Update !
Fuses arrived, replaced speaker fuse and combo back up and running fine.
Again, added 2nd TE cab and the combo instantly sound like the speakers had all blown, farting badly, next to zero volume.
Extension cab not much better. Fuse did not blow this time
Extension cab ( i may have already said this ) was tested through another amp, using the same cable and it was fine.
So it seems that the TE combo does not like a 2nd cab added, despite its ability to run two 8 ohm cabs ??
Any more ideas ??