The JJ ECC803 has a classic long plate design with a special grid to reduce microphonics noise. This is another offering from JJ and once again it's a beautiful sounding valve. It has a deep, tight low end that the ECC83S has but the mids in the ECC803S are even thicker and more harmonically complex than the ECC83S. The ECC803S is also a touch hotter in the high end than the ECC83S.
This is a great tube for V1 positions or for use in all positions in vintage amps. I do not recommend them for use in the gain stages of high gain amps if you like to run your gain full on. All preamp tubes are microphonic it's just a matter of where the threshold is and longer plate tubes will squeal before a short plate tube will, so for real high gain amps I would stick with the ECC83S. I wouldn't recommend these in small combos where the tubes are in close proximity to the speaker.