According to an old brochure I have on hand from the 80's the 6B info provided is:
Rated distortion: less than .02% I.M.
or THD from 20-20 KHz at rated power or below.
Rated power:
500 watts 8 ohms
800 watts 4 ohms
500 watts 2 ohms
800 watts 1 ohm
6400 cm2 of heat sinking, etc.
19" X 5.25" X 13.5", 50 lbs.
From the general specifications from all amplifiers:
Noise 100db below full output
Crosstalk - below noise 20 to 20 KHz
Slewing rate greater than 60 volts per microsecond
Power bandwidth less than 1 Hz to over 100 Hz
Damping factor over 500 at 20 Hz, ref. 8 ohms