DRRI ails

[jgyn]

Hi all!
After playing my DRRI a few minutes, a slightly less than voice level buzz erupted. Turned off standby, turned it back on again and buzzing resumed. Constant buzzing, whether guitar was plugged in or not, even at amp volume 0. Guitar audible when plugged in, and affected by amp volume knob, but at only 30% volume with a kind of ghosting distortion (think tuberculosis).
Do you think it's a preamp tube? Or something more dastardly?
Thanx,
-jan

[SatelliteAmps]

First possibility is tube. Could be other things, but that is the first thing to check.

[jgyn]

Thanks!