Where did you find instructions? What steps did you perform for this mod?

Sounds like a loose solder joint - as Modman suggested. Fender amps sound great but they have some notoriety for solder joint problems. I would suggest (if you are VERY CAREFUL) checking the soldering on the boards. Before starting, make sure that you are comfortable working with high voltages...if ...

Thanks for the thanks!!! Sorry I didn't think about resoldering the sockets - I should have known. The DeVille is similar to the Deluxe and the Deluxe has this as a problem. The tubes will get hot and soften the solder. In the past I have purchased three different Deluxe amps for very little money, ...

First - if you are not comfortable with following the steps below - take the amp to a tech. There are deadly high voltages in the amp. Tubes can be bad - right out of the box. Usual cause of the symptom you describe is a bad tube...but it seems to follow the socket. Is the glow red or orange? Red me...