powered up my valve power amp this morning to a swishing sound in the left channel and a burning smell . Turned it off within seconds and the speakers thankfully have survived. Taken the lid off and at the base of each valve there are 2 resistors . These have cooked themselves on one of the valves only . Does anyone know valve circuit design , are these a final safety system if a valve goes short or would a faulty valve cause these to burn out ?? They are very low wattage resistors . A bit drastic I know but just wondered if anyone can shed some light on it for me . All was well when I turned it off before the fatal switch on !