The 10A is linestage only, could that be why?/
According to what I read at their site, the 10AL is linestage only, while the 10A includes a phono stage. Although it was in the line stage of the 10A that the gain reduction was made; apparently an identical phono stage was used on both the 10 and 10A.
I take it that changing tubes is not a solution?
I don't think so. A good circuit design is designed to be as independent as possible of variations in tube characteristics, within the range of variation that can be expected for the specified tube type. Although in a no-feedback design such as this there will probably be somewhat more variability as a function of tube characteristics than with a design that uses a lot of feedback. But I still don't think that is the way to approach the problem.
Regards,
-- Al