Marshall vs 100 head

[Gunn_Slinger]

Hey Guys
I have a used marshall vs 100 head.
It works ok but I would like to replace the 12ax7.
Do i have to take the amp out of the box ???
I do not see any access to the tube to my surprise

Thanks
Clay

[Ronsonic]

Yes, amp comes out of the cabinet for a tube swap.