ECC81 is 12AT7 medium gain pre-amplifying double triode. Can be also used as replacement for 12AX7 in many applications. Very smooth and warm sound. Very low microphonic. Good for phase inverters or reverb drivers.
6V6 S is a beam power pentode with octal base and a maximum plate dissipation of 14W. It has fat low end and full mid tones with very good tone separation and a smooth, clean high end. Known to be a very powerful 6V6 due to its robust construction. In general, a very balanced tone. It can be used also in some 6L6 amplifiers