Yes , it's coming from the power amp section ... I'm losing my mind : all caps are new and tested, all resistors values are ok, all diodes are new. voltage values are ok. It's not a lack of earth noise. I also tried different transistors ... The only way would be a breakpoint in the circuit i think.

Hi guys !
It's been a long time but I was ill, so I couldn't do anything on my amp.
Now I'm recovered !
I changed all vishay diodes, and put a brand new pair of transistors. I do have change all diodes of the power amp stage.
Well, it works ... but !
But now I have a pretty loud buzz, ca 100hz. I can hear any input ...
I don't know if it's come from preamp or power amp ... Any idea ?

The board without ics ...

Progressing : i put a BC557 at the mysterious transisor place. Nothing seems to fry !
Now, I try to check up signal path. I put à 220hz sine wave in the input jack. If U3, U4, U5 ad U6 are not on the board, the signal is ok at the fx send and at the phones jack.
So, there is a problem with the eq stage and / or the preamp op amp. voltage at all tl072 is correct.

Here are the pics of the bord and the faulty transistor. Looks like the others mps8599 or 8099 on the board.

Thank you phatt, Only have to find a old bulb  and not led  !
And thank you  g1 , I let you know the progress !

Hello !
Thank you for your replies ... There was a transistort here, and no resistor ! It's a factory modification. As the transistor burns, I dont know the reference, either the purpose.
Here is the schematic I have. There is no match with this circuit !
My amp is a WT300, but the board is labelled WT400 !
Should I just put a resitor ?

Hi there !
Who can tell me what transitor fits at the end of the yellow wire on the photo ?
(It's not on the design of the schematic circuit ...)
Thanks guys !

It's called CR13 (one of these in the heat sink)
Seems to be good but the vf value is different from the others (616mv vs 840mv)

Thank you for this wise advice ... I tought that the amplifier must be loaded by a speaker. Today, I  made different tests : it seems that everything is okay before the power amp section. Something seems wrong with one of the vishay diodes ... (BYV26D). I'm out of these components. Should I order BYV26E (1000v vs 800v) ?
I'll change every diodes, zener and transistors of the last stage, it's not too expensive ;-) and let you know the results !

Ok thank you, effectively  I didn't mount heatsink completly. Let's make a trial !

Hi there,
I have a difficulty with the repair of my old Deluxe 85.
Power transistors have fried , RIP ...
One of the 1N4448 diodes seems to be the cause. I changed all the diodes, zener, caps. Power voltage is ok.
As soon as i put new couple of transistors, they fry ... sometimes I hear a buzz before. Any specialist ?
Thank you !