Question about the tube in the Vincent PHO-700

Lots of cats enjoy the 701. But there are also difference in both stages as the new 701 has switches for the MC. And I've heard that the   tube in the window can be rolled as its in the circuit.

If you remove the tube and the preamp still works then you will know that it is not part of the circuit. Why would the tube be controlled with the dimmer switch?  It seems that the tube is there just for looks!

As I mentioned, the tube is in the circuit.  This tube does not replace any solid state circuitry however.  I am very familiar with the circuitry on the 08, the 700 and 701.  The 700 is literally a 08 with an additional audio stage added for the 12 AT7.  Obviously, the tube has been added in addition to the 08 circuit to add a tube flavor if you will.  The 701 is a 700 with the addition of an internal A/D converter which is connected to a USB jack on the unit so the digital stream can be routed to a computer for recording purposes.  Tube rolling can help, but the tube in the 700/701 is an additional circuit the 08 doesn't have.  In other words, the 08 provides the most direct signal path.  Strange but true.

Basically it seems that the tube serves as a buffer stage.