Maybe HiFi news didn't know what the taps were for?
mac 501 output power - hifi news June issue
The new issue of HiFi News - a british magazine - has a report of the Mcintosh 501 in which they indicate that power output is 195/300/700 into 8/4/2 ohms for < 1% THD, respectively with dynamic power a little higher. I always thought it was 500 watts into 8 or at least into 4. Any comments or any actual measurements?