Two Marshall Haze 40's with the same difficult problem

[Corben]

Got my second haze 40 with a similar problem and the output transformers are ok. It just starts breaking over into this filthy distortion at like 3 on the volume not gradually but all at once. I noticed when i pull connector 6 that 80 percent of the distortion goes away and i can still get allot of gain out of it. It still sounds kinda dirty though. I'm just really lost on this tried everything i can think of Tubes are good, Ive checked for burnt through traces dirty sockets, bad caps, open resistors, Ive started replacing some of the coupling caps just to see but so far nothing. Another thing i noticed when i have both 6l6s in it goes into this early distortion all the way down to the phase inverter at least. If i pull v5 only it sounds way better. If i pull V4 only it distorts almost instantly. When i pull both v5 and v4 the signal looks really good on the scope all the way down to the preamp tubes.
Anyone have any kind of issue like this? Thanks for any help

[Corben]

I posted this late last night, still hoping i get a helpfull reply

[Enzo]

REally ought to post the schematic so everyone will know what CON6 and V5 might be.


COnnector 6 appears to be the NFB line from the output.

V4 and 5 are EL34 power tubes according to my schematic. You are using 6L6s?

So then:
Do the power tubes bias up OK? Spec says 39mv on either side.
If not, is there B+ on pin 3 AND 4 on BOTH popwer tube sockets? And is the bias voltage present at pin 5 on BOTH?

Have you tried different EL34s in the amp? A different 12AX7 phase inverter?

Plug the guitar into the FX return. Does it still sound bad out the speaker, or is that pretty clear?

If the power amp has the issues, then you have a scope, use it. Apply a signal, preferebly a sine wave, at the FX return. How does it look at pin 7, the input to the PI? And then at each plate of the PI. Are both sides looking clean? And now at the grids of the power tubes.