OK, I've never seen/heard a decent explanation of what goes on with a valve
amp with 4 and 8 ohm taps when it is hooked up to speakers of 6 ohm nominal
impedance.

Instinctively I use the 8 ohm tap but, quite recently, one of the yoofs in
HFW wrote 'simply use which one sounds the loudest' or words to that effect.
I know it doesn't appear to make a lot of odds, but summat must happen
differently in the amp on each of these tappings. I've seen references to
the valves 'working harder' one way and the trannies 'not liking it' another
and so it goes on.

Anybody really know? - I would love to hear the correct explanation....