svt 4 pro going mute

[t bake]

while playing mute light came on out to speaker loss also fx send signial loss.pluged bass direct to board, cable & bass working.Loud tech could not tell me if that was a protect mode. checked speakers found filter foam melted to coil.thought i found prob. next useing backup cab mute came on no output. testing at home with pa cab played 3hr no mute.BUT!!!preamp section seems weak input light will not light till in gain is maxed tubes feel to cool output at bass .039vac . dont think it went thermal ran running did not feel verry warm. thanks for any help.