here's a discussion of the "standby" mode on a BAT VK-30se preamp with input from Victor Khomenko of BAT. I'm pretty sure the VK-31se behaves the same way.
http://db.audioasylum.com/cgi/m.mpl?forum=tubes&n=86582&highlight=standby+vk&r=&session=
http://db.audioasylum.com/cgi/m.mpl?forum=tubes&n=86582&highlight=standby+vk&r=&session=