Golden Tube

I would like to know if anybody has increased the input gain on their SE40 above where it's set new? My maual says to change the tube in the "V2" socket, and change the jumpers. I do not place alot of trust in these manuals, and my dealer has never changed one. Changing one tube does not sound correct since there are two tubes but, that is why I'm asking. Thanks much for any helpful info
I have adjusted the gain in my SE40, both of the driver tubes need to be changed to 6SL7 tubes and the jumper moved. Mine worked fine. I would also readjust bias if it changes.