Ok, I almost fixed the problem.
In fact I just disengaged the fx loop... So I put all my effects in front of the amp... and it works well.
My phaser sound better, my delay (numerique) a little less but good enough, my boost become... an unboost.
I remember a post before who said that Steeve D. wouldn't have an fx loop and Marshall (Jim ?) wanted one. Well Steeve was right it's good enough without using the fx loop.
But, if I want a durable repair I think (after some research) to replace FET and if I need to change one, maybe I 'll change all the three. I hope it will work.
And remember crack isn't good for health... sex is better.
VM 2266C/Epiphone VJ 5W.
Hohner Les Paul loaded with SD Alnico Pro 2
Lag Arkane loaded with EMG 81/85
Jackson RR loaded with SD SH8/TB10
Strat Ibanez home restored loaded with S/S Fender pickup and Kent Armstrong Humbucker
Full Stock BC Rich Warlock
Chity chinese telcaster home relic load with Fender 62 RI
Dunlop Wha/Tube overdrive/Rocktron Zombie Rectified Distortion
Boss Chorus CE1/EH LPB1 Boost/Biyang Delay and Phaser/MXR KFK 10 bands eq