The Studer A820 has a built-in headblock identification circuit that immediately detects when you have installed a half-inch (or a quarter-inch) headblock. The tape tensions then automatically change over to the appropriate values. Those values can be the factory furnished defaults, or optionally, custom tension settings programmed in by you.
It's with the A80 transports (and not the A820!) where the changeover from quarter-inch to half-inch format (and back) requires changing a host of hidden internal parts and a tedious, expert tension recalibration.