Aronteo wrote:
Chad is really a cool chap - be very careful when biasing and always use only one hand in the amp (leave the other one in your pocket). It is a very easy procedure, but safety first. The tubes I suggested above are the very same ones John Mayer uses - for the moment, just use the stock ones Chad will send you. In the future, you can experiment.

Tubes really change the feel of an amp, much more than speakers IMO.
Hey hey, 

I'm intrigued by your statement: "The tubes I suggested above are the very same ones John Mayer uses" 
How do you know this, where did you get this information?

Cheers,

Robert.