bjp

Thanks for your reply Jesstaa
The power transformer is vibrating slightly, I think I'm more aware of it, because I'm looking for faults and scrutinizing every part now. The power transformer has had a maximum use of 10 hours and was a fresh Marshall replacement which I purchased from a service tech who used to be our Marshall service agent. The output transformer appears to be perfect as, I said , I have checked it for shorts and readings of the taps seem to be right. Through out testing it remained cool, and the amp did sound good. I am aware that there is a hell of lot more to testing transformers than I have carried out, but I think they are good. Thanks for reassuring me though
, in the past I sold many Marshalls but it never occurred to me listen to the amps when they were just switched on, these amps being new I guess I never really looked for anything other than that the amp worked and sounded good. Many thanks for your reply. All the best

BJP