Problem with my Marshall 76' Master Volume

[Samplegod]

Hello all,

I totally refurbished my 76's Marshall Master Volume.
I posted in another thread some issues regarding the OT wiring that I think I solved.
All the caps, tubes, sockets are brand new.
The bias is propertly adjusted, all working and sounding good!
The guitar in the "low" input works perfectly, but in the "high", lots of more gain all seems to be ok untill the "pre-amp" knob reaches "8" after that some high frequency apears and the sound become thin, in other words, loose all the bottom.
I'm leaving a link below with a video about what I'm talking about!

[BBvideo 425,350][/BBvideo]

Any help is welcome!
Cheers

Eddie

[Herbvis]

Possibly a bad pot

[Samplegod]

Hi all... problem solved.

In fact it was the grid stopper resistor... In a 2203 PCB build this resistor appear in the middle of the PCB. It's not a good idea since you need to have two "long" wires connecting it to the tubes's grid pin... here is a photo that what I'm talking about...



This will cause interferences and unwanted noises. I read once that the best is to get this grid resistor directly connected to the socket's pin, so I removed the wires and the resistor, connected the resistor directly to the socket's grid pin, used a shielded wired to get rid of the interferences, and voilá!!! all working smootly and clear!
Here is a photo of the after... the green path is the shield, just connected to the ground in one lead and clipped right befor the grid resistor.



Cheers

Eddie

[sikter]

Well done!