"Arny Krueger" wrote in message
...
"Iain M Churches" wrote in message
So should I take measurements at different power levels?

For a tubed amp, FR & phase response might change a fair amount at higher
levels.

Arny. Thanks for that.
I am aware of the differences between FR (at 1W) and power band width
and have plotted these. However, I did not realise that phase response
might differ, until you mentioned it.

Iain