ECC803 S TAD Premium Selected. In the Tradition of the Famous Telefunken ECC803S A long-plate ECC83 / 12AX7A in the tradition of the famous. Telefunken ECC803S. 1dB less gain than the RT003 (ECC83-Cz) but very detailed and defined, close to the RT001 (12AX7A), Its strong cathode current makes it an ideal choice for the audio driver stage as well as for HiFi applications.