amp question

[Linda Delong <delongj@xxxxxxxxxxxxx>]

  I have a question for you amp techs out there.I play with a CR bullet
through a Harp Commander into a BF Deluxe.The tubes in the Fender are in
stock configuration.I'm very happy with the sound of this setup, but
after the amp has been on for a couple hours, it seems to lose a little
volume without changing any settings.Is this a sign of a developing
problem? The change is slight so it might just be my old ears playing
tricks on me but I think it's real.The power tubes are about 3 years old
and I use the amp 3 to 5 hours a week - should I replace them?Other than
replacement tubes and speaker, and a 5meg input resistor the rest of the
amp is stock.Any advice or comments would be appreciated.
                                                Thanks,
                                                         Jeff