Versions the ECC81 comes in are:
♦ECC81/12AT7, ECC81 and 12AT7 are exactly the same, 12AT7 is the USA name and ECC81 is the name used in Europe. The CV455, CV8154, CV9859, CV10662 are the militairy numbers for these tubes.
♦6201, 12AT7W(A)(B)(C), 6060, E81CC are the special quality long life versions of the ECC81/12AT7. These tubes mostly has thicker mica for lower microphonics and extra support rods for more stabilisation, etc. Later ECG (Philips) version do not have these extra's and shouldn't be called 6201/12AT7WA. The gold pinned versions are often also called ECC801S. The CV4024 and CV5212 the the militairy versions of the 12AT7WA and 12AT7WB respectively.
♦The M8162 is the English version of the CV4024, one of the best sounding 12AT7's ever made.
♦The 6679 is the mobile version of the ECC81. It is the same as the ECC81, but can maintain good specs with a variation of +/- 20% of the heater power.
-7728 is the premium instrument grade tube made only by CBS/Hytron. This tube has heavily plated gold pins.
♦ECC801(S) is the premium version of the European ECC81. These tubes were made and tested for low microphonics and low noise. The "S"-version is specially selected for low noise.
♦The B309 is the old English version of the ECC81. This is the real vintage and very rare.