i know, it's risky ...buts, it's work...
the amp and the psu was isolated from vibration&shock
when it switch off, the remaining high voltage from cap, will go to 5v at 1/10 second
accidentally any shortcircuit from anything (ex: alarm, horn, lamp,....or..) the Amp.psu will shut off
actually this amp was built from '06,... and the valve was fine until now...(i'm from growing country/Indonesia, "you know, the road was far from smooth ")