintage tubes!) - other examples of this include specific kind of getters (square, "D", or double halo getters versus later single halo getters), black plates vs. grey plates, triple micas vs. double micas, pinched waists vs. straight tubes, larger and prettier getter flash patches (e.g. Sylvania "chrome dome" 6sn7), etc.

The "smooth plates" are a pretty unique feature and pretty much always refer to the Telefunken 12ax7/12au7 tubes. Those are excellent tubes. Ei (Yugolsavia) later bought the old Telefunken tooling and made smooth plate tubes for some years - these are good tubes too, but perhaps not as good as the original Teles.

With new tubes you can find tall and short plate variants of 12ax7/12au7. If I were to generalize (though probably badly badly), the tall plates tend to give a sweeter sound but the short plates could be less microphonic (less to rattle around).

Hi,
trust a reputable dealer for NOS (brand new) tubes. ECC83 (7025, 5751, ECC803, CV4004, M8137) is a very common tube so you have plenty to choose from, Teslas, Teles, Mullards, RCA’s, CBS, Raytheon, GE....Define first what short of sound you want with the tube rolling, but all of them, short or long, ribbed or smooth plates are fine tubes. Only by trying out you'll find the ones that suit your phono stage.

Caveats, in relation to "tube rolling".  First, in my experience mediocre sounding gear does not become wonderful sounding gear via tube rolling.  If you don't like the sound of your preamplifier, don't expect to transform it by buying expensive "rare" tubes.  Maybe that which is already "good" can be made a little better, at best. However, with some understanding of circuit design, sometimes changing a capacitor or the basic topology, here or there, can make a big and permanent difference.  Second, keep an open mind.  Sometimes you will be surprised by a Chinese or Russian made tube compared to an NOS Euro or US made tube.  Also, in some rare cases, you can substitute one TYPE for another which can be a big step up, but you need to know that the replacement tube will be connected to the circuit the same as the discarded tube.  Any time you can get rid of a 12AU7 or ECC82 in favor of a 6FQ7 or 6CG7, you will be happy, but in some cases you will need to do some soldering.  (6FQ7 and 6CG7 are electrically like a 12AU7 but filament current and voltage and connections need to be considered.)

I suggest trying some 6FQ7s with good paint. Conrad Johnson used them back when they were in production. Matched pairs $25-$50.
RCA sounds better than Sylvania to me.

To avoid a lot of disappointment and frustration: just follow tomcy6's advice.