[Amps] titan 425 dimming, dropping power

[mike george]

hi new to list hope someone can help with this. fired up the 425 and noticed the 1500wts was down 3 or 4 hundred wts. looked at the rf deck and the lights were dimming out on peaks.the plate and grid current is ok but the plate voltage drops from 2200 to 1500 on peaks.i tried on dummy load same result. other amp on same 220 outlet works fine on same ant. i dont see anything obvious inside the power supply. tubes are not getting hot. not sure where to go. thanks mike george