Thanks Sam. Dimension-wise it is identical to the -8 type.

Besides the dimensions, I cannot see any other physical or performance differences between the -8 and -13. Even the weight is shown to be the same.

The type numbers on the labels (according to the datasheets) are different:
-8 has 577009-1153-000
-13 has 577009-1161-000
and mine, the -15, has 577009-1169-000

So maybe the -15 is the -8 package with a binned tube. In any case a 6.5 mA supply rather than a 7 mA should work without overload.

I have emailed LASOS but I won't hold my breath.

Alex